05000336/LER-2013-002
| Millstone Power Station - Unit 2 | |
| Event date: | 03-07-2013 |
|---|---|
| Report date: | 05-06-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3362013002R00 - NRC Website | |
1. EVENT DESCRIPTION
On March 7, 2013, with Millstone Power Station Unit 2 (MPS2) in MODE 1 at 100% power, during a turbine driven auxiliary feedwater (TDAFW) pump surveillance test, the operators and other personnel in attendance left the door to the TDAFW pump room open. This condition existed for approximately 30 minutes. The door is a high energy line break (HELB) barrier. With the door open there is no HELB protection for the motor driven auxiliary feedwater (AFW) pumps thus potentially rendering both trains of AFW inoperable. Additionally, during the surveillance run the TDAFW pump was declared inoperable.
This issue was determined not to be reportable as an eight hour report pursuant to 10 CFR 50.72(b)(3)(v) since at the time of discovery the door was closed and therefore the condition did not exist.
This event is being reported pursuant to 10 CFR 50.73(a)(2)(v) as any event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to:
(B) Remove residual heat; and (D) Mitigate the consequences of an accident.
Background Information:
The auxiliary feedwater system (AFWS) is designed to provide feedwater for the removal of sensible and decay heat, and to cool the primary system to 300 degrees F in case the main condensate and steam generator feed pumps are inoperative due to loss of normal electric power sources.
In order to perform its safety-related function, assuming a single failure, the AFWS is comprised of two full capacity subsystems. One subsystem consists of two motor driven AFW pumps, that are automatically connected to the diesel generators in the event of a loss of offsite power. The second subsystem consists of one turbine-driven pump that is independent of AC power and may be started by operator action.
The AFW pumps are located in two separate pump rooms at elevation 1 foot 6 inches in the MPS2 Turbine Building. Access to the first room which houses the two motor driven AFW pumps is by stairs leading down from the groubd floor at elevation 14 feet 6 inches. The enclosure over the pump room stairwell serves as a protective barrier against direct water streams into the pump room due to a possible overhead pipe failure. The second room which houses the TDAFW pump is a vault physically separated from the motor driven AFW pump room by a reinforced concrete wall. The only access means to this room is through a water-tight fire door. This door is also the HELB barrier between the motor driven AFW pumps and the TDAFW pump room.
2. CAUSE
The HELB requirements during operation of the TDAFW pump were not fully considered during the pre- job brief.
3. ASSESSMENT OF SAFETY CONSEQUENCES
The consequences of this event were not safety significant. In the unlikely event that a high energy line break occurred in the turbine building during the 30 minutes the HELB barrier was breached, it is possible that the main feedwater pumps, the condensate pumps and both trains of AFW would not be available to maintain the core and RCS heat removal safety functions. In this scenario, both steam generator levels would decrease. The existing loss of all feedwater Emergency Operating Procedure (EOP) guidance would direct the operators to establish once through cooling when steam generator wide range levels dropped to 70 inches. This once through cooling EOP strategy utilizes the pressurizer PORVs to depressurize the RCS and the charging and high pressure safety injection pumps to maintain the RCS inventory and core heat removal safety functions. Since using this existing EOP strategy would have precluded core damage in this extremely unlikely event, there were no safety consequences.
4. CORRECTIVE ACTION
Management has reinforced expectations to Operations Department personnel and station personnel on the need to ensure the requirements for any barrier are met prior to opening any door or duct. Training for Operations, Maintenance and Engineering is planned to reinforce understanding of expectations concerning passive design features, like flood barriers, fire doors and HELB barriers. Additional corrective actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES
MPS3 LER 2010-003-00, Secondary Containment Rendered Inoperable Due to Misaligned Dampers.
6. Energy Industry Identification System (EllS) codes
- Auxiliary feedwater system - BA
- TDAFW pump - TRB, P
- Electric motor driven auxiliary feedwater pump - MO, P
- Door - DR