JAERI-Conf 99-003 JP9950202

17. The Conceptual Study of Accelerator Driven Radioactive Clean Nuclear Power System (AD—RCNPS) in China

Ding Dazhao China Institute of Atomic Energy P.O.Box 275, Beijing 102413 e-mail [email protected]

Abstract The research activities related to AD-RCNPS in China is described. Some basic features of the system had been drawn from our conceptual study. Examples of accelerator driven fast reactor and accelerator driven reactor were given. In order to reduce the beam intensity required, a fast- thermal coupled system is proposed. In this system the inner fast assembly not only may be used as a MA burner, but also as an amplifier of the external neutron number for the outer thermal assembly. A verification facility is proposed to construct in next ten years. The facility is consists of a 150MeV, 3mA low energy Linac and a light water moderated sub-critical reactor with a changeable core structure. This facility will be a multi-used one, such as material irradiation, neutron nuclear reaction etc.

1. Introduction Power supply is a stern issue in China's economic development. Various predictions indicate that the demand on the primary energy resource will reach 4-5 billion tons standard coal, a fact of 4-5 higher than present level, when China steps on the level of the middle-developed country in the middle of the next century. In the constitution of our present primary energy resources, fossil contributes about 90%. About 70% of the total electricity comes from coal burning. Environment protection is a key link in the sustainable development strategy. The part of the fossil energy resource in the total newly increased power supply should be reduced and the light-pollution energy resources should be developed. Nuclear energy is, of course, a most important and most prospect option. As the fusion energy is now still far away from practicability, in several decades from now on, the nuclear power will be, in all senses, the application of fission energy. As China is speeding up her nuclear power station construction, it is worthwhile to exploit some novel technological option which may release the problems caused by the nuclear power stations based on U-235 fission induced by thermal neutron. Such as: the ultimate disposal of the high level radioactive waste, low resource utilization capability and better reactor safety for better public acceptance to nuclear power. An innovation technological option in nuclear power has been exploited intensively in last ten years or so. That is the nuclear power system comprised of a medium energy high current accelerator driven sub-critical reactor (ADS). Numerous system study and system or project design were proposed or carried out in Japan, United States, Europe, France, Russia and other countries in recent years.fl] [2] The main characteristics of this system may summarized as: 1) The long-life radioactive nuclear waste can be effectively "destroyed" and only short-life and low poison waste are discharged from the system—radiologically clean system; 2) The conversion of U-238 and/or Th-232 in the sub-critical reactor may form an "equilibrium" nuclear fuel inventory in the system for nuclear power production; 3) The intrinsic safety of the sub-critical reactor may improve the public acceptance to the nuclear power.

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In China the study of this noval nuclear power system is named as AD-RCNPS since middle of 1995. A group of scientists in the fields of nuclear physics, reactor physics and technology, accelerator physics and nuclear chemistry from China Institute of Atomic Energy, Institute of High Energy Physics, Beijing University and Qinghua University are involved in it. Some results from the conceptual study on the system are outlined in section 2 and a proposed verification facility in order to exploit the basic property of the system and to promote the advance of the related technologies is described in section 3.

2. Outline of the results of conceptual study

A. Basic idea

By injecting an external neutron «0 into a sub-critical reactor with neutron multipling factor k (k<\), the neutron will successively multiply according to 2 3 Ns=n0(l + k + k +k +---) = n0/(l-k) (1) Where no is neutron number normalized to one proton's spallation yield. In the stationary regime

condition, Ns-na is increased by fission in reactor. If express in tern to one fission

It terns out, that in this system the "effective" average neutron number per fission may express as v* = v I k (3) This makes high neutron surplus in the reactor. Neutron surplus is defined as the difference between neutron number produced in the reactor and total neutron consumption, including the neutron needed for

maintaining the chain reaction, neutron leakage and all kind of parasitic absorption. By taking Nc and Nk as the neutron surplus of critical reactor and sub-critical reactor with external neutron source, the enhancement of neutron surplus reads as

Nk~Nc= y(^p) (4)

This makes the system suitable to transmute waste and/or to convert the fertile into fissile.

As it is shown in (2), the number of neutron produced by fission is Ns-n0 and corresponding to total

number of fission occurred in the system is (Ns - n0 )lv This makes the output thermal power of the system is

while the beam power of accelerator is E I. This makes the energy gain of the system is

Ep v \-k

where E f is the energy deposit per fission, n0 — neutron produced in spallation by one proton, E — the proton energy and V — average neutron number per fission. According to (4), less the k value, more the neutron surplus, but it will be achieved at the expense of less energy gain of the system, according to (6). The anticipated working condition of the system for k value is 0.85-0.97. The upper limit is defined by the reactor safety, the low limit is defined by roughly half of the output energy may feed to the grid. To transmute the waste in this system, the apparent decay rate of a nucleus may express as

X = XQ + aR

A.o is the intrinsic decay rate of the nucleus, (p -the neutron flux and (XR is the total reaction cross section excluding the elastic and inelastic scattering. In thermal neutron reactor, successive absorption of neutrons makes the MA's into fissiles, while in fast reactor with hard neutron spectra, say the average energy higher than 600keV, the MA's may directly undergo fission as the fissiles.

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In Table 1, the main conclusions from our conceptual study are summarized. The calculation is based on simplified burn up equation, CENDL file and assuming the fission neutron spectrum in the fast reactor.[3], [4] Table 1 Conceptual Research For Th~»U and U-»Pu Systems Thermal and Fast Systems Parameter Th-»U Systems U->Pu Systems T-System F-System T-System F-System <1>, cm'Y1 ~5xlO13 ~3xlO15 ~1014 ~5xlO15 Loading, ton Th,20 Th,20 U,20 U, 20 Power, MWt 866 1500 330 1390 MA Production <

B. Two examples Proton Bom Tube

We have calculated two examples to Lend Taigm ( Flo* In ) illustrate our conclusions mentioned above.

1)AD-FBR A medium size sodium cooled fast breeder reactor drived by an accelerator with lGeV/16mA shows its advantages over the ordinary one, such as less Pu inventory required, higher breeding ratio Lead Target; Flow Oul) and reasonable transmutation rate ( which may support two sets lOOOMWe PWR ) at expense of less 15% energy output. The 0 Np-15Pu-30Zr ^ U-lOZr core structure is given in Fig. 1 and the main O AmO-35Pu-10Y parameters are given in Tab.2. The U-lOZr- @ U-19Pu-10Zr comparison with ordinary fast breeder with U-lOZr same core structure is given in Tab.3. This CO) U-lOZr calculation gives us some idea about how (#) the fast sub-critical reactor is in favour of ^ Gas Expanding Assembly the MA's transmutation and fissile breeding.[5] Fig. 1 ADFBR Core Configuration

Table 2 Sub-Critital Blanket FBR Parameter Value Accelerator Ep (GeV) 1.0 Ip (mA) 16 Target Pb BlanketType pool Coolant Na Keff 0.971 Energy Gain 47.5 Average Neutron Energy (keV) 650 Average Neutron Flux (cm'V) 3.87 xlO15 Maximun Neutron Flux(cm'V) 6.47 x 10" Average Burnup (MWd/t) 105 Pu Inventory (Kg) 1187 MA Inventory (Kg) 715 MA Transmutation Rate (Kg/y) 29.8 MA Production (Kg/y) 6.4 Support Ratio (Roughly) 2GWe PWR

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Table 3 Comparison of AD-FBR WithFBR Parameter AD-FBR FBR Power (MWt) 760 880 Pu Inventory (Kg) 1187 1324 BR 1.37 1.27 Breeding Time (y) 12.5 17.1 Keff 0.97 1 .02

2) AD-PHWR The pressured heavy water moderated reactor (CANDU type) was adopted for the analysis both for Th-U and U-Pu fuel cycles. Four central pressured tubes were substituted by the beam pipe and lead target. The parameters for Th-U fuel and for U-Pu fuel are given in Tab.4 and Tab.5 respectively. It is shown, that AD- PHWR is favour to Th-U fuel cycle not only higher burn up, but also with slight breeding capability. While in U-Pu fuel cycle, the fuel may self-sustainable only with relative higher beam current, smaller k value and with a little higher burn up than ordinary CANDU. [6]

Table 4 Sub-Critical Blanket AD-PHWR (Th-U) Parameter Value Accelerator Ep (GeV) 1.5 Ip (mA) 1 0 Target Pb Blanket Type Pressured Tube D2O moderated (CANDU Type) Keff 0.985 Fuel Composition UO2+ThO2 Vm/Vf 8.93 Burnup (MWd/t) 3xlO4 Loading U-233 (kg) 959 Th-232 (kg) 64000 Equilibrium Enrichment 1.46% Breeding Ratio 1.01 Power (MWt) 1840

Table 5 Sub-Critical Blanket AD-PHWR (U-Pu) Parameter Vaule Accelerator Ep (GeV) 1.5 Ip (GeV) 45 Target Pb Blanket Type Pressured Tube D2O moderated (CANDU Type) Keff 0.82 Fuel Composition UO2 Vra/Vf 5.94 Breeding Ratio 1.00 Power (MWt) 1500

As the accelerator driven system provides a new technological option for nuclear energy, we may construct the paradigm of fission energy system as in Fig.2. When one concerns the U-Pu fuel cycle in thermal blanket, one may notice that the requirement of accelerator beam power will be three or four folds higher then other system. This leds us to analysis the so-called fast- thermal coupled system.

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1 Thermal Fast Thermal Fast Fast-Thermal Reactor Reactor Blanket Blanket Coupled Blanket

Neutron Flux (n/cm2sec) <1014 l5 Breeding Capability Th-U U-Pu, Th-U Th-U U-Pu U-Pu Selfsustain U-Pu Transmutation Capability x MA probably FP MA MA,FP Reactor Safety good good Excellent Excellent Excellent Energy Production Excellent Excellent Excellent Th-U Excellent Excellent Accelerator beam High for U-Pu Modest Low power required*) Modest for Th-U

*) High >50MW; Modest —20MW; Low —10MW

Fig. 2 the paradigm of fission energy system

C. Fast-Thermal Coupled System We consider a system which is consists of an inner core of fast blanket and an outer core of thermal blanket with thermal neutron reflector in between. This means that the thermal neutron cannot diffuse into the inner one while the fast neutron may comes out from the inner one into the outer one. The inner core is a small sized fast blanket, which is used as the transmutor of MA's and to amplify the external neutron number produced in spallation reaction by fission in it. The outer one is, suppose, CANDU type one with Th-U or U-Pu fuels. It is used to produce the energy and to transmute the LLFP's. By using a 44 group constant, the calculation was carried out for a one dimensional (spherical) structure. Taking the target volume as a radius 20cm Pb and a fast blanket of radius 42.5cm with uniformed mixed 500kg Np and 5000kg U-238, the amplifying factor will be 2.3 and 5.1 for k=0.89 and 0.96 respectively. If the fast blanket with same radius is devided into two layers, first is pure Np of 200kg and second is uniformly mixed Np and U of 300kg and 5000kg, the amplifying factor will be enhanced to 2.5 and 6.1 for the same k value mentioned above.[7] If this system really works, the beneficial effect is to reduce the beam power of accelerator required. This may makes easier life for accelerator specialists.

3. A proposed verification facility for AD-RCNPS

A. Scientific goals of the verification facility AD-RCNPS is an entirely new approach for the exploitation of the next generation nuclear energy, which including new physics basis, neutronics in high power sub-critical reactor, new technical issues of the reactor system, challenge to the high current medium energy accelerator with high reliability and material problems both for beam extraction window, target system and reactor components etc. All these problems could be solved step by step both indidually or integrally. According to present technical status in China, we think a small size multi-purpose verification system is a rational choice. CIAE and IHEP have proposed such a facility consists of a 15OMeV/3mA low energy accelerator, a swimming pool light water sub-critical

- 136 - JAERI-Conf 99-003 reactor, which is a modified core structure of an existed and some laboratories for neutron nuclear reaction measurement, material testing and target assembly testing. The conceptual layout of the verification facility is shown in Fig.3 and the configuration of the accelerator and modified core structure of the swimming pool reactor are shown in Fig.4 and Fig. 5 respectively.

Target

area

Sub-critical reactor Neutro'rr- • reaction •—•© area p - 2-3 MW

Sub-critical Light water swimming-pool type with changable core structure Target area Pb/Bi Target test bed with P^-O^ MW Neutron reaction area (p,n) reaction and neutron reaction measurement with mlcropusle mode Irradiation area Isotop production material test simulation (window) RIB area Spallation production analysis and extraction Transmutation with MA sample

Fig. 3 Conceptual layout of verification facility for AD-RCNPS

B. Rationalization of parameters of the verification facility According to various estimation and empirical fitting, the neutron yield is roughly one to one proton at 150MeV.[8] We may take this value as the "threshold" of the spallation reaction. The proton range in lead is roughly 3.5cm at 150MeV, this makes the possibility to mock up the target heat extraction and hydraulic properties. The maximum output power of the original swimming pool reactor is 3.5MW. We take the maximum beam current up to 3mA may fit the requirement of running the sub-critical reactor with k value ranging from 0.90 to 0.97. On the other side, 150MeV/3mA low energy accelerator consists all accelerating structure, such as RPQ, CCDTL and CCL, which are essential components for the construction of the full scale accelerator. The 5% duty factor 50HZ pulse operation mode of the accelerator will be the first step for the CW mode of the accelerator with tens milliamper current. We may gain a lot of accelerator physics, technology and operation experience from this low energy accelerator with reasonable fund and lay the base for full scale accelerator construction. The accelerator will operate normally in 50HZ pulse mode, while for the neutron nuclear reaction study, the micro-pulse mode with ns pulse width and few hundred ns interval in between is essential. So, some chopper will be arranged in the LEBT and MEBT after ion source and RFQ. The average current is expected to be <\0jua. The modified core structure of the swimming pool reactor is shown in Fig. 5. The fuel elements and assembly will be the same as original one, while 3X4 assemblies of the fuel in the central of the core is substituted by beam pipe and lead target with some space for different materials for the purpose to verify various conceptions of blanket structure, including the fast-thermal coupling, transmutation and so on.

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LEBT MEBT

ECR RFQ (200 MHz) CCDTL (200MHz) CCL(400MHz)

50KeV 3X2.5MeV 7.5MeV 80MeV 150MeV 60mA 3mA 3mA 3mA a) Pulse mode b) Micropulse mode repetation rate 50 Hz Pulse Width ~lnsec duty factor 5% average current 5aonA average current 3 mA

Fig. 4 Conceptual Configuration of Low Energy Part of High Current Medium Energy Accelerator

D Fuel assembly with light-water moderator/coolant (68x68) El Innercore with changeable structure and material

Target pb Moderator pb Length of core 500 mm Fuel U-235 (10%) k 1.035 Anticipated keff 0.94-0.98, power < 3MW

Fig. 5 Core Lattice Structure of Verification Facility Blanket

The k value is 1.035 when all cells are filled by the fuel assembly besides the central part is filled by lead modrator. This give us a quite large range to vary the k value by changing the fuel assemblies used and/or the fuel management in meeting the requirement of k value from 0.90 to 0.97. The construction of the verification facility is expected in two phases until 2007, as is shown in Tab.6. In phase one, the technical development will be carried out individually, while in phase two the integral will be undertaken. On the base of this verification facility, we expect that a full scale demonstration experimental facility may be realized in the middle of 2010's.

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Table 6 Demonstration Verification Facility Experimental Facility 1998—2002 2003—2007 2008-2017 Phase I Phase II Key components development Low energy part of LINAC Full scale • ECR High current source Pulse Micropulse Accelerator Ep=50KeV,Ip=60mA mode mode • RFQ injector Ep=150MeV Ep=150MeV CW-LINAC Ep~2.5-3MeV, Ip—3mA Ip=3mA Ip—lOfA Ep^lGeV accelerator • CCDTL cavity Further study on High energy Ip^lOmA High energy accelerating Accelerating structure Structure • SC-CCL • CCL(normal conductivity • CW-mode operation of and / or super-cond.) LINAC Accelerator Physics • Basic theoretical study of beam dynamics in LFNAC and cyclotron • System conception study LWR sub-critical reactor Power output • Neutronics study using driven by LINAC — lOOOMwt Zero-power sub-critical Pout^3MWt Blanket assembly driven by D-T • Changable core structure external source (Both • Power density flatten thermal and fast assembly) • Transmutation simulation

Pb/Bi test loop • Pb/Bi test bed

Pbeam=S0.5MW Material • W solid state test

target Pbeam=S0.5MW • Window material test

• Neutron data evalution • Spallation neutron • Medium energy nuclear source property Nuclear physics reaction theory measurement • Proton,neutron transport • Neutron data code development measurement

Chemistry Basic research on Technics on partitioning process partitioning process

Acknowledgement This work is done by a group of scientists, the author would like to express his sincerely gratitude to Profs. Z.X.Zhao, Z.L.Luo, Y.S.Zhang, X.Q.Xu, G.S.Liu and S.X.Fang for their contributions to this study and provide their calculated results prior to publication.

References [1] S.Saito: "Research and Development Program on Accelerator-Driven Trasmutation at JAERI" Proc.2nd Intern. Conf. on Accelerator- Driven Transmutation Technologies and Applications, June3- 7, Kalmar, Sweden, p.52(1996) C.Bowman: " Optimization of Accelerator-Driven Technology for Light-Water Reactor Waste

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Transmutation" ibid, p. 11 M.Salvatores,I.Slessarev,A.Tchistiakov: " Nuclear Power Development and Hybrid System Role" ibid, p.169 V.Kazaritsky: " Feasibility Study of Technologies for Accelerator-Based Conversion of ilitary Plutonium and Transmutation of Long-Lived Radioactive Waste (ISTC supported Project #17)", ibid, p.77 [2]C.Rubbia,J.A.Rubio,S.Buono,F.Carminati,N.Fietier,J.Glavez,C.Geles,Y.Kadi, R.Klapisch, P.Mandrill on,J.P.RevoI and Ch.Roch: " Conceptual Design of a Fast Neutron Operated High Power Energy Amplifier" CERN/AT/95-44(ET), 1995 [3] Ding Dazhao: " Accelerator Driven Radiologically Clear Nuclear Power System Joint IAEA/CNNC Seminar on 21st Century Nuclear Energy Development in China, May22-23, Beijing.China, 1997 [4] Zhao Zhixiang, Ding Dazhao, Xu Xiaoqin, Shi Yongqian, Lou Zhanglin,Liu Gui-sheng, Shen Qingbiao and Fan Sheng: Ref[l] p. 186 [5] Zhang Yushan Private Communication [6] Xu Xiaoqin Private communication [7] Liu Guishen Private communication [8] J.M. Carpenter: " Pulsed spallation sources for slow neutron scattering" Nucl. Inst Meth. A145, p.99,(1977) Lone et.al.: " Total neutron yields from lOOMeV proton on Pb and 7Li target" Nucl. Instr. Meth. A214, p333,(1983)

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