PACS PROGRAMME — PROJECT FOR ANALYSIS OF COMPONENTS AND SYSTEMS OF NUCLEAR PLANTS

S. CURCURUTO, G. GRIMALDI

Italian Directorate for Nuclear Safety and Health Protection (ENEA/DISP), Rome, Italy

Abstract

O b j e c t i v e of the PACS Proqrammo is to e v a l u a t e claln of abnormal e v e n t s on r i a l Lan NPI's j ri o p e r a t i o n , for bat kf i II Ing and d e s i g n i m p r o v e m e n t s

p u r p o s e s ,

l o w t h r e s h o l d e v e n t s w i l l h o a n a l y s e d w J I h s t a l i s l j c a l melhodo l o q y , a i mod tu e v a l u a t e re.liabi lily parameters of < omponanls and s y s t e m s

R e s u l t s of a n a l y s i s w i l l be stored in a c o m p u t e r i / e d data baso, und updated L i m e by t j i n o , as now oporaL L n rial d a l a w i l l be a v a i l a b l e

Some r e s u l l h of PGn s Lud i es, a l r e a d y pi1 r formed, w i l l be r e v h . e d u L i l i / i n q p^-inL s p é c i f i e d a t a , drawn oui by PrtCtt pnx^i-Miiiiiie

1. O b j e c t i v e and Scope

O b j e r l i v e of the PACS proqranime is lo c v a l u a l e , in f\ s y s l e m a l i( w<:iy, lha (jpor'atiriq c j x p a r i arice ( o . e . ) of I t a l i a n planlj in opérai i on, for

bark f J Ltinq purposes sind d e s i q n improvemenl s of new p L a n l s .

I irst of a l l , d c \ l a of Colors o I3WR ploint w i l l bo a n a l y / e d , t a k e n i n t o drcounl the f o l l o w i n g :

this is the most rerenl" J t a l i a n plant in operation;

m o s t o f i t s o . e . i s e x p e c l e d w i I I b e a p p l i c a b l e l o M o n l a l l o HWR plant, now in cons t r u r l i on;

Mol hudoloqy cine! software package are expected could bo applied to plants other (.ban m.u, I ear ones.

F u r t h e r m o r e - t e c h n i c a l r e s u l t s CDU) d g i v e some i n d i c a t i o n of behaviour of components used in conventjonal p l a n t s as well, at least for some selected failure mode-'*. O b v i o u s l y d i f f e r e n t design and opérât Jonal criteria should bo taken into account

Methodology of a n a l y s i s w i l l bo of both q u a l i t a t i v e¹ and quantitative typo, so lhat first by predominant faHijros and failure modes w i l l bo

searched, in a second s ! atjo data w i l l be analy^od with sLrttisiical techniques, aimed id find out r o l J a b i J j L y paramoLcrs of the arialy/ed parts.

Hs a result of the programme, a software package for r e l i a b i l i t y analysis w i l l be a v a i l a b l e and a data bank containing r e l i a b i l i t y parametars of toiiiponenl') an<l r.ysloms

I he software package w i l l be developed on personal computer. Guided mannes w i I I be provided, with a p r o v i s i o n Lo update, time by t i m e , data entry o<; new dale» w i l l become a v a i l a b l e . Jn such a way " l i v i n g " r e l i a b i l i t y data w i l l be a v a i l a b l e ; , and indication of degraded failure rate w i l l bo drawn out,

if any, on the basis of trend analysis.

Some connections w i l l be e s t a b l i s h e d w i t h other l.l\IIIA/l)rSP a c t i v i t i e s , such as p r o b a b i l i s t i c safety s t u d i e s (PGn), already performed for Caorso and flontalto plants, fiome results of PSA studies w i l l be revised, u t i l i s i n g plant

s p e c i f i c dala drawn out from PfiCC! programme¹,

M a i n l y I. he job w i l l include I he following steps:

d e f i n i t i o n of components and systems to bo analysed, on the basis of the master part l i s t of Caorso plant and the classifications already used for PSn studies;

d e v e l o p m e n t of Lho software package, data e n t r y and o u l p u l formal, t e c h n i c a l a n a l y s i s of I ho «so I 'u, ( od < omponorit •> and s y s t e m s arid s t o rag o o f r o s u lis;

plant bac k f J. l ti nq and desiqn m o d i f i c a t i o n s i m p j emonl al j on, if ciny 2. P i lot Study and Ongoing Programme*

ft pilot study was performed manually on d i e s e l generators of all [Lallan plants j ri operation, with the aim to o r i e n t a t e the e n t i r e proqrcxiniiic¹, Lo improuo plant safety on the ariaJy/od system <\nd to dofjne Lho software resoiircas needed.

We anaJy/ed t h i s system, as an exampJo of two d i f f e r e n t cond i l 10111. , a system in s t a n d - b y arid in o p e r a t i o n . In ;>u<. h »A way we had a c o m p l e t e

mod e l l i nq of p o s s i b l e fail u re mod e :;

f urthcrmore DOs arc one of the most import<\nl, safely related s

[n fact, m^ny PSA studies underline the importance of DGs performance;

in c o n t r i b u t i n g to core damage frequency.

Data were arialy/od w i t h the aim to e v a l u a t e the f o l l o w i n g parameters1

imauailabi 1 i ty on demand, r e l i a b i l i t y in operation.

lor the first parameter, we considered all. °Aartups of the d i e s e l s and the failures to startup were <onsjdered.

For Lho second one, the time of real operation of these engines and the pertinent failures to operate were evaluated.

Reliabj l i t y parameters of s i n g l e I)G and total ones were found out.

ns r e s u l t s u f (.ho a n a l y s i s Iho f r i l l owing aspects wore; focal i/od.

s u r v e i l l a n c e programme of Caorso p l a n t is adequate;

a better performance of the d i e s e l s could bo reached with Lha implement al i on of n prehoater system of Ihr lubrication oil;

d i shomogene ily was found among tha 4 d i o s o l s of Cojorso p l u n L , ma i n l y for UG? ;

c r J t J r a l sub^ysLoms wore found oui for each diosol and for earn p l ani.

F u r l h o r s t u d i o s are now in progress on.

d r i l ' L of i ns IrumtjnUil ton of amorgoncy safely sysLoms of Caorso p l(\nt ;

ma I f iiru l i oii'i of unJuc-:-. of safely r o l a l o d systems of Caorso and I r i n o p l an L

Average r e l i a b i l i t y paraiuoLoi-'i of all pressure ins trumentalion has been ovaluaU'd und compared wil.h Lh(^ target ui I I I I I ' i O O . Mow s p a c i f i c e v a l u a t i o n i «

in progrès;', for each system, instrument type and manufacturing.

A n a l y s i s of valves m a l f u n c t i o n s was recently started up. At the. moment r l a s s i f i c a 1 ion of v a l v e s is in progress, aimed to group valves according to s y s t e m , type, si^o, manufacturing and environment c o n d i t i o n .

IAEA'S EXPERIENCE IN COMPILING A 'GENERIC

Reliability data are an essential part of a probabilistic safety assessment. The quality of data can determine the quality of the study as a whole. Among all the data which are needed for performing a PSA study, component failure data are the ones most frequently mentioned.

It is obvious that component failure data originated from the plant being analyzed would be most appropriate. However, in few cases complete reliance on plant experience is possible, mainly because of the rather limited operating experience and usually limited number of failures for meaningful statistics. Nuclear plants, although of different design, often use rather similar components, so some of the experience could be combined and transferred from one plant to another. In addition information about component failures is available also from experts with knowledge on component design, manufacturing and operation.

That bring us to the importance of assessing generic data. (Generic is meant to be everything that is not plant specific regarding, the plant being analyzed ). The generic data available in the open literature, can be divided in three broad categories. The first one includes data base used in previous analysis. These can be plant specific or updated from generic with plant specific information (latter case deserve special attention). The second one is based on compilation of plants' operating experience usually based on some kind of event reporting system. The third category includes data sources based on expert opinions (single or aggregate) or combination of expert opinions and other nuclear and non-nuclear experience. If one is to use generic data sources either directly or as a prior for updating, much information is required about the different aspects of generic data sources.

This paper reflects insights gained compiling data from generic data sources and highlights advantages and pitfalls of using generic component reliability data in PSAs.

Considering current I A E A efforts to prepare a computer code package for event tree and fault tree analysis in personal computers (PSAPACK) and the associated need for a reliability data base, a compilation of published component reliability data was undertaken at the IAEA. Some of the features of the data base, like the coding system, are, therefore directly governed by the package.

As of today the generic data base contains about 1000 different records, including practically all the components which are accounted for in PSA studies of Nuclear Power Plants.