ML19319D804
| ML19319D804 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 12/29/1977 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19319D805 | List: |
| References | |
| NUDOCS 8003250799 | |
| Download: ML19319D804 (1) | |
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' SACRAMENTO MUNICIPAL UTluTY DISTRICT C 6201 S Street, Box 158]O, Sacramente, Califomia 95812; (916) 452 3211 December 29, 1977
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Director of Regulatory Operations i-p ATTN:
Mr. R. H. Engelken p3]
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Ei NRC Operations Office, Region V s 2.7 1990.N. California Boulevard
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SG Walnut Creek Plaza, Suite 202 5'
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Walnut Creek, California 94596 R
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a Re: Operating License DPR-54 Docket No. 50-312
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Reportable Occurrence 77-21
Dear Mr. Engelken:
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In accordance with Technical Specifications for Rancho Seco Nuclear Generating Station, Section 6.9.1, and Regulatory Guide 1.16, Revision 4,
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Section C.2.a(9), the Sacramento Municipal Utility District is hereby submitting this followup report to Reportable Occurrence 77-21.
d As stated in the initial notification of Dece=ber 56,1977, Babcock and Wilcox Company notified tbn District that an error in the plant computer software had resulted in nonconservative estinates of positive power i= balance as ' calculated using incore detector signals. The error was located in the relation that ap,p, lies depletion and sensitivity corrections to the detector signal. The equation c,urrently applies these correction factors to the detector signal, then adds the result to the background signal. The proper relation would first add the detector and background
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signals together, then apply correction factors to the resultant sum. The effect of this discrepancy is greatest in the upper half of the core, where background
' levels are highest. Also, since the depletion factor is calculated using the integrated total current generated by a detector, this factor is underestimated to a greater extent in the upper half of the core than the lower half.
The magnitude of these errors is dependent' on the exposure history of the detectors. The error.s increase with increasing burnup and B&W has determined that a mnfmum 1.7 percent negative bias existed at the ti=e of discovery..They have Z
determined that the bias will be no more than 2.2 percent at 100 EFPD following discovery of the problen and will not exceed 3.1 percent by the end of Cycle 2.
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Mr. R. H. Engelken December 29, 1977 Babcock and Wilcox has stated that a revision to the computer software package will be issued within 100 ETPD which will ocrrect the problem. As an interim measure, administrative controls have been established to maintain positive imbalance 2.2 percent below the operational limit established by Technical Specifications Figure 3.5.2-5.
Babcock and Wilcox has verified that the Reactor Protection System had adequate conservatism in the positive imbalance setpoints M
M to tolerate any bias introduced through calibration of the out-of-core detectors to incore detector output data.
There was no plant transient, shutdown or operation in the bias reduced I
region associated with this occurrence.
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espe c KJ.J.Matti{
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Assistant General Manager
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