VVER-1000 REACTOR PLANT: DISTINCTIVE FEATURES

OF DESIGN, RESULTS OF START-UP OF FIFTH UNIT OF

NOVOVORONEZH ATOMIC POWER PLANT, AND WAYS OF

FURTHER IMPROVING THE PLANT

Y u . V. V i k h o r e v , V. A . V o z n e s e n s k i i , V. P . D e n i s o v , A . S . D u k h o v e n s k i i , N. A . I s a k o v , A . N. K a m y s h a n , V . K . S e d o v , V , A . S i d o r e n k o , a n d V. V . S t e k o l ' n i k o v

UDC 621.311.2:621.039

The fifth unit of the Novovoronezh Atomic Power Plant (NAPP) with a VVER-1000 w a t e r - m o d e r a t e d - w a t e r - c o o l e d power r e a c t o r , cons t ruc t ion of which began in 1972, has come into opera t ion . This unit is the pi lo t unit for a l a rge s e r i e s of a tomic power plants (APP) equipped with VVER-1000 w a t e r - m o d e r a t e d - w a t e r - cooled power r e a c t o r s in p r e s s u r e v e s s e l s .

The unit was des igned at the Insti tute of The rma l and E l e c t r i c a l Design, the Gidropres Expe r imen ta l Design Office was the main d e s i g n e r of the n u c l e a r s t e a m - g e n e r a t i n g plant (NSGP), and the I. V. Kurchatov Inst i tute of Atomic Energy prov ided the sc ient i f ic superv i s ion of the development work. Leading e n t e r p r i s e s of the count ry , such as the I zhorsk and Kirov P lan t s , the E l e k t r o s i l a Indus t r ia l A s s oc i a t i on , and the Kharkov Turbine Works , p a r t i c i p a t e d in the cons t ruc t ion of the unique a tomic power plant equipment .

D i s t i n c t i v e F e a t u r e s o f P l a n t f o r F i f t h U n i t o f N A P P

In developing the VVI~R-1000 p ro j ec t for the NAPP the goal was to c r ea t e a 1000-MW(elec t r ica l ) unit, using equipment t r a n s p o r t a b l e by r a i l r o a d and a t ta ining a subs tan t ia l i nc rea se in i ts unit power with a view to improving the spec i f ic technica l and economic i nd i ca to r s . At the same t ime the des igne r s t ack led the p rob l em of cons t ruc t ing a unit which would fully mee t the a tomic power plant safety r e q u i r e m e n t s in t roduced in the e a r l y 1970s.

Sat is fac t ion of the condit ion of r a i l r o a d t r a n s p o r t a b i l i t y Hmits the d i a m e t e r of the r e a c t o r v e s s e l to 450- 460 cm. With a co r r e spond ing r e a c t o r core d i a m e t e r of 310-320 cm, i ts spec i f ic power should r each 110-120 k W / l i t e r , which is 30% h igher than in the VVl~R-440. The cons t ruc t ion of such a core r e q u i r e d special m e a - s u r e s to equal ize the f ield of energy r e l e a s e in the r e a c t o r : the choice of opt imal r echa rg ing condi t ions , the use of b locked bu rn t -up a b s o r b e r s in f r e sh a s s e m b l i e s se t up on the p e r i p h e r y of the r e a c t o r c o r e , and p r o - f i l ing the UG~ en r i chmen t ove r the c r e s s sec t ion of the a s s e m b l y .

The p r inc ipa l c h a r a c t e r i s t i c s of the fuel were de t e r m i ne d in opt imiza t ion ca lcu la t ions [1] with computa - tion of the economic i nd i ca to r s . The values chosen were fue l - e l emen t d i a m e t e r 9.1 ram, ra t io of a r e a of w a t e r to a r e a of UO 2 in the core 1.85; the 4.4% enr i chmen t of the fuel m a ke - up in three r echa rg ings during a 3 - y r run c o r r e s p o n d s to the min imum n o r m a l i z e d expend i tu res of r e a c t o r cons t ruc t ion and opera t ion and en - s u r e s a mean fuel bu rn -up f rac t ion of 40 M W . d a y / k g U in the spent fuel a s s e m b l i e s . In the USSR the p r e - r equ i s i t e s ex i s t for a t ta ining such values of the mean bu rn -up f rac t ion in uranium dioxide fuel e l emen t s . F o r example , two VVI~R-1000 a s s e m b l i e s in MR loops r eached a mean burn -up f rac t ion of more than 40 M W - d a y / kg U. Tes t s with five a s s e m b l i e s a re continuing. To complete the e xpe r i m e n t a l demons t ra t ion that the fuel e l emen t s a r e capable of ope ra t ing at a high burn-up f rac t ion p rov i s ion has been made for annual r echa rg ing of half the fuel dur ing the f i r s t pe r iod of opera t ion of the fifth unit of NAPP. In this case the mean burn -up f r a c - t ion does not exceed 30 MW. day /kg U.

The r e a c t o r core contains 151 fuel a s s e m b l i e s . Two cont ro l s y s t e m s , a boron and a mechan ica l s y s t e m , have been p rov ided for compensat ion of the r e a c t i v i t y m a r g i n . The la rge number of mechan ica l cont ro l mech- an i sms (109) with a r e l a t i v e l y sma l l number of a b s o r b e r e l emen t s in a bundle (12) r e su l t ed f rom an endeavor

T rans l a t ed f rom Atomnaya l~nergiya, Vol. 50, No. 2, pp. 87-93, F e b r u a r y , 1981.

0038-531X/81/5002-00695 07.50 �9 1981 Plenum Publishing Corpora t ion 69

to create in the pilot unit a capability for operative action on the power distribution in the reactor core and to limit the decrease of the coolant surface in the fuel assembly with channels for shifting the absorber elements.

The control elements are divided into 14 symmetric groups, two of which contain a half-length absorber for equalizing the axial power distribution. The elements of the control and safety system (CSS) are shifted by a linear step drive at a rate of 5 em/sec.

The distribution of the energy release in the core is monitored with a temperature sensor at the outlet of each fuel assembly and 31 neutron measuring probes (NMP) with seven n -* B detectors over the height. Of the 31 NMP, 22 are uniformly distributed in the core and the remainder are located in fuel assemblies from different symmetry groups.

The VVER-1000 vessel had to be made from a material possessing greater strength than that of the 15Kh2MF steel used for Vu On the basis of results of the development of a technology for the fabri- cation of the vessel in the supplier plant, it was decided to choose 15Kh2NMFA steel.

The main circulation system (MCS) of the fifth unit at NAPP incorporated a 3000-MW(thermal) reactor and four loops with piping with an inner diameter of 850 ram, each of these loops comprising a GTsN-195 main circulating pump (MCP), a PGV-1000 steam generator, and one main gate valve (MGV) in the cold and hot piping of the loops. Connected to the undetachable part of the MCS are a volume compensator and pipes of the system for emergency boron intake and emergency shut-down cooling. Pipes from four liquid tanks for emer- gency flooding of the core in the event of large leaks are connected direct ly to the r eac to r vessel , in pairs into the top and bottom spaces.

The star t ing point in designing the fifth unit of the NAPP was the condition of ensuring the safety of the population in a maximum accident: instantaneous rupture of a DUB50 pipe, coinciding in time with conditions of total deenergizing of the atomic power plant. The entire MCS is contained in a protective envelope of p re - s t r e s sed re inforced concre te , designed to withstand a p r e s su re of 0.55 MPa. Provision has been made for triple 100% redundancy of all active sys tems ensuring the safety of the APP. In the event of a malfunction of the uni t ' s control panel (UCP) there is a backup control panel which can be used to c a r r y out the neces sa ry operations to control the safety, shut-down, and shut-down cooling sys tems of the APP.

The e lec t r ica l equipment of the control and safety sys tem includes sys tems for forming emergency p ro - tection (EP) signals, for collective and individual control of control e lements , and for automatic control with the neces sa ry apparatus and reliable supply devices. Tripping of the EP and the operation of the power regu- lator took place according to the " two-out -of - three" principle.

The "Uran-V Complex" sys tem was crea ted for p rocess ing and present ing the data in the APP; this sys tem compr ises an M-60 complex, an M-7000 computing complex, and "Orion" data displays.

Equipment for the MCS with operating charac te r i s t i c s and conditions meeting the requirements for VV]~R-1000 was being built in the USSR for the f i rs t t ime. At the same t ime, work was undertaken on the development of severa l types of MCP with a ro to r angular velocity of 105 and 157 r a d / s e c . The development of a reliable shaft seal and complete validation of the design by ful l -scale stand tests were accomplished most quickly for the GTsN-195pump, with an angular velocity of 105 r a d / s e c , and this pump was chosen for the fifth unit at the NAPP. Saturated s team at a p re s su re of 6.3 MPa is produced in s team gene ra to r s of the horizontal type usually employed with VV]~R reac to r s [2], with turbines made of 0KhlSN10T austenitie s teel , whose effi- ciency has been confirmed by operational experience in atomic power plants in the USSR.

To ensure the efficacy of the solutions during the operation of the pilot trait with unique equipment, gate valves were installed in the circui ts of the MCS and two K-500-60/1500 turbogenera tors were provided for e lec t r ic i ty generation. The condensers of the turbines are cooled with the aid of an art if icial cooling pond.

R e s u l t s o f S t a r t - U p o f F i f t h U n i t o f N A P P

Main Stages in Start-Up and Adjustment Operations. Start-up and adjustment operations in the fifth unit of NAPP were carried out in the following stages: functional testing of the individual systems; hydraulic test- ing and circulatory flushing of the MCS; first inspection of NSGP equipment; hot running tests of the NSGP; testing of the protective envelope; charging of the reactor core; physical start-up; and power start-up and stage-by-stage power build-up.

The duration of the s ta r t -up and adjustment work, beginning with the stage of hydraulic tests and c i r cu - latory flushing up to the development of the design power (without allowance for unforseen repa i r s to equipment)

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was planned to be equal to 316 days . At al l s tages up to power s t a r t - u p , in p a r a l l e l with the adjus tment of the equipment of the r e a c t o r plant s t a r t - u p and ad jus tment opera t ions were c a r r i e d out in the machine room, in- eluding s t a r t - u p of the t u r b o g e n e r a t o r s with s t eam f rom the th i rd and fourth units of the A PP.

The s t a r t - u p and adjus tment ope ra t ions in the fifth unit began in Apr i l , 1978, a f t e r a power supply was p rov ided to the pumping stat ion for f i l l ing the cooling pond and in Sep tember , voltage f rom a r e s e r v e t r a n s - f o r m e r was appl ied to the 6-kV sec t ions of the in ternal power -consuming device in the APP.

Comprehens ive tes t ing of the equipment and s y s t e m s of the A P P began in June, 1979, with the f i l l ing of the p r i m a r y loop for hydraul ic t r i a l s .

The actual durat ion of the sepa ra t e s tages of the s t a r t - u p and ad jus tment p r o c e d u r e s , including the n e c e s - s a r y r e p a i r s , was: hydraul ic t e s t s and c i rcu la t ion flushing (from June 20, 1979) 20 days; f i r s t inspect ion (from July 10, 1979) 102 days; cold and hot running t e s t (from Oct. 20, 1979)-21 days; second inspect ion (from Nov. 10, 1979) 53 days ; second hot running t e s t (from Jan. 2, 1980) 56 days; th i rd inspection (from Feb. 27, 1980), including eore charging (April 1-6, 1980) 38 days; sea l ing the r e a c t o r and hydraul ic tes t ing of MCs 62 days ; phys ica l s t a r t - u p (from Apr i l 30, 1980) 17 days; p r e p a r a t i o n for power s t a r t - u p and connection into power g r id (from May 17, 1980) 13 days ; power bu i ld-up f rom May 30, 1980.

During the second inspection and before the beginning of phys ica l s t a r t - u p the p ro tec t ive envelope was t e s t ed five t imes for s t rength and densi ty .

Opera t ions in the Individual Stages . Hydraul ic Test ing and Circula t ion Flushing of the P r i m a r y Sys tem. The r e a c t o r was sea led with the aid of a technologica l lid (the r e g u l a r lid had not yet a r r i v e d on the s i te by that t ime) . The r e s i s t a n c e of the r e a c t o r core was s imula ted with the aid of spec ia l equipment. The p r e s s u r e in the r e a c t o r and the p r i m a r y sys t em was r a i s e d to 24.5 MPa a f te r the coolant had been heated to 100~ with heat f rom the opera t ing MCP. The s t r e s s e d s tate of the equipment of the MCS was s tudied with 200 t enso - r e s i s t o r s and more than 50 the rmocoup les set up on one of the loops, a vo lume-compensa t ion sys t em, and wate r tanks. The va lues of the mechan ica l s t r e s s e s were de t e rmined in the bol ts of the main joint. Among the va r ious p r o - g r a m s , mention should be made of the tes t ing of the GTsN-195pump and i t s aux i l i a ry s y s t e m s ; m e a s u r e m e n t of the hydrau l i c c h a r a c t e r i s t i c s of the p r i m a r y s y s t e m ; act ivat ion of the s team g e n e r a t o r s ; a c o u s t i c - e m i s s i o n inspect ion of the r e a c t o r ve s se l .

The wa te r t e s t s were success fu l ly conducted. The s t r e s s e s in the e l ements of the cons t ruc t ion did not exceed the al lowable va lues . Ana lys i s of the a c o u s t i c - e m i s s i o n m e a s u r e m e n t s showed that the r e a c t o r v e s s e l had no flaws that would genera te acous t ic s igna ls . During the c i rcu la t ion f lushing all four MCF were t e s t ed in ope ra t ion , r evea l ing a number of minor faul ts both in the MCP t he m s e l ve s and in t he i r aux i l i a ry s y s t e m s (oil- ing s y s t e m , make -up s y s t e m , and in t e rmed ia te c i rcu i t ) . The quali ty of the wa te r of the p r i m a r y sys t em was brought up to s t andard ind ica to r s .

F i r s t Examinat ion of MCS Equipment . During the f i r s t examina t ion , be s i de s an inspect ion and e l i m i n a - t ion of defects in the c i rcu la t ion f lushing equipment , the a s s e m b l y of the r e g u l a r s y s t e m s of the A P P was com- p le ted and spec ia l expe r imen t a l m e a s u r i n g sy s t e m s were a s s e m b l e d for carefu l study of the s t r e s s e d state and v ib ra t ions in the r e a c t o r and i n - v e s s e l equipment (WE), the MCS equipment , as well as for studying the pu l s a - l ions in the coolant p r e s s u r e and the hydrodynamic c h a r a c t e r i s t i c s of the MCS during hot running t e s t s .

An idea of the sca le of this work can be had f rom the following f igures : about 500 t e n s o r e s i s t o r s for m e a s u r i n g the s ta t ic and dynamic s t r e s s , 266 t he rmocoup le s , 73 v i b r a t i o n - d i s p l a c e m e n t pickups, and more than 80 p r e s s u r e - p u l s a t i o n pickups were ins ta l led on the r e a c t o r v e s s e l , the IVE, the bol ts of the main joint , the upper b lock , the piping of loop No. 4, the sheath of MCP No. 4, volume compensa to r (VC), the piping of the VC, the ve s se l and co l l e c to r s of s team g e n e r a t o r PG-4 , and the piping of the tanks of the emergency c o r e - cooling sy s t em. The core was charged with i m i t a t o r s with the same geomet r i c d imens ions as the r e g u l a r fuel a s s e m b l i e s . To m e a s u r e the hydraul ic c h a r a c t e r i s t i c s of the c o r e , a m e a s u r i n g sys t em was a s s e m b l e d with about 50 tubes to de te rmine the flow r a t e s and to r e c o r d the s ta t ic p r e s s u r e at the en t rance and exi t of the fuel a s s e m b l i e s .

During the f i r s t examinat ion al l four MCP were inspected . Slight defects (rubs on the lining of the hydro- s ta t ic b e a r i n g , fouling of f i l t e r s , etc.) were e l imina ted .

A large volume of work was done on inspect ing the me ta l of the r e a c t o r v e s s e l , the piping, and the equip- ment of the MCS. The welded jo ints of the ve s se l were t e s ted by u l t r a son ic inspection and magne t i c -powder inspect ion . Dye -pene t r an t inspection of the inner sur face of the ve s se l and of the welded seams of the Du850 piping was c a r r i e d out.

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Signa l s f r o m the p i ckups of the m e a s u r i n g s y s t e m s , s e t up ins ide the r e a c t o r v e s s e l , a r e b r o u g h t out t h r ough f i t t i ngs fo r a d j u s t i n g c o n t r o l s on the r e a c t o r l id . A c c o r d i n g l y , fo r l ife t e s t s and for check ing the e l e c t r i c c i r c u i t s of the CSS 69 out of the 109 d r i v e s w e r e i n s t a l l e d .

F i r s t Hot Running T e s t . D u r i n g the f i r s t hot runn ing t e s t at a p r e s s u r e of 15.7 M P a and a t e m p e r a t u r e of up to 280~ m e a s u r e m e n t s w e r e m a d e of the t h e r m o h y d r u a l i c c h a r a c t e r i s t i c s of the M C P and the r e a c t o r c o r e , m e c h a n i c a l s t r e s s e s and v i b r a t i o n s in the p ip ing and e q u i p m e n t of the NSGP, a s we l l a s coo lan t p r e s - s u r e pu l sa t ion at v a r i o u s po in t s of the p r i m a r y s y s t e m .

The m e a s u r e m e n t s we re m a d e u n d e r s t e a d y - s t a t e cond i t i ons wi th d i f f e r e n t n u m b e r s of MCP in o p e r a t i o n , in a r e g i m e of hea t ing and coo l ing of MCS and ind iv idua l c i r c u l a t i o n l oops , and in a r e g i m e when the sa fe ty d e v i c e s a r e t r i p p e d . The coo lan t flow with the fou r loops in o p e r a t i o n and at a t e m p e r a t u r e of 280~ was ~ 90,000 m3/h at a p r e s s u r e d rop of 0.62 M P a in the M C P .

The v i b r a t i o n of the e l e m e n t s of the p r i m a r y s y s t e m and the i n - v e s s e l d e v i c e s p r o v e d to be i n s i g n i f i c a n t . The m a x i m u m a m p l i t u d e of the v i b r o d i s p t a c e m e n t s of the IVE did not e x c e e d 30 p m for b l o c k of p r o t e c t i v e t u b e s and 9 t~m fo r the o t h e r e l e m e n t s . The v i b r a t i o n of the p ip ing of the MCS was no m o r e than 100 t~m and tha t of the M C P was no m o r e than 120 ~m. The s t r e s s e s in the s t r u c t u r e s of the NSGP did no t e x c e e d the a l l owab le v a l u e s . It was e s t a b l i s h e d tha t in t r a n s i e n t r e g i m e s the h ighe s t m e c h a n i c a l s t r e s s e s a r e found in the f i t t ings of the r e a c t o r v e s s e l and the p ip ing of the vo lume c o m p e n s a t o r . The da ta o b t a i n e d a l l owed r e c o m - m e n d a t i o n s to be m a d e a s to the b e s t m e t h o d s of conduc t ing r e a c t o r o p e r a t i n g c o n d i t i o n s . The p r e s s u r e p u l s a - t ion ins ide the r e a c t o r v e s s e l does not e x c e e d 0.02 M P a (the m a x i m u m value in the r eg ion be tween the v e s s e l b o t t o m and the r e a c t o r p i t ) . It should be po in ted out t ha t the r e s u l t s of the i n v e s t i g a t i o n s c o r r e s p o n d to the da ta ob t a ined e a r l i e r on a l a r g e - s c M e m o d e l of a VVI~R-1000 r e a c t o r p l an t (1 : 5 s c a l e ) .

In the p e r i o d of the hot runn ing t e s t the d r i v e m e c h a n i s m s and e l e c t r i c a l c i r c u i t s of the CSS, M C P , e m e r g e n c y s y s t e m s , v o l u m e - c o m p e n s a t i o n s y s t e m , m a k e - u p and p u r g i n g s y s t e m , the i n t e r m e d i a t e c i r c u i t , the r e a c t o r - p i t coo l ing s y s t e m , e t c . , w e r e c h e c k e d and a d j u s t e d .

In a c c o r d a n c e with the p r o g r a m seven of the d r i v e m e c h a n i s m s se t up e a c h p e r f o r m e d c o m p l e t e t w o - w a y t r a v e l 300 t i m e s and t r i p p e d the s c r a m s y s t e m 20 t i m e s w h e r e a s the r e m a i n d e r c a r r i e d out t w o - w a y t r a v e l 30-40 t i m e s .

The l a r g e s t n u m b e r of m a l a d j u s t m e n t s d u r i n g the hot runn ing t e s t o c c u r r e d in the o p e r a t i o n of the e l e c - t r i c a l c i r c u i t of the CSS. The m a i n c i r c u l a t i o n pumps d i s p l a y e d oi l l e a k s a t the e l e c t r i c m o t o r connec t i ons w h e r e a s M C P No. 1 s u f f e r e d a b r o k e n t o r s i o n sha f t .

Second E x a m i n a t i o n of NSGP E q u i p m e n t . The r e a c t o r was d i s m a n t l e d and the e x p e r i m e n t a l m e a s u r i n g s y s t e m s w e r e r e m o v e d f r o m i t s e q u i p m e n t . When the hous ings of the CSS d r i v e m e c h a n i s m s w e r e i n s p e c t e d i t was found tha t the l o w e r g r a p h i t e b e a r i n g s s u f f e r e d d a m a g e ( sp l i t t i ng and c r a c k i n g ) ; c r a c k s a p p e a r e d at the po in t s of connec t ion in ind iv idua l a r m a t u r e s c o n s i s t i n g of t h r e e w e l d e d p a r t s . On the b a s i s of so lu t i ons a d o p t e d , the g r a p h i t e b e a r i n g s w e r e r e p l a c e d b y b r o n z e b e a r i n g s and the c r a c k s in the a r m a t u r e s we re r e - p a i r e d by r e w e l d i n g . Changes w e r e a l s o m a d e in the o i l s y s t e m of the M C P and in the des ign of the t o r s i o n sha f t .

In view of the f a i l u r e of the e l e c t r i c a l c i r c u i t of the CSS and the c ha nge s in the de s ign of the d r i v e m e c h a n i s m s and M C P it was dec ided to r e p e a t the hot runn ing t e s t with an i m i t a t i o n r e a c t o r c o r e .

Second Hot Running T e s t . When the M C P w e r e t u r n e d on i t was found tha t the c h a n g e s made to the o i l s y s t e m in some o p e r a t i n g r e g i m e s l e ad to a d i s r u p t i o n in the oi l supp ly to the e l e c t r i c - m o t o r b e a r i n g s , c aus ing t h e m to o v e r h e a t . A d d i t i o n a l m e a s u r e s w e r e u n d e r t a k e n ( i n c r e a s i n g the vo lume of the o i l t ank in tended fo r " r u n n i n g - d o w n " o p e r a t i o n , the i n c i s i o n of a i r ven t s in the p i p e s fo r d i s c h a r g i n g o i l f r o m the oi l t ank , r e g u i a - t ion of the oi l f low, e tc . ) which a l l owed the o p e r a t i o n of the p u m p s to be s t a b i l i z e d . In the runn ing t e s t 98 d r i v e m e c h a n i s m s were l i f e - t e s t e d ; 300 t w o - w a y t r a v e l m o t i o n s w e r e c a r r i e d out with 55 d r i v e m e c h a n i s m s and 100 with e a c h of the r e m a i n i n g d r i v e m e c h a n i s m s .

The o p e r a t i o n of the CSS e l e c t r i c a l c i r c u i t b e c a m e m u c h b e t t e r . When the r e a c t o r was d i s a s s e m b l e d it was found tha t the d e c i s i o n to r e p l a c e the b e a r i n g s in the CSS d r i v e m e c h a n i s m s was c o r r e c t .

T h i r d E x a m i n a t i o n of NSGP Equ ipmen t . An i n v e s t i g a t i o n of the cause of c r a c k i n g in the a r m a t u r e s of the CSS d r i v e m e c h a n i s m s showed tha t the m a t e r i a l has an inadequa te i m p a c t s t r e n g t h at the j o i n t s . To i m p r o v e the p r o p e r t i e s of the m e t a l the j o in t s in a l l the a r m a t u r e s w e r e hea t t r e a t e d by a s p e c i a l t e chn ique . F u r t h e r c h a n g e s m a d e to the des ign of the M C P a l l owed b e t t e r c e n t e r i n g of the sha f t s of the primp and e l e c t r i c m o t o r d u r i n g o p e r a t i o n .

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B e f o r e the r e a c t o r c o r e was c h a r g e d the s y s t e m s fo r e m e r g e n c y i n t r o d u c t i o n of b o r o n and f o r r e a c t o r coo l ing we re f lushed and f i l l e d with b o r i c ac id . The c o r e was c h a r g e d with a c h a r g i n g m a c h i n e .

When the r e a c t o r was s e a l e d and f i l l e d and the CSS, s a f e t y , and i n t e r l o c k i n g s y s t e m s of the r e a c t o r w e r e c h e c k e d , on A p r i l 29, 1980 the c o n t r o l rod b a n k s w e r e r a i s e d to the top p o s i t i o n and s t e p s w e r e taken to l o w e r the b o r i c a c i d c o n c e n t r a t i o n in o r d e r to r e a c h the c r i t i c a l s t a t e .

P h y s i c a l S t a r t - U p . The r e a c t o r was put into the c r i t i c a l s t a t e a t 4:35 on A p r i l 30, 1980 with a b o r i c ac id c o n c e n t r a t i o n of 8.1 g / k g H2C in t h e p r i m a r y s y s t e m : t e m p e r a t u r e 107~ p r e s s u r e 15.9 M P a , and with the l a s t c o n t r o l rod b a n k , No. 14, in a p o s i t i o n 245 c m f r o m the b o t t o m of the r e a c t o r c o r e (the o t h e r b a n k s w e r e in the top pos i t i on ) .

Dur ing p h y s i c a l s t a r t - u p m e a s u r e m e n t s we re m a d e of the e f f i c i e n c y of the c o n t r o l r o d s at v a r i o u s t e m - p e r a t u r e s , the t e m p e r a t u r e and b a r o m e t r i c c o e f f i c i e n t s of r e a c t i v i t y at v a r i o u s b o r i c a c i d c o n c e n t r a t i o n s in the c o o l a n t , the e f f i c i e n c y of the b o r i c a c i d , and the p o w e r c o e f f i c i e n t of r e a c t i v i t y in the r ange of 0-30% n o m i n a l p o w e r .

The to ta l efficiency of the rod of the c o n t r o l r o d s was 0.055 at 107~ and 0.071 at 281~ The t e m p e r a - t u r e coe f f i c i en t of r e a c t i v i t y at the b e g i n n i n g of the f i r s t c h a r g i n g with the c o n t r o l r o d s completely wi thd rawn is s l i gh t ly p o s i t i v e [ (2 -7) . 10-5/~ the b a r o m e t r i c e f f ec t is n e g a t i v e and very s m a l l ( - 4 . 1 . 1 0 - 6 / M P a ) , and the efficiency of the b o r i c ac id at 280~ is 0 .023/ (g H3BO~/kg H20). The c a l c u l a t e d c h a r a c t e r i s t i c s w e r e found to be in good a g r e e m e n t with the m e a s u r e d c h a r a c t e r i s t i c s a s wel l as with the r e s u l t s of e a r l i e r e x p e r i m e n t s wi th the r e g u l a r c o r e of the fif th uni t of the N A P P on a h a l f - s c a l e s t and .

Dur ing the p h y s i c a l s t a r t - u p t e s t s wi th t r i g g e r i n g at r e d u c e d p r e s s u r e in the p r i m a r y s y s t e m we t e s t e d t h e b o r o n - i n j e c t i n g s y s t e m e n s u r i n g s a f e ty (pumps f o r emergency i n j ec t ion of b o r o n into the w a t e r tank) .

A f t e r a s tudy of the r e g i m e of n a t u r a l - c i r c u l a t i o n coo l ing of the r e a c t o r c o r e , t u r b o g e n e r a t o r No. 14 with a 150-MW load was connec t ed into the g r i d on May 30, 1980.

P o w e r B u i l d - U p in F i f th Unit of N A P P . On J a n u a r y 1, 1981, the r e a c t o r r e a c h e d a t h e r m a l p o w e r equa l to 75% of the n o m i n a l va lue . In the c o u r s e of the p r o c e s s of b u i l d i n g up the p o w e r in a c c o r d a n c e with the s t a r t - up p r o g r a m the o p e r a t i o n of the A P P in the r e g i m e of to ta l d e e n e r g i z i n g was s u c c e s s f u l l y v e r i f i e d , t e s t s w e r e m a d e on the s e l f - r e g u l a t i o n of the A P P and the b e h a v i o r of the uni t when l o a d s a r e s h e d , and a s tudy was made of the i r r e g u l a r i t y of energy l i b e r a t i o n in the r e a c t o r c o r e and the s t a t e of fuel e l e m e n t s a c c o r d i n g to r a d i o - c h e m i c a l a n a l y s e s . The t u r b o g e n e r a t o r s w e r e c h e c k e d in o p e r a t i o n at a p o w e r of 500 MW ( e l e c t r i c a l ) .

The i n v e s t i g a t i o n s showed tha t the d i s t r i b u t i o n of t h e r m a l l oads in the c o r e a c c o r d s with that in the d e - s ign (the m a x i m u m i r r e g u l a r i t y of the p o w e r of the fuel a s s e m b l i e s fo r a g iven s t age does not e x c e e d 1.4). The l eve l of the f i s s i o n - f r a g m e n t a c t i v i t y of the coo lan t is qui te low. AH of the m a i n equ ipmen t of the NSGP o p e r - a t e s p r a c t i c a l l y without anyth ing wor thy of c o m m e n t .

At the p r e s e n t t i m e p r e p a r a t i o n s a r e b e i n g c o m p l e t e d f o r b r i n g i n g the fif th uni t of N A P P up to n o m i n a l p o w e r .

C o n c l u s i o n s . The s t a r t - u p and a d j u s t m e n t o p e r a t i o n s and the t e s t i n g done on the f if th uni t of the N A P P c o n f i r m e d the c o r r e c t n e s s of the p r i n c i p a l d e s i g n and s t r u c t u r a l s o l u t i o n s adop ted fo r b u i l d i n g the s y s t e m s and e q u i p m e n t of the NSGP. Al l of the m a i n e q u i p m e n t of the fif th uni t was b u i l t fo r the f i r s t t i m e in the Sov ie t Union. Th is cou ld exp l a in the i s o l a t e d f laws of a de s ign and t e c h n o l o g i c a l c h a r a c t e r .

The d i s s e m i n a t i o n and p r a c t i c a l i m p l e m e n t a t i o n of the e x p e r i e n c e ga ined f r o m the c o n s t r u c t i o n of the fif th unit of the N A P P wi l l m a k e p o s s i b l e a s u b s t a n t i a l r e d u c t i o n of the t i m e r e q u i r e d to a d j u s t the e q u i p m e n t of uni t s with VVV.R-1000 r e a c t o r s .

F i r s t S t a g e o f M o d e r n i z a t i o n o f V V ] ~ R - 1 0 0 0 R e a c t o r P l a n t s

F o r t h e f i r s t two uni t s of the South Ukra in i an and K a l i n i n s k A P P and the t h i r d unit of the Rovno A P P the l ayou t and m a i n e q u i p m e n t of the r e a c t o r p lan t r e m a i n much l ike tha t of the f if th uni t of the N A P P , but s u b - s t a n t i a l changes have been m a d e in the de s ign of the r e a c t o r i t s e l f . B e c a u s e of the t r a n s i t i o n to a de s ign wi th - out cans it ha s b e c o m e p o s s i b l e to a r r a n g e 163 fuel a s s e m b l i e s i n s t e a d of 151 in the r e a c t o r c o r e whi le m a i n - t a in ing the s a m e ins ide d i a m e t e r of the r e a c t o r v e s s e l and the s a m e f u e l - e l e m e n t s p a c i n g . The n u m b e r of c o n t r o l r o d s in a bank has been i n c r e a s e d to 18 f r o m the p r e v i o u s 12. As a r e s u l t , the h e a t - e x c h a n g e a r e a in the r e a c t o r c o r e has i n c r e a s e d by 6%; a long with the r e d u c t i o n of the m i c r o i r r e g u l a r i t y in the e n e r g y l i b e r a - t ion o v e r the fuel a s s e m b l i e s t h i s m a k e s i t p o s s i b l e to s o m e w h a t i n c r e a s e the t h e r m a l p o w e r of the r e a c t o r .

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Of the o t h e r changes m e n t i o n e d use should be m a d e of a n o t h e r c o n t r o l - r o d d r ive m e c h a n i s m , mak ing it

p o s s i b l e to sho r t en the r e a c t o r he ight by 3.4 m and to i n c r e a s e the vo lume w h e r e the e n e r g y l i b e r a t i o n in the

r e a c t o r c o r e is m o n i t o r e d by us ing n ~ / 3 d e t e c t o r s . E l e c t r i c i t y was p r o d u c e d with a K - 1 0 0 0 - 6 0 / 1 5 0 0 t u r b o -

g e n e r a t o r with a p o w e r of 1000 M W ( e l e c t r i e a l ) , and th i s r e d u c e d the c o n s t r u c t i o n c o s t s of the unit . The p r o -

j e c t s fo r the A P P u n d e r c o n s t r u c t i o n w e r e deve loped fo r r e g i o n s with a s e i s m i c i t y of 5-6 uni ts on the MSK-

1964 s c a l e .

S e c o n d S t a g e o f M o d e r n i z a t i o n o f V V t ~ R - 1 0 0 0 R e a c t o r P l a n t s

F u r t h e r m o d e r n i z a t i o n of the VV]~R-1000 r e a c t o r p lan ts (see Table 1) is to be c a r r i e d out , a c c o r d i n g to

p r o p o s a l s , by us ing i m p r o v e d e q u i p m e n t , s i m p l i f y i n g the layout of the A P P as a who le , o p t i m i z i n g the the r m o - t e c h n i c a l p a r a m e t e r s and r e c h a r g i n g cond i t i ons , and i n t roduc ing s y s t e m s f o r o p e r a t i v e m o n i t o r i n g of the

s t r e n g t h and the work ing e f f i c i e n c y of the e q u i p m e n t . The p r i n c i p a l de s igns p e r t a i n i n g to the c o n s t r u c t i o n of the r e a c t o r and i ts c o r e , which w e r e adopted in the f i r s t s t a g e , a r e be ing kept .

I m p r o v e m e n t of the layout of the MCS in the p r o j e c t s is a c h i e v e d by doing wi thout m a i n gate v a l v e s ; once

the d e v e l o p m e n t has b e e n c o m p l e t e d , c o n s i d e r a t i o n wil l be g iven to the p o s s i b i l i t y of us ing a pumping unit with

a shaft angu l a r v e l o c i t y of 315 r a d / s e c and weight c h a r a c t e r i s t i c s roughly twice as good as those of GTsK-195

p u m p s ; the t r a n s p o r t a t i o n of i n - r e a c t o r d e v i c e s dur ing r e c h a r g i n g wi l l , it is p r o p o s e d , be c a r r i e d out unde r

a l a y e r of w a t e r , thus mak ing it p o s s i b l e to r e d u c e the height of the paths benea th the c r a n e in the p r o t e c t i v e

enve lope by ~ 6 m. As a r e s u l t of the m e a s u r e s m e n t i o n e d above fo r a f o u r - l o o p MCS, the vo lume of the p r o -

t e c t i v e enve lope is r e d u c e d by 20-30%. The l i m i t i n g p a r a m e t e r s of the s t e a m - a n d - a i r m i x t u r e in the even t of

a m a x i m u m acc iden t (0.49 M P a , 150~ adopted in the d e v e l o p m e n t of the e q u i p m e n t , a r e m a i n t a i n e d b e c a u s e of the reduction of the volume of the MCS.

Further simplifications of the VVI~R-1000 reactor plant are possible by using IKCS arrangements with two to four MCP and two steam generators.

For VVI~R-1000 put into service by 1990 one should not expect the regular use of any nuclear fuel other than UO 2. Some improvement of the fuel cycle, however, is possible by optimizing the recharging conditions. In particular, proposed measures (reduetion of the reactor assembly-disassembly time and the time of

TABLE 1. C o m p a r a t i v e C h a r a c t e r i s t i c s of VVI~R-1000 R e a c t o r P l an t s

Parameter Fifth unit of Stage I of Stage II of NA PP m oderniz ation m oderniz ation

Thermal power MW Coolant pressure, MPA Average coolant temperature, ~ 3 Coolant flow rate through r e a c t o r m /h External diameter of reactor vessel, mm Reactor height in assembly mm Equivalent ~iameter of rea~tor core, am Height of reactor core in working state, cm Specific power of reactor core, kW/liter No.of fuel assemblies Fuel assembly shape and size

Size of'ready" assembly, mm Fuel charge in reactor core (UO~). tons External cJiam, and spacing of fuel elements, mm Mean thermal flux, W/cm Fuel operating, period, yr No.of rechargmgs per o~r period Enrichment oT ffes5 fuer in steady-state recharging}

conditions, % Mean fuel buFn-up rate MW .day/kg No. of control meehaniems No.of absorbers in control mechanism

No. of temperature pickups at fuel-assembly exit No. of in-reactor neutron-flux detectors

No. of MGP Angular velocity of MCP, rad/mc Presence of gate valves in MCS loops No. and type of turbogenerators

g ree volume of hermetically sealed premises, m 3 pecial conditions taken into accountin design

3 000 t5.7 306

80 0O0 4 535

22 592 3t2 356 i l l 151

3 000--3 200 t5,7

306--307 80 000 4 535

18 770 3t6 356

107- 1t5 t63

3 00O--3 200 15.7

306--310 80 000 4 535

19 t37 3t6 356

107 -I15 163

Hexahedron with can

238 75,5

9,1/12,75 175

2/3 2/3

2,3/4,4

27/40 t09 12

t5i 31•

4 t05

Yes 2• IG500 60/t500

70 000

Hexahedron without can

234 80

9,t/t2,75 166 --177

3 3

4,4

40 6t .18

About 100 72x7

4 t05

Yes 1 • 11-1000-60/t50~

70 000 Seismiclty of

5-6 units

ttexahedron without can

234 80

q,t/12,75 166 --177

3 3/6

4,0--4,4

40 61 18

About 100 72x7

4 157/315

No t • If-I000--60, I x tl-1000--65, 2 X Tli-500-- 60

55 OOo Setsmicity of 8-9 units, tropical climate

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prevent ive equipment maintenance) would make it convenient to go ove r to two fuel r e cha rg ings a y e a r with a reduct ion of the fuel component of the e l e c t r i c energy cos t by 8-9%.

It is p roposed to fu r the r i n c r e a s e the safe ty of VV1~R-1000 r e a c t o r p lants by developing s y s t e m s of in- r e a c t o r m e a s u r e m e n t s and in t roducing opera t ive s y s t e m s for moni to r ing the state of the MCS equipment and me ta l . At the p r e sen t t ime the Soviet Union and the CGMECON count r ies a re c a r r y i n g out a joint p r o g r a m (including t e s t s on ope ra t ing r e a c t o r s ) to develop methods of r e c o r d i n g va r i a t ions in the noise spec t rum during d i s rup t ions to the n o r m a l opera t ion of the r e a c t o r p lant , including those occu r r i ng when boi l ing begins in the r e a c t o r co re .

The sc ien t i f ic b a s i s is being developed and appara tus is being cons t ruc ted for detect ing and c las s i fy ing flaws in the m a t e r i a l s of MCS equipment by the acous t ic emi s s ion method.

As the r e s e r v e s of conventional fuel a r e exhaus ted the number of reg ions in the Soviet Union where it is economica l ly d e s i r a b l e to cons t ruc t A P P will grow in the for thcoming decade. In view of this as well as with an eye to poss ib le e x p o r t s , p r o m i s e is held out by r e a c t o r p lants des igned to withstand s e i s m i c ac t iv i ty with a force of up to 9 units (maximum acce l e r a t i on at ground level 0.4 g), to use s eawa te r for cooling the a n c i l l a r y equipment , and to be ins ta l l ed on s i t e s with a humid t rop ica l c l ima te .

It is p roposed that a tomic power p lants with VVI~R-1000 r e a c t o r s will be used to provide for a va r i ab le schedule of load on an energy sy s t em. The r e q u i r e m e n t s on such an A P P are being formula ted at the p r e s e n t t ime and p rov i s ion is being made for dai ly d isconnect ion f rom the g r id , i n c r e a s e d r a t e s of load va r i a t ion , and maintenance of the opera t ion of units of the power plant when the frequency is lowered down to 46 Hz. A whole n u m b e r of p r o b l e m s r ema in to be solved, f i r s t of a l l , design and expe r imen ta l t es t ing of a fuel e l emen t capable of functioning under pro longed cyc l i ca l loads . It may well be that VVI~R-1000 r e a c t o r s , intended to regula te the power and f requency in a s y s t e m , will opera te with lower t he r m a l loads than the base r e a c t o r s but at h igher coolant p a r a m e t e r s .

An impor tan t a spec t of the use of VVI~R-1000 is that of employing them for cen t ra l heating pu rposes . Technical and economic cons ide ra t ion of va r i an t s of c e n t r a l - h e a t i n g suppl ies for a number of l a rge c i t i e s in the European p a r t of the USSR f rom sou rce s opera t ing with n u c l e a r and foss i l fuels has indicated that it is advantageous to use a t o m i c - c e n t r a l heat ing p lants (ACHP) for genera t ing heat and a tomic c e n t r a l - h e a t i n g and power p lants (ACHPP) for the combined genera t ion of heat and e l e c t r i c i t y when c o m p a r e d with b o i l e r houses and c e n t r a l - h e a t i n g power p lants opera t ing on foss i l fuel. The choice of an ACHPP o r ACHP depends on the condit ions of the given ci ty .

No s igni f icant changes are p roposed in the VVt~R-1000 plant for ACHPP. The heat suppl ies to con- s u m e r s will be de l i ve r ed by b leeding f rom a TK-500/60 c e n t r a l - h e a t i n g condensing turbine ensur ing a m a x i - mum product ion of heat at the ra te of 450 Gca l /h at an e l e c t r i c a l load of about 450 MW.

I~ 2.

LITERATURE CITED

V. A. Voznesensk i i et a l . , At. Ene rg . , 43, No. 6, 445 (1977). V. F. Titov et a l . , "The main d i r ec t ions in the development of s t eam g e n e r a t o r s for A P P with VVER r e a c t o r s in the Soviet Union" [in Russ ian] , P a p e r read at S o v i e t - I t a l i a n Seminar "Modern P r o b l e m s of Power Eng ineer ing , " Moscow, Nov. 21-24 (1977).

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