ML20024G257
| ML20024G257 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 09/13/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20024G258 | List: |
| References | |
| NUDOCS 9102080431 | |
| Download: ML20024G257 (2) | |
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f NS53 NORT HEHN STATCS POWER COMPANY u e N s t. A p o t. i s,. M i w N e m o t A es4ot e..
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Dear Mr.
O' Lea ry :
MO:;T1 CELLO I;UCLEAR CE:iERATiliG PIAL;T Docket 1;o. 50-263 License 1;o. DPR-22 Change lequer Dated September 13, 1973 Attached are threc signed originals and 37 conformed copies of a request f or a change o.1cchnical Specificat. ions, Appendix A, of the Provisional Operating License, DPR-22, for the Monticello !iuelcar Generating Plant.
This change request has been reviewed by the Operations Comittee and the Safety Audit Committec.
We request these changes as a result of a reanalysis of pressure tran-sients for the end of cycle fuel exposures. We believe that these proposed changes do not introduce concerns not previously raised or reviewed by the Commission.
Also included in this transmittal are 40 copies of a report prepared by General Ele tric Company which presents transient analyses in support of the reques.;cd char;,c dn Technical Specifications.
This report is provided to supplement your review.
It should be noted, however, that this rey ct is ba',cd on a reference exposure threshold of 2400 MWD /S10.
This caposure threrhold was determined as a refinement of the 2250 MWD /
STU fi ure report ed in our June 1,1973 letter.
Concomitanc with the t
prepara -ien of tt e attached analyris, information was obtained indicating that the $ssumed relief valve delay timc. may not. be conservative. A new figure of 20uu WD/STU based on a longer delay in initial valve opening time var rcperted in an August 1, 1973 letter.
Subsequently, in lieu of more refined calculations verifying that figure, conservative estir.ating techniques have identified an even icver exposure threshold of 1640 WD/
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Rod patterns have been fixed at Monticello, as of September 13, 1973 at a conservative exposure Icvel of 1540 m'D/STU in the manner discussed l
in our August 21, 1973 1ctter.
This 1640 !WD/STU threshold is currently being used as a basis for operating limitations.
The exposure threshold in increased by the change in safety valve set points discussed herein and a reanalysis to determine the revised threshold is currently in preparation.
This updated analysis will account for the planned modifi-cations to the relief valves to reduce the delay time and the new safety valve set points, and will be submitted in support of operation to the end of cycle 2.
(The reanalysis is expected to justify extension of the limiting exposure threshold to about 2680 E'D/STU.) It should be recognized that plant operations at Monticello are being conducted conservatively in reopense to new infornation relating to end-of-cycle transients.
Informa-tien roccived subsequent to the attached report has not altered the validity of the report with respect to the bases for changes in the safety valve set points.
A second aspec; requiring clarification relates to the safety valve rir.irm transiento and associated safety valve marglur.
Safety valves were initially sized assuming no credit for scram. After the Code was changed to allow indirect scram, reanalysis indicated that only tw safety valves were required. lisp arbitrarily elected that four, of the originally planned tucIve, safety valves be retained. At that time, it ' ras cc,nsidered prudent to retain some of the margin gained through the Code change. Havever, no attempts were nade to take credit for the additional valves since there was no obligiation to provide nargius beyond that required by the Code.
It should be noted that the reported allowabic end of cycle power level of 91% of rated power is based on the relief valve capacity. Calculations to verify sufficient capacity of the four safety valves show extensive margin for a main steamline isolation transient occurring at rated power.
Should credit for the safety valves be limited to present requirements, this sizing transient would not be controlling with respect to power level.
Yours very truly, Dh L 0 Mayer, pE Director of 1;uc1 car Support Services LO:!/DWJ / b r cc:
J G Kepplcr G Charnof f Minnesota Pollution Control Agency Attn E Dzugan l
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