the fi l l ing of the s y s t e m with sodium should be completed in August , 1978. Cr i t ica l i ty is to be reached in August , 1979, and full power is to be reached in F e b r u a r y , 1980.

I N T E R N A T I O N A L S Y M P O S I U M ON C O N T R O L A N D

S A F E T Y S Y S T E M S A N D M O N I T O R I N G - M E A S U R I N G

F O R N U C L E A R P O W E R S T A T I O N S

I . S. K r a s h e n i n n i k o v a n d V . S. F i l o n o v

More than 300 spec ia l i s t s f r o m 35 countr ies and a lso the r ep r e sen t a t i ve s of 5 internat ional o rgan i za - tions par t ic ipa ted in the Symposium held at Cannes , F r ance , and organized by the IAEA in cooperat ion with the French Atomic Energy Commiss ion .

A t the p lenary ses s ion the inc reas ing role of nuc lear power generat ion in the wor ld balance of genera ted e l ec t r i c power was emphas ized and it was noted that its success fu l development was due to the fu r the r i m p r o v e - men t of moni tor ing and control s y s t e m s of nuclear power s tat ions. At p r e s e n t the ave rage opera t ing eff iciency of nuclear power s tat ions amounts to 60-65%: the ut i l izat ion of the 35-40% r e s e r v e will depend on inc reas ing the re l iabi l i ty of the equipment and ensur ing the opera t ing control of nuclear power s ta t ions in va r iab le load condi- t ions.

The par t i c ipan t s in the sympos ium were concerned about the necess i ty for developing internat ional equip- ment s t andards , ensur ing safety moni tor ing of nuc l ea r power s ta t ions , and the development of equipment for moni tor ing the envi ronment .

During the five working days of the Symposium 68 r e p o r t s were hea rd and d iscussed: these were d i s - t r ibuted over 7 sect ions: exper ience in the insta l la t ion, s ta r tup and opera t ion of control and safety s y s t e m s and equipments of nuclear power s tat ions (16 repor t s ) ; observa t ion s y s t e m s for r e a c t o r units (11); power d i s - t r ibut ion in the r e a c t o r core , and control (4); safety s y s t e m s and e m e r g e n c y signall ing (8); new designs of moni tor ing and control s y s t e m s (7); moni tor ing ins t ruments (19), and re l iabi l i ty (3).

An analys is of the r epo r t s allowed the pr inc ipa l future t rends to be decided, along which r e s e a r c h will be conducted, and new developments for the purpose of achieving a h igher opera t ing eff ic iency of nuclear power s ta t ions , e s t ima t ion of moni tor ing and control , and a s ignif icant i nc rea se of equipment re l iabi l i ty .

Grea t at tention was paid to the widespread use of compute r s y s t e m s for the purpose of effect ing f lexible control of nuclear power stat ions in va r iab le load opera t ing conditions, for reducing the ef fec t of ope ra to r s on the operat ion of nuclear power s tat ions and for the el iminat ion of negat ive a f te ra f fec t s caused by faulty o p e r a - tion. Based on the analys is of the opera t ing resu l t s of 39 r e a c t o r s , opera t ing fo r a to ta l of m o r e than 200 r e a c - t o r - y e a r s , the f i rm of West inghouse a r r i v e d at the conclusion that eve ry ope ra to r in 1 y e a r makes an average of 1.32 e r r e r s , w i t h t h e l o s s of 27.26 h in each case. The loss amounts to about 350,000 do l la r s pe r yea r . The f i r m had succeeded in cut t ing.considerably the number of faulty opera t ions , by the introduction with displays on cathode ray tubes.

The use of m i c r o p r o c e s s o r s in the c r i t i ca l pa r t s of the computer s y s t e m s inc rea se s significantly the opera t ing re l iabi l i ty and, as supposed, will even p e r m i t the i r use in safety sy s t ems .

�9 An impor tan t fac tor for the development of automated compute r ized s y s t e m s is the development of models of the p r o c e s s e s and a lgor i thms for handling the information. The complexi ty of the models can be judged by the descr ip t ion of the t ra in ing equipment for the AGR r e a c t o r . The behavior of the r e ac to r is considered on the bas i s of 50 di f ferent ia l f i r s t - o r d e r equations and 130 a lgebra ic equations.

Compute r techniques a re being used pa r t i cu la r ly success fu l ly in sy s t ems for moni tor ing the power poten- tial dis tr ibut ion. When p r o c e s s i n g the data on the power potential dis t r ibut ion, s eve ra l approaches will be used. The Japanese spec ia l i s t s consider the dis t r ibut ion f i r s t of all as two-dimensional (with r e s p e c t to radius) with the subsequent introduction of e r r o r s in height. By using the data f r o m 32 fou r - sec t ion neutron

T rans l a t ed f r o m Atomnaya Energ iya , Vol. 45, No. 4, pp. 317-318, October , 1978.

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d e t e c t o r s , the m e a n - s q u a r e e r r o r of the power dis t r ibut ion calculat ion for the BWR r e a c t o r amounted to 1.7~. The p rocedure r eq u i r e s the expendi ture of 35 sec of machine t ime (type IBM 370/158 computer) . Using the l a r g e - n e t method for a r e a c t o r of the BWR and PWR type (area of cell covers 9 a s s e m b l i e s , height 1 m) , spec ia l i s t s f r o m the F ede ra l Republic of Germany have shor tened the calculat ion t ime to 0.4 sec , with an e r r o r of about 4%. For the dis t r ibut ion calculat ions in CANDU r e a c t o r s in the r e a l - t i m e cycle , r e g r e s s i o n a l ana ly- s i s has been used with a p r e l i m i n a r y calculat ion and with invers ion of the s ta r t ing m a t r i c e s . Fi f ty- two vanad- ium de tec to r s s e r v e d as the data source , with an ave rage sp read of the read ings of 4.6%; in consequence of the sp read , the e r r o r of the calcula t ion amounted to 6.2%. The p rocedure r equ i r e s a smal l compute r m e m o r y (15K words) and the expendi ture of machine t ime within the l imi t s of I sec. The calcula t ions a re feas ib le fo r a r e a c t o r power s ta r t ing with 2% of nominal ,

At the same t ime , invest igat ions a re underway for in tegrated s y s t e m s , capable of moni tor ing and con- t ro l l ing nuc lear power s ta t ions as a whole, as a unit complex subjec t , and of developing ra t ional control cy - c les , depending on the situation. These invest igat ions a r e focused on the region of development of the future and flexible a rch i t ec tu re of s y s t e m s based on a d is t r ibuted s t ruc tu re . The g rea t e s t succes se s in this d i rect ion have been achieved by the Canadian spec ia l i s t s . They have developed the f i r s t v e r s i o n s of basic " s t ruc tu ra l un i t s , " providing a l ink between the s y s t em s t r u c t u r e s , MODEMY, interchannel connecting a s s e m b l i e s , d iag- nost ic mon i to r s , etc. The authors mention the diff icult ies in the path to achieving the s y s t e m and es t ima te the p roposed per iod fo r the complet ion of development at 5 y e a r s .

One of the pr inc ipa l f ea tu res of the d is t r ibuted s t ruc tu re is the approximat ion of logic faci l i t ies for p r o - cess ing the data , " in te l l ec t , " to the region of location of the s enso r s and auxi l iary mechan i sms . Severa l r e - po r t s we re devoted to the const ruct ion of these devices . Special is ts f r o m the U.S.A. have ca r r i ed out a detai led technicoeconomic ana lys i s of the poss ib le ach ievement of a d is t r ibuted s t ruc tu re for a complex control s y s t e m for nuclear power s ta t ions , as the bas i s of which a r e used pe r iphe ra l mul t ip lexers made in va r ious design v e r s i o n s , including CA MAC units.

When designing nuclear power s ta t ion moni tor ing s y s t e m s , not re la ted to the category of safety a s s u - r ances but having 3000-3500 moni tor ing points , the use of pe r iphe ra l mul t ip lexers gives an economy of 25-50% by compar i son with the cen t ra l i zed vers ion .

The French spec ia l i s t s r epor t ed on the development of an e lec t ron ic sy s t em for nuclear power s ta t ions with a d is t r ibuted s t ruc tu re and logic , designed on KONTRBLOK modules . The " s t ruc tu ra l unit" module has 256 inputs or outputs, a buil t- in m e m o r y with the capabil i ty of r e p r o g r a m m i n g , and galvanic decoupling be - tween inputs and outputs. Based on these modules , it is p roposed to build moni tor ing s y s t e m s for future French nuclear power s ta t ions with a capaci ty of 1300 MW. The s y s t e m s , containing 660 modules , will ensure total control automat ion of the nuclear power stat ion except for the r e a c t o r safety sys t em. M i c r o p r o c e s s o r s and o ther novel e l ec t ron ic components have been widely used in the development of the modules.

In the r e p o r t of the Westinghouse spec i a l i s t s , the main c h a r a c t e r i s t i c s were d iscussed of the internal a rch i t ec tu re of the modules intended for the crea t ion of in tegra ted safety s y s t e m s for nuclear power s tat ions. The ba s i s data of the ex te rna l a rch i t ec tu re of the sy s t em were r epor t ed at the Symposium in 1976 at Munich. The c r i t e r i a , fixed as the bas is for the development of the in ternal a r ch i t ec tu re , take into account the quan- t i tat ive and quali tat ive f ea tu res of a r e a c t o r safe ty sys t em: the re l iabi l i ty of fulfil l ing the safety funct ions, con- venience of opera t ion and maintenance sui tabi l i ty , taking account of the r e m o t e n e s s of the modules and the in- f requent inspection. The poss ib i l i ty has been provided for achieving logics of 2/4 and 2/3, and protec t ion f r o m faul ty act ions of the o p e r a t o r s ,

In o rde r to s impl i fy the p r o g r a m m i n g in the modules , an ana log -d ig i t a l hybrid design is being inves t i - gated, which has been chosen a f t e r careful ana lys is of the functions of each type of module.

Taking account of the functional poss ib i l i t i es of new technical means , a l te rna t ives were cons idered in a number of r epo r t s for the construct ion of equipment s y s t e m s for fas t r e a c t o r s , having specif ic cha rac t e r i s t i c s ; unique solutions have been provided in the moni tor ing s y s t e m in the French WSuperph6nixW r e a c t o r .

Notable s u c c e s s e s in the provis ion of plant moni tor ing have been achieved by the use of the noise analysis method; these methods provide the poss ibi l i ty of detect ing anomal ies at an ea r ly stage. The no ises f r o m d i f - f e ren t s enso r s insta l led in r e a c t o r s c a r r y valuable informat ion about the behavior of the plant , which up to the p r e s e n t has not been used, because of the nonavailabi l i ty of the essen t i a l sufficiently complex equipment , methods of ex t rac t ing the in format ion , and i t s in te rpre ta t ion . The authors of the r epo r t s used the signals f r o m neutron s e n s o r s , ins ta l led in the core and outside the r e a c t o r , f r o m f l o w - r a t e , p r e s s u r e and t e m p e r a t u r e s e n s o r s , and v i b r o s e n s o r s .

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In a l m o s t all the p a p e r s , the technique of a p r e l i m i n a r y analog r eco rd has been used for the r e p r e s e n t a - tion of s ignals with a durat ion of 10-14 rain in a magnet ic r e c o r d e r . In o rde r to d i sc r imina te the useful in fo r - mat ion , a calculat ion of the spec t r a l power densi ty of the noise is used , by means of a h igh-speed F o u r i e r - t r a n s f o r m a lgor i thm, the calculat ion of mutual ly co r r e l a t ed functions and coherence functions for the mutual ly dependent s ignals .

During invest igat ions of the mechanica l v ibra t ions of plant and s t ruc tu r e s of the r e a c t o r units and the t he rma l -hyd rau l i c p r o c e s s e s , many in teres t ing phenomena have been detected in the f requency band of 0-20 Hz. An invest igat ion of the effect of the c i rcula t ing pumps has been c a r r i e d out ove r the range 0-120 Hz. In the region of higher f requencies ,50-540 kHz, the phenomena of liquid leakage f r o m h i g h - p r e s s u r e v e s s e l s we re invest igated. In a typical configuration of an expe r imen ta l equipment , band f i l t e r s we re used: a m p l i f i e r s , ana - log signal c o m m u t a t o r s , Special equipment for handling the a lgor i thms of the h igh-speed F o u r i e r t r a n s f o r m , o r un iversa l min icompute r s .

In te res t ing data have been obtained by the F rench spec ia l i s t s . Based on the ana lys i s of neutron noise , the v ibra t ions of the control rods a t a f requency of 12-14 Hz w e r e detected, and osci l la t ions of the core in the region of 3.8-4.8 Hz, depending on the r e a c t o r power .

Extens ive invest igat ions have been under taken by Swedish spec ia l i s t s on a boiling r eac to r . They have in- ves t iga ted the noise of s ignals f r o m neutron de tec to r s located in the core . The f luctuations of the de tec to r s ig - nals we re caused by local ef fec ts , but mainly by the fo rma t ion of s t e a m bubbles. When ca r ry ing out the e x p e r i - m e n t s , the spec t r a l densi ty dis t r ibut ions of the noise intensi ty we re obtained, which were concentra ted in the f requency range of 0-1.5 Hz.

Based on neutron noise ana lys i s , m e a s u r e m e n t s we re under taken of the speed of movemen t of s t eam bub- bles in the r e a c t o r channel, and a t t empts w e r e made to m e a s u r e the magnitude of the f low- ra te of the coolant in the channel; however , a dependence of the speed of movemen t of the bubbles on the coolant flow ra te was obse rved only in the lower p a r t of the core .

In the r e p o r t of the Japanese spec i a l i s t s , in te res t ing data were p re sen ted on the applicat ion of the noise ana lys i s method for detect ing the r e g i m e of instabi l i ty in the opera t ion of the evapora to r and the s t eam s u p e r - h e a t e r with sodium coolant. It was found to be poss ib le t ode t ec t the r eg ime of instabi l i ty at dif ferent s tages of development of the phenomenon. Based on the expe r imen ta l work ca r r i ed out, a s tate number has been con- s t ruc ted , functioning in r e a l - t i m e conditions.

The F rench spec ia l i s t s r epo r t ed on the high sensi t iv i ty of the acoust ic noise ana lys i s method: in the detect ion of l eakages f r o m p r e s s u r e v e s s e l s in the range 50-250 kHz, they succeeded in detect ing leakages of up to 1 l i te r /h . However , U.S.A. spec ia l i s t s noted that there a r e many diff icult ies in the path of introducing this method.

A cons iderable number of r epo r t s was devoted to the development of individual ins t ruments and dev ices , n e c e s s a r y for organiz ing the moni tor ing of nuclear power s tat ions. I t should be noted that extensive inves t iga - t ions a r e being c a r r i e d out and s e a r c h e s made for new const ruc t ive solutions for building the mos t impor tan t components of moni tor ing s y s t e m s - s ens o r s and spec ia l cables . The invest igat ions a re being d i rec ted at inc reas ing the re l iab i l i ty , working t e m p e r a t u r e and radia t ion s tabi l i ty , and inc reas ing the reproducibi l i ty of the m e a s u r e m e n t r e su l t s dur ing a prolonged per iod of opera t ion. The g r e a t e s t impor tance in this case is al lot ted to reducing the d imens ions of the i n t r a r e a c t o r s e n s o r s , thei r speed of r e sponse , and the analys is of the signal s t ruc tu re f r o m s ens o r s of the DPZ type.

The excel len t organiza t ion of the Symposium should be ment ioned, the sp i r i t of goodwill and r e spec t , and a lso the w a r m r ega rd toward the Soviet delegat ion of the F rench spec ia l i s t s - the o rgan ize r s of the Symposium.

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