ML20078Q164

Part 21 Rept Re Result in Slight Increase in post-accident Containment Temp.Licensees Have No Current Operability Concerns Due to Low Ultimate Heat Sink Temps at Present Time

ML20078Q164
Person / Time
Site:	Calvert Cliffs
Issue date:	12/09/1994
From:	Sly C BALTIMORE GAS & ELECTRIC CO.
To:	NRC
References
REF-PT21-94 NUDOCS 9412210178
Download: ML20078Q164 (4)

Text

DEC 9 '94 !! 51 FROM C CNPP / NRf1 2-NOF PAGE.001

- s 10 CFR PART 21 VERBAL NOTIFICATION:

NON-CONSERVATIVE MODELING OF RCS SENSIBLE IIEAT FOR CONTAINMENT PRESSURE RESPONSE SAFETY ANALYSIS COULD RESULT IN A SLIGHT INCREASE IN POST-ACCIDENT ~

CONTAINMENT TEMPERATURE L

SUMMARY

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During a review of our Updated Final Safety Analysis Report (UFSAR) Safety Analysis concerning containment pressure response we determined the Bechtel analysis of the long-term cooling pl]ase of a loss.

of coolant accident (LOCA) did not model heat transfer from Reactor Coolant System (RCS) metal components to the RCS coolant. 'Ihis omission pear *i=Hy results in a non conservative calculated

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contamment temperature during a specific time period in the analysis (after contamment peak temperature until several days after the event). Prelimmary analysis for Calvert Cliffs indicates this issue has no impact on containment peak temperature or pressure and no impact several days after the event initiates. Under the current analysis assumptions, this omission increases the post accident load on our Service Water (SRW) system which removes heat from containment via the contamment air coolers. We do not have a current L

operability concern because ultimate heat sink temperatures are currently low enough to ensure full compliance with our plants current design and licensing basis.

IL BACKGROUND Chapter 14.20 of our UFSAR, " Containment Pressure Response," is an analysis of the pressure and 3 temperature response of our contamments to design basis accidents such as a main steam line break or a

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@ LOCA. A spectrum of RCS break sizes were considered to determine the worst condition of RCS mass oo and energy releases in combination with sensible and shutdown heat sources during the blowdon phase of y

-o a LOCA.

The cantamment response to these breaks was analyzed assuming minimum operable safety oj injection systems with two containment air coolers and one containment spmy pump in operation.

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1 DEC 9 '94 11:52 FROM CCNPP/ NRM 2-NOF PAGE.002 l

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l 10 CFR PART 21 VERBAL NOTIFICATION:

NON. CONSERVATIVE MODELING OF RCS SENSIBLE HEAT FOR

• CONTAINMENT PRESSURE RESPONSE SAFETY ANALYSIS COULD RESULT IN A SLIGHT INCREASE IN POST-ACCIDENT CONTAINMENT TEMPERATURE  !

'Ihe RCS blowdown transient results in primary ecamin-at pressure and tempenture peaks as a result of  :

the mass 'and energy transferred from the reactor core to the pnmary coolant and to the containment  ;

atmosphere. During the reful and reflood phases of the accident scenario, beat in the steam generator wster  !

mass is transfe'rred to the pnmary coolant via a revene heat flow and then into the,contamment atmosphere. In addition, safety injection water reflooding into an uncovered core and the hot RCS system picks up heat from those sources and deposits it into the Containment as saturated or even superheated <

stea m.

( i The mass and energy transfer from the RCS for urious phases of the accident are calculated by ,

Combustion Engineering (CE) and Bechtcl. He blowdown phase is modeled using the CE FLASII code, the refill and reflood phases by the FLOOD code and the long-term cooling phase by Bechtcls' Contamment Pressure and Temperature Transient Analysis (COPATTA) code. During the long-term  !

cooling phase (after reflood) the transfer of sensible heat from the RCS metal back into the coolant is not modeled. When RCS metal sensible heat is included, this results in coolant with a higher cathalpy flowing from the RCS break into ' Containment and leads to slightly higher containment temperatures for several days after the containment temperature peak.  ;

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IIL ASSESSMENT OFISSUE We have asked ABB-CE to provide new mass and energy transfer dataht accounts for sensible heat transfer from the RCS metal to the coolant. De revised data produced by CE will be provided to Bechtel l

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DEC 9 '94 11:52 FROM CCNPP/ NRM 2-NOF PAGE.003 10 CFR PART 21 VERBAL NOTIFICATION:

NON CONSERVATIVE MODELING OF RCS SENSIBLE HEAT FOR

' CONTAINMENT PRESSURE RESPONSE SAFETY ANALYSIS COULD RESULT IN A SLIGHT INCREASE IN POST-ACCIDENT CONTAINMENT TEMPERATURE ,

to produce revised contamment pressure and temperature response curves. The results of the revised containment response curves are expected to show:

A. Containment primary peak pressure and temperature will be unaffected. ,

B. The intermediate containment temperature will be increased by less than 2T.

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C. The containment ternperature and prcasure will be essentially unaffected beginning several days after the start of the ewnt.

The results of thic reanalysis are being evaluated for impact on other aspects of our current licensing basis.

The most significant potential impact was the increased load on our SRW system via the containment air coolers. We have no current operability concerns due to low ultimate beat sink temperatures at the present ,

time.

IV. CONCLUSIONS Even though this problem has minor safety consequences for Calvert Cliffs, we feel the deficiency in the modeling method used by Bechtel may potentially present a Safety Consequence to other licensees who use the same method. Thus, we are conservatively reporting it under 10 CFR Part 21.

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POWER REACTOR EVENT NUMBER: 28125 FACILITY: CALVERT CLIFFS REGION: 1 NOTIFICATION DATE: 12/09/94 UNIT: [1] [2] [ ] STATE: MD NOTIFICATION TIME: 11:47 [ET]

RX TYPE: [1] CE, [2] CE EVENT DATE: 12/09/94 EVENT TIME: 11 : 00 (EST)

NRC NOTIFIED BY: CRAIG SLY LAST UPDATE DATE: 12/09/94 HQ OPS OFFICER: DICK JOLLIFFE NOTIFICATIONS EMERGENCY CLASS: NOT APPLICABLE 10 CFR SECTION: '

CCCC 21.21 UNSPECIFIED PARAGRAPH UNIT SCRAM CODE RX CRIT INIT PWR INIT RX MODE CURR PWR CURR RX MODE 1 N Y 100 POWER OPERATION 100 POWER. OPERATION 2 N Y 100 POWER OPERATION 100 POWER OPERATION EVENT TEXT

- HEAT TRANSFER FROM RCS METAL TO Rx COOLANT NOT MODELED IN SAFETY ANALYSIS DURING A REVIEW OF THE UFSAR SAFETY ANALYSIS CONCERNING CONTAINMENT PRESSURE RESPONSE, LICENSEE DETERMINED THAT THE ANALYSIS OF THE LONG TERM COOLING PHASE OF A LOCA DID NOT MODEL HEAT TRANSFER FROM REACTOR COOLANT SYSTEM METAL COMPONENTS TO THE REACTOR COOLANT.

WHEN THE Rx COOLANT SYSTEM METAL SENSIBLE HEAT IS INCLUDED, THIS RESULTS IN REACTOR COOLANT WITH A HIGHER ENTHALPY FLOWING FROM THE REACTOR COOLANT SYSTEM BREAK INTO CONTAINMENT AND LEADS TO SLIGHLY HIGHER CONTAINMENT TEMPERATURES FOR SEVERAL DAYS AFTER THE CONTAINMENT TEMPERATURE PEAK.

THIS OMISSION INCREASES THE POST ACCIDENT LOAD ON THE SERVICE WATER SYSTEM WHICH REMOVES HEAT FROM CONTAINMENT VIA THE CONTAINMENT AIR COOLERS.

HOWEVER, THE LICENSEE DOES NOT HAVE AN OPERABILITY CONCERN BECAUSE ULTIMATE HEAT SINK TEMPERATURES ARE LOW ENOUGH TO ENSURE FULL COMPLIANCE WITH CURRENT PLANT DESIGN AND LICENSING BASIS.

LICENSEE INFORMED THE NRC RESIDENT INSPECTOR. .