ML20214X315

Forwards Addl Info Justifying Schedule for Replacing Identified Parts During Cycles 12 & 13 Refueling Outages,Per Evaluation of torus-to-drywell Vacuum Breakers

ML20214X315
Person / Time
Site:	Oyster Creek
Issue date:	12/03/1986
From:	Wilson R GENERAL PUBLIC UTILITIES CORP.
To:	Zwolinski J Office of Nuclear Reactor Regulation
References
5000-86-1101, NUDOCS 8612110060
Download: ML20214X315 (3)

Text

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Nuclear Ra" a T ""-

Route 9 South Forked River, New Jercey 08731-0388 609 971-4000 December 3, 1986 Writer's Direct D;al Number:

5000-86-1101 Mr.: John A. Zwolinski,; Director, BWR Project Directorate #1 Division of BWR Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Oyster Creek Nuclear Generating Station Docket No. 50-219 Mark I Containment Torus-to-Drywell Vacuum Breakers By letter dated May 23, 1986, GPUN documented the results of the evaluation of the Torus to Drywell Vacuum Breakers at the Oyster Creek Nuclear Generating Station and committed to replacing identified parts during the Cycle 12 and Cycle 13 refueling outages. Subsequent to that letter, your staff reauested that an additional submittal be made to further justify the schedule which we pro-Attachment I to this letter fulfills that reauest.

If any further information is reauested, please contact Mr. John Rogers of my staff at (609)971-4893.

ry tr ly yours, 2.

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.. F. W i Ts"on

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Vice President Technical Functions RFW/JR/pa Attachment cc: Dr. Thomas E. Murley, Administrator Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 Mr.: Jack N.EDonohew,:Jr.

U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue, Phillips Bldg.

Bethesda, MD 20014 e612110060 861203 A0p/

PDR ADOCK 05000219

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PDR NRC Resident Inspector

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I; Oyster Creek Nuclear Generating Station GPU Nuclear Corporation is a subsidiary of the General Pubhc Utilities Corporation

ATTACHMENT I References A.

NRC Letter dated December 24, 1984, D. B. Yassallo, Chief Operating Reactors Branch #2, Division of Licensing, to H.C. Pfefferlen, Manager, BWR Licensing Programs, General Electric Company; Subject; Evaluation of Model for Predicting Drywell to Wetwell Yacuum Breaker Valve Dynamics.

B.

Continuum Dynamics Inc. (CDI) Report No. 84-3, " Mark I Wetwell to Drywell Yacuum Breaker Load Methodology."

C.

CDI Tech Note 82-31, " Mark I Vacuum Breaker Improvea Dynamic Model-Model Development and Validation."

D.

CDI Tech Note 84-23, Revision 0, " Mark I Wetwell to Drywell Differential Pressure Load and Yacuum Breaker Response for the Qyster Creek Nuclear Power Plant Unit 1", January 1985.

E.

CDI Tech Note 84-23, Revision 1, " Mark I Wetwell to Drywell Differential Pressure Load and Vacuum Breaker Response for the Oyster Creek Nuclear Power Plant Unit 1", December 1985.

F.

MPR Associates, Inc. Letter dated January 29, 1986, N.J. Marrone to W.

F. Duda, "Qyster Creek Nuclear Generating Station Torus-to-Drywell Vacuum Breaker Evaluation for New Chugging Slamming Load Definition".

Bases GPU Nuclear has determined that the deferment of valve modifications to the Cycle 12 and Cycle 13 refueling outages is justified based on the following information:

1.

Section II of the Safety Evaluation contained in Reference A stated, " Opening impacts and hence the vacuum breaker damage observed in test M1, are not anticipated in domestic Mark 1 plants." This quote, from Reference B, evolves from the fact that the Full Scale Test Facility (FSTF) test velocities are not considered prototypical because the drywell volume in the FSTF is much smaller than any domestic Mark 1 plant, giving very conservative results.

2.

Section III.1 of the Safety Evaluation contained in Reference A stated, "Comparision of the predicted valve impact velocities based on the improved model still bounded all test impact velocities with approximately a 12% margin." This fact was documented in Reference C.

3.

Based on Reference C, vacuum breaker impact velocities at Qyster Creek were calculated to be 3.64 radians /second, as documented in i

Reference D.

Assuming this impact velocity to be correct, the following vacuum breaker parts were determined to be overstressed:

O a.

Counterweight arms b.

Disk arms c.

Disk arm keys d.

Shaft e.

Counterweight arm hub f.

Counterweight arm hub keys 4.

Further analysis were performed as documented in Reference E.

These further analyses removed the 12% margin and thereby red.uced the impact velocity to 2.04 radians /second. With this new impact velocity, the overstress condition was removed from all valve parts excepting the counterweight arm hub and counterweight arm hub keys.

5.

Section III.3 of the Safety Evaluation contained in Reference A noted that during the FSTF tests 400 chugging events produced 179 vacuum breaker valve actuations. Of these, three runs exhibited significant chugging; and of these three runs the most conservative run was used to determine tF? CDI Model, Reference B, condensation rate. Therefore, the model chosen was based upon an event that occurred 0.25 percent of the time during the FSTF tests.

==

Conclusions:==

Modifications to the Oyster Creek torus-to-drywell vacuum breakers are required by either CDI Tech. Note 84-23 Rev. O or Rev.1. GPUN is presently reviewing the impact of the reduced impact velocity calculated under CDI Tech. Note 84-23, Rev.1. The exact nature of the vacuum breaker valve modifications to be made will be determined by this review.

In either case, Rev. O or Rev.1, redesign and procurement of valve parts is reauired, as is the preparation of baseline documents (system design descriptions, safety evaluations, fire hazards analyses) and detailed installation drawings and specifications.

The documentation needed by GPUN to formulate this decision was not in place until late January,1986 (Reference F). At this time, the workscope for the current Oyster Creek outage was frozen and it was decided, because of the negative impact of adding additional jobs to an already crowded inventory of work, to delay this modification until a later date.

Therefore, based on:

1) the extremely conservative model selected for this analysis; 2) the very low probability of the conservative model actuation event occurring during a chugging event; and 3) the l

significantly reduced nature of the modifications reauired if the 12% margin were not included; the deferment in the installation of the identified modifications until the Cycle 12 and Cycle 13 refueling outages is justified.

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