PNO-V-89-025, on 890407,reactor Put Into Unscheduled Shutdown for More than 48 H.Caused by Reactor Trip Due to Drop in Voltage on Rod Drive Bus After Breaker Trip,Atmospheric Dump Valve V-8421 Not Operating Properly & Leak in Vent Line
| ML13316A466 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/11/1989 |
| From: | Caldwell C, Johnson P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | |
| References | |
| PNO-V-89-025, PNO-V-89-25, NUDOCS 8904200120 | |
| Download: ML13316A466 (3) | |
ACCELERATED D TIBUT]ON DEMONShATION SYSTE 00 REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:8904200120 DOC.DATE: 89/04/11 NOTARIZED: NO DOCKET #
FACIL:50-362 San Onofre Nuclear Station, Unit 3, Southern Californ 05000362 AUTH.NAME AUTHOR AFFILIATION JOHNSONP.
Region 5, Ofc of the Director CALDWELL,C.
Region 5, Ofc of the Director RECIP.NAME RECIPIENT AFFILIATION R
SUBJECT:
PNO-V-89-025:on 890407,unscheduled shutdown greater than 48 h,atmospheric dump valve problems & leakage in SIV line.
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PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-V-89-25 Date: 04/11/89 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information presented is as initially received without verification or evaluation and is basically all that is known by Region V staff on this date.
FACILITY:
SOUTHERN CALIFORNIA EDISON Emergency Classification San Onofre Unit 3 Notification of Unusual Event Docket No. 50-362 Alert San Clemente, California Site Area Emergency General Emergency
= Not Applicable
SUBJECT:
UNSCHEDULED SHUTDOWN GREATER THAN 48 HOURS; ATMOSPHERIC DUMP VALVE PROBLEMS; AND LEAK IN SAFETY INJECTION VENT LINE Unit 3 tripped at 5:55 a.m. (PDT) on April 7, 1989 after one rod drive motor generator (RDMG) output breaker tripped. Although the other RDMG continued to hold the control rods, voltage on the rod drive bus dropped after the breaker tripped.
This drop in voltage was seen by the turbine trip circuitry as indicating a reactor trip, and initiated a turbine trip. The turbine trip then resulted in a reactor trip. Plant systems functioned normally after the trip, and plant conditions were promptly stabilized. The licensee determined during investigation over the weekend that the rod drive bus voltage drops from an initial value of 240 volts to as low as 223 volts when one RDMG is lost, and that the undervoltage (UV) relay setpoints are different for Units 2 and 3. While Unit 2 UV relays are set at a nominal 216 volts, the relays on Unit 3 were set at 225 volts. The licensee is considering lowering the setpoints on Unit 3, and is evaluating what the voltage setpoints should be.
RDMG output breaker performance has been and continues to be the subject of ongoing evaluation.
During the evening of April 7, 1989, in response to a recent Part 21 report, the licensee tested atmospheric dump valve (ADV) V-8421. Initial results indicated that the valve did not operate properly. After further testing over the weekend, the licensee has concluded that the slow initial operation (approximately one minute) is due to piston ring leakage and the need to initially depressurize the chamber above the main piston. After this chamber is depressurized, the valve responds normally to further control signals. The licensee has concluded that this performance is consistent with valve performance as described in the FSAR, which states that the ADV must operate within 30 minutes in the event of a steam generator tube rupture. The licensee's position is still being evaluated by Region V and NRR. The licensee also discussed with Region V and NRR the provisions which have been made for manual ADV operation (if necessary). The other Unit 3 ADV, V-8419, was tested on April 8, 1989 and operated properly with both air and nitrogen. The licensee also plans to test Unit 2 ADV's in the near future.
On April 8, 1989 the licensee identified a leak between the two valves in a 3/4-inch vent line off a safety injection line just upstream of its connection to the reactor coolant system. The leak was in the heat-affected zone of a weld, and was stopped by closing the inboard vent valve more tightly. The plant was cooled down to Mode 4, and repair is in progress. The licensee intends to restart Unit 3 after this repair is completed and tested and after questions regarding ADV operation and UV relay setpoints are resolved (2-3 days).
8904200120 890411 PDR I&E PNO-V--89-0 2 5 PDC
-2 The resident inspectors and Region V are following the licensee's activities.
Region V and NRR are evaluating the licensee's position on ADV operation.
This information s current as of 8:00 a.m. on April 11, 1989.
CONTACT: P.
n C. Caldwell FTS 146-745 (714) 492-2641 DISTRIBUTION BY 5520:
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CA RES RV FORM 211 Revised: 8/19/87