ML082631012

Special Inspection Charter for Loss of Normal Offsite Power to Non-Safety Buses and Resultant Reactor Scram on 9/11/2008

ML082631012
Person / Time
Site:	Monticello
Issue date:	09/18/2008
From:	Pederson C Division Reactor Projects III
To:	Mcghee J Division Reactor Projects III
References
Download: ML082631012 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION REGION III 2443 WARRENVILLE ROAD, SUITE 210 LISLE, IL 60532-4352 September 18, 2008 MEMORANDUM TO:

James M. McGhee, Special Inspection Team Lead Senior Resident Inspector, Quad Cities Division of Reactor Projects FROM:

Cynthia D. Pederson, Director /RA by G. Shear Acting for/

Division of Reactor Projects

SUBJECT:

SPECIAL INSPECTION CHARTER FOR LOSS OF NORMAL OFFSITE POWER TO NON-SAFETY BUSES AND RESULTANT REACTOR SCRAM, AND OTHER COMPLICATIONS AT THE MONTICELLO NUCLEAR PLANT ON SEPTEMBER 11, 2008 On September 11, 2008, at 10:50 pm CST, Monticello had a breaker fuse fault on the supply line to the 2R transformer. The 1R transformer was out-of-service for planned maintenance.

With both the 1 and 2R transformers unavailable, the offsite electrical power supply to the non-safety buses was lost, resulting in a loss of the normal heat sink (i.e., feedwater, condensate, circulating water and recirculation systems were lost). The 1AR transformer was available and supplying the safety-related buses. Both emergency diesel generators (EDGs) started and were running, but did not load as offsite power was available to the safety-buses. Since the normal heat sink was lost, operators used the reactor core isolation cooling (RCIC) system, the high pressure core injection (HPCI) system, the safety relief valves (SRVs) and the torus cooling system for pressure/level control. All control rods fully inserted and the licensee decided to place the plant in Mode 4 (Cold Shutdown) pending assessment of the transient.

Subsequently, the licensee restored the 1R transformer and returned power to the non-safety related buses. As of September 15, the plant was in mode 4 [depressurized] with shutdown cooling in-service.

On September 17, at 9:45 am CST, Monticello experienced a lockout of the 1R transformer after a truck with a self-power man lift struck a power line providing offsite power to the plant. The 2R transformer was out-of-service due to the September 11, partial loss of offsite power event.

With both the 1 and 2R transformers unavailable, the offsite electrical power supply to the non-safety buses was lost, resulting in a loss of shutdown cooling. The 1AR transformer was available and supplying the safety-related buses. Additionally both EDGs started and were running, but did not load as offsite power was available to the safety-related buses. The licensee declared a Notice of Unusual Event at 10:30 am CST and the NRC subsequently entered Monitoring Mode. The licensee subsequently restored shutdown cooling.

J. McGhee During the September 11, 2008, scram recovery, the following complications were noted:

HPCI did not auto-isolate when reactor water level reached the high level setpoint (48 inches), resulting in the operators having to manually isolate it. The licensee determined the cause to be the failure of the steam admission trip valve to open on demand.

The licensee was unable to either remotely or locally reduce the speed of the 12 EDG to shut it down. The licensee initially identified the cause to be the failure of the engine stop delay relay coil to energize, preventing the fast start lock-in from releasing. The licensee replaced the coil on September 16; however, during the September 17 event, the 12 EDG experienced a similar issue with the inability to either remotely or locally reduce speed.

The automatic depressurization system (ADS) actuation timer started as designed, but was manually inhibited after the timer display was lost. Although the ADS timer started when the lo-lo-level reactor water level signal was received as designed, the ADS does not actuate unless a coincident signal indicates that one of the low pressure emergency core cooling system pumps has started. The low pressure pumps were not required to start, therefore ADS was not needed for this event and was considered available.

Several days after the September 11, 2008, reactor scram, the licensee determined that several hours following the initial transient, reactor water level may have increased to about 110 inches. This is above the main steam line piping (108.5 inches), but below the RCIC and HPCI steam supply piping (126 inches). At this time, the main steam isolation valves were closed and the operators were using the control rod drive pumps (and possibly RCIC) and SRVs for pressure/level control.

The licensee has identified two cable faults associated with the 2R transformer. One fault was associated with the A phase cable, which is buried underground (not inside conduit) just outside of the protected area fence. The other fault was associated with the B phase cable, adjacent to the 2R transformer, and located inside a conduit. The licensee has identified about 20 other cables (of similar age) that should be examined.

The most significant of these are associated with the 1AR transformer. The licensee is in the process of testing the 1AR transformer cables and is planning on inspecting other cable locations for evidence of standing water.

Based on the criteria specified in Management Directive 8.3 (Part I criterion (e) and (h)) and Inspection Procedure 71153, a Special Inspection was initiated in accordance with Inspection Procedure 93812 and Regional Procedure RP-8.31. The Special Inspection will commence on September 17, 2008, and will be led by James McGhee, Senior Resident Inspector (Quad Cities). In addition to Mr. McGhee, the team will include Michael Bielby, Senior Operator License Examiner; Zelig Falevits, Senior Electrical Team Lead; Lucas Haeg, Resident Inspector (Monticello); and April Scarbeary, Reactor Engineer.

J. McGhee The Special Inspection will evaluate the facts, circumstances, and licensee actions surrounding the September 11 and 17, 2008, events. Elements of the inspection should include: the cause of the 1R and 2R transformer lockouts; the HPCI, 12 EDG and ADS equipment issues; the licensees efforts to identify the extent of the cabling issues; and the licensees response during both events. A Charter was developed and is enclosed.

Enclosure:

As stated cc w/encl:

J. Caldwell, RAO M. Satorius, RAO S. West, DRS, M. Bielby, DRS Z. Falevits, DRS A. Scarbeary, DRP

J. McGhee The Special Inspection will evaluate the facts, circumstances, and licensee actions surrounding the September 11 and 17, 2008, events. Elements of the inspection should include: the cause of the 1R and 2R transformer lockouts; the HPCI, 12 EDG and ADS equipment issues; the licensees efforts to identify the extent of the cabling issues; and the licensees response during both events. A Charter was developed and is enclosed.

Enclosure:

As stated cc w/encl:

J. Caldwell, RAO M. Satorius, RAO S. West, DRS, M. Bielby, DRS Z. Falevits, DRS A. Scarbeary, DRP DOCUMENT NAME: G:\\MONT\\SIT Charter 9-18-08.doc X Publicly Available G Non-Publicly Available G Sensitive X Non-Sensitive To receive a copy of this document, indicate in the concurrence box "C" = Copy without attach/encl "E" = Copy with attach/encl "N" = No copy OFFICE RIII RIII RIII NAME KRiemer:dtp SWest CPederson by GShear for DATE 09/18/08 09/18/08 09/18/08 OFFICIAL RECORD COPY

Enclosure This Special Inspection is charted to assess the circumstances surrounding the September 11 and 17, 2008, Monticello partial loss of offsite power events. The inspection should include the cause of the 2R transformer lockout, the operator response during the transient (including the control over reactor water level), and the licensees resolution of the equipment issues involving the HPCI, 12 EDG and ADS systems. Additionally, the inspection should focus on the licensees monitoring program for inaccessible and underground cables per Generic Letter 2007-01. The Special Inspection will be conducted in accordance with Inspection Procedure 93812, Special Inspection, and will include, but not be limited to, the following items:

1. Establish a sequence of events of the September 11, 2008, event including: the lockout of the 2R transformer; the reactor scram; the automatic start of the HPCI, ADS, and EDG systems; the manual isolation of the HPCI and ADS systems; and the shutdown of the 12 EDG.

2. Monitor the licensees human performance investigation regarding operator performance during the September 11 event. Evaluate the actions taken by the operating crew to maintain reactor water level, including operators use and understanding of systems used for pressure/level control, instrumentation used to monitor reactor water level, and procedures/operating instructions used for event response.

3. Evaluate the licensees cause evaluation regarding the HPCI failure to auto isolate upon a high reactor vessel water level during the September 11 event. Verify that for the licensee corrective actions, the post-maintenance testing will ensure HPCI operability, including whether the HPCI turbine will automatically and manually (i.e., via the push button) isolate upon high reactor water level (48 inches);

4. Evaluate the licensees evaluation/troubleshooting of the cabling issues. Observe, if possible, the testing and as found condition of the cables and review the licensees determination of the cause of failure. In particular, review the licensees response to Generic Letter 2007-01 and determine whether the licensees program for monitoring inaccessible and underground cables was adequate. Verify that the licensee has appropriately considered extent of condition and that any cabling issues are appropriately addressed.

5. Evaluate the licensees troubleshooting and repair of the 12 EDG. Verify that the post-maintenance testing will validate that the speed control for the 12 EDG will operate as designed following a fast start and while running in the unloaded condition. Evaluate whether the licensee has determined the affect on the diesel reliability for the period in which it ran in an unloaded condition;

6. Evaluate the licensees troubleshooting and repair of the ADS system. Verify that the post-maintenance testing will validate that the timing and timer display function properly upon a lo-lo reactor water level signal;

7. Establish a sequence of events for the September 17 partial loss of offsite power event; including, the lockout of the 1R transformer, auto start of the emergency diesel generators, and the loss and subsequent restoration of shutdown cooling.

8. Evaluate the licensee cause evaluation and subsequent response for the September 17 partial loss of offsite power event.