What Really Happened At Oyster Creek, Report Released

The US NRC has finally issued an inspection report on Oyster Creek and the events during hurricane Sandy. During the storm the public was left with many unanswered questions and a considerable lack of information about what was going on at Oyster Creek nuclear plant.

On October 31st Reuters reported a 6.8 feet water level. The NRC official event report is more vague, only citing “over 6 feet“. A few reports admitted the full 7.4 feet of flooding but this didn’t get widely distributed via the press or the NRC’s public website. The full flooding height at Oyster Creek was 7.4 feet. The concrete deck at the intake structure sits at 6 feet. Existing documents at the plant stated that the bottom of needed intake pumping equipment was 7 feet. Water over that level would force the equipment to be shut down cutting off cooling to the spent fuel pool. The NRC report identifies a change made after workers checked and found the bottom of these pumps and electrical systems actually sat at 10 feet above sea level, not 7.

This caused a major issue with the public who were being told differing flood water level readings even days after the storm. The public had been informed of the 7 foot level for equipment failure potential but the public was never informed of the change to 10 feet for equipment failure. This left the public with a very confusing narrative of flood waters between 6.8 to 7.4 feet and an equipment failure level of 7 feet, yet declarations there wasn’t a problem.

The reactor was open with the containment & reactor caps off as they were in the middle of the refueling process. 10 fuel assemblies had been stored in the spent fuel pool. The NRC cites 28 hours until boiling if they had lost cooling capability for both the reactor and the pool. The intake based cooling system is the cooling system for the spent fuel pool. Workers could have added water to continue to keep the spent fuel covered but this doesn’t fully cool the fuel and does create a problematic situation that could make the situation much worse. The reactor vessel was also open. We have not done any research into this aspect and what would happen if all cooling function was lost with an open reactor. Exelon did have some portable pumps on hand and would have hopefully continued to at least be able to add water if cooling was lost. In short this was not an ideal situation to be facing in a storm and held the potential to greatly complicate any response should a larger problem arise. The public was also largely left in the dark about all of these details even days after the storm. There was considerable worry among the public exactly what was going on at the plant and how close they were or could be to a potential serious incident. The lack of clear and honest information can be far worse than giving people the facts and allowing them to comprehend and decide for themselves what risk the situation poses. Not wanting to panic the public does not excuse Exelon or the NRC’s behavior in not telling the public what was going on. There were many in the media and questions directed at the NRC that were asking these very questions about the current condition at the plant. Sadly NRC’s public response during the storm is quite similar to how Japan’s government handled public information during the Fukushima disaster.

Cooling was lost to the reactor and the spent fuel pool for about an hour. The public was not informed of this clearly. News and NRC public reports cited there was a brief power outage during the switch to emergency generators. This additional information comes out months after the incident and only buried in the investigation report. While an hour of loss of power is from a technical aspect a manageable problem, the public was never told about the incident. The hour didn’t turn into more hours but averted problems do not absolve the lack of honest reporting of the plants condition to the public. Again, a situation where honest detailed information with some clear context about what it means is better than lying by omission to the public.

Confusion, piecemeal, and conflicting information caused the public to worry more than they would have had the entire body of information been told to the public in a timely manner. This is a communications failure of the NRC and Exelon and raises bigger questions. Is either party required to tell the public exactly what is going on in a timely manner? The NRC has some mandatory public reporting rules but they don’t seem to include full disclosure of what is going on. These kind of events erode public confidence, better communication is needed.

OysterCreekSandyInvestigation_ML13010A470 OC IR 2012-009

 

1) On October 29, 2012, Hurricane Sandy, a Category 1 hurricane, was expected to make landfall in the vicinity of the OCGS. OCGS was shutdown on October 22 for a scheduled refueling outage and partially defueled (approximately 10 bundles had been moved to the spent fuel pool) with a time to boil of 28 hours for the core and spent fuel pool. Decay heat removal was via shutdown cooling and spent fuel pool cooling.  The reactor vessel head was removed and secondary containment was intact.

2) At 7:54 p.m., offsite power line R144 tripped and caused a resulting trip of the fuel pool cooling system. Operators entered ABN-16, “Loss of Fuel Pool Cooling.” At 8:08 p.m., the modem that was relaying intake level data to the control room recorder (points 23 and 24) failed and rendered the primary means of measuring intake level unavailable. Operators that had been stationed at the intake structure were also relaying intake level readings to the control room from two local pressure indicators (PI-533-1173 and PI-533-1172). At this time, the intake levels were 4.6 psig (5.3 feet) and 4.5 psig (5.1 feet) on pressure indicators 1173 and 1172, respectively. Control room operators had to rely on these secondary indicators to make emergency action level decisions.

3) Offsite power to OCGS was lost at 8:18 p.m., and operators entered ABN-36, “Loss of Offsite Power.” The loss of offsite power caused a trip of the shutdown cooling system. Subsequently, the senior reactor operator (field supervisor) overseeing equipment operators at the intake structure reported to the emergency diesel generators (EDGs) to facilitate post-start checks of the EDGs that automatically started on the loss of offsite power. The EDGs were automatically aligned to restore power to the emergency busses.

4) When the field supervisor returned to the intake structure at approximately 8:29 p.m., he reported to the control room that intake level was 4.9 psig (6.0 feet) on both of the local pressure indicators. The Shift Manager reviewed the Alert emergency action level threshold of greater than 6.0 feet intake level and determined that it had not been met, and he requested another intake level reading from the operators at the intake structure. At 8:32 p.m., the field supervisor reported that he could no longer safely monitor the local pressure indicators (PI-533-1173 and PI-533-1172) to determine intake level due to the rising water level. The inspectors noted that this is consistent with caution statements in ABN-32 because the intake structure deck is at a height of six feet mean sea level and electrically energized motor control centers are mounted on the deck. The field supervisor also reported that intake level was 6.25 feet and rising on a staff gauge located on the intake structure upstream of the traveling screens. The intake staff gauge was an alternate method of monitoring intake level when the primary and secondary level indicators are unavailable

5)  At 8:44 p.m., the operations Shift Manager declared an Alert (HA-4) in response to the report that intake level was greater than 6.0 feet on the intake staff gauge. State and local notifications for the Alert were completed at 8:51 p.m.. The SIT determined that these notifications were accurate and timely. The shutdown cooling and fuel pool cooling systems were returned to service at 8:50 p.m. and 9:19 p.m., respectively.

6) At 11:11 p.m., intake level on the staff gauge was 7.0 feet (Note: the staff gauge is not available above 7 feet). At approximately 12:18 a.m. on October 30, 2012, the maximum intake level of 7.4 feet was reached as determined by water level measurements above the base of the service water pumps. Water levels remained below the service water pump motors and well below the design basis flood height of greater than 22 feet that is documented in UFSAR section 2.4.5.4.

7) Due to the local loss of electrical power, the EOF was initially ready to be activated with the facility’s emergency generator supplying electrical power to the building. Shortly thereafter, that generator began to trip off line, and with no power to the building, the CED did not activate the EOF. The EOF staff diagnosed the generator’s tripping as a result of a mechanical fault in the EOF’s air conditioner. Once the EOF staff opened the air conditioner’s circuit breaker, the generator successfully and consistently supplied power to the building. At that point, the CED activated the EOF and assumed command and control. Due to the local loss of electrical power, the EOF was initially ready to be activated with the facility’s emergency generator supplying electrical power to the building. Shortly thereafter, that generator began to trip off line, and with no power to the building, the CED did not activate the EOF. The EOF staff diagnosed the generator’s tripping as a result of a mechanical fault in the EOF’s air conditioner. Once the EOF staff opened the air conditioner’s circuit breaker, the generator successfully and consistently supplied power to the building. At that point, the CED activated the EOF and assumed command and control.

8) Based on a review of abnormal procedures implemented during Hurricane Sandy, interviews of OCGS personnel, and discussion with NRC inspectors that were monitoring operations onsite on October 29, 2012, the inspectors observed that a change to ABN-32 for increasing the intake level that would require securing the service water pumps was not preplanned. The inspectors noted that revision 18 of ABN-32 directed operators to secure all of the service water pumps when the intake level reached seven feet MSL. However, the day shift operating crew identified that the bottom of the service water pump motors was located at approximately 10 feet MSL. Therefore, approximately three feet of available margin existed before the service water pump motors would be impacted. The normal method of decay heat removal from the shutdown cooling and fuel pool cooling systems would therefore remain available. The day shift operating crew discussed revising ABN-32, but did not communicate this contingency plan to the Outage Command Center (OCC) and the procedure change was not pursued further during the day shift.

9) As intake level rose towards seven feet MSL, the night shift operating crew coordinated with the OCC to have ABN-32 revised to raise the required intake level for securing the service water pumps. Revision 19 to ABN-32 was completed shortly before the intake level reached seven feet MSL. Although intake level rose to approximately 7.4 feet MSL, the intake level did not approach the new higher ABN-32 required limit for securing the service water pumps. OCGS documented this issue in issue report 1438850. The inspectors considered this issue minor because the delay in revising the procedure did not affect the availability, reliability or capability of the shutdown cooling or fuel pool cooling water systems.

 

 

 

 

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