ML19317F906
| ML19317F906 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 10/22/1976 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19317F907 | List: |
| References | |
| NUDOCS 8002210630 | |
| Download: ML19317F906 (2) | |
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IE FILE gg rD sMuc SACRAMENTO MUNICIPAL UTluTY DISTRICT C 1708 59th Street, Box 15830. Sacramento, Cadfernia 95813:(916)452-3211 October 22, 1976
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_~i ', ;*h, h Mr. R. H. Engelken f,fg M
g Director of Regulatory Operations C
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NRC Operations Office, Region V s
1990 N. California Boulevard
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s Re: Operating License DPR-54 wm j,;
Docket No. 50-312
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Reportable Occurrence 76-12
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Dear Mr. Engelken:
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In accordance with Technical Specification for Rancho Seco Nuclear Generating Station, Section 6.9.1, and Regulatory Guide 1.16, Revision 4, Section C.2.a (8), the Sacramente Y.unicipal Utility District hereby sub-mits a written follow-up report on Reportable Occurrence 76-12, initially 9 ];
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submitted to NRC on October 12, 1976.
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As stated in the previous submittal on this occurrence, during pre-parction for plant heatup on October 7,1976 all four safety control rod groups (groups 1-4) were withdrawn.100% at 1934 hours0.0224 days <br />0.537 hours <br />0.0032 weeks <br />7.35887e-4 months <br />, taking the reactor shutdown margin less than -1% ak/k. An actual shutdown calculation prepared prior to withdrawal predicted that with the four safety groups 100% WD, the
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net reactivity would be +0.53% ak/k. To counteract the reactivity insertion that would result from safety rods withdrawal, baron was added to the RCS.
However, the amount of boron added was not sufficient to yield a reactivity of -1.0% ak/k if the safety groups were withdrawn because of an operator misinterpretation of the calculation results. The operator incorrectly assumed that the net reactivity calculated included the -l% ak/k shutdown.
Therefore, boron was added to counteract the +0.53% ak/k determined by the calculation. After the boron injection, the safety groups were withdrawn and the c^ountrate monitored to insure the final value did not exceed the calculated value for rods withdrawn.
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Following the shift change at 2400 hours0.0278 days <br />0.667 hours <br />0.00397 weeks <br />9.132e-4 months <br />, a new actual shutdown Z
calculation was performed. At 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br /> on October 8, 1976, the new cal-culation showed an actual shutdown reactivity of -0.411% ak/k.
I= mediate addition of boron was initiated to obtain a shutdown of at least -1.0% ak/k, verified by a calculation at 0510 hours0.0059 days <br />0.142 hours <br />8.43254e-4 weeks <br />1.94055e-4 months <br />, showing a shutdown of -1.47% ak/k.
Even though no violation of Technical Specifications existed, the unit q.
was in a less conservative condition that that assumed in the safety analysis
,e for the ej ected rod accident with the unit subcritical.
In review of this
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occurrence, it was discovered that the reactivity calculation format gave 8 0 02 210 NO n[
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m m Mr. R. H. Engelken October 22, 1976 rise to some confusion regarding whether or not the -l% ak/k shutdown margin was included in the summing of all contributions to core reactivity. To prevent recurrence of the misinterpretation of the actual shutdown calcula-
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tion, the calculation sheet will be revised to better define the meaning of parameters calculated, and this revision will be reviewed with all operating d
crew. All Licensed personnel will be instructed to maintain a minimum
-l% ak/k shutdown margin except for physics testing or approach to criticality.
Respectfully submitted,
-J. J. Mattimoe GENERAL MANAGER
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Assistant General Manager and Chief Engineer
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