ML20069C517

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Forwards Addl Info Re in-core Detector String Operability, in Response to NRC 830202 ltr.In-core Detector Sys Not Required Nor Designed to Measure off-normal Power Distribution Due to Dropped Control Element Assembly
ML20069C517
Person / Time
Site: Fort Calhoun Omaha Public Power District icon.png
Issue date: 03/11/1983
From: William Jones
OMAHA PUBLIC POWER DISTRICT
To: Clark R
Office of Nuclear Reactor Regulation
References
LIC-83-068, LIC-83-68, NUDOCS 8303180012
Download: ML20069C517 (3)


Text

Omaha Public Power District 1623 HARNEY e OMAHA, NEBRASKA 68102 m TELEPHONE 536 4000 AREA CODE 402 March 11, 1983 LIC-83-068 Mr. Robert A. Clark, Chief U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Licensing Operating Reactors Branch No. 3 Washington, D.C. 20555

Reference:

Docket No. 50-285

Dear Mr. Clark:

Incore Detector String Operability The Omaha Public Power District received your letter dated February 2, 1983 requesting additional information regarding the incore detector string operability at the Fort Calhoun Station.

Please find attached the District's response to the Commission's questions on Fort Calhoun incore detector string operability.

Sincerely, if&Q -

W. C./ Jones Divid on Manager Production Operations WCJ/TLP:jmm Attachment cc: LeBoeuf, Lamb, Leiby & MacRae 1333 New Hampshire Avenue, N.W.

Washington, D.C. 20036 Mr. L. A. Yandell, NRC Senior Resident Inspector

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8303180012 830311 j PDR ADOCK 05000285 '

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.a OMAHA PUBLIC POWER DISTRICT'S' RESPONSE TO QUESTIONS ON FORT CALHOUN INCORE DETECTOR STRING OPERABILITY Question 1 How many incore detector strings failed during Cycle 6 and Cycle 7 and approximately when in cycle did each failure occur?

Responge Fourteen (14) incore detector strings failed during Cycle 6 and five'(5) incore detector strings failed during Cycle 7. The approxinate schedule of failures during Cycle 6 is as follows:

Cycle 6 Burnup Number of Date (MWD /T) Failed Strings 9/30/80 3,051 3 10/31/80 3,686 3 11/30/80 4,385 4 12/31/80 5,110 5 1/31/81 5,786 8 2/28/81 6,508 8 4/30/81 7,545 10 5/31/81 8,009 11-6/30/81 8,653 13 8/31/81 10,427 14 9/19/81 10,929 14 Four (4) incore detector strings were 'not operational-at ~ the beginning of Cycle 7'in December of 1981. The fifth incore detector string failure occurred on July 20, 1982. The Cycle 7 burnup was 6,300 MWD /T at this time. No additional failures occurred prior to the shutdown at the end of Cycle 7 at 9,725-MWD /T.

Question 2 Assess the effect of loss of incore detector strings on the ability to adequately determine the axial shape index for excore detector calibration.

Response

Upon loss of the operability of more than 25% of the incore de-tector strings, the axial shape index cannot be determined. The current Technical Specification 2.10.3(3) provides for continued operation without calibration of the excore detectors by reducing the axial power distribution monitoring limits and trip setpoints.

The adequacy of this specification was further discussed in the Cycle 6 SER, which was attached to the Conmission's letter to the District dated April 1, 1980. In this SER, the Commission recog-nized this specification as acceptable.

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Question 3_

Demonstrate that the loss of 80% of the incore detector strings can adequately determine off-normal events such as a fuel loading error.

Response

The District takes credit for the operability of the incore detector system for the purpose of.off-normal event detection during startup testing following fuel reload only. An off-normal event during startup testing following fuel. reloading would be detected as an off-normal power distribution. In order to assure this function is. accomplished, current Technical Specification.

2.10.4(4) requires that after each fuel load, the incore detector system shall be operable with 75% of the incore detector strings operable.

\ failure of 80% of the incore detector strings at any time fol-lowing the startup will not adversely affect the capability to i determine off-normal events because the system is not relied'upon for that purpose.

Question 4 I

Assess the effect of the loss of as many as 80% of the incore detector strings on the measurement of off-normal power dis-tributions-such as that due to a dropped or nisaligned CEA.

Response

As previously stated in the response to Question 3, the District does not take credit for the operability of the incore detector system to measure of f-normal power distributions except during startup tenting following each fuel loading.

The incore detector system is not' required nor designed to measure an off-normal power distribution due to an event such as a dropped or misaligned CEA. Actions to.be_taken following the detection of a dropped or misaligned CEA are found in Technical Specifications 2.10.2(4), 2.10.2(5), and 2.10.2(6).

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