ML20058K819
| ML20058K819 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 06/18/1974 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| AO-263-74-14, NUDOCS 9102140466 | |
| Download: ML20058K819 (2) | |
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use NORTHERN STATES POWER COMPANY
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Mr. J F O' Leary, Director IE JUN2 0 i974 -
Directorate of Licensing k,,
Office of Regulation
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U S Atomic Energy Co:mnission Washington, DC 20545
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ABNORMAL OCCURRENCE REPORT TO THE AEC Malfunction of HPCI Steam Supply Line Low Pressure Isolation Switc
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Report Number: A0 263/74-14 ff.f g9 w
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.k 2A. Report Date:
June 18, 1974 2B Occurrence Date: June 8, 1974 3
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Facility: Monticello Nuclear Generating Plant (DPR-22)
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Monticello, Minnesota 55362 mf l
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4.
Identification of Occurrence:
This report concerns a pressure switch setpoint drift which constitutes an Abnormal occurrence and is reported in accordance with Section 6.7.3.1, Appendix A Technical Specifications, of Provisional Operating License DPR-22.
5.
Conditions Prior to Occurrence:
Routine startup operation 6.
Description of Occurrence:
On June 6, 1974, while a reactor startup was in progress, the High Pressure Coolant Injection (HPCI) steam line low pressure isolation instruments did not reset until a reactor pressure of approximately 167 psig was attained.
Section 3.5.0 of the Technical Specifications requires that the HPCI system be operable whenever reactor pressure is greater than 150 psig. As a result of the failure c: the 5PCI steam line low pressure isolation instrumentation to reset, the HPCI syatem was in an inoperable condition until a reactor pressure of 167 psir, was reached.
7.
Designation of Apparent Cause of Occurrence:
Ihe pressure switches used in the HPCI steam line low pressure isolation application have a histor'/ of drif t between subsequent calibrations.
In addition, the deadband of the pressure switches is significant.
It is concluded that excessive instrument drift and a large instrument deadband were the initiating causes of the abnor:nal occurrence, over T RYDOCKETFILE COPv 9102140466 7406 CF ADOCK 05000263 CF
NORTHERN CTATES POWER COMPANY S.
Analvsis of Occurrence:
The pressure switch setpoint drift of apnroxir.ately 17 psi did not present a significant safety hazzard.
The fully redundant Automatic Pressure Relief System and Reactor Core Isolation Cooling, Core Spray, and Low Pressure Coolant Injection were fully operable.
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Corrective Action:
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on June 10, 1974, the four HPCI steam line low pressure isolation switches were calibrated and functionally tested to de=onstrate that the desired reset action occurs at i 150 psig. As a temporary measura, the instrument calibration frequency has been increased from once per six months to once per quarter to reduce the setpoint drif t accumulated between subsequent calibrations.
Pressure switches having a smaller deadband and less drif t potential are being investigated as a possible long term solution.
In addition, a precautionary note has been inserted in the plant startup procedure to insure that reactor pressure is not increased beyond 150 psig until the ECCS operability requirements have been complied with.
10.
Failure Data:
There have been four previous malfunctions involving similar pressure switches at Monticello. All of the previous malfunctions were attributed to conditions unrelated to this occurrence.
It is believed that the corrective actions taken are adequate to prevent a recurrence.
Nameplate Data:
Barksdale Model BZT-M12SS Lo A v /buu L 0 Mayer, PE Director of Nuclear Support Services LG1/kn cc:
J G Reppler G Charnoff Minnesota Pollution Control Agency Attn. E A Pryzina a
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