05000336/LER-2016-001

LER-2016-001, Turbine Driven Auxiliary Feedwater Putnp Room HELB Door Left Open

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function
3362016001R00 - NRC Website

LER 16-001-00 for Millstone Power Station Unit 2 RE: Turbine Driven Auxiliary Feedwater Pump Room HELB Door Left Open

ML16187A324
Person / Time
Site:	Millstone, Docket Number
Issue date:	06/27/2016
From:	Daugherty J R Dominion, Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 16-001-00
Download: ML16187A324 (6)

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Pnvacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. EVENT DESCRIPTION

On April 27, 2016, with Millstone Power Station Unit 2 (MPS2) in MODE 1 at 100% power, plant personnel inadvertently left the door to the turbine driven auxiliary feedwater (TDAFW) pump room open. Upon discovery the door was closed. Door access records indicate the door could not have been open for more than 57 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.

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 (SG) 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 ground 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 cause is human performance error. The door is conspicuously labeled on each side that it is a HELB boundary door and must be closed except for entry and exit from the room.

3. ASSESSMENT OF SAFETY CONSEQUENCES

The consequences of this event were not safety significant. This condition existed for approximately one hour. In the unlikely event that a HELB occurred in the TDAFW pump room during the short time 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 reactor coolant system (RCS) heat removal safety functions. In this scenario, both SG levels would decrease. The existing loss of all feedwater Emergency Operating Procedure (EOP) guidance would direct the operators to establish once through cooling when SG wide range levels dropped to 70 inches. This once through cooling EOP strategy utilizes the pressurizer power operated relief valves 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 Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Pnvacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

4. CORRECTIVE ACTION

This was a human performance problem and was addressed in accordance with appropriate policies.

Corrective actions are being taken in accordance with the station's corrective action program.

5. PREVIOUS OCCURRENCES

MPS2 LER 2013-002-00, Turbine Driven Auxiliary Feedwater Pump HELB Door Left Open During Surveillance Test.

6. Energy Industry Identification System (EIIS) codes

• Auxiliary feedwater system — BA

• TDAFW pump — TRB, P

• Electric motor driven auxiliary feedwater pump — MO, P

• Door — DR

• Steam Generator — SG