ML20024G117
| ML20024G117 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 05/21/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20024G115 | List: |
| References | |
| NUDOCS 9102070548 | |
| Download: ML20024G117 (4) | |
Text
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Jta NUCLE MOULATORY COMMith..d r,
WASHINGTON. Q. c. 20Lf 5 l
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l SAFETY EVALUATION BY Tile OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING TI2!PORARY RELAXATION OF Ti1E DRYWELL-TORUS
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DIFFER 121TIAL l'RESSURE REQUIREMENT AT MONTICELLO d
NUCLEAR CENERATING Pl. ANT FOR TESTING PURPOSES DOCKET No. 50-263 INTRODUCTION By letter dated 11ay 10,1976, Northern rtates Power ce. ny (NSP) subinitted
'l plans for the performance of an In-Plant Safety / Relief Valve Test at the flonticello Nucicar Generating Plant during the week of liay 23, 1976.
To provide meaningf ul results, such testing will require an " unbiased" initia) water level in the relief valve blowdoun line and thus the temporary (approximately 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />) cessation of the 1 PSI drywell-torus differential pressure voluntarily itaposed by NSP af ter the Tebruary 26, 1976 meeting of the BWR Mark I owner's group and the NRC staff.
BACKGROUND A January 6,1976 letter f rom Mr. Ivan F. Stuart of General Electric to
!!r. R. S. Boyd of the USNRC described an In-Plant Saf ety/ Relief Valve Test to be performed as part of the long-term program for evaluation of Mark I containment systems.
NSP agreed to perform the test at the !!onticello Nucicar, Generating Plant.
Testing was originally to have been performed in !! arch 1976.
llowever, reanalysis of the torus support downward Joad/
strength ratios in February 1976 indicated that the margins of safety of the torus structure were not as large as hai been previously calculated.
Th us, at the meeting of February 26, 1976 NSP, along with other Mark 1 licensees, agreed to establish the differential pressure between the drywell and the torus to provide a reduction in the potential loads during a postulated loss of coolant accident and an associated restoration of the margins of safety to obtain a factor of safety of about two.
'Ihi s agreement was confirn.ed in a February 27, 1976 letter f rom !!r. Benard C. Rusche, Director, Of fice of Nuclear Reactor Regulation, NRC, to NSP.
Subsequently, NSP has undertaken a program of structural modifications to enhance the safety margins of the I!onticello torus. A description of the modifications and the resulting loading tables are included as an attachment to NSP's liay 10,1976 letter.
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t DISCUSSION AND EVALUATION The NRC staff agrees with NSP and the Mark I owner's group that the In-plant Safety / Relief Valve Test will provide data essential for the development of long-term solutions to the Mark I problem.
Our concern is mainly that there is reasonable assurance that the torus would remain intact and function as intended should the extremely low probability Loss-of-Coolant Accident (!;0CA) occur during the relatively short period of time (96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />) that the differential pressure would be relaxed.
In their May 10, 1976 letter, NSP committed to restore the differential NH~
pressure should the test be interrupted for periods anticipated to exceed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
6Sp has submitted data, as an attachment to its Flay 10, 1976 letter.
which supports the NSp conclusion that the modifications, which have been completed, produce a W. improvenent in ratios of load to ultimate capacity without the differential pressure.
Improvement of over 1004 is claimed for up-loads. We have completed a preliminary review of i
data which has been provided and agree with ssp's statement concerning the increased safety margins with the modifications installed and the differential pressure removed.
Additionally, we concur that conditions under which the test will be performed "will provide safety margins conservatively within and consistent with the margins of safety discussed in tir. Rusche's letter of February 27,1976" (i.e., factors of snfety of about two),
e test does not involve an unreviewed safety question in that (1) the probability of occurrence or the consequences of an accident or mal-function of equipment important to safety previously evaluated in the safety analysis report is not increased, (2) the possibility for an accident or malfunction of a different type than any evaluated previously in the safety analysis report is not created, and (3) the margins of i
safety as defined in the bases for the technical specifications are not reduced.
4 On the basis of the above considerations, we have concluded that elimination of the dryvell-torus pressure dif ferential during the relatively short period l
of time required to perform the In-Plant Safety / Relief Valve Test is
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accept abic.
l Date: May 21, 1976
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1 DETEPQNATION OF PROPOSED LICENSING ACTION l
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I Licensee: Northern States Power Company (NSP) (Monticello)
Request for: NSP has indicated that they will submit, within the next few weeks, a request for a temporary waiver from the 1 PSID AP (drywell to torus) requirement defined in the NRC to NSP letter of February 27, 1976. De waiver will be requested for a period of about 3 days during the planned relief valve testing.
Bis test i
is an integral and important part of the total Mark I Containment Program in progress.
l.i Request Date: Estimated by May 7,1976 Proposed Noticing Action: ()
Pre-notice Recommended
()
Post-notice Recommended
() Determination delayed pending completion of Safety Evaluation (X) No Notice Recommended Basis for Decision: As indicated, the 6P requirement was imposed by a letter.
It is not a license requirement. NSP has already initiated various " permanent" solutions to the torus structure problem, n ese solutions include:
1.
Addition of heavy-schedule " scab" piping to the tortts support columns to substantially increase the area of torus-to-column welded support.
2.
Modification of support column elevis pin attachment to substantially increase the area across which forces transmitted to the clevis pins will act.
3.
Addition of new grouted hold-down bolts to the support column base-plates to assure minimal upward movement.
%e staff has undertaken preliminary revie,< of the data proposed " fixes" and has reviewed sufficient to determine that the results will be favorabic.
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. li NSP is working toward completion of the long-term fixes prior to performing the relief valve testing.
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Degree of completion, and adequacy of this status,
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will be determined prior to approval of the testing program.
Based on the above, the temporary waiver of the 1 PSID AP will not present an increased hazard, especially since the test will be conducted under
- controlled and closely-monitored conditions. Thus public notice of the event is not considered
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necessary and a letter from the NRC to NSP, detailing the conditions of the waiver, will be M issued to authorize perfonnance of the test and variance from the 1 PSID torus-drywell requirement.
The test is presently scheduled to be performed in mid May, 1976.
Proposed NEPA Action: ()
EIS Required
() Negative Declaration (ND) and Enivronmental Impact Appraisal (EI A) Required (X) No EIS, ND or EIA Required
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Determination del:yed pending completion of EIA Basis for Decision:
As noted sbove, the testing will be conducted under closely monitored conditions. 'Ihere will be ne power increase, or change in amount or types of effluents and thus there will be no significant effect upon the human environment.
Noticing Concurrence r Date:
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