ZJE/72/ /1970/
F. DRÁB. B. LNĚNIČKA, L. KOČANDRLE / SINGLE-PURPOSE DIGITAL COMPUTER IN NUCLEAR ENGINEERING
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ŠKODA-Concern NUCLEAR POWER PLANTS DIVISION, INFORMATION ZJE 72 1970
F. Drab, В. Lněnička, L. Kočandrle
SINGLE-PURPOSE DIGITAL COMPUTER IN NUCLEAR ENGINEERING
ŠKODA CONCERN Nuclear Power Plants Division, Information Centre FLZEU, CZECHOSLOVAKIA ABSTRACT
The article deals with the possibilities of using a digital computer in nuclear engineering, with special reference to the control of nuclear reactors.
Printed by Czechoslovak Atomic Energy Commission Centr» for Scientific and Technical Information Zbraslav nad Vltavou L Introduction
Nuclear power engineering experimental nuclear physics, ttie applica tion of radioisotopes in various branches of science and engineering, the research of the effects of nuclear radiation on materials and living organisms, etc., those are the fields in which the task of measuring and recording the most varied kinds of nuclear radiation occurs. The results of measurements then serve either for the determination, of the parameters of the object producing nuclear radiation or for the control of these parameters. The measurement and control of the objects can be characterized, in a general form, by the diag-ams in Pig. 1. k\ both cases the information of the object is obtained on the detector output cc ied in an electric signa]. In the case of measurement the purpose of the measuring process is an analysis of that signal, in the case of control of fho process further operations have to be carried out the object of which is the creation of a c The materialization of both the measuring and the control process is markedly affected by the nature of the signal on trie output r4de of the detec tor equipment. According to this nature the following signals are differentiated between : a) An analogue signal / / The information is contained in the magnitude of d. с current • .1 \ The fundamental duty is the measurement of the value 6/*-/and of its time de rivative Л'4/ %w.' . Къг most purposes meawjrpme nt with a constant time error ... & w a 4/ -» const, is satisfactory. -lO -4 TypicaJr l range of measurement : i . • Ю ampsr 1 - i • lO amps, ^ ^ min ^ max * b) A discrete signal The information is contained in the magnitude of the time interval bet ween two electric impulses and in the amplitude of the impulse. The fundamental task is the measurement of the instantaneous value of the average count rate of impulses A (t) and of its time derivative AAJM . For most purposes measurement with a constant relative error • const, is satisfactory» A Typical range of measurement i J[ , . */* «4 ~k ,_6 . .-.7, A Jr ^ -^min » 1 «ifnp s ,/lmax • lO to lO imp s . A considerable part of the problems of measurement and control in nuclear engineering can be reduced to the solution of several types of problems which repeat themselves frequently. The development of nuclear engineering demands a search for the most perfect algorithms and equipment which would solve these problems» Important in this connection are a high precision, reliability and the obtaining of information in the shortest possible Ume. Not evnn economic points of view remain disregarded. Attention is directed to the digital technique which can best satisfy a number of require- ments. Thus single-purpose digital units come into being which are, funda- mentally, computers with a fixed programme for the solution of the individual problems. The importance of these problems grows with the introduction of controlling computers, for these single-purpose units become a connecting link, i. e. a converter between the process under investigation and the central computer. Such a converter supplies the computer with information which is already processed. This substantially reduces the demands for speed in the feeding of information into the central computer. In addition to that single— -purpose digital equipment can serve for the control of the process and thus create, together with the object controlled, a sub-system in relation to the controlling computer. Thus the possibility is created of using large systems with a hierarchical structure, with a high reliability given by the redundance in the sub-system. 2* MQteriaJi^ation of Singte-Ригрозе Digital Computer The technical realisation of the equipment for the measurement of the characteristics of nuclear radiation is influenced primarily by the nature of the signal and varies markedly with the kind of signal it processes, i, e, analogue or discrete. For the processing of an analogue signal sensitive amplifiers are usually used mostly connected as operational ones, which can operate with minimum - 4 - -И currents in the neighbourhood of Ю amps* Difficulties encountered when a wide dynamic measuring range is demanded (this requirement is characteristic of measureme nts and output control of a reactor) are dealt with either by a changeover of the range cf the instrument or by the use of a logarithmic scale in which case, however, the precision of measurement is lower* The processing of an impulse signal by itself does not cause any funda mental difficulties» The crux of the problem is moved rather to the region of the evaluation of the average count rate of impulses, for the time intervals between two impulses are incidental and are governed by statistical laws. The usual method of evaluation of the average count rate is to count the impulses for a preset period or to measure the period which is necessary for the countin of a preset number of impulses. In either case the count rate is determined as the quotient of the number of impulses and of the time. Prom these data also the result is determined. In Д/ it is proved that these methods are not the optimum ones from the point of view of the time necessary to obtain the informa tion in the specified quality and a more favourable method is proposed, i. e. the so-called method of sequential analysis. Since the question of the speed which the information of the specified quality is obtained with is an important one, particularly in the matter of the control of the objects (e. g. in the control of a reactor), it is obviously of advantage to build, for this cnee, an equipment which utilizes the principle of sequential analysis /2,3/. Such an equipment is a unit designed arid built as a laboratory .sample in 1966 in the Control Research and Experimental Physics Group /*/. The block diagram of this unit is shown in Pigs. 2a and 2 b. The sequence of impulses from the object, of a measured count rate A (t), passes to one of the inputs of a comparison circuit to the second input" of which a reference sequence of impulses is connected, of the known frequency _A ~ from a controlled generator of the reference frequency. The comparison circuit keeps on comparing the two frequencies as long as it cannot decide, with the spe cified quality, whether Л^ Á or -Aa"^ Д. When it has made the decision the deciding impulse leads, in a case according to Pig, 2a, to the reference fre quency change Д -ЛфЬу means of the control circuit. Thus it is achieved that the indicated reference frequency A. ~ follows the measured count rate _A(t) and is thus its approximation. /• By a suitable connection of the control circuit, it can be achieved that the dynamic properties of the unit do not depend on the region of the measu red frequency A in which work is being done. With the same connection the so-called period T (jz »-j • —r ) , a quantity important for the control of the rtuclear reactor, can easily be determined. When a connection according to Fig. 2b is used the deciding impulse can be used directly for the control of the object, i. e. of the nuclear reactor. The equipment as described can be designed entirely with the use of the digital technique. This ensures, č»part from the favourable properties gene rally attributable to the digital technique, the possibility of easy adaptation of the equipment to other purposes than to the measurement of the output and period of a nuclear reactor. For instance, it is easy to change the dynamic properties of the equipment in dependence on the error -A-vt^or on the relative error Г •&* ап€* ** *s likewise simple to modify the equipment for the measurement of the time derivative of the frequency 6V -— . jib t The advantages of the described equipment include also the capability, in conjunction with a special analog-to-firequency converter, to process even an analog signal from a nuclear radiation sensor. This property makes the described equipment suitable for universal application in nuclear engineering as well as wherever work v.'ih nuclear radiation is done. After the experience gained with the first sample of this equipment a unit was designed and manufactured in a modification intended for the measu rement and control of the output and period of a nuclear reactor /5/. This unit is built of logic elements Logites TESLA (except for the supply unit, control ling parts and indicating equipment), mostly NF 14О ferrito-transistor elements. The complete unit for the processing of an impulse signal consists of three panels. One panel contains the assembly of the ferritc—transistor elements shown in the photograph, another panel the feeding sources and a third panel the control part and indicating equipment» When work is being done with an analog signal the set of the three panels is supplemented by a fourth panel in which the amplifiers and the analog-4o«frequency converter are accommodated. Trie complete assembly of all four panels above each other is lOOO x 600 x 490 mm in size, the total weight is 64 kg. - 6 - References /if Wold A. : Sequential Analysis (John Wiley, Now York, 1950) Щ Dráb F. : Sequential Analysis and its Applications in Hie Control - Measureme nt Area (in Rub-ian). Proceedings of a Comecon Symposium held at Prague, June U - 16, 1965 /3/ Dráb F. : Optimum Coun* — Rate Estimate for a Poisson Pulse Train. Riso Report, M - 867, 1969 Danish Atomic Energy Com-nission /i/ Kočandrle Lw Statistical Filter for an Optimum Count - Rate Lněnička В. : Estimate (in Czech) Report N— Ae 1148/Dok, Nuclear Power Plant Division ŠKODA, 1967 /5/ Kočandrle L.: A Small Digital Unit SADÍC for Measurement Lněnička В, : and Control of the Output and Period of a Dráb F. : Nuclear Reactor (in Czech) Report N— Ae 1666jbok, Nuclear Power Plant Division ŠKODA, 1969 - 7 - POKATtON Z (О n(t) PfíOC£SS/AřC OBJ£CT D£7£CT0P Of ШГОЙМЛПОН F/g 1a/ PPOCFSS /4£AS(SP£Af£:A/r Zo (t) ii (t) , za) СОЛ/rPOL BLOCK OBJ£CT DZnCTOfí Fq. 1b PPOCZSS COAVrfiOL 08J£CT CONPAP/SON CIRCUIT REF£*CMC£ FP£Q fý 2 as RfACTOR PARAM£T£R S£GU£/VT/Al M£ASUR£M£Nf сонтяи COMPARISON ORGANS or CIRCUIT OBJ£CT авлсг MOO/f/CATION SP£CIMC/9TlOAf Of рАЙАНГТгек Of SIGNAL Of OBлет F'S 26 RCACTOR P4RAM£T£R S£GU£A/flAL CO/VfROL