ML20147B104
| ML20147B104 | |
| Person / Time | |
|---|---|
| Site: | Washington State University |
| Issue date: | 09/18/1978 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| R-076-A-008, R-76-A-8, NUDOCS 7810030260 | |
| Download: ML20147B104 (4) | |
Text
U. S. NUCLE AR HEGULATORY COMMISSION N R*c, F O W. c oG
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DATE C0 8 Su bl DOCK ET NUMBEH os 69 EVENT OATE EVENT DESCRIPTION ArJD PROBABLE CONSEQUENCES h M i Westinghouse has advised that a non-conservatism has been discovocod in the calcul a- I p i3i i tions performed by the Axial Power Distribution Monitorina System (APDMS). The i gj [ impact of this situation has been evaluated with the determination that this nvent I EM1Ldid n t result in conditions in which the health and safety of the aeneral nublic was_]
[o ;C j l endangered. This event is reportable as per T.S. 6.9.1.8.b. I I
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33 34 35 31 40 di CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l i l o l l This event was a resul t of datsa value round-off by thn APnMs. Immediato enrrnctivo l
[i li l l action was to lower the Input valuesmed by the APDMS to insurn enncoruntive limit I j,i7; i values. Permanent corrective action will involve either a modification to the APDMS I l~iiai L r a Tech Spec change that accounts for this non-conservatism. I I
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Virginia Electric and Power Company
Attachment:
.Page 1 of 2 florth Anna Power Station, Unit flo.1 -
1 Docket flo. 50-338 Report flo. LER 78-98/01-T -0 '
Description of Event ,
On October 4, 1978, Westinghouse advised Vepco that a non-conservatism' l j
had been discovered in the calculations performed by the Axial Power Distribu-
. tion Monitoring System (APDMS). . Specifically,, the APDMS, in calculating LOCA peaking factor shape limits, K (Z) (T.S. Figure 3.2-2), rounds-off the three digit setpoint to two digits. Rounding off to two digits causes some of the Fj (Z) limit setpoints (T.S. 3.2.6) generated to be less conservative than the 1 Technical Specifications limits The largest possible non-conservatism is 1.11%. l This event is reportable under Technical Specification 6.9.1.8.b since roundoff error in the APDMS calculations resulted in Fj (Z) limit values that were less conservative than the limits in the Technical Specifications.
Probable Consequences of Occurrence i There were no adverse consequences associated with this occurrence. A review of the records has shown- that throughout the period of its use, the APDMS has indicated that more than enough margin has existed to accommodate this non-conservatism. In view of these circumstances, it is considered that the health and safety of the general public were not endangered.
Cause of Occurrence This occurrence was caused by a non-conservative calculational technique that is used by the APDMS.
i 1
r Immediate' Corrective Action The input. values 'used by the APDMS have been lowered by 1.5% in order to t
accommodate the non-conservatism in the limit setpoint values calculated by the l
APDMS. J
- ?f
.. 6, Virginia Electric and Power Company
Attachment:
Page 2 of 2 North Anna Power Station, Unit No. 1 Docket No. 50-338 Report No. LER-78-98/01-T -0 Scheduled Corrective Action Either a modification will be made to the APDMS that eliminates or accommodates this non-conservatism, or a change to the Technical Specifica-tions will be proposed that specifically accounts for this non-conservatism.
Actions Taken to Prevent Recurrence No actions to prevent recurrence are planned since this event is non-recurring in nature, i
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