B17766, Application for Amend to License DPR-65,to Return Hydrogen Purge Sys to Former Classification of Being within Scope of Maint Rule Program,But Not as risk-significant Sys

Application for Amend to License DPR-65,to Return Hydrogen Purge Sys to Former Classification of Being within Scope of Maint Rule Program,But Not as risk-significant Sys

ML20212H162
Person / Time
Site:	Millstone
Issue date:	09/23/1999
From:	Necci R NORTHEAST NUCLEAR ENERGY CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
B17766, TAC-MA4580, NUDOCS 9909300229
Download: ML20212H162 (3)

Text

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l Northeast Rope Feny Rd. (Route 156), Tcterford, CT 06385 Nuclear Energy wiii.io.e Nociear Po.e, staiioo horiheest Nuclear Energy Company P.O. Bos 128

.. .- Waterford, CT 06385-0128 (860) 447-1791 Fax (860) 444-4277

'ne Northeast Utilines System SEP 2 31999 Docket No. 50-336 B17766 U.S. Nuclear Regulatory Commission Attention: Document Control Desk 3 Washington, DC 20555 l I

Millstone Nuclear Power Station, Unit No. 2 Request for Change of Commitment Relating to the Classification of the ,

Hydronen Purae System Within the Maintenance Rule Prooram (TAC No. MA4580) '

in a letter dated January 18,1999," Northeast Nuclear Energy Company (NNECO) proposed to amend Operating License DPR 65 by removing the Technical Specification related to the Hydrogen Purge System from the Millstone. Unit No. 2 Technical Specifications. In a letter dated March 17,1999,* following subsequent discussions with the NRC staff regarding future maintenance of the Hydrogen Purge System, NNECO committed to maintain the Hydrogen Purge System as a risk- i significant system under the Maintenance Rule Program. In a letter dated April 12, 1999," the NRC approved removal of the Hydrogen Purge System from the Technical Specifications and stated in the Safety Evaluation Repoft that the Hydrogen Purge System will be maintained as a Maintenance Rule risk-significant system.

The purpose of this letter is to request approval to retum the Hydrogen Purge System to the system's former classification of being within the scope of the Maintenance Rule s Program, but not as a risk-significant system. O m M. L. Bowling, Jr. letter to U.S. Nuclear Regulatory Commission, " Millstone Nuclear Power Station, Unit No. 2 - Proposed Revision to Technical Specifications, Deletion of The QcFl I

- Technical Specification Related to The Hydrogen Purge System," dated January 18,1999.

• M. L. Bowling, Jr. letter to U.S. Nuclear Regulatory Commission, " Millstone Nuclear Power Station, Unit No.- 2.- Additional Information Regarding the Proposed Revision to Technical Specir,cetions Deletion of the Technical Specification Related to the Hydrogen Purge System," dated March 17,1999.

• R. B. Eaton (USNRC) letter to R. P. Necci, " Issuance of Amendment - Millstone Nuclear ,

Power Station, Unit No. 2 (TAC No. MA4580)," dated April 12,1999.

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U.S. Nucle r Regul tory Commission B17766\Page 2 Discussion When the Maintenance Rule Program for Millstone Unit No. 2 was originally developed, the Hydrogen Purge System was determined to lie within the scope of the program since the system is used in the Emergency Operating Procedure (EOP) for containment hydrogen control. If an event capable of generating large quantities of hydrogen were to occur, such as a Loss of Coolant Accident (LOCA), and if both trains of the safety grade hydrogen recombiners were to fail, the Hydrogen Purge System is credited as a backup to the Hydrogen Recombiner System to reduce the. hydrogen concentration in containment ,

The Hydrogen Purge System is also included in the Severe Accident Management 1 Guidelines (SAMG) for Millstone Unit No. 2. Containment venting via the hydrogen purge lines is credited in several of the Millstone Unit No. 2 SAMG computational aids.

As a system monitored under the Maintenance Rule, the system / function is monitored j by tracking Maintenance Rule Functional Failures (MRFFs). These are maintenance related or preventable failures which could affect a system's Maintenance Rule function. In order to be classified as a risk-significant system under the Maintenance Rule Program, a system must impact the Core Damage Frequency (CDF) and/or Large Early Release Frequency (LERF). In order to impact the CDF or LERF, a system must have a high- probability of initiating an accident or be needed for accident prevention / mitigation. For those systems determined to be risk-significant, unavailability monitoring is performed for the system in addition to tracking MRFFs.

While the Hydrogen Purge System does not initiate an accident, it is credited in EOPs ,

and could be utilized as an accident management strategy for beyond design basis events. In the latter case, it is an alternate method of reducing containment hydrogen concentration if both trains of the safety grade hydrogen recombiners fail, a condition that is beyond design basis, and it provides a means for containment venting under the Millstone Unit No. 2 SAMG. The.. Hydrogen Purge System is not modeled in  ;

Probabilistic Risk Assessment (PRA) and has no impact on the CDF. Furthermore, I from a Level-ll PRA perspective, hydrogen bum is not a dominant contributor to early i containment failure for Millstone Unit No. 2.

Since the Hydrogen Purge System does not meet the scoping criteria to be considered risk-significant under the Maintenance Rule Program, NNECO requests approval to return the Hydrogen Purge System to the system's former classification of being within the scope of the Maintenance Rule Program, but not as a risk-significant system.

There are no regulatory commitments contained within this letter.

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U.S. Nuclear Regulltory Commission B17766\Page 3 If you have any addition.=! questions concerning this submittal, please contact Mr.

Ravi Joshi at (860) 440-2080.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY l

R. P."Necci l

l Vice President - Nuclear Oversight and Regulatory Affairs cc: H. J. Miller, Region 1 Administrator R. B. Eaton, NRC Senior Project Manager, Millstone Unit No. 2 D. P. Beaulieu, Senior Resident inspector, Millstone Unit No. 2 l

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