ML20137H029
Text
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, April 17, 1979 l
2 REX 329CCATICNS OF WE NUCIZAR REGULNIORY COG 4ISSION ADVISCRY COMITTEE Di RfAD. SMICLARCE RE:GARDING WE MMtCH 78, 1979 AccIDort A7 3 .
WE WREE MIt2 ISIMD NOCLEAR STATION LNIT 2
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i- Presented orally to, and discussed with, the NRC
- i : Cbmissioners during the ACRS-Commissioners Meeting on April 17, 1979 - Washington, D. C.
Natural circulation is an important mode of reactor cooling, both as a planned process and as a process that may be used under abnormal cirewstances. De Committee believes that greater understanding of this ande of cooling is required and that detailed analyses should be developed by licensees or their suppliers. De analyses should be supported, as necessary, by experiment. Procedures should be de-veloped for initiating natural circulation in a safe manner and for providing the operator with assurance that circulation has, in fact, been established. Wis may require installation of instrumentation to measure or indicate flow at low water velocity.
Se use of natural circulation for decay heat removal following a loss i of offsite power sources requires the maintenance of a suitable over-pressure on the reactor coolant system. %fs overpressure may be assured by placing the pressurizer heaters on a qualified onsite r source with a suitable arrangernent of heaters and power distri-l tion to provide redandant capability. Presently operating PNR plants should be surveyed expeditiously to determine whether such 4
arrange ents can be provided to assure this aspect of natural circula-
- tion capability.
Se plant operator should be adequately informed at all times con-cern!ng the conditions of reactor coolant system operation sich ;
j sight affect the capability to place the systet in the natural circu-lation mode of operation or to sustain such a mode, of partleular importance is that information which-c.ight indicate that the reactor coolant systen is approaching the naturation pressure corresponding-1 to the core exit temperature. 21s impending loss of system over-pressure will afgnal to the operator a possible loss of natural circulation caw bility. Such a warning may be derived frorn pressur-iser pressure Lnstruments and hot leg temperatures in conjunction with ontwentional steam tables. A suitable display of this information should be provided to the plant operator at all times. In addition, pensideration should be given to the use of the flow exit tempera-i taares from the fuel subassemblies, eere available, as an additional indication of natural circulation.
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- 4. Thd cult temperature of coolant from the core is currently sensured by;thermocouples in many PWRs to determine core performance. We Coenittee recommends that these temperature measurewnts, as currently eva,11able, be used to guide the oprator concerning core status. %e range of the information displayed and recorded shculd include the tvil capebility of the thermocouples. It is also recommended that other existing instrumentation be examined for its possible use in assisting operatirs action during a transient. -
me Acms recommends that operating power reeetors be given pescrity with regard to the definition and implementation of instrumentation dich provides additional informatio,n to help diagnose and follw the course of a serious accident. This should include improved sampling procedures under ace! dent conditions and techniques to help provide improved guidance to offsite authorities, should this be needed. We committee recommends that a phased implementation approach be en-ployed so that techniques can be adopted shortly after they are judged to be appropriata.
l he ACR$ recawends that a high priority be placed on the developent and implenentation of safety research on the behavior of light toter reactore during anomalous trans!ents, he NRC may find it appropriate
, to develop a capability to simulata a wide range of postulated tran-sient and accident conditions in order to gain increased insight into measures dich can be taken to improve reactor safety. ne AcRs wishes to reiterate its previous recommendations that a high priority be given to research to improve reactor safety.
- consideration should be given to the desirability of additional l
equipent status sonitoring on various engineered safeguards features l and their supporting services to help assure their availability at
. all times.
De Acts is continuing its review of the implications of this ace! dent and hope to provide further advice as it is develnped, c .
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EXTRACT OF B&W ColHUNICATION - RECEIVED BY NRC Enclosure 1
.f7RODUCT,IOR Poge [ of 4 IE CONT!flulflG REVIEW OF 1ME SEQUENCE OF EVENTS LEADIrfG 70 Tile INCIDErli AT
!!-2 ON MRCH E8,1979 SHOWS TilAT ACTIOrl CAri BE tat'.EN TO PROVIDE A55URNatE AT THE PSLOT-OPERATED RELIEF VALVE (PORY) toutlTED ON Tile PRE 55URIZER OF Bf,y ANT 5 WIL4, NOT BE ACTUATED BY AffTICIPATED TRAfl51EffT5 Wi!Ctf HAVE OCCUR 4f D OR
.VE A 1
T ICNIFICAffT PROBABILITY Or DCCURRING IN TitESE PLA'tTS. Tit!5 ACT10*i tiesi NO DE THE 5AFETY OF THE ArFECTED PLA*lT5 WITil RESPECT TO TitEIR RE5PO'GE L; UP5ET OR ACCIDUf7 C0flDITIOfl5 NOR LEAD TO UNREVIEVED SATETY C0tiCERNs,
- E ANTKIPATED TRAN5!DITS OF COHCERN ARE
- j. LO5' 5 N tXTERML ILECTRICAL LOAD -
- 2. TUR8INE TRIP ..
S. LOSS OF MAIN FEEDWATER
! 4. LD55 0F CONDErLSER VACUVM
- 5. INADVERTENT CLOSURE OF MIM STEAM ISOLATION V?.LVE5 ('f5f y). .
l RR-3ER
.0W INCLUDING: OF ALTERftATIVES WERE CON 5IDERED IN DEVELOPING THE ACTIONS PROPO liESTRICTING THE PORY. THEREACTOR POWER TO A VALUE WICH WOULD ASSURE NO ACTUATIO REACTOR PROTECTI0'i SYSTEH, DESIGN PRESSURE A!iD PORY SET-POINTS ADIAINED AT THEIR CURRLNT VALUES.
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10ERING THE HIGH PRES 5URE REACTOR TRIP SETPOINT TO A VALUE WHICll WD A55URE NO ACTUATION OF THE PORV.
j THE DE51Grl PRESSURE OF THE REACTOR Nio THE SETPOINT FOR PORY ACTUATION RENAINED AT TilEIR CURRENT VALUES.
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(C'!ERING TWE HIGl PRESSURE REACTOR TRIP SETPOINT MlU ADJU5T!!tG Tile 07ERATING PRESSURE (AND TCP:PERATURE) 0F THE REACTOR TO ASSURE fl0 PORY ACTUATION OPERATING PRESSURE.
AND TO PROVIDE ADEQUATT. PMRGIN TO ACC0hT10DATE VA9IATIONS CURRENT VALUE. THE SETPOINT FOR PORY ACTUATION REP'AINED AT ITS THIS ALTERNATIVE WOULD REDUCE HET ELECTRICAL OUTPtTT.
IDAr5TIRG THE HICH PRE 5suRE TRIP AND THE PORY SETPOINTS TO A55u -
PC.1V ACTUATION FOR THE CLASS OF ANTICIPATED EVENTS OFTHE CONCERN.
DESIGN PRES 5URE OF THE REACTOR REMAINED AT IT5 CURRENT VALUE.
LflALYSIS OF THE IMPACT OF THESE VARIOUS ALTERMTIVES Afl0 THEIR C0flTRIDUTIO,'l LSSURING THAT THE PORY HILL NOT ACTUATE FOR THE CLASS OF ANTICIPAT XWARN HAS BEEM COMPLETED. THE RESULTS SHOW THAT:
i0ERING THI 'HIGH PRES 5URE REACTDR TRIP SETPolNT FROM 1I15 PSIG 70 2300 P5IG -
ARD -
RAISING THE SETFOINT FOR THE PILOT OPERATED RELIEF VALVE PRO;11255 PSIG TO 2450 P31G IDE5 NE REQUIRE 0 AS5URANCE. TH!$ ACTION HA5 THE FURTilER ADVAtlTAGES OF:
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. Enclosure 1
- EXTRACT OF B&W C0muNICATION - RECEIVED BY RRC 4/20/79 E'9' 2 'I 4 iEDOCING THE PRDBASILITY OF kORY AND ASME CODE PR ACTd4 TION FOR OTHER INCREA5tPG PAISSURE TRAftSIENTS. *
- kVING PRESSURE RELIEF C5PkCITY .FOR ALL HIGH PRESS 1
tLtHINkTING THE POS$191LITT 6F If(TRODUCING WIREYlEWED ,
IEDUCfMG THE T!!E AT NIICH THE STEAM SYSTEN llEAT SINK W THE EVENT EMERGENCY FEEDb:ATER FLOW WERE DELAYEO.
i SIMMART IAPLSIEf!TS IS OFGIVEN TWE In TABLE INPACT 1. OF THE PROPOSED SCTPOIffT CHMGE5 ON '
4
.4 AD OR PLANT TRIP OF5THE A'RE TUllBINE. CURRENT 1.Y CAPABLE OF Rth8ACK TO .15% OF ERATED RELIEF VALYES. THIS CfJ' ABILITY REQUIRES ACTUATIO!! 0F Tile PILOT-THE CAPABILITY INCREASES THE RELIADILITY OF POWER PPLY iTR THESE TDTRANSIENTS.
THE SYSTEM 8Y RETURNING .THE tlNITS TO PouER GEllERATI0tl P 4CTOR BE TAIPPED FOR TilESE EVEff75.THE ACTION PROPOSED ABO NOTE:
l The effect of changing the reactor coolant system pressure trip setpoint upon peak pressurizer pressure is typifieif by the attached figure 1. which was developed by SW for a loss of feedwater transient.
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TABLE 1 Enclosure 1
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5t>MUtY OF PROTECTIOM ArAIN5T PORY ACruATton PROVIDED BT PROPOSED 5ETPDINT CHMGES FDR ALL ,
__ ANTICIPATED TRMISIENT5 _
EXTRACT Of 844 CO W NCCATIDN RECEIVED BY MRC 4/20/79 NNTICEPATED TRANSIENT 5 WHICH MAVE OCCURRED AT B&W fD%LY ACTIVATE PORV AT THE CURREWT SETPOINT (2255 PSIC): -
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A. TURBINE TRIP t
$. SDSS OF UTEfHAL ELECTRICAL LSAD -
C. 1955 0F NRIN FEEDuATER -
- 6. LSES bF COllDDtSER VACUW E. 11U3VERTErtT, CLOSURE OF M51V e
A'!TICIPATED TRANSIENT 3 WHICH HAVE OCCURRED AT B&W PLANTS NID W!!!CH EDULD EDRHALLT ACTUATE PORY AT THE PROPOSED SETPOINT (2450 PSIG REME AhTICIPATED TAANSIEliT5 WHICH HAVE ff3T OCCURRED AT B&W PLANTS (LOW , ,
IR03ASILITY EVENTS) AND WHICH WOULD NORM *,LLY ACTUATE PORY AT THE
$88&E SETPOINT (2255 P' SIG):
A. SOME CONTROL ROD GROUP WITHDRAWALS (MODERATE TD HIGil REACT!YITT
, WORTH SROUPS NOT OTHERWISE PROTECTED Sk HIGH FLUX TRIP).
$. fiDDERATOR DILUTION.
MICIPATED TRAN3IENTS WHICH HAVE ROT OCCURRED AT 88W PdulTS EVElffs)cNIO WHICH WOULD ACTUATE THE PORY AT THE PRDPD5ED_5CTP0lNT l (2450PSIS): -
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SOE CofffROL ROD CROUP UITHDMWALS (HIGli REACTIVITY WDATil t:07 OfMEftlI5E PROTECTED SY HIGH FLUX TRIP).
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Enclosure 1 .
Page 4 of 4
- EXTRACT OF 54W C009 m ICAT20N - RECE!YED BY NRC 4/20/79
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