ML20128E089

States That Although Net Increase in Safety Valve Set Point Is Only 20-30 Psi,Aec Will Consider Code Requirements & Safety Valve Set Points at Other BWRs in Evaluation of Info Yet to Be Submitted by Util

ML20128E089
Person / Time
Site:	Monticello
Issue date:	09/13/1973
From:	James Shea US ATOMIC ENERGY COMMISSION (AEC)
To:	US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9212070468
Download: ML20128E089 (4)

Text

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D p *e UNITED STATES f( b .

t' ATOMIC ENERGY COMMISSION I 'I 7*J l I wasmunvow, o c, rosas SEP 131973 Files (Docket No. 50-263)

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MONTICELLO CORE 001 ANT RELIEF VALVE RESPONSE TIMES AND SAFETY VALVE SET POINT INCREASES (NORTHERN STATES POWER COMPANY)

By letter dated August 21, 1973, Northern States Power Company (NSP) described " Planned Reactor Operation from 2000 MWD /STU to the End of Cycle 2". Previous analyses (references 1 through 4) have focused on the overpressure transient following a turbine trip without bypass and concluded that shorter scram times and the requirement that four relief valves be in service would limit the coolant overpressure transient during the first 2250 MWD /STU of Cycle 2 operation such that full power operation was acceptable. We approved Technical Specification changes to reduce scram times and require four operating relief valves for continued reactor operation through 2250 MWD /STU of Cycle 2 operation at power icvels up to 100% (Ref. 5). NSP later reduced the exposure threshold from 2250 MWD /STU to 2000 MWD /Snl (Ref. 6) to account for the reduction in opening speed of the relief valves.

According to the August 21, 1973 letter, NSP plans to submit additional analysis for the period beyond 2000 MWD /STU exposure threshold of Cycle 2 and additional Technical Specification changes to minimize or eliminate the power restriction to be imposed based on all rods out scram reactivity curve (84% according to item IV of the NSP August 21, 1973 letter), the condition achieved near the end of Cycle 2.

The reanalysis by NSP of the reactor power level limits for core life-time beyond the 2000 MWD /STU exposure threshold will be based on (1) completion of modifications to the relief valve to restore the original opening speed (0.2 see instead of 0.8 observed by GE in some instances at unidentified BWRs), (2) faster scram times, at least for the remainder of Cycle 2 life beyond the 2000 MWD /STO exposure threshold, and (3) resetting of safety valve set points upward from 1210-1220 psi to 1240 psi.

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Files SEP 131973 For the period beyond Cycle 2, the letter indicates that the addition of more relief valves is being considered to perinanently eliminate the less than 100% power level restrictions required by the current analysia.

Although the net increase in safety valve set point is only 20-30 pai, we will consider the ude requirements and safety valvo set points at other BWRs in our evaluation of the information yet to be submitted by NSP.

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James J.' Shea Operating Reactors Branch #2 Directorate of Licensing cci AEC PDR Local PDR D. J. Skovholt T. J. Carter D. L. Ziemann J. J. Thea R. H. Diggs L. Mayer, NSP 1

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REFERENCES 1

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1. " Report of a Change in the Transient Analysis as Described in the

FSAR", NSP letter dated August 14, 1972.

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j NSP report of reanalysis of transients discussed in FSAR based i on EOC conditions which is different from the FSAR results. - The i change involves a slower rate of negative reactivity insertion

! for the first half of the control rod insertion stroke caused by spatial distribution of reactivity depletion in the core.

! 2. " Supplemental Report of a Change in the Transient Analysis as Described in the FSAR", NSP letter dated February 13, 1973.

NSP presented GE "Results of Transient Reanalysis for Monticello i Nuclear Generating Plant"_ with end-of-cycle core dynamic charac-teristics. NSP, on the. basis of this analysis, promised to submit, in the near future, a proposed technical specification change to  ;

j specify (1) shorter scram times and (2) operation with all- four  :

relief valves instead of three and to revise the bases for the

technical specification.

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3. " Request for Authorization to Operate with Reload Fuel in the 1

Core", NSP letter dated February -20,1973.

l NSP claims that the reload core fuel does not respond significantly k

< different from the initial core. Page vie 8 of the attached report F assumed that the scram reactivity curve for EOC-1 was valid for j Cycle 2 operation.

4. " Request for Changes to the Technical Specifications", NSP-letter dated June 1,1973.

Scram times were reduced and four safety relief valves were required

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, for reactor operation and reactor operation at 100% power was restricted to the first 2250 MWD /STU of the second fuel cycle.

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5. Approval of Change 8 requiring four relief valves and shorter scram times, AEC letter dated July 2, 1973.

The AEC letter of approval also requested that analysis and tech-nical specification changes for the period beyond 2250 MWD /STU be submitted for AEC review at letst 30 days prior to the 2250 MWD /STU deoletion.

6. " Observed Relief Valve Opening Times Dif ferent Than Those Assumed in the Transient Analysis", NSP letter dated August 1, 1973.

General Electric informed NSP of delayed opening observed for target rock relief valves, i.e, 0.8 second to open vs 0.2 second reported in Monticello FSAR. NSp cannot measure opening times of the relief valves, but assuming such a delay results in a reduction of the exposure threshold from 2250 MWD /STU as previously approved (Ref. 5 above) to 2000 MWD /STU.