ML20090M610

Forwards Facility Cycle 2,scram Reactivity Considerations, Analysis & Mods in Response to Requesting EOC Transient Analysis

ML20090M610
Person / Time
Site:	Monticello
Issue date:	10/10/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20090M612	List: ML20090M610 ML20090M615
References
NUDOCS 9105070372
Download: ML20090M610 (3)

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FILE FITdd: DATE OF DOC DATE REC'D LTR MEMO RPT OT!!UR Northern Staten Power Cornpany ttinneapolis, Winn. 55401 Hr. L.O. Mayer 10-10-73 10-17-73 X TO: ORIG CC OUlER SENT AEC PDR xyy II,L <;Lnvholt 3 CLASS V:; CLASS l' ROP INTO IUPUT 1;0 CiS REC'D DOCKET lios XXX 40 50-263 DESCRTbTION ENCLOSURES:

Ltr te our 10-2-73 ltr..... concern LOC REPORT: lbnticello-Cycle 2 Scram Reactivity Transient Analynis. . .and t rans the f ollowing. . . Considerations, Analynis and Modifications, dtd 10, 1973.

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NSF NORTHERN STATES POWER COMPANY u i N N a a s= o u s . u s u N a n o t A s e 4 oi October 10, 1973 U, h Q

Mr. D J Skovholt O Assistant Director for Operating Reactors i

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Of(ice of Regulation United States Atomic Energy Comission

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Dear Mr. Skovholt:

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c,j y' MONTICELLO NUCLEAR GENEPATING PLANT Docket No. 50-263 License No. DpR-22 Response to October 2,1973 Letter Requesting EOC Transient Analyris Your October 2, 1973 letter transmitted Technical Specification Change No.10 which allowed the Monticello safety valve set points to be in-creased to 1240 psig. During the Monticello outage which comenced September 28, 1973, this set point change was made. In addition, modi-fications were made to the relief valves as discussed in our August 21, 1973 1ctter. This modification has been demonstrated to result in a significant improvement in valve opening time. The transient analyses submitted with our September 13, 1973 request for increasing the safety valve set points took credit only for these set point changes; they did not include the effect of improved relief valve response. We are, there-fore, submitting the attached transient analysis report which covers all phases of cycle 2 using the appropriate plant conditions. It includes the information required by your October 2,1973 letter to remove the 1200 MWD /STU control rod inventory restriction.

In brief, the attached analysis justifies full power operation to 2680 MWD /T at which time the control rod inventory will remain fixed until the power coasts down to 917. of rated. The reactor will then be operated at 917.

power until all control rods are fully withdrawn. We are choosing this operating plan to maintain a calculated 25 psi design margin between peak vessel pressure and the safety valve set points in the event of a turbine trip without bypass transient. The analyses show that a main steamline isolation valve closure with failure of the direct scram, the transient of prime safety concern, can be tolerated from full power at any time in the

<g cycle with sufficient safety margins.

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Oc tobe r 10, 1973 D J Skovholt In our September 13, 1973 letter, vc infomed you that estimation techniques, believed to be conservative, had recently indicated that the 25 psi design margin to safety valve set points would be reached at 1640 FMD/T in cycle 2.

As reported, we acted conservatively and fixed the control rod pattern at ,

1540IND/T. On September 24, 1973, af ter coasting down to approximately 987. of rated power with the 1540 IND/T control rod pattern, we were infortned of the preliminary results of the General Electric transient analysis attached. In particular, we Icarned that the margin to safety valve set points calculated for 1640 FND/T vas 17 psi. Control rods were innedtately inserted and fixed in the 1200 IND/T inventory, dropping power to 937., to assure a margin of approximate 1f 25 psi. Thet control inventory was main.

tained until the c,utage. It should be noted that had the unlikely tiSIV closure with failure of direct scram occurred at rated power during this 11 day interval, calculations show that the peak vessel pressure would have remained 99 psi or more from the vessel design limit.

'1he calculations presented in the report are complete transient analyses for the Monticello reactor. They are inherently conservative in that they use Technical Specification, rather than the much faster measured, scram time. Likewise, coni.ervative design multipliers are used in applying Doppler and void feedback coefficients and in the scram reactivity used to calculate the tranatent effects.

No Technical Specifications must he changed as a result of this analysis.

Certain values and statements in the Technical Specification Bases must be updated to reflect the recent analytical results; they vill be considered with future change requests.

Yours very truly,

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L 0 Mayer, PE Director of Nuc1 car Support Services Lot 4/tniv/br cc: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn K Dzugan Attaclanent