ML20086L236
| ML20086L236 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 04/04/1974 |
| From: | Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086L241 | List: |
| References | |
| AO-74-16A, AO-74-16B, AO-74-16C, AO-74-16D, NUDOCS 8402070532 | |
| Download: ML20086L236 (4) | |
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.e April 4,1974 Mr. A. Giambusso Deputy Director of Reactor Projects United States Atomic Energy Conmission Directorate of Licensing
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Washington, DC 20545
Dear Mr. Giambusso:
Subject:
Abnormal Occurrence The following occurrence was reported to Mr. R. A. Feil, A.E.C. Region I Regulatory Operations Office on March 26, 1974.
Written notification was made to Mr. James P. O'Reilly, Region I Regulatory Operations Office on March 26, 1974.
In accordance with Section 6.7.2.A of the Technical Specification, Appendix A of DPR-44 for Unit 2 Peach Bottom Atomic Power Station, the follcuing report is Scir:0 submitted to the Directoral.e of Licensing as ar. Ar,r.ormai Occurrence.
Reference:
License Number DPR-44, Arrendment No.1 Technical Specification Reference 3 6.0.2(a) 3 5.E.2 Report No.:
50-277-74-16A, B, C, and D 3 5.C.2 Report Date:
April 5,1974 3 6.0.2(b)
Occurrence Date: March 26,1974 Facility:
Peach Bottom Atomic Power Station, Unit 2 R. D. #1, Delta, Pennsylvania 17314 Identification of Occurrence:
A.
Reactor RV 71D bellows assembly leak B.
Reactor RV 71K failure to operate manually C.
HPCI turbine speed control malfunction D.
Reactor RV 71C bellows assembly leak indication Conditions Prior to Occurrencc:
Reactor at approximately 7% power and. 950 psig.
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'Mr. A. Giambusso April 4,1974 Page 2 Description of Occurrence:
Following vendor recommended modifications on all relief valves and repairs to RV 710, which had f ailed to rescat, each relief valve was successfully operated at about 150 psig pressure. Pressure was then increased to about 950 psig and relief valves again tested. During this testing period, relief valve 71D bellows assembly leak indication occurred (AO-16A) and relief valve 71K f ailed to open when the manual control switch was placed in the open position (AO-16B).
An inspection of these two valves inside the drywell verified a bellows leak on RV 710, but did not reveal any cause for the failure of RV 71K to operate. The air supply and electrical connections to RV 71K solenoid valve were verified as being correct during this in-spection.
Af ter determining that RV 71K (one of five ADS valves) was inoperabic, the required system surveillance testing was initiated.
A test of the HPCI identified an electrical problem in the turbine control system which failed the turbine control valve to the open position (AO-16C). Prcmpt action by the operator shutdown the turbine before it could trip on overspeed. Repairs were made within several hours. Plant shutdown operations were initiated af ter the HPCI was determined to be inoperable. Power level was recovered af ter the HPCI was successfully retested.
Shortly, thereaf ter, relief valve 71C bellows assembly leak indication occurred (AO-160) and the decision madd to shutdown the reactor. The primary system was cooled to less than 212 F within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
Designation of Apparent Cause of Occurrence:
A. and D.
Following shutdown, inspection of these valves identified a leak at the bellows to pre-load spacer "0" ring on RV 71C and RV 71D. Additional inspections of the other valves identified a similar leak on RV 71H.
B.
The reason for the failure of RV 71K to operate at rated reactor pressure was not identified. After the valve failed to operate, a drywell entry was made, and the air operator solenoid was rapped manually. Following this entry and during the reactor shutdown, RV 71K was successfully actuated from the control room, as had been done at 150 psig during the reactor startup.
C.
Control system electrical component failure.
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Mr. A. Giambusso April 4,1974 Page 3
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Analysis of Occurrence:
At the time of this occurrence, the reactor was operating at minimum power level sufficient to support post maintenance testing of relief valves having previously been shutdown for approximately one week. Decay heat load in the reactor was minimal.
Because sufficient relief valve capacity, and emergency core cooling systems were available at all times to respond to any plant transient initiated from a full power condition, no safety significance is associated with this occurrence.
Corrective Action:
A. and D.
The leaking "0" ring in the bellows assembly of RV 71C and D was replaced by a vendor service engineer, and the valve set-point adjusted using nitrogen. The pilot and bellows were then success-fully leak tested.
As a resul t of the bellows "0" ring leakage experienced on RV 71 C and D, a decision was made to leak test the bellows assemblies of RV 71 G, H, and J, since these valves had been reworked by vendor representatives the previous week, as were RV 71 C and D.
RV 71 G and J did not exhibit any bellows leakage when pressurized to 970 psig wi th nitrogen, but RV 71H did show excessive leakage and was repaired as described for RV 71 C and D above. The bellows leak detection pressure switch from RV 71H was removed and bench tested since no control room leak annunciator was observed for this va lve during the period the reactor was pressurized. The switch was found to be operating normally.
It was therefore concluded that the leak was small enough so that the switch had not beem sufficiently pressurized to actuate during the period of time the reactor was at pressure.
B.
The air operator section of RV 71K was unbolted from the ba'se assembly and actuated from the control room prior to disturbing either the electrical or pneumatic connections.
The air operator was found to operate normally when actuated from the control room.
This section was then removed and completely disassembled for inspection. No condition was found in either the ai r operator, or the solenoid which admits air to the operator, which would explain its failure to operate at rated reactor pressure.
The second stage piston was operated by applying manual
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force, as soon as the air operator was removed, and no abnormalities were observed.
The base assembly was then removed from the valve so the vendoFs service engineer could perform a detailed inspection. The second stage valve was successfully actuated in the test stand.
Removal of the second stage assembly from the base revealed no abnormalities of any kind.
The electrical circuit from the hand switch in the control room.to the solenoid terminals was tested and found to be operating normally.
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Mr. A. Giambusso April 4,1974 Page 4 RV 71K was reassembled using a new second stage valve (disc, stem and nut) and a previously inspected and tested ai r operator and solenoid assembly (not the same operator which was installed when the valve failed to operate). The second stage and pilot valves were successfully leak tested in the test stand prior to installation. The bellows / pilot assembly was not disturbed during any portion of the inspection or testing.
At the request of the Nuclear Steam System Supply vendor, the air operators were removed from all eleven reactor relief valves for a low pressure friction test.
During this test the lowest air pressure required to stroke the air operator was recorded 20 times for each operator. All air operators were found to operate satisfactorily.
Duri ng thi s test, the second stage piston nut retainer modification performed the previous week by the valve vendor was inspected by a cognizant engineer from the Nuclear Steam System Supplier.
As a final test, all eleven valves were successfully actuated from the control room at reactor pressures of 150 psig and 950 psig during plant startup.
C.
The electrical malfunction in the HPCI control circuitry was traced to a local speed control potentiometer which was open circulted. The open circuit was caused by the failure of the potenti-ometer stops to limit slide motion. A potentiometer with proper stops was installed to correct the deficiency. The HPCI was successfully tested following repairs to the control ci rcuitry.
Failure Data:
Three bellows assembly leaks have occurred since initial startup. On two occasiens, relief valves have failed to rescat af ter manual ini tiation. On one occasion, a relief valve failed to rescat on the first attempt folicwing manual initiation but did release on the third attempt.
Very truly yours,
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'M./J. Cooneyl Asst. Gent. Supt.
Generation Division cc:
J. P. O'Reilly l
Director, Region I l
U. S. Atomic Energy Commission 631 Park Avenue l
King of Prussia, PA 19406 f
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