ML20196G042

Safety Evaluation Supporting Amend 145 to License NPF-1

ML20196G042
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	06/23/1988
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20196F990	List: ML20196F987 ML20196G026 ML20196G042
References
NUDOCS 8807050402
Download: ML20196G042 (3)

Text

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1. 'o g UNITED STATES

! o NUCLEAR REGULATORY COMMISSION

$ WASHINGTON, D. C. 20555

• \...../

SAFETY EVALUATION BY THE OFFICE OF 14UCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.145 TO FACILITY OPERATING LICENSE N0. NPF-1 PORTLAND GENERAL ELECTRIC COMPANY THE CITY OF EUGENE, OREGON PACIFIC POWER AND LIGHT COMPANY TROJAN NUCLEAR PLANT DOCKET N0. 50-344

1.0 INTRODUCTION

By letter dated December 18, 1987, as su l d March 15, 1988, Portland General Electric Com requested a change to the Trojan Technical Specifications (TS)pany which would (PGE) revise the means pp emente by which source range neutron flux instrumentation would be calibrated. Due to the use of low-noise source range preamplifiers, the manufacturer of the preamplifiers recomends the technique of obtaining discriminator bias curves rather than obtaining high-voltage plateau curves (as currently specified by the TS), to determine source range detector degradation.

2.0 Discussion and Evaluation Source range neutron de'.ectors monitor leakage flux at the lowest reactor power levels and during shutdown. They provide outpet to indicating alarms and reactor trips. Source range detectors used in Westinghouse reactors are of the boron triflouride (BF ) type. These detectors emit a pulse rate output which is proportioria1 3to the amount of thermal neutron flux to which they are exposed. These pulses are conditioned by electronic circuitry which provides amplification and a means to discri-minate between neutron flux and other types of radiation, primarily gamma.

Gama radiation stimulates the sensors to generate lower amplitude pulses.

These low-level pulses are removed from the detector signal by 'rse of a pulse amplifier-discriminator.

The current channel calibration requirements of TS Table 4.3-1 call for developing high voltage plateau curves for each BFthese Thesecurves curveswith are the manufactur obtained by varying the supply voltage to the detectors and recording the corresponding change in voltage plateau (count rate). Any appreciable deviation in the curve's profile from that of the manufacturer's recomendation indicates probable detector degradation, kogy $h P

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Obtaining discriminator bias curves involves-a markedly different technique.

This is done by varying the discriminator bias over a specified range of voltages and recording corresponding changes in the count rate. A graph of count rate versus discriminator bias is then made. The discriminator bias operating point is determined from this graph and set on the channel.

The count rate is then observed to determine if the correct operating point has been obtained. If the correct point has not been determined, the procedure is repeated with increased voltage. Detector degradation is determined by a downward shift in the discriminator bias curve from that of previous curves. This downward shift results because pulses detected by failing sensors have lower amplitudes; thereby, reducing the actual number of pulses counted at various bias voltages.

The intent of TS Table 4.3-1 Functional Unit 6 is to assure, as reasonably as possiDie, that means are available to periodically assess the condition of source range detectors. The TS refers to "voltage plateau curves" because these curves have traditionally been employed for the purpose.

In the staff's view, there is no reason an alternate method cannot be used as long as the stated purpose is accomplished. In this case, the manufacturer has recommended the alternate method as the more accurate one. As such, the staff finds acceptable PGE's request to use "discri-minator bias curves" in place of "voltage plateau curves" in TS Table 4.3-1, Functional Unit 6.

3.0 CONTACT WITH STATE OFFICIAL The NRC staff has notified the Oregon Department of Energy of the proposed issuance of this amendment along with the proposed determination of no significant hazards consideration. No comments were received.

4.0 EllVIRONMENTAL CONSIDERATION This amendment involves a change in surveillance requirements. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously published a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, the amendment meets the eli for categorical exclusion set forth in 10 CFR 551.22(c)(9)gibility

. Pursuant to criteria 10 CFR 651.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amend-rent.

5.0 CONCLUSION

I We have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such

, O activities will be conducted in compliance with the Connission's regu-lations, and (3) the issuance of the amendment will not be inimical to the comon defense and security or to the health and safety of the public.

PRINCIPAL CONTRIBUTOR:

T. Chan Dated: June 23, 1988 l

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