ML20150D087

Responds to NRC 880219 Request for Addl Info Re Application for Amend to License NPF-1 Consisting of License Change Application 160 Re Deleting Requirement for source-range Plateau Curves

ML20150D087
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	03/15/1988
From:	Cockfield D PORTLAND GENERAL ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
TAC-66871, NUDOCS 8803230084
Download: ML20150D087 (4)

Text

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t M M m Portland GeneralElechicCompany David W. Cockfield Vice President. Nuclear c

March 15, 1988 Trojan Nuclear Plant Docket 50-344 License NPF-1 U.S. Nuclear Regulatory Commission '

ATTN: Document Control Desk Washington DC 20555 ,

Dear Sir:

Additional Information Related to License Change Application (LCA) 160 - Deletion of Requirement for Source Range Plateau Curves (TAC No. 66871)

Portland Ceneral Electric Company (PGE) submitted LCA 160, proposing to revise Trojen Technical Specification Table 4.3-1, un December 18, 1987.

PGE was requested to provide additional information concerning the proposed change in an NRC letter of February 19, 1988. Our response to the informa-tion requested is provide'd in the attachment.

Sincerely, Attachment c: Mr. John B. Martin Mr. William T. Dixon l Regional Administrator, Region V State of Oregon U.S. Nuclear Regulatory Commission Department of Energy l Mr. R. C. Barr Mr. Michael J. Sykes  ;

NRC Resident Inspector Chairman of County Commissioners i Trojan Nuclear Plant 8003230084 880315 60(

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Trojan Nuclear Plant Document Control Desk Docket 50-344 March 15, 1988 License NPF-1 Attachment Page 1 of 2 PORTLAND GENERAL ELECTRIC COMPANY (PGE) RESPONSE TO NUCLEAR REGULATORY COMMISSION (NRC) REQUEST FOR

'INFORMATION RELATED TO LICENSE CHANGE APPLICATION 160 NRC Ouestion 1 Describe the plant's specific procedure for obtaining high-voltage plateau curves.

PGE Response To obtain high-voltage plateau curves for the source range nuclear instrument detectors, PGE follows the guidance provided in the Nuclear Instrumentation System Technical Manual. Specifically, the procedure requirements are as follows:

1. Gutput is bypassed from the source range drawer to be adjusted.

2. The high voltage applied to the detector is adjusted, in 50-Volt direct current (V de) increments, from 1,700 to 2,300 V dc. Detector output is monitored by means of a scaler-timer, and the results are graphed (counts per second versus detector volts).

3. The graph obtained should indicate an area of minimum slope (a "plateau"), at least 100 V de in width.

4. The high-voltage applied to the detector is then adjusted such that the detector operating voltage is approximately 30 percent of the width of the plateau curve above the lower "kneo" of the curve.

NRC Ouestion 2 l Describe the plant's specific procedure for obtaining discriminator bias curves.

PGE Response Guidance provided in the Nuclear Instrumentation System Tecnaical Manual is also used for obtaining discriminator bias curves. Specific procedural steps are as follows:

1. With output bypaesed from the source range drawer to be adjusted, the discriminator bias is adjusted to -0.05 V dc.

2. Count rate output (monitored by a scaler-timer) is recorded.

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W' Trojan Nuclear Plant Document Control Desk Docket 50-344 Macch 15, 1988 License NPF-1 Attachment Page 2 of 2 i Step 3 is repeated for discriminator biar voltage settings of -0.075 and

-0.10 V de, then in 0.10 V increments between -0.10 and -0.60 V de, and in 0.2-V increments between -0.60 and -4.0 V dc.

4. Output count rate versus discriminator bias voltage is then plotted on semilog graph paper. A typical graph is shown in Figure 1.

5. A best-fit straight line is drawn along the linear portion of the graph (ie, along the curve between 0 and -2.5 V, see Figure 1).

6. The point below -1.0 V de where the response curve departs from the best-fit straight line represents the point at which the output count rate is adversely affected by system noise. The discriminator bias voltage corresponding to this point is recorded.

7. The operating bias voltage for the discriminator is set at 0.2 V de less (more negative) than the voltage recorded in Step 6.

NRC Ouestion 3 Describe how discriminator bias curves give indication of detector degradation.

PGE Response If a usable discriminator bias curve (similar to that shown in Figure 1) is not obtained by the procedure described above, the high voltage applied to the detector is adjusted and a new discriminator bias curve is obtained.

Detector degradation is indicated by the need for high-voltage adjustments I to obtain acceptable discriminator bias curves.

NRC Ouestion 4 Does either test cause any measurable or otherwise observable detector degradation?

PGE Response No, detector degradation is not caused by either the high-voltage plateau or the discriminator bias-curve determinations.

ARA /2399P

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Trojan Nucicar Plant Document Control Desk Docket 50-344 March 15, 1988 f License NPF-1 Figure 1 7

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FIGURE I - Typical Graoh of Count Rate Versus Oiscriminator Bias s

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