ML20128D993
| ML20128D993 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 04/02/1976 |
| From: | Eisenhut D Office of Nuclear Reactor Regulation |
| To: | Goller K Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20128D934 | List: |
| References | |
| NUDOCS 9212070442 | |
| Download: ML20128D993 (5) | |
Text
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k NUCLEAR REGULATOHY COMMissli 4
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g 1976 Docket No. S'0-263 Karl R. Goller, Assistant Director for Operating Reactors Division of Operating Reactors
' REVIEW OF fl0RTHERN STATES POWER REQUESTS FOR CHANGE IN MAIN STEAM ISOLATION PRESSURE SETPOINT VALUE & OPERAT!!iG MINIMUM CRITICAL POWER RATIO LlHITS RESPONSIBLE BRN1Cil & PR11ECT MANAGER:
ORB-2, R. Snaider OPERATIONAL TECMi40 LOGY BRANCli INVOLVED:
Reactor Safety REVIEW STATL'S:
Comolete Enclosed is the Operational Technology evaluttion of Northern States Power Company)s (NSP) letter of December 1,1975 in which they toquested(1 a reduction in the Main Steamline isolation setpoint from 850 psig to 825 psig and (2) a reduction in the operating MCPR limits from 1.41 to 1.38 and from 1.33 to 1.29 for 8x8 and 7x7 fuel assemblies respectively. NSP orovided additional information by letter dated Februsty 27, s1976.
We have completed our review of NSPs proposals and find them a ceptable,.
9, Ib Darrell G. Eisenhut, Assistant Director for Operational Technology l
Division of Operating Rear, tors Enclosurei As stated i
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R. Baer nn R. Snaider l
R. Satterfield O. Berlinger i
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$AFETY EVALUATION REPORT-1
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_MONTICELLO fluct. EAR GEllERATING PLANT _
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DOCKET N0'. 50-263
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1.0 Introduction Northern States Power Company (NSP) requested by letter dated December,1,1975, proposed changes to the Monticello t
l Technical Specifications with respect to*(1) decreasing the s
main steamline low pressure set point from 850 psig to 825 psig
'and (2) decreasing the operating minimum crit cal power ratio-i (MCPR) limits from 1.41 to 1.38 and from 1.33 to 1.29 for r
8x8 and 757 fuel assemblies respectively. Northern States Power Company provided supplement'al information on the aSove Proposed changes by letter dated February 27. 1976. Our l
evaluation of NSPs proposed chan,ges are discussed below.
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..). 0 Main Steam 11ne Pressure Set Point Reduction
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, Installation of the main 'steamline low pressure sensors was T
required to provide reactor isolation in the event of an abnonnal transient associated with the failures of the initial turbine pressure regulator in the open direction.
No credit was taken for these low pressures sensors in any of other postulated abnormal operating transients or accidents.
The current isolation setpoint is 850 psig; the proposed setpoint is 825 psig.
NSP referenced the flatch -1 analysis dated October'9.1975 which perforned a bounding analysis for a reduction in the main steamline low pressure setpoint fro,m 880 psig to 825 psig.
We have reviewed the flatch I analysis in regard to its applicability to NSPs proposed changes and conclude that changing the pressure setpoint from 850 psig to 825 psig fiad insignificant effects on previously analysed transients and is acceptable.
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_ Reduction in Operatino Minimum Critical Power Ratio Limits The operating limit MCPR is based on the most limiting transient, a turbine trip without bypass from 100% power and 100% flow condition.
The calculated decrease in MCPR during this transient, which assumed the fuel was operating at MCPR limits of 1.38'for 8x8 fuel and 1.29 for 7x7 f0el, is 0.23 for 7x7 fuel and 0.32 for 8x8 fuel.
The proposed operating MCPR limit of 1.29 for 7x7 fuel and 1.38 for 8x8 fuel therefore would not violate the MCPR Technical' Specification limit of 1.06 in
~n the event of the occurrence of the most limiting transient.
The required operating limit MCPR is a function of the magnitude and location of the axial and ro'd-to-rod power peaking.
In determining the required MCPR, axial and local _ peaking representative of beginning of-cycle were assumed.
That is R-factors of 1.10 for 7x7 fuel and_1.102_ for 8x8 fuel and an axial peaking factor of 1.40 at a mid core point was assumed.
The transient analyses l
included the input data which is the worst consistent set of local and-axial peaking factors.
During the cycle the local peaking and theref9re the R-factor is reduced while the peak in the axial shape moves toward the bottom of the core.
Although the operati.ng limit MCPR would be increlsed by-approximately 1% by the reduced end-of-cycle R-factor,_ this is offset by the reduction in MCPR resulting from the relocation of-the axial peafi to below the midplane. We conclude that the above proposed Technical
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Specification changes are acceptable.
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'"~:lg 4.0 Conclusions Based on our evaluation'of NSPs proposed change we conclude that decreasing the main steamline low pressure isolation setpoint from 850 psig to 825 psig and reducing the operating MCPR limits from 1.41 to 1.38 and from 1.33 to 1.29 for 8x8 and 7x7 fuel assemblies respectively are acceptable.
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