ML19327A044

Responds to IE Bulletin 80-12, Decay Heat Removal Sys Operability. Procedures & Adminstrative Controls Reviewed for Adequacy of Safeguarding Against Loss of Redundancy & Diversity of Decay Heat Removal Capability

ML19327A044
Person / Time
Site:	Millstone
Issue date:	06/30/1980
From:	Counsil W NORTHEAST UTILITIES
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
A01020, IEB-80-12, NUDOCS 8008010097
Download: ML19327A044 (4)

Text

. _ _ _ _ _ _ _ - _ _ .

O1 .

g NORTHEAST UTIlJTIES 1 C 2'#."C '.*O ~ f8SdnE CONNECTICUT 06101

==='=i'l""~ no:n e*eeii L '  ; :""=="J.1.'=~

l ll June 30,1980 i Docket No. 50-336 A01020 Mr. Boyce H. Grier Director, Region I Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission 631 Park Avenue l King of Prus ia, Pennsylvania 19406

References:

(1) B.H. Grier letter to W.G. Counsil dated May 9, 1980 (2) W.G. Counsil letter to B.H. Grier dated June 4,1980 (3) J.F. Opeka letter to B.H. Grier dated April 12, 1979 Gentlemen:

Millstone Nuclear Power Station, Unit 2 I&E Bulletin No. 80-12 1 Decay Heat Removal System Operability In reference (1), Northeast Nuclear Energy Company (NNECo) was requested to respond to Staff concerns regarding loss of decay heat removal capability in Pressurized Water Reactors. Of particular concern were conditions involving plants in a refueling or cold shutdown mode.

In reference (2), NNECo infonned the staff that additional time would be required to formulate the response requested by reference (1) and that the requested response would be submitted by July 1, 1980.

In accordance with that request, the following information is provided pursuant to the provisions of 10CFR50.54(f). NNECo has reviewed the circumstances and sequer,cas of events at Davis-Besse as described in IE Information Notice No. 80-20 and has reviewed facility records for Decay Heat Removal (DHR) degradation events.

A previous event at Millstone Unit 2 resulted in loss of Shutdown Cooling (SDC) during cold shutdown operations (reference (3): LER No. 79-08/3L-0). Cn this occasion the reactor coolant system (RCS) was open (for Steam Generator eddy current testing) with SDC providing RCS cooling. Loss of prime on the SDC piping resulted in loss of SDC. The Refueling Water Storage Tank (RWST) was used to prime the Low Pressure Safety Injection Pump (LPSI) and restore SDC.

8 0 o s o 10077_----

o k Mr. Boyce H. Grier U. S. Nuclear Regulatory Commission Page 2 During this evolution, containment integrity was established and personnel cleared from the containment. Following this event, SDC suction vacuum priming was incorporated into SDC procedures. In addition, procedures were strengthened to ensure adequate and timely response in the event of loss of SDC.

NNECo has reviewed its hardware capabilities to prevent DHR loss events. The system consists of two 100% capacity pumps, two 100%

capacity heat exchangers and associated pipes, valves, instrumentation and controls to constitute a system that has adequate redundancy and reliability. The SDC system design is described in Section 9.3 of the Millstone Unit No. 2 Final Safety Analysis Report. The two SDC pumps are powered from separate emergency buses, each capable of being supplied by its associated emergency diesel generator. Instrumentation and controls are powered from instrument A.C. buses that have redundant power supplies. Instruments and controls that use instrument air are supplied by two redundant instrument air compressors with automatic backup from a third station air compressor and a cross tie with the Millstone Unit 1 air system. Each instrument air compressor is powered with a vital MCC and can be supplied from an emergency diesel generator in the event of loss of off-site power.

Procedures for responding to loss of DHR were reviewed and found adequate.

They are specific and detailed as to steps to take to restore SDC and concurrently ensure containment integrity and personnel safety as conditions warrant. Administrative procedures provide instructions for removing vital equipment, buses and protective systems from service to ensure maintenance of the facility in a safe condition is not jeopardized.

Procedures and administrative controls were reviewed for adequacy of safeguarding against loss of redundancy and diversity of DHR capa bility. This review indicated that while operational philosophy has been to ensure redundant DHR capabilities, strengthening of procedures is warranted in this area. Consequently, procedures for Millstone 2 cooldown, heatup, SDC operations and refueling operations will be revised as indicated below. Changes to these procedures will be accomplished by July 26, 1980 to ensure they are in effect when Millstone 2 begins its 1980 refueling.

In Mode 5, one reactor coolant loop will be in operation with a LPSI pump providing circulation as required in Technical Specification 3.4.1.

In addition, either a SG will be operable (RCS integrity and SG level on scale), a second SDC loop available, or a HPSI pump available that is capable of being started within two hours and taking suction on the RWST.

Mr. Boyce H. Grier U.S. Nuclear Regulatory Comission Page 3 The normal or emergency power source may be inoperable for backup LPSI and HPSI pumps provided Technical Specification requirements for electrical power systems are met.

In Mode 6 when refueling water level is less than 23 feet above the top of irradiated fuel assemblies seated within the reactor vessel, one SDC loop will be operable as required in Technical Specification 3.9.8. In addition, either a second SDC loop will be available or a HPSI pump available that is capable of being started within two hours and taking suction on the RWST. The normal or emergency power source may be inoperable for backup LPSI and HPSI pumps provided Technical Specification requirements for electrical power systems are met.

In Mode 6 when refueling water level is 23 feet above the top of irradiated fuel assemblies sested within the reactor vessel, one SDC loop will be operable as required in Technical Specification 3.9.8. RHR requirements for this evolution are consistent with present procedures and requirements.

We trust you find the above infonnation satisfactory to resolve the reference (1) concerns.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPA

/. '/T[//ldt-it.G. Counsil Senior Vice President

• i e

STATE OF CONNECTICUT )

) ss. Berlin de' /9 Po COUNTY OF HARTFORD )

Then personally appeared before me W. G. Counsil, who being duly sworn, did state that he is Senior Vice President of Northeast Nuclear Energy Company, a Licensee herein, that he is authorized to execute and file the foregoing information in the name and on behalf of the Licensees herein and that the statements contained in said information are true and correct to the best of his knowledge and belief.

Yb}l) At. l9a2kly Notary Public' My Commisslort Expires March 31,1981 I

I

- - - - ,__