AECL-6876
ATOMIC ENERGY ^fflS L'ENERGIE ATOMIQUE OF CANADA LIMITED TiBV DU CANADA LIMITEE
SIGNALS PRODUCED BY INCONEL MINERAL INSULATED COAXIAL CABLES IN NEUTRON AND GAMMA-RAY FIELDS
Signaux produits par des cables coaxiaux a isolation minerale en Inconel dans des champs de neutrons et de rayons gamma
C.J. ALLAN and G.F. LYNCH
Chaik River Nuclear Laboratories Laboratoires nucle'aires de Chalk River
Chalk River, Ontario
July 1980 juillet ATOMIC ENERGY OF CANADA LIMITED
SIGNALS PROVUCEV BV INCONEL MINERAL INSULATED COAXIAL CABLES IN NEUTRON ANP GAMMA-RAV FIELPS
by
C.J. Allan and G.F. Lynch
Chalk River Nuclear Laboratories Chalk River, Ontario KOJ 1J0
1980 JU1^ AECL-6876 L'ÉNERGIE ATOMIQUE DU CANADA, LIMITÉE
Signaux produits par des câbles coaxlaux â isolation minérale en Inconel dans des champs de neutrons et de rayons gamma
par
C.J. Allan et G.F. Lynch
RÉSUMÉ
Les câbles à isolation minérale, employés de concert avec des détecteurs de flux auto-alimentés dans les réacteurs CANDU, ont leur gaine et leur fil de noyau faits en Inconel 600 et leur isolation faite en MgO. On a entrepris une étude pour mieux connaître fondamentalement les processus produisant du courant dans les câbles à isolation minérale et pour déterminer dans quelle mesure ces processus sont apparentés aux geometries des câbles. Un certain nombre de câbles en Inconel-Inconel ont été irradiés dans le NRU, le ZED-2 et les réacteurs piscines d'essai à Chalk River ainsi que dans un irradiateur Gammacell-200 au cobalt-60. D'autres données ont été obtenues dans la centrale nucléaire Bruce A.
Laboratoires nucléaires de Chalk River Chalk River, Ontario KOJ 1J0 Juillet 1980
AECL-6876 ATOMIC ENERGY OF CANADA LIMITED
SIGNALS PROVUCEV BY INC0NEL MINERAL INSULATED COAXIAL CABLES IN NEUTRON ANP GAMMA-RA/ FIELDS
by
C.J. Allan and G.F. Lynch
ABSTRACT
Mineral insulated (MI) cables used with self-powered flux detectors in CANDU reactors employ Inconel 600 as the sheath and core-wire material, and MgO as the insulation. A study was undertaken to obtain a more fundamental understanding of the current producing processes in such MI cables and to determine how these processes are related to cable geometries. A number of Inconel-Inconel cables were irradiated in the NRU, ZED-2, and Pool Test reactors at CRNL and a Gammacell-220 6°Co irradiator. Additional data were obtained from the Bruce Nuclear Generating Station-A.
Chalk River Nuclear Laboratories Chalk River, Ontario KOJ 1J0 1980 July AECL-6876 TABLE OF CONTENTS
Page
LIST OF FIGURES [II)
LIST OF TABLES \lv)
1. INTRODUCTION 1 1.1 The Use of Mineral Insulated Cables in 1 Reactors 1.2 The Interaction of Reactor Radiation with 2 Cables 1.3 Cable Geometries Studied 5
2. EXPERIMENTAL STUDIES 5 2.1 Gamma-Ray Studies 5 2.1.1 Gammacell Tests 5 2.1.2 Reactor Gamma Rays 12 2.1.3 Conclusion on y~RaY Sensitivity 17 2.2 NRU Irradiations 18 2.2.1 Introduction 18 2.2.2 Variation of Signal with Core 21 Penetration 2.2.3 Variation of Sensitivity with 24 Core-Wire Diameter 2.2.4 Conclusions 34 2.3 Irradiations in the Pool Test Reactor 35 2.4 ZED-2 Tests 38 2.5 Results Obtained from Bruce NGS-A 43 2.5.2 Results from Unit 3 43
2.5.3 Summary . 55
3. SUMMARY AND CONCLUSIONS 56
4. ACKNOWLEDGEMENTS 58
5. REFERENCES 58 \U]
LIST OF FIGURES
FIGURE 1 Variation of the y-ray Sensitivities for Lead Cables SC-601 to SC-606 with Sheath Mass
FIGURE 2 Variation of the yray Sensitivities for 11 Lead Cables VC-501 to VC-505 and TC-101 to TC-105 with Sheath Mass
FIGURE 3 Schematic of the Test Section of the X-6 14 Test Loop in the NRX Reactor. The Detectors are Designated RV for Vanadium, RP for Platinum and RC for Cobalt. In Total, some 14 Detectors are Mounted Along the Length of the Pressure Tube. Only the 6 Detectors Contained Within the 3He Coil Are Shown Here.
FIGURE 4 Cross Section of the NRU Test Assembly in 19 Which the Lead Cables Were Irradiated
FIGURE 5 The Current Generated in the Miniature 20 Fission Chamber Used to Measure the Lead Cable Sensitivity as a Function of TFD Position FIGURE 6 Variation of the Total Sensitivities of 26 the IMI Cable with Core-Wire Diameter FIGURE 7 Variation of the (n,g) Sensitivity, 28 S(n,$) with Core-Wire Diameter FIGURE 8 The Variation of the So-Called Reduced 30 Sensitivity, SR, with Core-Wire Diameter FIGURE 9 Variation of the (n,Y,e) Sensitivity 32 with Core-Wire Diameter for the IMI Cables Irradiated in NRU FIGURE 10 The Currents Generated in Lead Cables 36 TC-101 to TC-105 and VC-501 to VC-505, as a Function of Core-Wire Diameter, for an Irradiation in the Pool Test Reactor LIST OF FIGURES (continued)
Page FIGURE 11 The Current Generated in Lead Cables 39 TC-101 to TC-105, as a Function of Core-Wire Diameter, for an Irradiation in the ZED-2 Reactor FIGURE 12 Schematic Representation of the ZED-2 40 Reactor Showing the Location of the Test Rod Relative to the Fuel Assemblies FIGURE 13 Schematic Representation of the Test 4 2 Assembly Used for Irradiating Lead Cables UC-103 to UC-106 in the ZED-2 Reactor FIGURE 14 Schematic Representation of the Bruce 44 NGS-A Reactor Showing the Location of Flux Detector Assemblies NFM-1 to NFM-20 FIGURE 15 Schematic Representation of Flux Detector 4 5 Rod, NFM-1, Installed in the Bruce NGS-A, Unit 1 Reactor FIGURE 16 Relative Sensitivities of Lead Cables 4 6 TC-101 to TC-105, as a Function of Core-Wire Diameter, Determined in the Bruce NGS-A, Unit 1 Reactor FIGURE 17 The Signal for a Test Lead Cable, 50 Installed in the Bruce NGS-A, Unit 3 Reactor, as a Function of Time, Following the Reactor Trip. The Results were Obtained During Phase B Commissioning of the Reactor FIGURE 18 Relative Sensitivity for the 1.0 mm 53 O.D. Lead Cables Installed in the Bruce NGS-A, Unit 3 Reactor as a Function of Core-Wire Diameter FIGURE 19 The Flux Distribution Along Flux 54 Detector Rod NFM-6, Bruce NGS-A, Unit 3, Determined During Phase B Commissioning of the Reactor LIST OF TABLES
Page TABLE 1 Description of Experimental Cables 6
TABLE 2 Summary of the Dimensions of the Lead Cables 8 Irradiated in the Gammacell-220 Irradiator and the y~RaY Sensitivities Determined in These Irradiations
TABLE 3 Summary of the Lengths and the Experimental 23 Results Obtained with the Lead Cables Which Penetrated the NRU Core to Different Elevations
TABLE 4 Summary of the Dimensions and the 25 Sensitivities of the IMI Lead Cables Irradiated in the NRU Reactor
TABLE 5 Summary of the Sensitivities Determined for 41 Lead Cables UC-103 to UC-106 in the ZED-2 Reactor and NRU Reactor
TABLE 6 Summary of the Currents from the Lead 48 Cables Installed in the Bruce NGS-A, Unit 3 Reactor as a Function of Time During Phase B Testing. The Reactor was Raised to 10~2 of Full Power at t=0 and Tripped at t=327 min. These Data Have Been Used to Estimate the Current Due to the Decay of 5eMn and 65Ni, I,(n,B), as Discussed in the Text.
TABLE 7 Summary of the Results Obtained from 49 the 1.0 mm and L6 mm IMI Lead Cables Installed in the Bruce NGS-A, Unit 3 Reactor
TABLE 8 Summary of the Currents Generated by 55 1.0 mm O.D. Lead Cables of Different Lengths, for the Nominal Bruce Core, as a Function of Time After Reaching 10~2 Full Power. The Lengths of the Lead Cables are Shown in Figure 16. SIGNALS PROVUCEV BV INCOMEL MINERAL INSULATEP COAXIAL CABLES IN NEUTRON ANP GAMMA-RA/ FIELPS
by
C.J. Allan and G.F. Lynch
1. INTRODUCTION 1.1 The Use of Mineral Insulated Cables in Reactors Because self-powered detectors (SPDs) are relatively simple, rugged, and cheap to manufacture, they are used exten- sively in CANDU nuclear reactors to (i) provide information on the distribution of flux throughout the core [1], (ii) for bulk and spatial control of the reactor [2], and (iii) for overpower protection. In most applications, a SPD consists of a coaxial cable having a metallic outer sheath, frequently the Ni-Cr-Fe alloy Inconel 600; a mineral oxide insulation layer, usually MgO or Al_O,; and a metallic central wire, commonly called the emitter. When such a device is placed in a radiation field, as for example in the neutron field in the core of a nuclear reactor and the central conductor is connected to the sheath through an ammeter, a current flows between the two electrodes without an external bias being applied. The magnitude of the current is proportional to the intensity of the radiation field, and hence can be used as a measure of the field strength. In most reactor applications, a SPD is used to measure the average flux over a localized region of the core and a lead cable must be used to bring the current signal from the detector to the measurement instrumentation. In CANDU reactors, the lead - 2 -
cable is a mineral insulated (MI) coaxial cable, 1.0 mm O.D., with reactor-grade Inconel 600 being used for the sheath and core wire, and compacted MgO being used as the insulant. For simplicity, this type of lead cable is referred to as an IMI cable which stands for Inconel-Magnesia-Inconel.
The lead cable itself acts as a self-powered flux detector but, by an appropriate choice of materials and dimensions, the signal produced in the lead cable can usually be made small relative to that produced in the detector. Such optimization has been reported for PWRs [3].
1.2 The Interaction of Reactor Radiation with Cables In a nuclear reactor, the current induced in a coaxial cable, be it a detector or a lead cable, can be attributed to four separate interactions: (i) Neutron capture in the materials of the cable can result in the formation of radioactive daughter nuclides that decay by 6-emission. These high-energy electrons, emitted by the daughter nuclide, are responsible for the current flow between the two electrodes. This process is referred to as the (n,(3) interaction. The current is proportional to the neutron flux but is delayed. The current follows changes in flux intensity with a time constant determined by the half-life of the daughter nuclide. This interaction is the dominant current-producing mechanism in detectors with vanadium or rhodium emitters [4,5].
In an IMI cable, the (n,3) current, I(n,$)r will result primarily from the (3-decay of 6 5Ni and 56Mn produced by neutron capture in 61*Ni and 55Mn. The current is delayed having a time constant of 352 s. Manganese is present as an impurity J i Inconel 600, but is specified to have a maximum - 3 -
concentration of 0.3 wt%. Depending on the relative amounts of manganese present in the core wire and sheath of the cable, this current may be either positive or negative. (ii) Neutron capture in the materials of the cable is normally accompanied by the emission of prompt capture y-rays. These y-rays interact with the materials of the cable liberating high-energy electrons, via Comptori and photo-electric processes, thus causing a current flow. This process is referred to as the (n,y,e) interaction. Also included in this interaction are conversion electrons emitted when the daughter nuclides created by neutron capture de-excite to the ground state. The current is proportional to the neutron flux and is prompt, i.e. the current follows changes in flux intensity instantaneously. This is the main current-producing mechanism in detectors with cobalt emitters, at the start of life [4,5,6], and is an important current-producing mechanism in detectors having platinum [5,7,8] or molybdenum emitters [9].
In an IMI lead cable, the same mechanisms can occur, leading to a prompt signal which is propor- tional to the neutron flux. (iii) Reactor gamma rays impinging on the cable can liberate free electrons, thus producing a current.
This process is referred to as the (Yfe) inter- action. These external y-rays can be separated into prompt and delayed components. The prompt component arises from fission and capture y-rays associated with neutron capture in the fuel and reactor hardware. Hence, this component of the y-ray flux and the resulting (y,e) induced current are proportional to the neutron flux. The delayed - 4 -
component arises from the decay of fission products and activation products. In a power reactor, a significant fraction O1/3) of the Y-rays are delayed [10]. Hence, the total (y ,e) current does not follow changes in flux instantaneously, but has a delayed component. The (y,e) interaction is an important current-producing mechanism in detectors having platinum or molybdenum emitters [5,7,8,9] and, indeed, in any detector for which the atomic number of the emitter is significantly larger than that of the sheath. Previous results [7] show that the (y,e) current, I(y,e), in an IMI cable is negative, i.e. external y~rays cause a net flow of electrons from the sheath to the central electrode.
(iv) External electrons from the reactor hardware and materials, impinging on the detector, also contribute to the overall output current [1]. This process is referred to as the (e) interaction. Such interactions, however, are considered parasitic, and an attempt is usually made to minimize them.
The sheath of the detector and lead cable are normally grounded. Thus, external electrons that stop in the sheath do not contribute to the current, I(e), while electrons that stop in the emitter pro- duce a negative component. On this basis, this current is expected to contribute a negative component. The four basic interactions described above can be further classified into 76 separate categories [11]. In any self-powered detector or lead cable, all four interactions occur and the net current is the algebraic sum of the individual currents arising from the different interactions. Thus we can write
"••Total = I(n'B) + Kn,Y,e) + Ky,e) + I(e)... (1) - 5 -
For a self-powered detector, the materials and dimensions are chosen so that one or two of the interactions will dominate and produce a relatively large net current. However, for a lead cable, the dimensions are chosen to minimize the net signal, so that the contribution of the lead cable to the total signal produced by a detector/lead cable combination is negligibly small.
The IMI lead cables presently used in CANDU reactors have an outside diameter of 1.0 mm. The core-wire diameter has already been chosen such that the net current produced from the lead cable in these power reactors is approximately zero. 1.3 Cable Geometries Studied The present study was initiated to determine the optimum core-wire diameter for an IMI cable 1.58 mm in diameter. The test program has extended over a period of several years and has included irradiations in several test reactors and a Gammacell- 220 Irradiator, as well as the Bruce Nuclear Generating Station-A. During the course of the study, its scope was expanded to include lead cables of other sizes and/or materials to better understand the effects of changes in materials and dimensions on the various current contributions. Thus, lead cables 1.0 mm in diameter were also irradiated in Bruce, and a few lead cables 2.2 mm and 3.0 mm in diameter were tested in the NRU and ZED-2 reactors at the Chalk River Nuclear Laboratories. One twin-core lead cable was included in the NRU irradiations.
The relevant characteristics of all the cables used in this study are summarized in Table 1.
2. EXPERIMENTAL STUDIES 2.1 Gamma-Ray Studies 2.1.1 Ga.mmac2.il Te-iti> Previous experiments have indicated that IMI cables have a negative y-ray sensitivity to 6QCo gamma rays [7]. These experiments have now been extended to include the effects of TABLE 1
DESCRIPTION OF EXPERIMENTAL CABLES
Dimensions Irradiated in Sheath Wall Identification O.D. Thickness Core Diameter (nun) (mm) Bruce NGS-A (nun) Gammacell PTR ZED-2 NRU Unit 1 Unit
VC-501 1.60 0.28 0.52 Yes Yes NO Yes No No VC-502 1.60 0.30 0.41 VC-503 1.59 0.30 0.35 VC-504 1.60 0.31 0.28 VC-505 1.60 0.34 0.14 TC-101 1.57 0.25 0.48 Yes Mo Yes TC-102 1.58 0.26 0.39 TC-103 1.57 0.28 0.30 TC-104 1.58 0.28 0.24 TC-105 1.56 0.30 0.15 SC-601 1.73 0.29 0.44 NO No No SC-602 1.58 0.28 0.37 SC-603 1.39 0.24 0.34 SC-604 1.24 0.24 0.30 SC-605 1.10 0.18 0.28 SC-606 1.00 0.17 0.26 VC-212 1.56 0.27 0.37 NO Yes VC-213 1.56 0.27 0.37 VC-214 1.56 0.27 0.37 TC-1018* 1.58 0.28 0.36 TC-1019 1.58 0.28 0.37 TC-1020 1.56 0.21 0.36 UCrlO3 2.99 0.51 0.70 Yes UC-104 2.99 0.41 0.67 UC-105 2.19 0.38 0.51 UC-106 2.19 0.30 0.49 UC-606** 3.00 0.45 0.57 A 1.02 0.17 0.15 No No Yes B 1.02 0.17 0.25 C 1.02 0.17 0.32 D 1.02 0.17 0.38 E 1.57 0.25 0.28 F 1.57 0.25 0.38 G 1.02 0.17 0.25 H 1.02 0.17 0.25
*The core wire of this cable is high-purity nickel, not Inconel 600. **This is a twin-core lead cable. geometry on the y-ray sensitivity. To determine the applicability of Gammacell data to reactor irradiations, the y-ray sensitivity of a Co detector (Co has approximately the same atomic number as Inconel) was determined in the NRX reactor. The latter results are discussed in Section 2.1.2.
As part of the study, cables VC-501 to VC-505, together with a second set of IMI cables, TC-101 to TC-105, having similar dimensions, were irradiated in a Gammacell-220 at a dose of ^1.3 x 10" Gy/h (1.3 x 1C6 rad/h). A third set of IMI cables, SC-601 to SC-606, whose dimensions are related to that of TC-102 by scaling factors, were also included in this study. The relevant dimensions of the various cables are summarized in Table 2, together with the y~"raY sensitivities obtained from the Gammacell measurements. For these irradiations, the cables were coiled on a threaded Lucite former 5 7.2 mm in diameter. The coil was placed inside a polystyrene cylinder, 38 mm O.D. with a 4 mm wall which served to prevent electrons produced by gamma-ray inter- actions in the walls of the Gammacell from impinging on the detector. In total, ^6.4 m of cable were wound on the former so that the current generated in the portion of lead cable leading from the coil to the top of the Gammacell could be neglected, compared with the current generated in the coiled portion of the cable. The dose rate over the coiled portion of the cable was measured, independently, by means of Fricke dosimetry [12]. As can be seen from Table 2, the sensitivities of lead cables SC-601 to SC-6 06 are all negative and the amplitude increases with increasing cable size. The negative current implies a net flow of electrons into the core wire. Because of the coaxial geometry of the lead cable, electrons displaced from the core wire will give a positive contribution, whereas electrons displaced from the sheath that come to rest in the core wire will give a negative contribution. Since the number of interactions per unit length in the sheath and the core wire TABLE 2
SUMMARY OF THE DIMENSIONS OF THE LEAD CABLES IRRADIATED IN THE GAMMACELL-220 IRRADIATOR AND THE Y-RAY SENSITIVITIES DETERMINED IN THESE IRRAJ..ATIONS
Sheath Wall Core-Wire Lead Cable O.D. Sensitivity Identification (ram) Thickness Diameter ,10~15 A-m-'l/tGyh"1) (mm) (mm) l
VC-501 1.60 0.28 0.52 -6.97 VC-502 1.60 0.30 0.41 -6.63 VC-503 1.59 0.30 0.35 -6.79 I VC-504 1.60 0.31 0.28 -6.85 00 I VC-505 1.60 0.34 0.14 -7.17 TC-101 1.57 0.25 0.48 -6.57 TC-102 1.58 0.26 0.39 -6.70 TC-103 1.57 0.28 0.30 -6.63 TC-104 1.58 0.28 0.24 -7.70 TC-105 1.56 0.30 0.15 -4 .38 SC-601 1.73 0.29 0.44 -9.01 SC-602 1.58 0.28 0.37 -7.84 SC-603 . 1.39 0.24 0.34 -5.27 SC-604 1.24 0.24 0.30 -4.08 SC-605 1.10 0.18 0.28 -2.70 SC-606 1.00 0.17 0.26 -1.81 - 9 -
will be proportional to the mass per unit length, the sensitivity per unit length of an IMI cable should be proportional to the mass difference between the sheath and the core wire, to a first approximation, i.e.
S = k(M -M ) (2) Y s c where M is the mass per unit length of the sheath s
M is the mass per unit length of the core wire.
For lead cables SC-601 to SC-606,
M rr^- w constant = A , M C so, for these cables, equation 2 can be rewritten
S M (3) Y« r (*-i> s' i.e. the sensitivity is proportional to the sheath mass. Figure 1 illustrates the variation of the measured y-ray sensitivities of lead cables SC-601 to SC-606 as a function of the sheath mass per unit length. As can be seen, the sensitivity varies approximately linearly, but the relationship is not one of strict proportionality. This is not really surprising since the above qualitative description is a highly simplified description of complex processes. Among other things, it ignores electron production in the MgO insulation and the effects of geometry on the electron transport. For the 1.58 mm O.D. cables, the sensitivities, apart from one anomaly are essentially independent of the core-wire diameter, Figure 2. From the previous results, these data are rather surprising since, as the core-wire mass increases for an essentially constant sheath^mass, the positive contribution from SHEATH MASS (g/m) 5 i ii i
e?
C/) z: cLnU
FIGURE 1 VARIATION OF THE y~RAY SENSITIVITIES FOR LEAD CABLES SC-601 to SC-6Q6 WITH SHEATH MASS CORE WIRE DIAMETER (mm) 0.2 0.4 0.6 0 1 1 1 1 1
+ -5h- •o o + o + o +
UJ w-io FIGURE 2 VARIATION OF THE y-RAY SENSITIVITIES FOR LEAD CABLES VC-501 TO VC-505 AND TC-101 to TC-105 WITH SHEATH MASS - 12 -
the core wire would be expected to increase and, hence, the amplitude of the net negative current to decrease. This is apparently not the case, even though the mass of the core wire varies by more than an order of magnitude. Two factors probably contribute to this result. Firstly, even for the cables with the largest core wires, the mass of the sheath exceeds that of the core wire by a factor of ^5, so that the number of y-ray inter- actions in the sheaLh far exceeds the number which occur in the core wire. Secondly, as the diameter of the core wire increases, so too does the probability that an electron produced in the sheath will be stopped in the core wire, i.e. the negative current arising from (y,e) interactions in the sheath increases, because the solid angle subtended by the core wire increases and because the mean capture probability of an electron which intercepts the core wire increases.
For the lead cables being considered, VC-501 to VC-505 and TC-101 to TC-104, the increase in the negative current with increasing core-wire diameter, therefore, just balances the increase in the positive current associated with (y»e) inter- actions in the core wire. It is thought that this result is particular to the dimensions of the above lead cables and is not a general rule.
As stated above, the sensitivity of cable TC-105 is significantly lower than that of the other detectors. An explanation for this anomaly is not available, but the results obtained from this cable in irradiations carried out in the ZED-2 and the Pool Test Reactor (PTR), at CRNL, and in the Bruce NGS-A, Unit 3 reactor, are also anomalous. However, they are consistent with a less negative y-ray sensitivity.
2.1.2 RuactoK Gamma. Ra.y& As reported in [7], a self-powered detector having an Inconel sheath and a cobalt core has a negative sensitivity in a Gammacell irradiator. Since the effective atomic number of Inconel is the same as that of cobalt, i.e. 27, the y-ray - 13 -
sensitivity determined for the cobalt detector can be assumed to be comparable to that of an IMI cable having the same dimensions. Results from a parallel experimental program with Co detectors have enabled us to determine the Y~ray sensitivity of a Co detector to reactor Y-rays. The cobalt detector results were obtained from detectors coiled on the test section of the pressure tube of the X-6 loop in the NRX reactor at CRNL. The test section was surrounded by a stainless steel coil through .which 3He gas was circulated. By varying the pressure of the 3He gas, the neutron flux in the pressure tube, and hence the power of test fuel, could be varied independently of the reactor power. Six detectors were coiled on the pressure tube, within the test section, two platinum detectors, two vanadium detectors, and two cobalt detectors. The arrangement is illustrated schematically in Figure 3.
During commissioning of the loop, tests were carried out with no fuel in the loop and with a trefoil of 3 elements con- taining fuel enriched to 6 wt% 235U in U. When the 3He pressure was varied, it was found that the relative change in the signals from the cobalt detectors were not the same as the relative change in the signals from the vanadium detectors, but that the two signals were linearly related. With no fuel in the loop, the data fitted to the following expression
IC_6(P) Iy(P) T (v ) = "0.088 + 1.087 _( > (4) *C-6l o' \K o'
where I ,(P) is the current from cobalt detector C-6 at a He pressure of P kPa. I—(P) is the average of the currents from vanadium detectors V-5 and V-8 at a He pressure of P kPa, and
PQ = 1135 kPa. - 14 -
PRESSURE TUBE
FLUX MONITOR ELEVATION (CM) ELEVATION IDENTITY (CM) TOP OF HE-3 COIL | 83.2 n I
/ \
TOP OF FUEL 172.1
168.0- •RP-IO- -h
160.1 -RC-9
153. I -RV-8 y
142.4 RP-7
135.7 RC -6 h
II 127.6 RV-5 BOTTOM OF FUEL |25.6 \J U 1 | BOTTOM OF HE-3 M3.9 COIL V FIGURE 3 SCHEMATIC OF THE TEST SECTION OF THE X-6 TEST LOOP IN THE NRX REACTOR. THE DETECTORS ARE DESIGNATED RV FOR VANADIUM, RP FOR PLATINUM AND RC FOR COBALT. IN TOTAL, SOME 14 DETECTORS ARE MOUNTED ALONG THE LENGTH OF THE PRESSURE TUBE. ONLY THE 6 DETECTORS CONTAINED WITHIN THE 3He COIL ARE SHOWN HERE. - 15 -
This result is interpreted as meaning that ^-9% of the total signal from the cobalt detector, at a He pressure of 1135 kPa, can be attributed to y-rays produced in the fuel and structure of the reactor surrounding the X-6 loop. The intensity of this y-ray field is not affected by the 3He pressure, and hence the reactor y-rays contribute a constant, negative component to the current from the cobalt detector.
Here we should note that the vanadium detectors have a small negative y-ray sensitivity which will be comparable, in absolute value, to that of the cobalt detectors [7]. However, the total current, per unit length, from the vanadium detectors is a factor of ^15 great«p than that from the cobalt detectors, so that the reactor y-ray^will affect the signal from the vanadium detectors by less than
Equation (4) indicates that for the cobalt detector we can write
where I fi(y,e) is the constant current which is attributed to reactor y-rays, and I_ , is the current which varies with changes in L local flux at the test section. !„ , results from (n,y,e) interactions in the detector, (y,e) interactions caused by y-rays produced by neutron capture in the structure of the loop and the 3He coil, as well as y-rays produced in the fuel contained in the test section.
T-L T / \ L T-COil, > , TX ^1. . . ,,. IS X :=1 In YiG) T* 1 ("YSJ"i~X fv gj (.0) - 16 - where I ,(n,y,e) is the current that results from y-rays produced by neutron capture in the detector itself,
1^°^ (Y(e) is the current that results from y-rays produced by neutron capture in the stain- less steel of the 3He coil and the pressure tube, and Fuel I , (y,e) is the current that results from y-rays produced in the fuel contained within the test section.
The three terms contributing to Ir_fi are all proportional to the local neutron flux. Since it was not possible experimentally to separate the terms, a local sensitivity, S_ ,, has been defined such that
where Sr-fi defines the sensitivity of detector C-6 to localized neutron flux changes, and cf) is the neutron flux at the surface of the pressure tube determined by the V detectors
we have, from equations (4) and (7),
I (Y e) = 088 I (P ) C-6 ' -°- C-6 o and 1.087 I (P ) cL c~6 ° SC-6 " *(P ) with no fuel in the loop. - 17 -
Using the sensitivities of the vanadium detectors, measured prior to their installation on the X-6 pressure tube, to determine
1 lj_6(y,e) = -2.4 x 10" « A (11)
sj , = 3.14 x 10"25 A/(n-m-2-s-M (12) with no fuel in the loop. A similar analysis of data obtained with the trefoil fuel in the loop gives
10 I*_6(y,e) = -2.4 x 10" A (13)
25 2 1 s£_6 =•• 2.79 x 10" A/(n«m- -s- ) (14)
Thus we see that in both cases the reactor y-rays contri- bute the same negative current to the total current. However, on adding fuel to the loop, the sensitivity, S ,, is reduced. This result is interpreted a^ evidence that the y-rays produced in the fuel also give rise to a negative current component, i.e.
Ir_, (y,e) is negative. Although this is not unexpected, it is an important result since the spectral distribution of the fuel y-rays and the reactor y-rays is expected to be significantly different, the mean energy of the reactor y-rays being smaller than that of the fuel y-i 2.1.3 Conclusion on y-Ray Sunbitlvlty In summary, these tests lead to the following conclusion: (i) IMI cables have a negative y~ray sensitivity to y-rays from a 6°Co Gammacell Irradiator and reactor y-rays. - 18 -
(ii) The y~ray sensitivity depends on geometry in general, but for the lead cables having a constant O.D. of ^1.58 mm, the sensitivity is essentially independent of the core-wire diameter. (iii) For practical cable geometries, the yray inter- action in the sheath dominates. 2.2 NRU Irradiations 2.2.1 I YitKodu.ztX.on A number of IMI lead cables, nominally 1.58 mm in diameter, were irradiated in the NRU research reactor at CRNL. Also included was one lead cable having an Inconel 600 sheath but a core wire of high-purity nickel as well as several lead cables of larger diameter and one twin-core lead cable. The test rod used for the irradiations is illustrated in Figure 4. It con- sists of a cluster of 18 thin-walled Zircaloy guide tubes arranged in two circles about a central guide tube. These tubes are contained within an outer Zircaloy shroud tube. A lead cable or detector can be put into any of the 18 guide tubes, while the central tube is reserved for a travelling flux detector (TFD) which is used to measure the flux along the test assembly.
The absolute sensitivities of the cables were obtained from such an "in-situ" calibration where a miniature fission chamber was used for the TFD. The absolute sensitivities may not be accurate to better than ^10%, but the relative sensitivities are believed to be accurate to ^-3%, in most cases. The accuracy of the in-situ calibration is discussed in greater detail below. The flux distribution along the length of the test assembly, obtained during the "in-situ" calibration, is shown in Figure 5. Also shown in Figure 5 are the positions of the various lead cables. The flux depressions which can ~"3 seen at the top and bottom of the core are caused by absorbers mounted on the test assembly to provide a TFD position reference. Before discussing the data in detail, it is well to point out that the fission - 19 -
FIGURE 4 CROSS SECTION OF THE NRU TEST ASSEMBLY IN WHICH THE LEAD CABLES WERE IRRADIATED E 2.0
tr cc Z> o
cr = 2646mm UJ -L = 2071 mm GO L= 1990 mm L= 1613 mm 1-0 L= 993 mm KJ L=0 O o LOWER REF PLUG UPPER REF PLUG o
CENTRE OF FUEL I -1.50 -1.0 -0.5 0 0.5 1.0 1.5 TFD POSITION RELATIVE TO REACTOR CENTRE-LINE (m)
FIGURE 5 THE CURRENT GENERATED IN THE MINIATURE FISSION CHAMBER USED TO MEASURE THE LEAD CABLE SENSITIVITY AS A FUNCTION OF TFD POSITION - 21 -
chamber used for the in-situ calibration did not exhibit a good "plateau". Thus, the flux shape used for the in-situ calibration may not be highly accurate. However, for lead cables £ 2000 mm long, the accuracy of the relative sensitivities is not a strong function of the flux shape.
The NRU results are discussed in detail in the following sections.
2.2.2 Vatii.ati.on o& Signal with Co^ie. Vnyi2.tn.atlon Since it is assumed that the total current from an IMI cable consists of four separate currents, as indicated by equation (1), we can define five separate sensitivities (per unit length) given by
ul>Yft:; S(n,Y,e) = ,T (15) (x)dx / •'el
Y e/ S(Y,e) = ^ ' (16) 'Ic|>(x)dx
(nfB) S(n,&) = f^ (17) J (j)(x)dx o
S(e) = I(e)/ / 4>(x)dx (18)
tal and ST = >° (19) - 22" -
where
Note that
ST = S(n,y,e) + S(y,e) + S(n,3) + S(e) (20)
Equations (15) to (19) are based on the assumption that the current generated in a lead cable is proportional to the integral of the neutron flux along the length of the cable. This would appear to be self-evident, but it was felt to be worth while demonstrating. For this reason, a set of lead cables, namely VC-214, TC-1019, VC-213, and VC-212, of different lengths but nominally identical in other aspects, were included. The relevant dimensions and experimental results for these cables are given in Table 3. Lead cable VC-214 extended from the reactor deck through to the bottom of the reactor shielding, a distance of ^4.9 m; lead cable TC-1019 extended approximately 36% of the way through the reactor core; lead cable VC-213 extended approximately 60% of the way through the core; and lead cable VC-212 extended approximately 100% through the core. As can be seen from Table 3, the relative total sensitivities of the latter three lead cables are essentially the same, confirming that the net signal is proportional to the integral of the flux along the length of the cable. On this basis, it is reasonable to assume that the individual contributions are proportional to the flux integral along the length of the cables. Although lead cable VC-214 did not extend into the core, a measurable, but negative, current was nonetheless obtained from this lead cable. The amplitude of the current was £ 1% of that obtained from the other three lead cables. This current is attributed to the Y~ray field which extends part way through the reactor shielding above the core and is negative, since the IMI lead cables have negative Y~rav sensitivities. Here it may he noted that the TABLE 3 SUMMARY OF THE LENGTHS AND THE EXPERIMENTAL RESULTS OBTAINED WITH THE LEAD CABLES WHICH PENETRATED THE NRU CORE TO DIFFERENT ELEVATIONS
Guide Tube rSL Current Sensitivity Lead Cable 27 Identification Used Core } (IQ" A-m"*)/(n-nr*
VC-214 1 0 -0.146 — TC-1019 13 993 12.63 6.43 VC-213 4 1S13 20.8 6.15 VC-212 7 2646 34.6 6.18 - 24 -
neutron field also extends part way into the reactor shielding. However, the neutron flux decreases more rapidly with distance than does the y~ray field, so that the dominant effect is that of the y^ay field.
2.2.3 Va/ilatlon oj Stytilt-ivltij with. Co fit-Wilt The pertinent dimensions and the important experimental results obtained from the lead cables irradiated in the NRU reactor are summarized in Table 4. In most cases, it has been possible to estimate values for the individual sensitivities S(n,Y#e), S(y,e) and S(n,6), from the measured values of the total sensitivity S .
As can be seen from Figure 6, the total sensitivity does not vary linearly with core-wire diameter over the complete range. For the larger core wires, the total sensitivity increases rapidly with increasing core-wire diameter. This is discussed further below. For core wires < 0.4 mm in diameter, a linear approximation fits the data reasonably well. A null signal is obtained for a core-wire diameter ^0.23 mm. For smaller core wires, the signal is negative, and for larger core wires, the signal is positive. The individual interactions that contribute to the total sensitivity are now considered beginning with the (n,B) interaction. By analyzing the decay of the signal from the IMI cables following a fast reactor shutdown, it was possible to determine the contribution to the total current from the decay of 65Ni and 56Mn. This analysis consisted of fitting the decay of the signal from the cable to the decay of the reactor flux as measured by the fission chamber, assuming the cable had a prompt signal and a number of first-order delayed components, as described in [13,14], The amplitude of the delayed component 1 having a time constant of 1.33 x 10 * sr corresponding to that of 56 6 5 Mn and Ni, determines the I., (n,0) contribution where I1(n,6) is the current attributed to the decay of 65Ni and 56Mn. Since this is thought to be the dominant current contributing to the TABLE 4
SUMMARY OF THE DIMENSIONS AND THE SENSITIVITIES OF THE
IMI LEAD CABLES IRRADIATED IN TEE NRU REACTOR
—£jXp6l lluSn tal
S h Length Observed Lead Cable Guide O.D. Wall Core-Wire S S(n,$) S(Y,e) S(n, ) F Identification Tube in Core Currents T Y.. P (mm) 'rh ss Di er Number Used (mm) (nA) 2 1 2 1 ^r <™> (10~ ' A-m" )/(n-m- • s- )-
VC-214 1 1.56 0.27 0.37 0*** -0.146 _ _ — — — -- TC-1019 13 1.58 0.28 0.37 993 12.63 6. 43 1.09 -1 8. 5 -- ' TC-1020 16 1.56 0.21 0.36 993 12.35 6. 28 -0.82 -1 8. 1 -- VC-213 4 1.56 0.27 0.37 1613 20.6 6. 15 -1.23 -1 8. 4 - 1 VC-212 7 1.-56 0.27 0.37 2646 34.6 6. 18 -1.42 -1 8. 6 1. 38 TC-1018* 10 1.58 0.28 0.36 2646 23.3 4. 16 -3.25 -1 8. 4 — U1 VC-501 6 1.60 0.28 0.52 2071 78.6 17. - -1.42 -1 20. 1 1. 15 1 VC-502 5 1.60 0.30 0.41 2071 32.1 7. 21 -2.81 -1 11. 0 1. 41 VC-504 3 1.60 0.31 0.28 2071 5.16 1. 16 -2.15 -1 4. 31 3. 60 VC-505 2 1.60 0.34 0.14 1970 -9.7 5 -2. .31 -1.83 -1 0. 52 -0..17 UC-103 9 2.99 0.51 0.70 2646 226 40. 4 -4.44 -3.5 48. 3 1..17 UC-104 17 2.99 0.41 0.67 2646 221 39. 4 -3.15 -2.6 45. 2 -- UC-105 18 2.19 0.38 0.51 2646 92.0 16.,4 -2.62 -1.7 20. 7 1,.41 UC-106 8 2.19 0. 30 0.49 2646 102.8 18. 4 -1.84 -1.6 21. 8 -- UC-606A** 14 3.00 0.45 0.57 2646 164 29.,2 -2.63 — — -- UC-606B 14 3.00 0.45 0.57 2646 181 32..3 -2.91 — -- —
* The core wire of this cable is high-purity nickel rather than Inconel 600. ** Twin-core lead cable. ***This lead cable extends through the reactor shield to the top of the core. - 26 -
O.I 0.2 0.3 0.4 0.5 0.6 0.7 CORE WIRE DIAMETER (mm)
FIGURE 6 VARIATION OF THE TOTAL SENSITIVITIES OF THE IMI CABLE WITH CORE-WIRE DIAMETER. - 27 -
(n,B) current, we have used the value of I^Cn,^) in equation (17) to solve for S(.i,3). These values are given in Table 4 and are shown in Figure 7 as a function of core-wire diameter.
As can be seen from Figure 7, there is no good correlation between the (n,g) sensitivity and the core-wire diameter. Even for fixed geometry, there is a significant variation in the intensity of this component. For example, detectors VC-502 and VC-213 are similar in construction, yet the amplitude of the I,(n,3) current differs by a factor of two between the two detectors. This variation is believed to reflect the variation in the concentration of Mn which is present as an impurity in the Inconel. For the lead cables with the smallest core wires, VC-504 and VC-505, the relative magnitude of this current is large, as it is for the lead cable having a pure nickel core, TC-1018.
Although all the (n,3) currents observed in the NRU irradiation were negative, there is no apparent reason why this contribution could not be positive. Moreover, irradiation of the cable will cause the manganese to burn out (at *M% per annum per 1018 n*m~2«s-1) and hence this component will vary with long irradiation times. Since Mn is present as an impurity, it can be concluded that the lead cable geometry that produces a net signal of zero will vary with the concentration of Mn in the core and in the sheath, and thus for a given O.D., there is no unique core-wire diameter that results in a null sensitivity. In view of the importance of Mn, it is perhaps surprising that the relative total sensitivities, ST, of the lead cables TC-1019, VC-213, and VC-212, turned out to be so close, but as can be seen from Table 4, the magnitudes of the I1(n,B) - 28 -
Or • 1.6 mm O.D. o 2.2 mm O.D. ° 3 mm O.D.
-1.0
CM i E c
< -2.0 CM b
7X -3.0 Ni CORE
CO
UJ _ CO
I I I 0.1 0.2 0.3 0.4 0.5 0.6 0.7 CORE WIRE DIAMETER (mm)
FIGURE 7 VARIATION OF THE (n,|3) SENSITIVITY, S(n,g) WITH CORE-WIRE DIAMETER - 29 -
currents from these three detectors were similar. The chemical analyses of the sheath and core-wire materials indicated that the Mn content was similar for the three cables. It can be seen from Table 4 that the difference in the total sensitivities of lead cables TC-1018 and TC-1019 can be attributed entirely to differences in the amplitudes of the I,(n,6) terms, which, in turn, is a reflection of the fact that high-purity nickel used for the core of lead cable TC-1018 does not contain any signi- ficant amount of manganese.
Although we have been able to estimate S(n,B) in all cases, we have not been able to determine S(n,y,e) and S(Y/e) directly. For this reason, we have defined a so-called reduced sensitivity,
SR, given by
h SR = (iT - i1Cn,e))/7 f' <|>(x)dx (21)
The reduced sensitivity, for lead cable VC-505, is negative, while that of all the other lead cables is positive. Figure 8 shows the variation of the reduced sensitivity, S , as a function of emitter diameter for the lead cables having a positive sensitivity. As can be seen, the sensitivity increases almost cubically with core-wire diameter. The rapid increase in the reduced sensitivity is believed to result primarily from an increase in I(n,Yr©) with core-wire diameter. The (n,Yre) interaction is a two-step process. Ignoring self-shielding, the (n,y) reaction rate per unit length will be proportional to the emitter area, i.e. the square of the emitter diameter, D2. Since the escape probability for electrons generated near the surface of the core wire, by Compton and photo-electric processes, is significantly larger than that for electrons generated in the interior of the core wire, we expect the "effective" (y»e) reaction rate to be approximately proportional to the emitter sur- face area, i.e. the diameter D. Thus we expect the magnitude of the Cn,y»e) current to vary approximately as D3. Since the reduced - 30 -
-25 10
£ c
-26 io
>- h- >
if) z
I027 I III I I I I I I 10" 10' CORE WIRE DIAMETER (mm)
FIGURE 8 THE VARIATION OF THE SO-CALLED REDUCED SENSITIVITY, SR# WITH CORE-WIRE DIAMETER - 31 -
sensitivity, S , varies in this manner, we assume that the major component contributing to the reduced sensitivity is the (n,Y,e) interaction.
As was discussed above, the 60Co y-ray sensitivity of the 1.58 mm lead cables does not vary significantly with core- wire diameter. Assuming that
(i) the reactor y-ray sensitivity is independent of core-wire diameter for 1.58 mm cables, (ii) S(n,y,e) varies as D3, and (iii) the current contributed by external electrons is negligible, we have sufficient information from the measured values of S for cables VC-505 and VC-502 to obtain
S(y,e) « -1 x 10"27 (A«m-1)/(n«m-2»s-1) (22)
S(n,y,e) = 1.97 x 1CT25 D3 (A'lrr1) /(n«m"2 -s"1) (23) where D is the core-wire diameter in mm. Note that the y~raY sensitivity is defined here in terms of neutron flux. Since the ratio of the y-ray flux to neutron flux is dependent on the type of reactor and, indeed, on the position within a reactor, the y-ray sensitivity thus expressed will also depend on the reactor. Thus the above value applies only to the location occupied by the test rod in the NRU research reactor.
The value of S(y,e) was estimated for the 2.2 and 3.0 mm IMI cables from the value for the 1.58 mm IMI cables, assuming that S(y,e) is proportional to the mass of the sheath. These values were then used to estimate S(n,y,e). Figure 9 shows the variation of the estimated value of S(n,Yr&) as a function of core-wire diameter. As can.be seen, the sensitivity varies as the cube of the emitter diameter, as expected. - 32 -
v25
CORE WIRE DIAMETER (mm)
FIGURE 9 VARIATION OF THE (n,y,e) SENSITIVITY WITH CORE-WIRE DIAMETER FOR THE IMI CABLES IRRADIATED IN NRU - 33 -
The estimated values of S(n,£>), S(y,e) and S(n,y,e) are summarized in Table 4. The calculated values of S(y,e) and S(n,y,e) are in excellent agreement with the values of S determined experimentally, thus indicating the internal consistency of the model. If we compare the values of S(y,e) and S(n,y,e), we see that for the cable with the smallest core wire, VC-505, S(y»e) is greater in amplitude than S(n,y,e), and so the y-ray interaction would result in a negative current from this cable even if S(n,B) were negligible. Since S(n,y,e) increases approximately cubically, S(y>e) becomes relatively unimportant for core-wire diameters > 0.4 mm. Also shown in Table 4 are the values of the prompt fraction determined for several of the cables. The prompt fractions, i.e. the fractions of the total signal that follow changes in the neutron flux without (measurable) delay, were determined by comparing the decay of the signals from the MI cable following a fast reactor shutdown with the decay of the signal from a miniature fission chamber. For these cables the prompt fraction approaches unity as the diameter of the core wire increases. In other words, with increasing core-wire size the cable comes close to being a completely prompt device. This can be attributed to the increase in the relative strength of I(n,y»e) since the (n,y»e) interaction is basically prompt.
In view of the above discussion, it is clear that an IMI cable can be used as a prompt-responding self-powered flux detector if the core-wire diameter is sufficiently large. It is interesting to note that in subsequent TFD scans of the NRU assembly, carried out after all the lead cables other than the lead cables TC-1019 and TC-1020 had been replaced with self-powered detectors, it was observed that inserting the TFD caused the signal from lead cables 1019 and 1020 to increase by - 34 -
For the twin-cored lead cable UC-606, the currents generated by the two core wires A and B were measured to be 164 nA and 181 nA, i.e. they differed by M.0%. The reduced sensitivities also differed by about the same amount. Thus the variation cannot be attributed to differences in the Mn content of the two wires but must be the result of differences in the diameters of the two core wires and the locations of the core wires relative to the sheath. Since the reduced sensitivity, and indeed for the larger lead cables, the total sensitivity, is such a strong function of the core-wire diameter, the most likely explanation for the discrepancies between the two currents is a small variation in the diameters of the core wires. 2.2.4 Conclusions
The results obtained from NRU can be summarized as follows: (i) The current attributable to (n,y,e) interactions increases almost cubically with core-wire diameter. As a result, this interaction dominates for large core-wire diameters and the (y,e) and (n,(3) inter- actions are relatively unimportant. (ii) For small core-wire diameters, the current attributable to the decay of 56Mn and 65Ni is important in determining the equilibrium current. However, since manganese is normally present as an impurity in both the sheath and core wire of Inconel-Inconel MI cables, the relative size of this current cannot be specified a priori. Although it has been observed to be negative in all cables irradiated in NRU, there does not appear to be any reason why it could not be positive. - 35 -
(iii) The results obtained from the lead cables having small core-wire diameters are consistent with the belief that (Y»e) interactions give rise to a negative current. Provided that the core-wire diameter is sufficiently small, the net current will be negative. In NRU, the core-wire diameter should be < 0.2 mm in diameter to obtain a net negative current from an Inconel-Inconel MI cable of vL.58 mm O.D.
(iv) To minimize the net current from an Inconel- Inconel MI cable, 1.58 mm in O.D. in the NRU reactor, the core-wire diameter should be ^0.2 mm. Depending on the relative concentrations of manganese in the sheath and core wire of the cable, the net current may be either positive or negative.
2.3 Irradiations in the Pool Test Reactor Cables VC-501 to VC-505 and cables TC-101 to TC-105 were irradiated in the Pool Test Reactor at CRNL. For these tests, the cables were coiled, close-wound, on a Lucite former, 35.8 mm in diameter, and irradiated one at a time at a constant reactor power. The coil contained «2.5 m of cable. No absolute flux measurements were made, but the cable sensitivities can be compared, on a relative ba_>is, by comparing the currents generated in the cables during the irradiation.
Figure 10 shoe's the current as a function of core-wire diameter for the two sets of cables. For cable set TC-101 to TC-105, the results were obtained for an irradiation time of 3.0 • TC-IOI TO TC-105 + VC-501 TO VC-505 2.0 o PREDICTED 1.0 < Q_ 0 or -1.0 -2.0 -3.0 1 0 O.I 0.2 0.3 0.4 0.5 0.6 CORE WIRE DIAMETER (mm) FIGURE 10 THE CURRENTS GENERATED IN LEAD CABLES TC-101 TO TC-105 AND VC-501 TO VC-505, AS A FUNCTION OF CORE- WIRE DIAMETER, FOR AN IRRADIATION'IN THE POOL TEST REACTOR - 37 - As can be seen, the net current is linearly related to the core-wire diameter (ignoring cable TC-105) over the limited range of diameters from 0.14 mm to 0.5 mm. As will be recalled, the results obtained in NRU indicate that the (n,y,e) current increases as the cube of the core-wire diameter. However, the results of the Gammacell irradiations (Section 2.2.1) indicate a negative y~ray sensitivity which is essentially constant as a function of core-wire diameter. The net current resulting from the linear combination of these two interactions, plus the (n,B) and (e) interactions, is a linear relation. As can be seen from Figure 10, the net current is zero for a core-wire diameter of 0.39 mm. Assuming that (n,f3) and (e) interactions are negligible, then for a core-wire diameter of 0.39 mm the (y,e) interaction must be cancelling the (n,y,e) current. Therefore, using the (n,y»e) sensitivity obtained for this size of core wire in NRU, it was estimated that, in PTR, S(y,e) is %-ll x 10~27 (A-m"1)/(n«m~2-s-1), i.e. a factor of 10 greater than in NRU. Using this value for the y~raY sensitivity and the (n,y,e) sensitivities obtained in NRU, and assuming (n,g) and (e) interactions are negligible, the relative currents to be expected in PTR, as a function of core-wire diameter, were predicted. The values are also shown in Figure 10, and as can be seen, the "predicted" values agree well with the measured data. As stated, the assumption of a negligible (n,£) current is reasonable for cables VC-501 to VC-505 because of the short time these cables were irradiated, but for cable set TC-101 to TC-105 there is no a priori reason to assume a negligible (n,8) current. However, the good agreement between the total sensitivities determined for these cables and the other set implies a small (n,3) current. The net current from cable TC-105 does not fall on the straight line relating the currents from the other detectors. The measured current from this detector is consistent with its having a substantially less negative y-ray sensitivity compared with the other cables, as was found in the Gammacell tests. The signal - 38 - from detector VC-5 05 also deviates somewhat from the straight line. This may be a reflection of experimental error, but it is interesting that this cable was irradiated for only ^12 minutes, so that the (n,B) current associated with the decay of 5SMn and 65Ni was only ^6% of its equilibrium value. In the NRU irradia- tions, this current was found tu account for ^80% of the total (net) current from this cable. Although the relative importance of this current is not as great in PTR as in NRU, it is clear that had the cable been irradiated for a longer period in PTR, the net current would have been smaller. To summarize: the results obtained from test irradiations in PTR indicate that the y~ray sensitivity, per unit neutron flux, is approximately an order of magnitude greater than in NRU. As a consequence, a null total sensitivity is obtained with a core-wire diameter of ^0.4 mm in PTR, whereas in NRU, a null total sensitivity is obtained with a core-wire diameter of ^0.23 mm. 2.4 ZED-2 Tests A variety of tests were carried out in the ZED-2 reactor at CRNL. Since the reactor environment (y-ray to neutron flux ratio) is similar to that of a CANDU power reactor, albeit the fluxes are about five orders of magnitude smaller, and since results -re available from tests carried out at the Bruce NGS-A, these results are discussed but briefly. Figure 11 shows the currents obtained from cables TC-101 to TC-105 with these cables coiled on a Lucite former and located in the centre of the reactor as shown in Figure 12. The currents from cables TC-101 to TC-104 are linearly related to the core-wire diameter, but the current from cable TC-105 is once again anomalously high. The latter result is consistent with the particular y-ray sensitivity of this cable. The results shown in Figure 11 were obtained for an irradiation time of ^30 minutes. In a separate experiment, cables UC-103 to UC-106 were irradiated in a test assembly somewhat similar to that installed - 39 - 1.2 • TC-IOI 1.0 / 0.8 • TC - 102 0.6 '_ i • TC-105 LLJ 0.4 ~ • • TC-103 O 0.2 / ^TC-104 0 -0.2 - / -0.4 i ii i 0.1 0.2 0.3 0.4 0.5 0.6 CORE WIRE DIAMETER (mm) FIGURE 11 THE CURRENT GENERATED IN LEAD CABLES TC-101 TO TC-105, AS A FUNCTION OF CORE-WIRE DIAMETER, FOR AN IRRADIATIQN IN THE ZED-2 REACTOR - 40 - O FUEL RODS TEST ASSEMBLY o oooiooo ooooooo ooocpooo O O O-Q- • -Q-O O O OOOOOOO ooooooo ooooooo o FIGURE 12 SCHEMATIC REPRESENTATION OF THE ZED-2 REACTOR SHOWING THE LOCATION OF THE TEST ROD RELATIVE TO THE FUEL ASSEMBLIES - 41 - in NRU. The assembly is illustrated in Figure 13. The cables were calibrated on an absolute basis and the results are pre- sented in Table 5, where for comparison the results obtained from the NRU irradiations are also shown. The agreement between the two sets of data is excellent. The twin-core cable, UC-606, was also irradiated in the latter test series, and, as was found in the NRU irradiations, the currents from the two cables were not equal but differed by ^20%. It was observed that the ratio of the two currents was not constant in time but varied from ^1.1 when the reactor was first brought up to power, to ^1.2 when the reactor was shut down. This phenomenon was not investigated further, but it is thought that it is related to charge transfer effects in the insulation, which can be important at the low current levels obtained in ZED-2. ^- " TABLE 5 SUMMARY OF THE SENSITIVITIES DETERMINED FOR LEAD CABLES UC-103 TO UC-106 IN THE ZED-2 REACTOR AND NRU REACTOR Sheath Sensitivity O.D. Wall Core-Wire Lead Cable Diameter ZED-2 NRU Identification (mm) Thickness (10~27 A-m-M/tn-nr^s-1) (mm) (mm) UC-103 2.99 0.51 • 0.70 38.0 40.4 UC-104 2.99 0.41 0.67 33.0 39.4 UC-105 2.19 0.38 0.51 18.0 16.4 UC-106 2.19 0.30 0.49 17.0 18.4 - 42 - ZIRCALOY SPACER ZIRCALOY DETECTOR GUIDE TUBE Cu FOILS ZIRCALOY ION CHAMBER GUIDE TUBE FIGURE 13 SCHEMATIC REPRESENTATION OF THE TEST ASSEMBLY USED FOR IRRADIATING LEAD CABLES UC-103 TO UC-106 IN THE ZED-2 REACTOR - 43 - 2.5 Results Obtained from Bruce NGS-A 2.5.1 RzAultA jfLom Unit ? Following the tests carried out with lead cables TC-101 to TC-105 at CRNL, these lead cables were mounted on flux detector assembly NFM-1 and installed in the Bruce NGS-A, Unit 1 reactor. The location of this assembly is shown in Figure 14, while the arrangement of the detector rod within the reactor is illustrated in Figure 15. The lead cables were strapped to the outside of the Zircaloy carrier tube. No dynamic measurements were made, but the equilibrium currents from the lead cables were measured on three separate occasions, 1977 February 22, 1977 November 30 and 1978 September 08. The results are summarized in Figure 16. As for the ZED-2 and PTR irradiations, the currents from cables TC-101 to TC-104 are linearly related to core-wire diameter while the current pro- duced by TC-105 is anomalous. If we ignore the current from this cable, the results indicate that a null current would be obtained with a core-wire diameter of ^0.18 mm, similar to the result obtained from the NRU and ZED-2 irradiations. Since the neutron to -y-ray flux ratio of the ZED-2 reactor is similar to that of a CANDU power reactor, the agreement between the ZED-2 results and the Bruce results is not surprising, but relatively close agree- ment between the NRU and Bruce results was not foreseen. 2.5.2 Rti,u.lt& jfiom Unit 3 A separate test set of lead cables was installed on flux detector rod NFM-1 in the Bruce NGS-A, Unit 3 reactor. The location of the assembly is shown in Figure 14. The designs of the detector assemblies are similar for the two reactors, but in the Unit 1 reactor the space between the carrier tube and the guide tube is filled with D-O from the moderator, whereas in Unit 3 the space is filled with helium gas. The cables were mainly 1.0 mm in diameter but two 1.6 mm cables were included, the actual dimensions of the lead cables - 44 - TOP VIEW SA - SHUTOFF ABSORBERS CA - CONTROL ABSORBERS FUEL CHANNELS NFM18O SA20 ' SAM, ONFM3 SA13 SA3 SA21 • SAI2 SA26* ONFM14 NFMIO NF°M5 SAI6 O CA1 SA27 • ONFMI6 NFM6 O SAI SA17 NFM9 NFMI O CA4 NFMI9O • SA25 • O O O • SA10 SA5 SA2B NFM13 NFHI1 CA3 SA18 NFM2O SA29O ONFM17 NFM7O SA2* SAI9 CA2O SA30 • ONFM15 ONFM12 SA9* • SA6 NFM8 SA23 4 • SA14 i ' SA22 O NFM20 SA24< • SA15 NFM4O FIGURE 14 SCHEMATIC REPRESENTATION OF THE BRUCE NGS-A REACTOR SHOWING THE LOCATION OF FLUX DETECTOR ASSEMBLIES NFM-1 TO NFM-20 - 45 - CALANDRTA MINERAL INSULATED LEAD CABLE ;; ^COILED DETECTOR CARRIER TUBE GUIDE TUBE GUIDE TUBE LOCATOR FIGURE 15 SCHEMATIC REPRESENTATION OF FLUX DETECTOR ROD, NFM-1, INSTALLED IN THE BRUCE NGS-A, UNIT 1 REACTOR - 46 - 2.0 1.6 TC-IOI 1.2 h- > 0.8 CO -z. 0.4 LU CO TC-105 0 LU -0.4- • 22 FEB 1977 + 30 NOV 1977 ° 8 SEPT 1978 -0.8 - I -1.0 I O.I 0.2 0.3 0.4 0.5 0.6 CORE DIAMETER (mm) FIGURE 16 RELATIVE SENSITIVITIES OF LEAD CABLES TC-101 TO TC-105, AS A FUNCTION OF CORE-WIRE DIAMETER, DETERMINED IN THE BRUCE NGS-A, UNIT 1 REACTOR - 47 - being given in Table 1. The important experimental results are summarized in Tables 6, 7 and 8. Two sets of data were obtained with these lead cables, one during Phase B commissioning of the reactor in 1378 December and the other in 1979 September. In the former case we have been able to make an estimate of the contribution to the total current from the g-decay of 56Mn and 65Ni, I (n,B). As part of the Phase B commissioning test program, the reactor power was raised to 10~2 of full power, following operation of the reactor at power levels < 10~" of full power held for ^3 27 minutes, and then the reactor was tripped. When the reactor was tripped, the signal from lead cable B, as monitored by a strip-chart recorder, drc ~>ed from V3.34 x 10~10 A to %-2.2 x 10"10 A and then rose monoton.. . ^lly towards zero. Figure 17 shows a plot of the signal as a function of time following the trip. As can be seen, the signal appears to con- sist of a single exponential decay component. A least squares fit of the data to an exponential gives I(t) = -2.0 x 10"10 Exp(-4.68 x 10~3 t) A (24) The value of the decay constant, 4.68 x 10~3 min"1, is suf- ficiently close to that of 56Mn (4.48 x 10~3 min"1) and G5Ni (4.58 x 10~3 min"1)* to conclude that the g-decay of these nuclides is largely responsible for the negative contribution to the current in this cable. If we assume that the total current consists of a prompt component, I , due to (n,y,e) and (y»e) interactions plus a delayed component, I,(n,g), due to the g-decay of 58Mn and 65Ni, it follows that 1=1 - I.(l-e~Xt), for 0 < t < T (25) o 1 — - and I = -I^l-e-ATje-Mt-x) , for t > T (26) TABLE 6 SUMMARY OF THE CURRENTS FROM THE LEAD CABLES INSTALLED IN THE BRUCE NGS-A, UNIT 3 REACTOR AS A FUNCTION OF TIME DURING PHASE B TESTING. THE REACTOR WAS RAISED TO 10"2 OF FULL POWER AT t"-0 AND TRIPPED AT t=327 min. THESE DATA HAVE BEEN USED TO ESTIMATE THE CURRENT DUE TO THE DECAY OF 56Mn AND 65Ni, Ij^n.,0), AS DISCUSSED IN THE TEXT. Lead Cable (nA) —Current and Time- T Identification (nA) (nA) Method A Method B Value Used -1.62x10-'° A -1.99x10-'° A -2.30x10-'° A -1.85x10-'° A at 361 min 0.22 0.28 0.25 -0.053 -0.30 0.B3 at 112 min at 185 min at 275 min CO 4.14x10-'° A 3.83x10"'° A 3.53x10 A monitored on strip chart 0.19 0.26 0.22 0.50 0.28 -0.79 at 98 min at 165 min at 256 min I 1.22x10"' A 1.25xlO"9 A -0.06x10-'° A at 353 min NA . 0.009 0.009 1.26 1.25 -0.007 at 101 min at 169 min at 263 min 1.60xl0"9 A 1.61x10"' A 1.67X10"9 A +0.45x10-'° A at 354 min NA -0.07 -0.07 1.62 1.69 +0.04 at 103 min at 172 min at 265 min 1.08x10"' A l.OlxlO"9 A 0.97X10"9 A -3.64x10-'° A at 355 min 0.34 0.54 0.54 1.28 0.74 -0.73 at 105 min at 175 min at 267 min 2.22x10"' A 2.21xl0"9 A 2.19x10*' A -1.9x10"'° fl at 357 min NA 0.28 0.28 2.39 2.1 -0.13 at 107 min at 177 min at 269 min 3.56x10" " A 3.24X10-10 A 2.94X10"10 A -1.96x10-'° A at 358 min 0.20 0.29 0.25 0.47 0.22 -1.14 at 109 min at 180 min at 271 min 1.83x10"'° A 1.63X1O"10 A 1.48X1O"10 A -1.08x10-'° A at 359 min 0.11 0.16 0.14 0.25 0.11 -1.31 at 110 min at 182 min at 273 min TABLE 7 SUMMARY OF THE RESULTS OBTAINED FROM THE 1.0 mm AND 1.6 mm IMI LEAD CABLES INSTALLED IN THE BRUCE NGS-A, UNIT 3 REACTOR Core-Wire Relative Sensitivity, S Lead Cable O.D. Length (mm) Diameter Identification (mm) 1977 Dec 197 8 Sept A 1.02 0.15 full length -1.1 -0 .90 I B 1.02 0.25 ii n 1.00 1 .00 C 1.02 0.32 II II 4.5 5 .25 D 1.02 0.38 ir ti 6.04 7.22 E 1.57 0.28 H n 2.6 3 .53 F 1.57 0.38 M II 7.5 8.82 - 50 - -10Ur- -10-' cc -10 -2 , I I I 50 100 150 200 250 300 350 TIME AFTER SDS-1 TRIP (minutes) FIGURE 17 THE SIGNAL FOR A TEST LEAD CABLE, INSTALLED IN THE BRUCE NGS-A, UNIT 3 REACTOR, AS A FUNCTION OF TIME, FOLLOWING THE REACTOR TRIP. THE RESULTS WERE OBTAINED DURING PHASE B COMMISSIONING OF THE REACTOR. - 51 - where X = 4.5 x 10 3 min"1 and time is defined such that the reactor was raised to 10~2 of full power at t = 0 minutes and tripped at t = x minutes. The currents generated by the other lead cables were not continuously monitored but were measured several times prior to and at least once following the trip. Assuming that equations (25) and (26) also hold for all the cables, these measurements can be used to estimate I.(n,3). This was done in two ways. Method A consisted of solving equation (25) for I] using the measured currents at times t K105 min and t «270 min before the trip. Method B used equation (26) together with the currents measured after the trip. The results are shown in Table 6. For lead cables C, D and F, Method A could not be used, while for lead cable E, the estimate of I.,, obtained using Method A, is quite inaccurate. Except for these cases, the average value of I7 was calculated for use in further analyses. Using equation (25), the currents measured at t «270 min and the average values of I,, values for IQ were calculated for each cable. The equilibrium values of the current, I , were then calculated from equation (27) below, ZT = To " h (27) The values of I , I and 1.^^,3)/I are also shown in Table 6. The results show that the relative amplitude of the (n,g) current covers a wide range of values. In fact, for lead cable D, the (n,g) current is apparently positive whereas for all other lead cables, as for the cables irradiated in NRU, the current is negative. As previously stated, the variation in the amplitude of this term is attributed to variations in the concentration of manganese present in the core wire and sheath as an impurity. The values for the total current determined during Phase B commissioning can be compared, on a relative basis, with the currents measured in September of 19 78 when the reactor was 52 - operating at ^85% of full power (see Table 7). In the latter case the currents were in equilibrium. The two sets of data are in reasonable agreement. The net currents from the various 1.0 mm lead cables are plotted in Figure 18 as a function of core-wire diameter. The current is approximately linearly related to the core-wire diameter and a null current is obtained with a diameter of ^0.2 mm. This result is almost the same as was obtained with the 1.58 mm lead cables installed in the Bruce NGS-A, Unit 1 reactor. However, a careful examination of the data indicates that for the 1.0 mm cables the null current is obtained with a slightly greater core-wire diameter. This result can be explained by assuming that external electrons, which produce a negative contribution, are more important in the case of the 1.0 mm cables than for the 1.58 mm cables, because they can more readily penetrate the thinner sheaths of these cables• Theoretical calculations indicate that yrays produced by neutron capture in the sheath of the IMI cable give a positive current, although the lower energy reactor y~rays result in a negative signal [15]. A positive response to y~rays from capture in Inconel has been observed experimentally, at least for large-diameter IMI cables. The larger number of captures in the sheath of the 1.57 mm cables, compared with the 1.0 mm cables, would therefore result in a greater signal. To conclude the discussion, we consider lead cables B, G and H which have the same geometry except that they penetrate the core to different lengths. By comparing the currents from these detectors, we have concluded that the current generated by the lead cable is proportional to the integral of the f-ax along its path, confirming the previous NRU results. Figure 19 shows the flux distribution, determined during Phase B com- missioning by a fission-chamber scan along flux detector rod TFM-6, for the normal reactor core. The locations of the three background cables under consideration are also shown. Although the lead cables are mounted on NFM-1, this assembly is adjacent - 53 - C/3 UJ 3» UJ a: 0. 0 0. 10 0. 20 0. 30 0. 40 CORE WIRE DIAMETER (mm) FIGURE 18 RELATIVE SENSITIVITY FOR THE 1.0 mm O.D. LEAD CABLES INSTALLED IN THE BRUCE NGS-A, UNIT 3 REACTOR AS A FUNCTION OF CORE-WIRE DIAMETER - 54 - eg o NOISSN FIGURE 19 THE FLUX DISTRIBUTION ALONG FLUX DETECTOR ROD NFM-6, BRUCE NGS-A, UNIT 3, DETERMINED DURING PHASE B COMMISSIONING OF THE REACTOR. - 55 - to NFM-6, so the flux shape along the two assemblies is expected to be similar. For the nominal core, the ratios of the integrated flux are 1 to 0.83 to 0.42, while the ratios of the measured cur- rents from lead cables B, G and H, at different times after the reactor power was raised to 10~2 of full power, are given in Table 8- As can be seen, the relative currents follow the flux integrals reasonably well. The agreement is excellent for times :> 100 minutes, etc. The apparently poorer agreement for times of 10 minutes and 60 minutes may not be real, since for these two measurements the signal from the electrometer was tending to drift down when the readings were taken for the two shorter cables, and had not truly equilibrated. TABLE 8 SUMMARY OF THE CURRENTS GENERATED BY 1.0 mm O.D. LEAD CABLES OF DIFFERENT LENGTHS, FOR THE NOMINAL BRUCE CORE, AS A FUNCTION OF TIME AFTER REACHING 10~2 FULL POWER. THE LENGTHS OF THE LEAD CABLES ARE SHOWN IN FIGURE 16. Relative Current Ratio of Integrated Designation at •VLO min 0 min ^100 min 160 min 250 min Flux B 1,.0 1 .0 1 .0 1.0 1.0 1.0 G 0..90 0 .90 0 .86 0.85 0.83 0.83 H 0.,45 0 .49 0 .44 0.43 0.42 0.42 5.3 SummaJiy To summarize, the results obtained from IMI cables of 1.0 mm and 1.5 mm diameter, installed in the Bruce NGS-A reactor, indi- cate that the generated signals are negative for a sufficiently - 56 - small core-wire diameter, and that a null current is obtained for a core-wire diameter of ^0.2 mm. The g-decay of 56Mn and 55Ni normally contributes a negative component to the total current. However, for a sufficiently small core-wire diameter, a net negative current will result, even without the (n,$) contri- bution, because of the negative y~ray sensitivity of the cables. 3. SUMMARY AND CONCLUSIONS Results obtained from the study of IMI cables have been presented. Experiments were carried out in a 6°Co Gammacell, the NRU, PTR and ZED-2 test reactors at CRNL, and the Bruce NGS-A reactors. These studies indicate that the net current from IMI cables results primarily from three main interactions. These are: (i) the (n,yfe) interaction which contributes a positive component. This component is a strong function of the core-wire diameter and varies approximately as the cube of the diameter. As a result, this interaction dominates for large core- wire diameters and the (y,e) and (n,3) inter- actions are relatively unimportant. (ii) The (y,e) interaction which contributes a negative component. This component depends primarily on the mass of the sheath and, for a fixed sheath mass, does not vary significantly with core-wire size, and (iii) the (n,B) interaction which usually contributes a negative component. This component is largely due to the B-decay of 65Ni and 56Mn, and since manganese is present as an impurity in Inconel 600, the relative size of this component can vary over a wide range. - 57 - In addition to the above interactions, external electrons pro- duced in the mounting hardware, which impinge on the lead cable, give rise to a negative component. Thus, depending on the size of the MI cable, the relative ratio of neutron to y-ray flux at the location of the cable, which depends on the reactor type and the location within the reactor, and the amount of manganese present in the core and sheath of the cable, the net current from an IMI coaxial cable may be positive or negative. In CANDU power reactors a null signal is obtained from lead cables 1.0 mm and 1.58 mm in diameter with a core-wire diameter of ^0.2 mm. For a given cable, the signal will be somewhat positive or negative depending on the amount of man- ganese present. In the NRU reactor, a null signal is obtained with a core-wire diameter of ^0.2 3 mm, while in the Pool Test Reactor, which can be considered to be representative of light water reactor types, a null signal is obtained for a core-wire diameter of %0.4 mm. For core-wire sizes close to that which gives a null signal, the net signal varies approximately linearly with core-wire size. Because the positive (n,y,e) interaction varies approximately as the cube of the core-wire diameter, the signal from a coaxial IMI will increase rapidly if the core-wire size is increased substantially from the value which results in a net null signal. Since the (n,3) interaction is delayed and a substantial fraction of reactor y-rays are also delayed, the net signal from an IMI cable will require several hours to reach equilibrium. Although a null signal can be achieved for equilibrium conditions, there is no geometry which will result in a null current at all times. The signal from a given IMI cable has been shown to be proportional to the integral of the flux along the length of the cable. Thus, the current generated in a given lead cable can be estimated by measuring the current produced in a reference back- ground cable and scaling this current by the ratios of the fluxes - 58 - at the positions of the two cables. In general, however, this method of compensating for lead cable effects will not be perfect since the amount of manganese present in the two cables will not be identical. The situation would be significantly improved if manganese-free Inconel, or some other material such as high-purity nickel, were used for the sheath and core wire. In view of the uncertainties associated with the presence of manganese as an impurity in Inconel 600, consideration should be given to specifying manganese-free Inconel as a material for MI cables or substituting some other material such as high-purity nickel. The results obtained in the present study can be used to estimate to first order the properties of nickel-nickel MI cables since Inconel 600 nominally contains 76% nickel. 4. ACKNOWLEDGEMENTS The authors would like to thank I.L. Mclntyre, L.L. Wright and A.A. Visentin who performed much of the experimental work, and the staff of Bruce NGS-A for their co-operation. Part of this work was financially supported by Ontario Hydro. 5. REFERENCES [1] G.F. Lynch, R.B. Shields and C.W. Joslin, "Environmental Effects on the Response of Self-Powered Flux Detectors in CANDU Reactors", paper presented at Nuclex 75, Basel, Switzerland, 1975 October. Also issued as Atomic Energy of Canada Limited report AECL-5386, 1976 January. [2] E. Hinchley and G. Kugler, "On-Line Control of the CANDU-PHW Power Distribution", paper presented at the IAEA Specialists' Meeting on Spatial Control Problems, Studsvik, Sweden, 1974 October. Also issued as Atomic Energy of Canada Limited report AECL-5Q45, 1975 March. - 59 - [3] H.D. Warren, "Neutron Detector with Gamma Compensated Cable", United States Patent 3,892^969, 1975 July 01. [4] J.W. Hilborn, "Self-Powered Neutron Detector", United States Patent 3,375,370, 1968 March 26. [5] C.J. Allan, "Response Characteristics of Self-Powered Flux Detectors in CANDU Reactors", paper presented at IAEA International Symposium on Nuclear Power Plant Control and Instrumentation, 1978 April 24-28, Cannes, France. Also issued as Atomic Energy of Canada Limited report AECL-6171, 1978 May. [6] J.A. Sovka, "Response of Cobalt Neutron Flux Detectors", Atomic Energy of Canada Limited, report AECL-3368, 1969 June. [7] R.B. Shields, "A Platinum In-Core Flux Detector", IEEE Trans, on Nucl. Sci. NS-20, 19 73 February, p. 60 3. Also issued as Atomic Energy of Canada Limited report AECL-4347, 1973. [8] G.F. Lynch, R.B. Shields and P.G. Coulter, "Character- ization of Platinum Self-Powered Detectors", IEEE Trans, on Nucl. Sci. NS-24, 1977, p. 692. Also issued as Atomic Energy of Canada Limited report AECL-5623, 1977. [9] J. Kroon, "Self-Powered Neutron Flux Detector", United States Patent 4,140,910, 1979 February 20. [10] A.W. Boyd and H.W.J. Connor, "Decay of the Gamma-Ray Dose Rate Following a Shutdown in the NRX Reactor", Atomic Energy of Canada Limited, report AECL-2563, 1966. [11] G.F. Lynch, "Some Theoretical Aspects of Self-Powered Detectors", Proc. of IAEA Specialists' Meeting on In-Core Instrumentation and Failed Fuel Detection and Location, Mississauga, 1974 May 13-15, Atomic Energy of Canada Limited, report AECL-5124, pp. 97-110, 1975 June. - 60 - [12] F.H. Attix and W.C. Roesch, "Radiation Dosimetry, Vol. II Instrumentation", p. 185 ff, Academic Press, 1966. [13] C.J. Allan, I.L. Mclntyre and L.L. Wright, "The Dynamic Response of Platinum Self-Powered Flux Detectors in CANDU Reactors", Atomic Energy of Canada Limited, unpublished report CRNL-1692, 19 78 June. [14] C.J. Allan, A.A. Visentin, I.L. Mclntyre and L.L. Wright, "The Dynamic Response of Self-Powered Flux Detectors in the Bruce A, Unit 1 Reactor on 1978 September 08", Atomic Energy of Canada Limited, unpublished report CRNL-1908, 1979 June. [15] J.S. Hewitt et al., "The Evolution of SPODE: A Monte Carlo Computer Code for Self-Powered Detector Response Calculations", paper to be presented at the 1st Annual Conference of the Can.. Nucl. Soc. , Montreal, 1980 June 18. ISSN 0067 - 0367 ISSN 0067 - 0367 To identify individual documents in the series Pour identifier les rapports individuels faisant we have assigned an AECL- number to each. partie de cette serie nous avons assigne un numero AECL- a chacun. Please refer to the AECL- number when re- Veuillez faire mention du numero AECL- si questing additional copies of this document vous demandez d'autres exemplaires de ce rapport from Scientific Document Distribution Office Service de Distribution des Documents Officiels Atomic Energy of Canada Limited L'Energie Atomique du Canada Limite'e Chalk River, Ontario, Canada Chalk River, Ontario, Canada KOJ 1J0 KOJ 1J0 Price $5.00 per copy Prix $5.00 par exemplaire 1726-80