ML19325E591

Responds to Generic Ltr 88-20,Suppl 1, Initiation of Individual Plant Exam for Severe Accident Vulnerabilities. Individual Plant Exam Will Be Performed Over 4-yr Period Beginning Jan 1990 in Order to Ensure Max Util Involvement

ML19325E591
Person / Time
Site:	Vermont Yankee
Issue date:	10/24/1989
From:	Murphy W VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-89-100, GL-88-20, NUDOCS 8911080065
Download: ML19325E591 (5)

Text

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VERM2NT YANKEE '

' NUCLEAR POWER CORPORATION t

?' Ferry Road, Brattleboro, VT 053017002 BVY 89-100 I j .

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[ ENGINEERING OFFICE

{%J t,80 MMN $1Rtf 1 E DotToN, MA 01740 i October 24, 1989 ""7*'" I i U.S. Nuclear Reoulatory Commission i

Washington, D.C. 20555 Attention

Document Control Desk

References:

a) License No. OPR-28 (Docket No. 50-271) I b) Letter, USNRC to All Licensees Holding Operating Licenses ,

and Construction Permits for Nuclear Power Reactor Facilities, NVY 89-180, dated 8/29/89 i c) Letter, USNRC to All Licensees Holding Operating Licenses and Construction Permits for Nuclear Power Reactor Facilities, NVY 88-259, dated 11/23/88  ;

d) NUREG 1335, " Individual Plant Examination: Submittal Guidance," published August 1989 e) Letter, VYNPC to USNRC, BVY 89-83, dated 9/1/89 i f) Letter, USNRC to All Holders of Operating Licenses for Nuclear Power Reactors with Mark I Containments, NVY 89-191, Generic Letter 89-16, dated 9/1/89 l

Dear Sir:

l

Subject:

Vermont Yankee Response to Generic Letter 88-20, Supplement 1:

Initiation of the Individual Plant Enamination for Severe Accident Vulnerabilities - 10 CFR 50.54(f) >

l The following information is submitted in response to Reference b). As requested, we are providing a cescription of our approach, methodology, and ,

schedule for performing the Vermont Yankee Individual Plant Examination (IPE). t l

APPROACH The purpose of the IPE, as stated in Reference c), is for each utility:

1. To develop an appreciation of severe accident behavior.

2. To understand the most likely severe eccident sequences that could occur at its plant, i

I 3. To gain a more cuantitative understanding of the overall probabilities of [

l- core damage and fission product releases.  ;

4. If necessary, to reduce the overall probabilities of core damage and fission product releases by modifying, where appropriate, hardware and pro-cedures that would help prevent or mitigate severe accidents. -

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. VERMONT YANKEE NUCLEAR POWF.R CORPORATION U.S. Nuclear Regulatory Commission October 24. 1989 Pape 2 l

Vermont Yankee has aggressively pursued initiatives that satisfy the 4ntent of these objectives. In 1986. a " Vermont Yankee Containment Safety Study" was performed to address the issue of severe accident containment performance. This  !

study calculated core damage frequency by modifying surrogate plant results to t account for Vermont Yanket-specific features. This study provided an i understanding of the most likely severe accident sequences and provided a quan-titative understanding of the probability of core damage.  ;

The Vermont Yankee Containment Safety Study also examined the containment i response for core damage sequences. This required an appreciation of severe j accident behavior, anc' included an examination of hardware and procedures to prevent or mitigate severe accidents. Following the study, a Vermont Yankee '

Containment Task Force was established to evaluate potential improvements and to provide recommendations. As a result, a number of plant improvements were -

implemented. These improvements address the Mark I containment performance ,

improvements contained in Enclosure 2 of Reference b), as discussed below.

a. Alternate Water Supply for Drvwell Sprav/ Vessel Injection  !

The objective is to provide an alternate supply of water and a pumping  !

capability that is independent of normal and emergency on-site ac power.

Vermont Yankee has the ability to inject water to the reactor vessel or ,

drywell spray using an existing diesel fire pump. This capability has been enhanced for extended Station Blackout (SBO) conditions by use of an r existing on-sito diesel generator to power the required ac operated valves.  ;

b. Enhanced Reactor Pressure Vessel Depressurization System Reliability The objective is to provide de power to the Automatic Depressurization  ;

System (ADS) valves during an extended SB0 where station batteries may be depleted. Along with the improvement described above for alternate water supply, Vermont Yankee has provided for use of the same diesel generator to charge station batteries. This enhances plant capabilities during extended l SB0 scenarios by increasing the reliability of de control power to the ADS valves. Vermont Yankee is also enhancing the pneumatic supply for ADS valve operation by purchasing a diesel-powered air compressor and by [

increasing the size of the ADS accumulators. '

c. Emeroen,cy Procedures and Trainina l The objective is to implement Revision 4 of the BWR Owner's Grouo Emergency j

Procedure Guidelines (EPG's). Verment Yankee is currently developing a

, revision to our Emergency Operation Procedures (EOPs) using Revision 4 of I

the EPGs. Implementation of the EOPs, including completion cf the necessary operator training, is expected in April 1990. As noted in i

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., VET.MONT YANKEE NUCLEAR POWER CORPCW4ATK)N f .U.S. Nuclear Regulatory Commission October 24, 1989 Page 3  !

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Reference b), the EPGs include many actions apropriate for severe accident management. Vermont Yankee's E0Ps also include procedures for utilizing  ;

plant capabilities under severe accident conditions, such as the alternate  ;

vessel injection /drywell spray discussed above.  !

In addition to these improvements, Vermont Yankee has committed (Reference >

e)) to installing a hardened vent as reouested in Reference f).

The plant-specific studies performed to date, along with the plant improve-ments already implemented, demonstrate that Vermont Yankee has actively addressed the intent of the IPE over the past several years. We recognize,  !

however, that the scope of analysis and documentation requested in References j b), c), and d) requires significantly more effort. We agree with NRC's )'

assessment that maximum benefit from the IPE would be realized if the licensee's staff was involved in all aspects of the examination. Thus, in order to insure  !

maximum utility involvement and to maintain other ongoing severe accident  !

assessment efforts at Vermont Yankee, we will perform the IPE over a four-year f period beginning January 1990. j Methodolooy Vermont Yankee will utilire Method 1 of Reference c) for performing the IPE. This method is a Level 1 Probabilistic Risk Assessment (PRA) using current i methods and information, plus a containment performance analysis that foliows [

the general guidance of Reference c). Documentation will be provided following i the guidance of Reference d).

As required in Reference c), the scope of analysis at this time includes internally initiated events. Because " internal flooding" is concerned with spa-  ;

tial phenomena that are normally addressed in " external events" analyses, we  !

have not included internal flooding in our scope. Examination of internal i flooding will be included as an external event, which Reference c) indicates {

will proceed separately and on a later (but currently undetermined) schedule. i The IPE will be performed primarily by our engineering support organiza- t tion, the Yankee Atomic Electric Company (YAEC). YAEC has developed con-  !

siderable expertise through their involvement in PRAs performed for the Yankee [

plant, Seabrook, and Maine Yankee. '

l Our dedicated level of staffing for each of the four years needed to i complete the IPE will be approximately 6ne person at Vermont Yankee and three persons at YAEC. Additional resources of approximately $100,000 per year will be used for outside consulting services. i i

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e VE MONT YANKEE NUCLE A"2 POWE] CORPOR ATION I

U.S. Nuclear Regulstory Commission l October 2A, 1989 Page 4 i

Schedule The Vermont Yankee IPE effort will begin in January 1990, and the results will bo submitted to the NRC by December 31, 1993. A summary of intermediate milestones is provided in Table 1.

We trust this information is responsive to your needs: however, 4hould you desire further information, please do not hesitate to contact us.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION i.. - pr '- {

Warren P Murphy /

Vice Pre ident an V Manager of Operations

/dm cc USNRC Regional Administrator, Region I USNRC Resident Inspector, VYNPS ,

USNRC Project Manager, VYNPS '

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ls TABLE 1 Milestones for Vermont Yankee 1P[

1/1/90 Effort Begins 6/1/90 Preliminary Initiating Event Groups 1/1/91 Preliminary Event Trees Developed 6/1/91 Preliminary Fault Trees Developed 6/1/92 hstimated Core Damage Frequency e -

1/1/93 Preliminary Containment Event Trees 9/1/93 Draft Report for Internal Review 12/31/93 Submittal to NRC i.

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