Morning Report for January 12, 2006
Headquarters Daily Report
Loss of Charging System Impact on Safe Shutdown Capability
| Licensee/Facility: |
DOMINION NUCLEAR CONNECTICUT, INC.
| Notification: |
MR Number: H-2006-0002
At 4:55 a.m. on January 9, Millstone experienced a reduction in the flow from "C" charging pump. Operators unsuccessfully attempted to restore system flow with the two standby pumps ("A" and "B"). TS 3.0.3 was entered and letdown and charging were isolated. The failure of the system was believed to be caused by a "B" discharge charging pump pulse dampener bladder failure and subsequent migration of nitrogen gas to the suction of the other pumps. At 5:44 a.m., the "C" charging pump was restored to service after venting the system and isolating the "B" charging pump. At 5:54 a.m., operators exited TS 3.0.3 and remained in the TS for one inoperable train.
At 1:43 p.m. on January 9, operators received a low flow alarm on the "C" charging pump. Charging and letdown were isolated and TS 3.0.3 was entered. Following additional venting through from the VCT through the "A" and "C" pumps (by manual operation of the pumps), the "C" charging pump was restarted. This second "C" charging pump oscillation may have been caused by failure of the "A" charging pump's discharge pulse dampener bladder. At 5:52 p.m., Operators exited TS 3.0.3 after discussions with engineering and based on: 1) "A" and "B" charging pumps were isolated with suction and discharge valves closed and drained in-between; and 2) engineering assessment that failure of the "C" pump pulse dampener bladder would not impact pump operability. The plant remained in TS 3.5.2 (72 hour LCO) for one train of charging inoperable. This event was communicated to the NRC in Event Notification 42245 on January 9, 2006. On January 10, 2006, Millstone restarted the "B" charging pump after replacing its bladder and exited TS 3.5.2. While continuing investigation into the bladder issue, the licensee will maintain two charging pumps running (in lieu one normally) to prevent the potential for a common mode failure in the event of another bladder failure.
The resident inspectors have followed the issue and performed walkdowns of the system. The regional office is coordinating with headquarters to receive support to further evaluate the potential gas impact. The region will continue to follow the licensee's actions 1) to evaluate the cause of the bladder failures; 2) to repair the system; 3) to ensure continued operability; and 4) to evaluate the design aspects with regard to single failure vulnerability.
The charging system has three positive displacement pumps with discharge pulse dampener bladders. The new pulse dampener bladders were installed following a 2003 loss of charging event. The system is not credited in Design Basis Accidents, however the charging system is credited in the Probabilistic Risk Assessment for Anticipated Transient Without Scram (ATWS) and a complete loss of secondary heat sink.
|Name ||Office Abbrev ||Phone No ||E-Mail |
|DENTEL, GLENN, T ||RGN-1 ||(603) 474-3580 ||GTD@nrc.gov |
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