B12198, Forwards Reviews of Isap Topic 2.06, Evaluation of RCS Loop Isolation Valves to Mitigate Steam Generator Tube Rupture & Isap Topic 2.07, Auxiliary Pressurizer Spray Nozzle

Forwards Reviews of Isap Topic 2.06, Evaluation of RCS Loop Isolation Valves to Mitigate Steam Generator Tube Rupture & Isap Topic 2.07, Auxiliary Pressurizer Spray Nozzle

ML20215B140
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	09/22/1986
From:	Opeka J CONNECTICUT YANKEE ATOMIC POWER CO.
To:	Charemagne Grimes Office of Nuclear Reactor Regulation
References
B12198, NUDOCS 8610060380
Download: ML20215B140 (5)

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l CONNECTICUT YANKEE ATOMIC POWER COMPANY B E R L I N. CONNECTICUT P o Box 270 HARTFORD. CONNECTICUT 06141-0270 TELEPHONE 203-665-5000 September 22,1986 Docket No. 50-213 B12198 Office of Nuclear Reactor Regulation Attn: Mr. Christopher I. Grimes, Director Integrated Safety Assessment Project Directorate Division of PWR Licensing - B U.S. Nuclear Regulatory Commission '

Washington, D.C. 20555 Gentlemen:

l Haddam Neck Plant Integrated Safety Assessment Program In a letter dated July 31,1985,(I) Connecticut Yankee Atomic Power Company (CYAPCO) was requested to provide the Staff with reviews of the planned CYAPCO plant improvement projects. )

In response to this request, and in accordance with our understanding of the ISAP process, we are providing the Staff with reviews of the following projects: 1 1

1) ISAP Topic No. 2.06 " Evaluation of RCS Loop Isolation Valves to Mitigate SGTR"

2) ISAP Topic No. 2.07 " Auxiliary Pressurizer Spray Nozzle" 1

As further reviews are completed, we will promptly forward them to the Staff '

for review.

If you have any questions on this material, please feel free to contact my staff. l Very truly yours, l 1

CONNECTICUT YANKEE ATOMIC POWER COMPANY i J. F. Opeka' b hadO l Senior Vice President 1

(1) H. L. Thompson letter to J. F. Opeka, " Integrated Safety Assessment Program," July 31,1985.

8610060380 860922 l 00, iV PDR ADOCK 05000213 I

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k Docket No. 50-213 B12198 l

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Haddam Neck ISAP Topic No. 2.06 Evaluation of RCS Loop Valves to i Mitigate SGTR l

l September 1986

Haddam Neck ISAP Topic No. 2.06 Evaluation of RCS Loop Isolation Valves to Mitigate Steam Generator Tube Rupture

Background

The steam generator tube rupture (SGTR) accident at the Robert E. Ginna Nuclear Power Plant in January 1982 represents a significant event that can occur at PWRs. It has one of the highest frequencies among the significant initiating events that can occur in PWRs. In order to mitigate an SGTR event a series of potentially complex operator actions are required. As a result of the Ginna accident, CYAPCO has initiated this project to help in prevention of occurrence and mitigation of consequences of SGTR events. l

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Project Description The RCS Loop Isolation Valves can be used to isolate a primary loop in cases of i RCS pump seal failure or other problems associated with one loop. Each primary loop is equipped with two motor-operated isolation valves at either side of the ,

reactor coolant pump (RCP) and the steam generator. This project was initiated l to evaluate the acceptability of utilizing the RCS loop isolation valves (LIV's) to mitigate the consequences of a steam generator tube rupture (SGTR) event, particularly where a steam generator safety relief valve is stuck open.

CYAPCO Evaluation The LIVs at Haddam Neck are capable of closing against a maximum differential pressure of 500 psi. Haddam Neck transient analyses have shown that for some scenarios this limit of 500 psi may be exceeded for a long period of time after shutdown. High pressure steam dump to condenser will be unavailable following i loss of offsite power due to loss of control air (high pressure steam dump valves are air operated), and also because circulating water pump trip will cause loss of condenser vacuum.  ;

i The following concerns have been identified involving the use of LIVs to mitigate the radiological consequence of SGTR:

o isolation of the wrong SG followed by the inability to unisolate may remove one of the heat sinks, o power source availability for the LIVs following a loss of offsite AC power, o injection of cold safety injection water downstream of a closed LIV, resulting in the potential for pressurized thermal shock, All three of the above concerns have been adequately addressed and fully resolved. It was determined that pressurized thermal shock would not be a potential problem, since power for the LIVs would be available following a loss of offsite AC power, and isolation of the faulted steam generator can be adequately assured. Hence, CYAPCO considers this ISAP topic closed.

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Docket No. 50-213  !

B12198 l

l Haddam Neck ISAP Topic No. 2.07 Auxiliary Pressurizer Spray Nozzle i

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September 1986

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1 Haddam Neck ISAP Topic No. 2.07 Auxiliary Pressurizer Spray Nozzle l l l l l

Background

I The auxiliary pressurizer spray is a system available as an alternative for providing primary system depressurization in case of a steam generator tube l rupture (SGTR), or any other event requiring depressurization. The large temperature difference between the auxiliary spray water (from the VCT) and the spray nozzle inside the " hot" pressurizer introduces the potential for thermal shock breaching of the spray nozzles and the connecting piping. This event can potentially lead to a loss of coolant accident. As such, there is an administrative technical specification that limits the use -of the auxiliary spray unless the temperature difference between the pressurizer and charging flow is less than l 2000F. '

Project Description The proposed project is an evaluation of the potential for thermal shock to the auxiliary pressurizer spray nozzle. To date, probabilistic safety implications of the issue have been quantified using the conservative assumption that given that auxiliary spray is used, it will fail (i.e., result in a pipe rupture) as a consequence of the thermal shock.

CYAPCO Evaluation it is expected that the impact on public safety due to thermal shock to the auxiliary pressurizer spray nozzle will be negligible. However, further analysis is ongoing and the issue will be further addressed in the integrated assessment.

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