05000336/LER-2014-004
| Millstone Power Station Unit 2 | |
| Event date: | 04-10-2014 |
|---|---|
| Report date: | 06-09-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3362014004R00 - NRC Website | |
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1. EVENT DESCRIPTION:
On April 10, 2014, with Millstone Power Station Unit 2 in MODE 6 at 0% reactor power, while de- terminating the motor leads for the 'B' Motor Driven Auxiliary Feedwater (MDAFW) Pump motor, foreign material (ty-wraps and a plastic bag) were found inside the cable environmental seal (Raychem boot) of the 'A' phase. An inspection of the electrical leads revealed no damage occurred. This motor was last re-terminated in May 2000. The motor leads to the other phases did not have any foreign material inside the Raychem boot. Since the Raychem boot was not in the as tested environmentally qualified (EQ) configuration the 'B' MDAFW pump was considered inoperable.
Plant Technical Specifications (TS) 3.7.2.1 Action d, states in part, that in operating MODES 1, 2, or 3, with two AFW pumps inoperable, the plant must be in at least HOT STANDBY within six hours and in HOT SHUTDOWN within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
A review of the control room logs for the past three years determined there were 4 occasions where there were two AFW pumps inoperable for longer than allowed by TS.
This condition is being reported in accordance with 10 CFR 73(a)(2)(i)(B) as any operation or condition which was prohibited by the plant's Technical Specifications.
2. CAUSE:
The direct cause was a historical inappropriate maintenance practice which rendered the MDAFW pump inoperable. The 'A' phase motor lead was subsequently properly re-terminated.
3. ASSESSMENT OF SAFETY CONSEQUENCES:
With the foreign material found in the Raychem boot on the 'A' phase of the 'B' MDAFW pump, the ability of the 'B' MDAFW pump to function following a postulated High Energy Line Break (HELB) in the turbine building is called into question. For all other scenarios, the 'B' MDAFW pump would remain fully capable of performing its event mitigation functions.
Following a HELB in the turbine building, the main feedwater and condensate pumps cannot be relied on to remove decay heat. Additionally, the temperature and pressure in the MDAFW pump room can be elevated following a turbine building HELB. The maximum MDAFW pump room temperature and pressure following a HELB in the turbine building is 189 degrees F and 15.46 psia.
A postulated break in the turbine driven AFW pump steam supply line is a limiting turbine building HELB scenario with respect to the ability of the AFW system to remove decay heat. In this scenario, the turbine driven AFW pump would not be available for event mitigation. Additionally, due the FME found in the Raychem boot on the 'A' phase of the 'B' MDAFW pump, only the 'A' MDAFW pump can be relied on for decay heat removal. During periods of time when the 'A' MDAFW pump was taken out of service, or if a single failure is postulated that renders the 'A' MDAFW unavailable, AFW may not have been available for event mitigation. If that had been the case, removal of decay heat could still have been accomplished by RCS feed and bleed in accordance with the Emergency Operating Procedures.
Based on the above discussion, the above described condition is considered to be of low safety significance.
4. CORRECTIVE ACTION:
The 'A' phase motor lead was properly re-terminated. During the most recent MPS2 refueling outage (spring 2014) the motor leads to the other phases had their Raychem boots removed with no issues noted. Motors similar to 'B' MDAFW pump motor have had their Raychem boots removed since 2000 with no similar issues identified. The 'A' MDAFW pump motor was re- terminated during the MPS2 refueling outage in the fall of 2012, with no discrepancies noted.
In May 2000, the foreign material exclusion program and practices were far less robust than the current practices outlined in current plant procedures. Additionally, current plant procedures require inspection by quality control (QC) inspectors and verification for each EQ splice. This QC inspection point is present to provide an adequate barrier in the prevention of any foreign material concerns within the configuration of an EQ splice. New environmental seals come in a kit and remain sealed until inspected by QC. There is little likelihood this condition would recur.
Additional corrective actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES:
None 6. Energy Industry Identification System (EIIS) codes
- Auxiliary Feedwater System — BA
- Pump — P
- Motor — MO
- Electrical Cable — CBL5