INTERNATIONAL SYMPOSIUM ON

OF NUCLEAR POWER STATIONS

A . V . K a r p o v

T H E RELIABILITY

An I A E A Symposium on the "Rel iabi l i ty of Nuclear Power Stations" was held f r o m Apri l 14-18, 1975 at Innsbruck (Austr ia) . Two hundred and th ree spec ia l i s t s f rom 40 count r ies and eight internat ional o r - ganizat ions par t ic ipa ted in the work of the s y m p o s i u m . F o r t y - e i g h t pape r s were r e a d . The g r e a t e r p a r t of the pape r s (22 papers ) was devoted to p rocedura l p rob l ems of calculat ing the re l iab i l i ty s, nd the a p p l i c s - tion of re l iab i l i ty ana lys i s du~-ing the planning of nuclear power station s y s t e m s . The pape r s d iscussed methods of calculat ing the re l iab i l i ty c h a r a c t e r i s t i c s in the absence of authentic s ta t i s t ica l data , and the re-- sui ts of re l iab i l i ty armlyses were p resen ted , a ssoc ia ted with ensur ing the safe ty of nuclear power s tat ions: e m e r g e n c y control s y s t e m s , e l ec t r i c power suppl ies , e m e r g e n c y cooling, e tc . In many countr ies , m a t h e - mat ica l methods of re l iab i l i ty armlysis of nuc lear power s ta t ions a r e being developed and numer[ca i p r o - g r a m s for compu te r s a r e being worked out. At p re sen t , there is stil l no unified and ver i f ied p rocedure for calculat ing the re l i ab i l i ty of nuc lear power s ta t ions . Because of the absence of authentic s ta t i s t i ca l data in r e l a t ion to nuc lear power stat ion plant, when analyzing re l iab i l i ty it is r e commended ~hat s t a t i s~ t i ca l data be used for the co r respond ing plant in conventional power s ta t ions . In the ptanning of nuclear power s t a t i o n s not only qual i ta t ive but a l so quanti tat ive ana lys i s of at1 the s y s t e m s and units of a nuclear power stat ion is n e c e s s a r y , f r o m the point of view of opera t ing re l iab i l i ty . Such analysi s Pe rmi t s the bes t a l t e rna t ives for a scheme to be chosen and the c r i t i ca l components to be de te rmined , whose replace~- ment leads to a significant i nc rea se of the re l iab i l i ty index of the nuclear power station as a whole. Thus, the economic c h a r a c t e r i s t i c s of a station can be improved cons iderably with the min imum of c o s t s .

Sta t is t ical data were p resen ted in 10 pape r s on the operat ion of plant and s y s t e m s of nuc lear power s ta t ions , the use of compute r s was discussed for the a s s e m b l y , s to rage , and use of data concerning plant opera t ion . I t can be seen that in a number of counLries, g r e a t at tention isbeingpa~d to the collect ion of s ta t i s t i ca l data about the opera t ion of nuclear power s ta t ions . In the USA, since the second q u s r t e r of 1974, r e p o r t s a r e being issued qua r t e r ly with the data f r o m 30 nuclear insta l la t ions [n the USA. Since 1970, in the tAEA, annual r e p o r t s have been issued about the exper ience in opera t ing nuclear power s ta t ions in the m e m b e r count r ies of the IAEA.

In the IAEA r e p o r t p resen ted a t the sympos ium, an ana lys i s was given of the operat ion of 107 nuclear power s ta t ions [n 15 c o u n t r i e s , I t showed that in 1973 the ave rage load fac tor of a nuc lea r power station amounted to 62.1% and the opera t ing fac tor at power was 72.9%. I f the KIdN* rea0 to r is excluded, which was shut down in 1975 for economic r ea sons , the exper imenta l power s tat ions with a capaci ty of l e s s than 100 1V~V(e) and a l so nuclear power s ta t ions which s t a r t ed up only in 1973, then the load fac tor of the r e - main ing 74 r e a c t o r s is 64.~{ and the opera t ing fac tor a t power is 75.670. I t is noted that these f igures a r e st i l l fa r f r o m the design load fac to r s of 75-80%. Compar i son of nuclear power s ta t ions with conventionai power s ta t ions shows that the c h a r a c t e r i s t i c s of the operat ing re l iab i l i ty of l a r g e - s c a l e t he rma l power s ta t ions , with a capaci ty in e x c e s s of 600 MW(e), a r e one o rder or sl ightly be t te r than the c h a r a c t e r i s t i c s of nuc lear power s ta t ions of the s ame capac i ty .

P r o b l e m s of moni tor ing and se rv ic ing of s y s t e m s and components of nuclear power s ta t ions during opera t ion were diseussed~ f i r s t and f o r e m o s t were methods of nondes t ruc t ive moni tor in~ of the meta l of r e a c t o r hulls , opera t ing under ve ry high s t r e s s condit ions. Work in this d i rec t ion is s ta r t ing to deve lop .

* P r e s s u r i z e d Boi l ing Channel R e a c t o r .

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Trans la ted f r o m Atomnaya Energ iya , Vol. 39, No; 3, pp. 232-233, September~ 1975,

01976 Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part o f this publication may be reproduced, . stored #1 a retrieval system, or transmitted, in any form or by any means, electronic, mecd~anieat, photocopying, microfilming, recording or otherwise, without written permission o f the pubKsher. A copy o f this article is available from the publisher for $t5.00.

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There have been some successes in France and the Federal German Republic in the construction of equip- ment for metal monitoring, based on the application of u l t rasonics and acoust ics . At the present t ime, defects with dimensions of one to two mm in steel sheets with a thickness of up to 350 mm can be de t e r - mined. As r ega rds the sys temat ic monitoring of reac to r hulls during operation, preparat ion for this work is now going ahead. Par t ia l checking of the condition of a reac tor hull has been car r ied out once in the Federal German Republic. An old defect of the hull was detected by means of u l t rasonics which, as was shown, had not changed.

In the papers and discussions, the necess i ty was mentioned for increasing the sensit ivity of moni- tor ing equipment capable of operating at a high tempera ture and in intense radiat ion. P rob lems of opt imiz- ation of technical servic ing of sys tems and plants of nuclear power stations during operation were considered. Thus, it was noted that due to improvement of technical servicing of sys tems in the Hartford reac to r , the read iness factor of the nuclear power station was increased significantly.

During discussions for ensuring the quality, rel iabil i ty of operation and efficiency of nuclear power stations, the necess i ty for p rocess ing the complex system of requi rements for nuclear power station pro j - ects was emphasized. It was found that the operating rel iabil i ty of nuclear power stations depends on both the assurance of safety requi rements and on a sufficiently high readiness factor of the nuclear power station. Economic optimization of nuclear power stations, f rom the point of view of safety and readiness factor , is essent ia l . The read iness factor of nuclear power stations should be 75-80%. In 1974, in the USA, it amounted to 68-73% on nuclear power stations in operation.

Because of the initial mass construct ion of nuclear power stations and the bringing in to the work of a large number of organizat ions and people, the decisive factor is the operating rel iabil i ty of the nuclear power station. A broad training for bui lders , des igners , and operating personnel of the nuclear power station is neces sa ry in methods of calculating the rel iabil i ty of plant and the optimization of technical serv ic ing .

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