ML20086L143

AO 74-23:on 740427,HPCI Turbine Isolated During Reactor Vessel Injection Startup Test.Caused by Stop Valve Opening Speed Faster During Start Up than Observed During Hot Start Up.Isolation Logic Reset

ML20086L143
Person / Time
Site:	Peach Bottom
Issue date:	05/07/1974
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086L146	List: ML20086L143 ML20086L151
References
AO-74-23, NUDOCS 8402070416
Download: ML20086L143 (3)

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I2151041 4000 'i e gfy &P May 7, 1974 Mr. A. Giambusso Deputy Director of Reactor Projects United States Atomic Energy Comnission Directorate of Licensing Washingten, DC 20545

Subject:

Abnormal Occurrence The following occurrence was reported to Mr. R. A. Fell, A.E.C.

Region I Regulatory Operations on April 28, 1974. Written notification was made to Mr. James P. O'Reilly, Region I Regulatory Operations Office on April 29, 1974. In accordance with Section 6 7 2.A of the Technical Specifications, Appendix A of DPR-44 for Unit 2 Peach Bottom Atomic Power Station, the following report is being submitted to the Directorate of Licensing as an Abnorma! Occurrence.

Reference:

License Number DPR-44, Amendment Number 1 Technical Specification 3 5.C.1 Report No.: 50-277-74-23 Report Date May 7, 1974 Occurrence Date: April 27,1974 Facility: Peach Bottom Atomic Power Station R.D.1, Delta, Pennsylvania 17314 Identification of Occurrence:

MPCI Turbine isolated during a reactor vessel injection start-up test.

f Conditions Prior to Occurrence:

Plant operated at cpproximately 50% power for the purpose of-performing start-up testing. ,

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Designation of Occurrence:

As part of the start-up test program, and as a follow-up to a HPCI system isolation which occurred on April 16, 1974, HPCI cold quick start vessel injection testing was being performed. Reactor power was at approximately 50Z in steady state operation. Following the cold quick start initiation, an HPCI Turbine isolation occurred. This isolation was caused by a high steam flow condition which is sensed hv differential pressure switch connected to an elbow tap flow clement in the steam supply line to the HPCI Turbine. Following the isolation, additional quick starts on the HPCI were performed to demonstrate that the system was operable both on the test loop and for injecting to the reactor vessel. This was proven by actually delivering -ated flow to the vessel following the initial isolation.

Designation of Apparent Cause of Occurrence:

Observation of the HPCI Turbine stop valve during the initial cold quick start appeared to indicate that the stop valve opening speed was significantly faster during this start-up than had been observed on a hot start-up. A testing program performed following the trip has shown that the stop valve motion is more rapid during a turbine start if the auxiliary oil pump has not been operated for more than 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> previous to that start. The rapid opening of the stop valve will cause a short term high steam flow condition sufficient to actuate the nign steam riow isolation switenes.

Analysis of Occurrence:

The initial isolation of the HPCI system during the cold quick s t a'r t ve s se l injection test has minimal safety implications in that the system was demonstrated immediately following this isolation to be cap-able of injecting water to the reactor vessel. This isolation increases the time from actuation unt il rated flow to the vessel is achieved by the short per iod of time required to reset the isolation signal. This delay is not considered significant at the power icvels achieved during the start-up program to date. Start-up testing is performed for the purpose of identifying and correcting minor control probicms with engin-cered safeguard systems prior to achieving reactor power levels where design system response is required to mitigate accidents.

Corrective Action:

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Following the initial isolation, the isolation logic was reset.

l Additional HPCI quick start were performed using the test flow loop.

l Adjustments were made to the steam flow orifices in the turbine stop l valve in an attempt to reduce the operating speed of this valve. Test i

esults indicated that some reduction in valve speed was obtained with l

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the valve in a hot condition. No determination of valve speed in the cold condition could be verified since it takes approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for the metal associated w

• th the valve to cool to ambient condi tions.

Following these adjustments, vessel injection tests were cuccessfully accomplished.

Following the testing program outlined above, additional transducers were installed on the system and cold quick starts were performed almost on a daily basis. As a result of these tests it was determined that the rapid motion of the hydraulic stop valve during a cold quick start is caused by an air pocket in the hydraulic cylinder of the stop valve. This air accumulates in the hydraulic cylinder dur-ing long periods of shutdown. During a quick start, rapid valve motion is produced after the pilot valve on the main disc opens to depressurize the area above the seat and permits the air trapped in the hydraulic cylinder which has been pressurized by the hydraulic system to expand rapidly. Tests have also shown that insufficient air to produce this rapid motion accumulates in the hydraulic cylinder if the oil pump is operated at 5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> intervals. Until a piping correction can be per-formed to prevent this air inicakage, the auxiliary oil pump on the HPCI system is being operated on a 4-hour interval. This operation ensures a successful cold quick start and places the HPCI system in a fully operable condition.

. 1 Failurc Data:

A previous HPCI system isolation was reported as Abnormal Occurrence 50-277-74-22.

Very truly yours, L

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M. J. Cooney' Ass't Gen't Superintendent Generation Division cc: Mr. J. P. O'Reilly Director, Region i United States Atomic Energy Commission 631 Park Avenue King of Prussia, PA 19406 P

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