ML20038A032
| ML20038A032 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 05/13/1974 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| AO-12-74, NUDOCS 8109100479 | |
| Download: ML20038A032 (4) | |
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Mr. John F. O' Leary, Director Re: Docket 50-15 'b sd **
Directorate of Licensing License DPR-6 s
US Ato:nic Energy Co=:nission A0-11 & A0-12, 19 Washington, DC 20545
Dear Mr. O' Leary:
Attached are two abnormal occurrence reports (AO-11-Th and A0-12-Th) for the Big Rock Point Plant.
Yours very truly, Ralph B. Sewell (Signed)
RBS/cel Ralph B. Seve11 Nuclear Licensing Administrator
-CC: JGKeppler, USAEC
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w ABNORMAL OCCffRRENCE REPORT Big Rock Point Plant P-
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Report No: AO-ll-7k, Docket 50-155 2.
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Report Date: May 13, 1974 b.
Occurrence Date: May 1, 1974 3
Facility: Big Rock Point Nuclear Plant.
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Identification: Containment vacuum relief sensor set point drift.
5 Conditions Prior to Occurrence: Refueling shutdown.
6.
Description of Occurrence: The set points of switches DPS/9051 and DPS/9052 were found, during a special surveillance test, to be out of specification in the nonconservative direction. The switches were adjusted and retested for proper operation. Switch DPS/9052 is a containment vacuum alarm which should operate on increasing vacuun at -3/h psig. The as-found setting was -1.04 psig. Switch DPS/9051 provides the signal for automatically opening the contain-ment ventilation supply valves and should operate at -1.0 psig. It was found at -1.hk psig. The testing was conduc':td with air shed temperature at 35*F.
During annual curveillance testing on April 12, 1974, these switches were tested at a temperature of about 90'F and were found to have i
unacceptable set point drift in the conservative direction. This fact was dist.:ussed by the Plant Reviev Cc==ittee on April 15, 1974 and was tentatively classified as an unusual event to be reported in 30 days. The co=:fittee reco::xr.endation was to retest the switches prior to power operation at a significantly lover temperature in the air shed tu check on characteristics of the anonaly.
7 Designation of Apparent Cause: It appears to be a combination of poor design application and unusual service condition based on our analysis below.
8.
Analysis of Occurrence: These diaphragm switches were installed as replacements for the eilting mercury switches on April k 1973 The origine.1 mercury switches exhibited poor reset characteristics and were difficult to set. The replacement diaphragm switches solved the reset problem but a.1 apparent application problem is still evident in that the require:ent for a switch with 30 psig proof test for con-tainment high-pressure accident conditions and reliable small vacuum set point repeatability is not cet. The temperature problem is felt to be contributing but probably not basic since the manufacturer's data indicates that using a set point at the lower end of the range is not good practice mechanically.
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'Ibe containment sphere is designed to withstand a vacuta of -1.22 psig. The switch set point exceeded this setting during cold shutdown conditions. However, thj*, did not cause a situation in which the containment design coa'l have been exceeded as the mech-anism (significant amount of steam in containment at atmospheric pressure fol)'vad by containment isolation) for developing a vacuum in containmec zists only when the plant is bested above 212*F.
The correctiv action described belov vill assure proper set points when the plan, is at temperatures greater than 212 F.
9 Corrective Action: Following plant bestup the pressu:4 switches were retested and determined to have an. acceptable drift in the conservative direction. Plant operators have been instructed to monitor air shed temperature and cut in auxiliary heating if the temperature approaches that which existed at the time of switch calibration. In addition, the switches vill be tested during i
cach cold shutdown until a permanent fix can be made.
10.
Failure Data: No previous similar failures.
Manufacturers' Identification: Barksdale Model No D2T-H1855 ii;
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