ML20031G907
| ML20031G907 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/20/1981 |
| From: | Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | Gammil W Office of Nuclear Reactor Regulation |
| References | |
| P-81247, NUDOCS 8110260189 | |
| Download: ML20031G907 (4) | |
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October 20, 198]
Fort St. Vrain Unit Nc. 1 g
P-81247 6)?',pri.,h i liIbI/Y 7
OCT2 3 sg 3 Director, Of f h e of Nuclear Regulations v
Attn:
W. P. Carmill, Chief E
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- YO Operating Reactors Safeguards Branch e
Division of Operating Reactors i^
N "d Q M [-
U. S. Nuc1 ear Regulatory Commiss on Washington, D.C.
20555
SUBJECT:
Base Reactivity Curve Cycle 3 Gentlemen:
In accordance with the requirements of LCO 4.1.8 of the Fort St.
Vrain Technical Specifications, I am forwarding a copy of both the original and the present (a revision to the original) Cycle 3 base reactivity curves.
Initial c ri tical i ty for Cycle 3 occurred at a withdrawn control rod reactivity worth approximately 0.0035ap lower than predicted by using the original Cycle 3 base reactivity curve which was reviewed and approved by our Nuclear Faci'ity Safety Committee prior to criticality.
Due to the mar.nitude of the difference between the predicted and observed critical rod positions, an error in the original curve was suspected, and submittal of the curve to the Nuclear Regulatory Commission was postponed.
The Fort St. Vrain base reactivity curves are obtained utilizing the four group GAUGE code which has proven to be extremely reliable in the past.
Therefore, investigations into the source of error in the calculations were concentrated about the input parameters.
These investigations revealed that an assumed 200 EFPD, rather than the actual 188 EFPD, Cycle 2 power history had been inputted and that a small reactivity bias which was introduced in the Cycle 2 base reactivity curve had been inadvertantly omitted.
The four group GAUGE code calculations were performed again using the proper Cycle 2 power history parameters and including the small reactivi*y bias introduced in Cycle 2.
The present Cycle 3 base reactivity curve wcs generated from these calculations and is in good agreement with the conditions observed at the initial Cycle 3 criticality.
The revised base reactivity curve has been reviewed and 'pl I
9 8110260189 811020 Pnp ADOCK 05000267 p
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A approved by our Nuclear Facility Safety Committee in accordance with Technical Specification requirements.
Very truly yours, ht~ Wensn/nw Don Warembourg Manager, Nuclear Production DW/1 sb Attachment i
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