ML20205J930
| ML20205J930 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 03/24/1987 |
| From: | Ainger K COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 2899K, NUDOCS 8704010466 | |
| Download: ML20205J930 (3) | |
Text
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One First Nabonal Plaza, Chca00, Illinois 3
Address Reply to: Post Omco Box 767 Ns Chicago, Illinois 60600 0767 March 24, 1987 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 i
Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 Application for Amendment to Facility Operating Licenses NPF-37 and NPF-66, Appendix A, Technical Specifications NRC Docket Nos. 50-454/455 and 50-456/457 c
References (a): September 15, 1986 letter from I.M. Johnson to H. R. Denton (b): February 5, 1987 letter from L. N. Olshan to D.L. Farrar
Dear Mr. Denton:
1 Reference (a) requested a change to the Technical Specifications that would replace the requirement to measure the source range flux instrumentation high voltage plateau curve with a requirement to measure source range flux instrumentation discriminator bias curves. Reference (b) requested additional information regarding this p.oposed change to the Technical Specifications, j
Attachment A of this letter contains the responses to the request for additional information.
please direct any questions you may have concerning this matter to this office.
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Very truly yours, 1
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K. A. Ainger Nuclear Licensing Administrator 1m 0704010466 070324 Attachment hDR ADOCK 05000454 PDR i
cc: Resident Inspector - Byron Resident Inspector - Braidwood 4
Region III Office
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ATTACHMENT A I
RESPONSE TO NRC QUESTIONS ON SOURCE RANGE TECHNICAL SPECIFICATION CHANGE 1
Question 1:
i Describe the plant specific procedure for obtaining high voltage plateau curves.
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Resporm:
The source range channel on which the high voltage plateau curve is to be obtained is placed in test. The high voltage signal is set to 1700 V and then increased in 50V increments up to 2300 V. The counts are recorded at each high voltage setting.
The high voltage is restored, the channt.1 is removed from test and a plot of counts versus high voltage is made. This plot is then compared to previous plateau curves and evaluated.
Question 2:
Describe the plant specific procedure for obtaining discriminator bias curves.
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Response
The source range channel on which the discriminator bias curvc is to be obtained is placed in test. The preamplifier gain setting is then determined. Next, the discriminator bias curve is obtained. This is done by setting the discriminator bias to the following values and recording the countrate at each point: -0.0 5 V,
-0.075V, -0.10V, -0.20V, -0.30V, -0.40V, -0.50, -0.60V, and then every 0.2V until j
-4.0V is reached. A graph of countrate versus discriminator bias is then made l
on semi log paper. The discriminator bias operating point is determined from
- i this graph and set on the channel. Then, a jumper is installed to remove the source range channel high voltage. The countrate is observed to determine if the correct operating bias point has been determined. If the correct operating bias point has not been determined, this procedure is repeated with an increased high voltage.
Ilased on the discussions with the vendor, the preamplifier gain setting is only required to be determined on initial installation or replacement of a detector
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or when the high voltage is increased per the previous paragraph. This is under review at the Station and may be removed from the procedure in the future.
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9 Question 3:
What is the relationship, if any, between discriminator bias curves and BF3 differential bias curves?
Response
The way this question is being interpreted is, "What is the relationship between DF3 discriminator bias curves and DF3 differential discriminator bias curves?"
The differential and integral discriminator bias curves convey the same information and one can be derived from the other. The amplitude of the differential curve at any point is given by the absolute value of slope of the integral curve at the same value. Where peaks appear in the differential curve, local maxima will occur in the slope of the integral curve. Conversely where minima appear in the differential curve, regions of minimum slope are observed in the integral curve. Because the Station has a scaler-timer installed as a part of the nuclear instrumentation system and does not have a multichannel analyzer installed, it is much simpler to obtain an integral discriminator bias curve. " Radiation Detection and Measurement" by Glenn Knoll, Chapters 3 and 14, was used as a reference for this discussion on differential and integral bias curves.
Question 4:
Describe how discriminator bias curves give indication of detector degradation.
Response
Detector degradation is indicated by a shifting of the tiseriminator bias curve downward. This downward shift occurs because detector degradation causes the pulse height to decrease thereby causing fewer pulses to be counted. The shape of the curve stays basically the same.
Question 5:
Does either test cause any measurable, or otherwise observable, detector degradation?
Response
Performing the surveillance to either obtain high voltage plateau curves or discriminator bias curves does not result in any measurable or otherwise observable detector degradation.
i ilowever, it should be noted, the vendor does not recommend the use of the high voltage plateau because it is susceptible to noise and differences in cable capacitance.
The recommended surveillance method is the discriminator bias curve determination, l
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