PNO-IV-98-012, on 980312,plant Experienced Reactor Trip as Result of Inadvertent Closure of One of Msivs.Caused by Loss of Instrument Air to Valves Actuator.Reactor Vessel Cooled Down to Facilitate Containment Entry for Investigation
| ML17292B284 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 03/12/1998 |
| From: | Bradley Jones, Pellet J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| References | |
| PNO-IV-98-012, PNO-IV-98-12, NUDOCS 9803190062 | |
| Download: ML17292B284 (4) | |
CATEGORY REGUL ORY INFORMATION DISTRIBUTI N SYSTEM (RIDS)
ACCESSION NBR:9803190062 DOC.DATE: 98/03/12 NOTARIZED: NO DOCKET FACIL:50-397 WPPSS Nuclear Project, Unit 2, Washington Public Powe 05000397 AUTH.BYNAME'UTHOR AFFILIATION PELLET,J.
Region 4 (Post 820201)
JONES,B.
Region 4 (Post 820201)
RECIP.NAME RECIPIENT AFFILIATION
SUBJECT:
PNO-IV-98-012:on 980312,plant experienced reactor trip as result of inadvertent closure of one of MSIVs.Caused by loss of instrument air to valve's actuator. Reactor vessel cooled down to facilitate containment entry for investigation.
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March 12, 1998 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-IV-98-012 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by Region IV staff in Arlington, Texas on this date.
Facititar Licensee Emer enc Classification Washington Public Power Supply System Notification of Unusual Event Washington Nuclear 2 Alert Richland, Washington Site Area Emergency Dockets: 50-397 General Emergency X Not Applicable
Subject:
REACTOR SCRAM AND ENGINEERED SAFETY FEATURES (ESF)
ACTUATION On March 11, at 5:07 a.m. (PST), WNP-2 experienced a reactor trip as a result of an inadvertent closure of one of the main steam isolation valves (MSIVs). The unexpected closure of the inboard MSIV on Steam Line D resulted in a high steam flow isolation signal on the other three steam lines. The subsequent closure of the MSIVs generated a reactor protection signal to trip the reactor. As expected, the main generator tripped.
The transient from the closure of the MSIVs resulted in a rapid reactor pressure increase.
The pressure increase was initially controlled by the actuation of safety relief valves..
Additionally, reactor water level rapidly decreased to the low-low level setpoint (lowest recorded level was approximately -50"). This resulted in the automatic initiation of the high pressure core spray (HPCS) and the reactor core isolation cooling (RCIC) systems.
The HPCS system was subsequently prevented from injecting by operator action. The RCIC system was utilized to maintain reactor vessel inventory.
-Following the reactor scram, drywell pressure increased to 1.65 psig because of the loss of the reactor closed cooling water system, which provides normal cooling to the drywell.
This resulted in the generation of additional ESF signals to start the. emergency diesel generators and the emergency core cooling system (ECCS). Since startup power was available to the plant, the emergency diesel generators did not load onto their respective buses.
The Division II emergency diesel generator started, but the Division II ECCS pumps (RHR B/C) did not start. The Divisions I and III equipment appeared to have started as expected. The licensee is investigating this anomaly.
Preliminary data indicate that the closure of the Steam Line D inboard MSIV was due to a loss of instrument air to the valve's actuator. Nitrogen consumption on the containment instrument air system, and the inability to reopen the Steam Line D inboard MSIV, support the assumption that the loss of air to the actuator was a result of a leak. As of 8 a.m.
(PST), March 12, 1998, the reactor vessel had been cooled down to about 165 degrees F
9803i90062 98031,2 PDR XSE PNQ-KV-98-012 PDR IIIIIII IIII IIIIIIIIIIIIIIIIIIIIIIIIII
4 to facilitate containment entry and investigation of the inadvertent MSIV closur'e In response to the event, the resident inspector monitored licensee actions from the control room. Also, Region IV has initiated a special inspection consisting of three inspectors.
The current focus of the inspection efforts is to review and evaluate both plant system and operator performance.
This will include: 1) establishing a sequence of events;
- 2) reviewing the apparent failure of Division II ECCS pumps to start following a high drywell pressure signal; 3) reviewing the appropriateness of operator response to the event (e.g., operator action to manually secure.HPCS injection); 4) reviewing the adequacy of the licensee's evaluation of possible precursor indications of an MSIV problem; 5) reviewing the adequacy of the information the licensee reported to the NRC in its initial and updated 10 CFR 50.72 report; and 6) determining whether the plant response was consistent with the analyzed response for an MSIV closure event.
The licensee has issued a press release.
The state of Washington has been notified.
Region IV received notification of this occurrence from the senior resident inspector at approximately 7:30 a.m. on March 11, 1998. Region IV has informed the OEDO, PAO, NRR, and AEOD.
This information has been discussed with the licensee and is current as of 10 a.m. (PST),
March 12, 1998.
Contact:
JOHN PELLET (817) 860-8159 BILLJONES (817) 377-2627