ML20077M758

Part 21 Rept,Determined That Bechtel Power Corp Analysis of long-term Cooling Phase of LOCA Did Not Model Heat Transfer from RCS Metal Components to RCS Coolant.Util Asked C-E to Provide New Mass & Energy Transfer Data

ML20077M758
Person / Time
Site:	Calvert Cliffs
Issue date:	01/10/1995
From:	Denton R BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-95 NUDOCS 9501130161
Download: ML20077M758 (4)

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RosenT E. DenTox Baltimore Gas and Electric Company Vice President Calvert Cliffs Nuclear Power Plant Nuclear Energy 1650 Calven Cliffs Parkway Lusby, Maryland 20657 410 586-2200 Eri.4455 loca; 4t0 260-4455 Baltimore January 10,1995 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 10 CFR Part 21 Report; Non-Conservative Modeling of Reactor Coolant System Sensible IIeat For Containment Pressure Resnonse Safety Analysis During a review of our Updated Final Safety Analysis Report Safety Analysis concerning containment pressure response, we determined the Bechtel analysis of the long-term cooling phase of a loss of coolant accident did not model heat transfer from Reactor Coolant System (RCS) metal components to the RCS coolant. This omission potentially results in a non-conservative calculated containment temperature during l a specific time period of the analysis (after containment peak temperature until several days after the l cvent). Although we have concluded this non-conservative assumption has no safety significance for Calvert Cliffs, we are reporting it under Part 21 because this problem may potentially represent a safety consequence to other licensees who use similar methodologies.

1 Bechtel has informed us that they are evaluating the generic implications, if any, of this modeling omission and will report the results of their evaluation to us.

A verbal notification and written summary were submitted to the Nuclear Regulatory Commission Operations Center via facsimile on December 9,1994.

Should you have any questions regarding this matter, we will be pleased to discuss them with you.

Very truly yours, es

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_%-t Control Desk January 10,1995 Page 2 cc: D. A. Brune, Esquire ,

J. E. Silberg, Esquire L. B. Marsh, NRC D. G. Mcdonald, Jr.,'NRC T. T. Martin, NRC P. R. Wilson, NRC R. I. McLean, DNR J. H. Walter, PSC t

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. 10 CFR PART 21 REPORT; NON-CONSERVATIVE MODELING OF RCS SENSIBLE HEAT FOR CONTAINMENT PRESSURE RESPONSE SAFETY ANALYSIS COULD RESULT IN A SLIGHT INCREASE IN POST-ACCIDENT CONTAINMENT TEMPERATURE Calvert Cliffs Nuclear Power Plant, Units I and 2 Docket Nos. 50-317 and 50-318 1

(i) Name and address ofindividual making notification:

R. E. Denton, Vice President, Nuclear Energy Baltimore Gas and Electric Company ,

Calvert Cliffs Nuclear Power Plant l 1650 Calvert Cliffs Parkway Lusby, MD 20657-4702 l

(ii) Basic Component Affected: l l

Updated Final Safety Analysis Report Chapter 14.20, " Containment Pressure Response."

Specifically the long-term cooling phase modeled by Bechtel's Containment Pressure and Temperature Transient Analysis (COPATTA) Code.  ;

(iii) Firms Supplying Component:  !

Bechtel Power Corporation (iv) Nature of Defect:

Chapter 14.20 of our Updated Final Safety Analysis Report (UFSAR), " Containment Pressure Response," is an analysis of the pressure and temperature response of our containments to design basis accidents such as a main steam line break or a loss of coolant accident (LOCA). A spectrum of Reactor Coolant System (RCS) break sizes were considered to determine the worst condition of RCS mass and energy releases in combination with sensible and shutdown heat sources during the blowdown phase of a LOCA. The containment response to these breaks was analyzed assuming various limiting single failures.

The RCS blowdown transient results in primary containment pressure and temperature peaks as a result of the mass and energy transferred from the reactor core to the primary coolant and to the containment atmosphere. During the refill and reflood phases of the accident scenario, heat in the steam generator water mass is transferred to the primary coolant via a reverse heat flow and then into the containment atmosphere. In addition, safety injection water reflooding into an uncovered core and ti.e hot RCS system picks up heat from those sources and deposits it into the Containment as saturated or even superheated steam.

The mass and energy transfer from the RCS for various phases of the accident are calculated by Combustion Engineering (CE) and Bechtcl. The blowdown phase of the LOCA is modeled using the CE FLASil code, the refill and reflood phases by the CE FLOOD code, and the long-term 1

. 10 C7R PART 21 REPORT; NON-CONSERVATIVE MODELING OF RCS SENSIBLE HEAT FOR CONTAINMENT PRESSURE RESPONSE SAFETY ANALYSIS COULD RESULT IN A SLIGHT INCREASE IN POST-ACCIDENT l CONTAINMENT TEMPERATURE cooling phase by Bechtel. The mass and energy transfer data is input to Bechtel's Containment Pressure and Temperature Transient Analysis (COPATTA) code for calculation of contaimnent pressure and temperature. 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, the result is a higher enthalpy coolant flowing from the RCS break into Containment. He higher enthalpy coolant flowing into the containment leads to slightly higher containment temperatures and pressures for several days after their peaks. Preliminary analysis indicates the problem has no effect on containment peak pressure or peak temperature. We have concluded that there are no adverse effects to our environmental qualification program.

(v) Date on Which Defect Was Identified:

He problem was identified by BGE during a review of the UFSAR Chapter 14.20 Safety Analysis, and documented on an Issue Report on November 9,1994.

(vi) Number and Location of Components:

Not applicable.

(vii) Corrective Actions Taken:

We have asked CE to provide new mass and energy transfer data that accounts for sensible heat transfer from the RCS metal to the coolant. The revised data produced by CE will be provided to Bechtel to produce revised containment pressure and temperature response curves. He results of the revised containment response curves are expected to show:

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

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

1 C. He containment temperature and pressure will be essentially unaffected beginning several days after the start of the event. ,

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%c results of this reanalysis are being evaluated for impact on other aspects of our current Ocensing basis. The most significant potential impact was the increased load on our SRW system l via the containment air coolers. We have no current operability concerns due to low ultimate heat l sink temperatures at the present time and expect that the final reanalysis will show the real effect !

on our current safety analysis margins will be minimal.

Bechtel has informed us that they are evaluating the generic implications, if any, of this modeling omission and will report the results of their evaluation by January 20,1995.

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