ML20128D962

Safety Evaluation Supporting Amend 19 to License DPR-22. Amend Changes Involved Reduction in MSL Low Pressure Isolation Setpoint & Reduction in MCPR for 8x8 & 7x7 Fuel

ML20128D962
Person / Time
Site:	Monticello
Issue date:	05/27/1976
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20128D934	List: ML20128D931 ML20128D962 ML20128D993
References
NUDOCS 9212070434
Download: ML20128D962 (3)

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UNITED STATES

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%,.....j SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMEW NO. 19 TO PROVISIONAL OPERATING LICEhSE NO. DPR-22 NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLAW DOCKET NO. 50-263 INTRODUCTION By Ictter dated December 1, 1975, as supplemented by letter dated February 27, 1976, the Northern States Power Company proposed changes to

'the Technical Specific' tions appended to Provisional Operating License No. DPR-22, for the Monticello Nuclear Generating Plant. The proposed changes involve a reduction in the main steam line low pressure isolation setpoint and reduction in the operating Minimum Critic.a1 Power Ratio (MCPR) for 8 x 8 and 7 x 7 fuel.

DISCUSSION AND EVALUATION A.

Main Steam Line Pressure Isolation Set Point Reduction 16sta11'ation of the main steam line low pressure sensors was required to provide reactor isolation in the event of an abnormal transient associated with the failure of the -initial turbine pressure regulator in the open direction. This reactor. isolation' function was provided to limit the duration and severity of-system depressuri::ation so that l

no significant thermal stresses are imposed on the primary system.

l No credit was taken for these low pressure sensors in any of the other l

postulated abnormal operating transients or. accidents. The current isolation set point is 850 psig; the proposed setpoint is 825 psig.

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,,' Northern States Power Company referenced Edwin I. Hatch Nuclear Plant Unit -1 (50-321) submittal dated October 9,' 1975'which provided a bounding analys'is for a reduction in the main steam line low pressure setpoint from 880 psig to 825 pstg. The NRC staff has reviewed the i

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Hatch I analysis-and has determined that it-is applicable to NSP's proposed changes.

In both cases (Hatch and Monticello) the additional temperature decrease and subsequent-reactor vessel thermal stresses, resulting from the additional pressure reduction during the abnormal transient, are negligible.

Because_ reduction of the low pressure isolation setpoint would not haveisignificant effects on previously analyzed transients, we have concluded that the proposed change is acceptable, B.

Reduction In Operating Minimum Critical Power Ratio (MCPR) Limits The operating limit MCPR, which is presently 1.41 for 8 x 8 fuel-and 1.33 for 7 x 7 fuel, is based upon the most limiting-transient, a turbine trip, without bypass,. from 100t power and 100F flow conditions.

Assuming the fuel is operating at the proposed MCPR limits of 1.38 for 8 x 8 fuel and 1.29 for 7 x 7 fuel, the calculated decrease in MCPR-during the transient is.32 for 8' x 8 fuel and.23 for 7'x 7 fuel.

Therefore, in the event of the occurrence of the most limiting transient, the MCPR Technical Specification Safety limit of 1.06 would not be violated.

The required operating limit MCPR is a' function of the magnitude and location of the axial and rod-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 l

7,x 7 fuel and 1.102 for 8 x 8 fuel and an axial peaking factor of 1.40 at a mid core point was. assumed..The transient analyses-included as input data the worst' consistent set of local and-axial peaking factors.

During the fuel cycle the Ipcal peaking, and_there-fore the R-factor,-is reduced while the peak in the axial shape moves-l toward the bottom of the core.- Although the operating limit MCPR would be increased by approximately 10 by the reduced end-of-cycle-R-factor, this is offset by.the reduction in MCPR resulting from the-r relocation of the axial peak to below the midplane.~ Because the MCPR-l will remain essentially constant over the fuel cycle and1because-the proposed MCPR limits will not result in violation of the Technical Specification Safety limit in event of the limiting. transient', the proposed reduction in MCPR Operating limits is acceptable.

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ENVIRONMENTAL CONSIDERATION We have determined that the amendment does not authorize a change in-effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.

Having made this determination, we have further concluded that the amendment involves-an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR 551.5(d)(4) that an environmental statement, negative declaration or environmental impact appraisal need not be prepared in connection with the issuance of this amendment.

CONCLUSION We have concluded, based on the considerations discussed above that:

(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the. public.

l Date:

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