ŠKODA ZERO POWER CRITICAL ASSEMBLY SR-OA

Transcription

1 ZJE /78/ /1970/ HMBS^oaMtMisani J. FLEISCHHANS. J. KOTT. A. ZBYTOVSKÝ ŠKODA ZERO POWER CRITICAL ASSEMBLY SR-OA ŠKODA - Concern NUCLEAR POWER PLANTS DIVISION, INFORMATION CENTRE PLZEŇ-Czechoslovakia ттштттт тштт

2 J. Fleischhans, J. Kott, A. Zbytov&ký ŠKODA ZERO POWER CRITICAL ASSEMBLY ŠR~OA ŠKODA CONCERN Nuclear Power Plants Division, Information Centre PLZEŇ. CZECHOSLOVAKIA

3 ABSTRACT The authors describe the purpose to which the reacto.* is to serve. The main part of the article is devoted to the description of the reactor. Printed by Czechoslovak Atomic Energy Commission Centre for Scientific and Technical Information Zbraslav nad Vltavou

4 Introduction The endeavour to determine experimentally the preparation of the physical start up of power reactors and the duties and obligations of the ŠKODA Corporation resulting from ft led to the building of the ŠR-OA experimental reactor of a zero power in the laboratories of the Nuclear Power Plants Division in Vochov. This assembly is further intended to perform the duty of a critical assembly on the basis of which will be studied the most suitable compositions of the core of the BARBORA Type swimming pool reactor of loo kw up to 20 MW thermal power which is included in the 3rd stage of development of the Experimental Base of the Nuclear Power Plants Division. It is also reckoned that a large group of designers and project engineers will make themselves familiar with the basic principles of operation and control of a nuclear reactor. The chosen type of reactor, i. e. water-water with а Ю % respectively 80 % enrichment fuel of the WWR-S or ШТ-М type is suitable as an experimental reactor, for its operational, technological and control qualities and its experimental possibilities do not require any particular location, skilled operators or high first costs which are the factors which under our conditions cannot easily be disregarded» Description of ŠR-OA Experimental Assembly The. ŠR-O is an experimental nuclear reactor of zero power (N IO watts) with a light water moderator and reflector, Ks core consists of WWR-S or IRT-M type fuel elements. It is situated in an aluminium vessel erected on a steel carrying plate which is anchored in the concrete foundation of the reactor» The SR-GA vessel is surrounded by concrete and water biological shielding the front part of which can be dismantled. The filling draining and treatment of water performes a technological circuit. The control and safe operation of the reactor are assured by means of a system of control devices and safety circuits. The reactor control is done from a control desk in a separate room, inside tne vessel channels are arrangod ior t' *.«- < >! t of neutron beams and for the pneumatic introduction of the neutron ecirce, as well аь. ockofcs for the filling and emptying of water and channels for the control ion- and. "V

5 fission chambers. Prom a special beam in the upper part of the vessel there are suspended control and scram rods as well as a system of pulleys used for the movement of the rods. The upper part of the vessel is enclosed by a steel shielding cover with holes for attendance. The core of the reactor is buili on a carrying plate filled to the bottom of the aluminium vessel. The WWR-S and IRT-M fuel elements used in the со» re have been tested for a long period of operation in many reactors of the VVWR-e and IRT-M type where their worth as safe and reliable element of the reactor has been proved. Prom the experimental, operating and safety points of view this experience is very valuable. Another advantage of this type of fuel is its eaey future availability and the reproducibility of its fundamental physical parameters. The fuel elements WWR-S are manufactured of UO + Mg O- enriched 235 to lo % U, plate type fuel elements FRTrM are produced of Al + U mixture 235 enriched to 80 % U, both of the fuel elements are covered with aluminium. The physical calculation of the macro - and mic restructure of the core were carried out by conventional methods of calculation and experimental results which had been obtained on several reactors of a similar type were taken into consideration. According to the technical literature on the WWR-S reactors available in the CSSR the following parameters of the reactor were determined: U The core will be formed of 26 to 28 fuel elements situated^i a carrying plate of aluminium with a total of 48 cells. For the control 2 cadmium filled berani rods and 1 steel control rod will be used. 2. The maximum.excess reactivity of the core will be 0.25/3 approximately. From the available certificates of the USSR the quantitypf UOp vi *h a lo % 235 U enrichment was found to be 1^3046 kp. With a pitch of the lattice of 17 mm the critical size as determined vari*»^ from 26 to 27 elements. The reactivity of the 28th cartridge is 1 '}. * This ensures: firstly the critical size of the ŠR-OA core with 26 2Я elements, secondly a sufficient excess reactivity for experimental purposes of a value up to 0.25/J. The arrangement of the core is shown in Pig. 1. The? safe and control system ensure uninterrupted maesurement, checking and control of the neutron output of the SR-OA reactor. The system consists of :i independent measuring channels which give information about tho instanto- t - 4

6 neous values of Ihe power output-and period of the reactor and about the deviations of these parameters from the preset values. These signals are further processed, in the block of logic circuits, for automatic or hand control of the power output of the reactor» The safety system of the reactor which forms part of the logic circuits, ensures the safety of operation of the reactor, uninterrupted checking of the measured parameters and a correct operation of the electronic apparatus, fr» case of a defect it stops the reactor automatically by the drop of two scram rods. Trie control of tne neutron output is done by i control rod. The detectors for the measurement of the neutron output are secured in the reactor vessel so that a movement is possible both in the radial direction and vertically. This always permits an optimum position to be found when the configuration of the core is changed. The reactor is equipped, for start up and for лоте experimental works, with a Ra-Be neutron source of an activity of I Ci Ra 226 wth a total emission of Ю n/sec up to 4 Jf The source is accommodated in a container in a concrete shielding truck which travels into a hole in the concrete foundation of the reactor. The source moves along the central vert i cal centreline of the reactor and its working position is immediately below the bottom of the core. The movement of the source is pneumatically operated, remote controlled trom the control desk. Pig. 2 shows a section of the ŠRHOA reactor. The filling with and draining of water and its treatment, the purification and storage is perfcrmed by technological circuit which consists of 2 tanks, 3 pumps, an ion exchanger column and the appropriate fittings and connecting pipework. An upper tank serves as a container of demineralized water, a lower tank as a service tank. The design of the circuit docs not permit on uncontrolled escape of the reactor water into the drain. To ensure unobjectionable working conditions and the? checking of them the reactor hall is equipped with a system of ventilation and air treat.'nont arid with a continuous dosimetric check with optical and acoustic signalling of radiation exceeding the preset level* Conclusion The ŠR-ОА experimental assembly is the first reactor equipment comple- 5 **

7 tely designed and manufactured in Czechoslovakia, The concept of the equip» ment ensures reliable operation which will be suitable for' a wide range of experimental work from the fields of physics and nuclear reactors as well as from the fields of reactor radiation detection and studies of eyslems of nuclear reactor control and protection» The core must be considered absolutely pure from the physical point of vie.v during the entire period of operation» The favourable first cost (approximately 8 million Kčs) and the exceptionally short period of construction (approximately 15 months) are further advantages of the conception used»

8 Illustrations Fig, 1 Fig. 2 ŠR*QA core arrangement ŠR-QA reactoi section Key 1 Core 2 Neutron start-up pneumatic driving mechanism 3 Control rod 4 Core carrying plate 5 Ion-chamber channel 6 Qoncrete biological shielding 7 Water biological shielding 8 Iron top shielding 9 Control rod drives 10 Horizontal beam plugs U Neutron source truck 12 Horizontal beam tube 13 Platform <

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