05000423/LER-2016-001

LER-2016-001, Automatic Reactor Trip on Reactor Coolant System Low Flow Due to Loss of 'B' Reactor Coolant Pump

Millstone Power Station Unit 3
Event date:	01-25-2016
Report date:	03-16-2016
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
Initial Reporting
ENS 51682	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation
4232016001R00 - NRC Website

LER 16-001-00 for Millstone Power Station Unit 3, Regarding Automatic Reactor Trip on Reactor Coolant System Low Flow Due to Loss of 'B' Reactor Coolant Pump

ML16082A268
Person / Time
Site:	Millstone
Issue date:	03/16/2016
From:	Daugherty J R Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
16-066 LER 16-001-00
Download: ML16082A268 (6)

1. EVENT DESCRIPTION:

On January 25, 2016 at 0147 hours0.0017 days <br />0.0408 hours <br />2.430556e-4 weeks <br />5.59335e-5 months <br /> an automatic reactor trip occurred at Millstone Power Station Unit 3 (MPS3) while the unit was in Mode 1, operating at 100 percent power. The Reactor Protection System (RPS) was initiated due to a reactor coolant system loop low flow. All control rods fully inserted into the reactor. The auxiliary feedwater pumps started as designed on low steam generator level and operators maintained steam generator level. All other post trip actions were standard and all safety systems operated as expected, stabilizing the plant.

The 'B' Reactor Coolant Pump (RCP) trip was caused by failure of one of three motor capacitors on the RCP motor. The failed capacitor on the affected RCP motor was replaced and the integrity of the motor windings, cabling, breaker, and associated protective relays were verified.

Based on an assessment of the event, the risk impact was determined to be very small. There were no radiological challenges and the health and safety of the public were not affected.

The actuation of the reactor protection system and the automatic start of the auxiliary feedwater pumps is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed in 10 CFR 50.73(a)(2)(iv)(B).

2. CAUSE:

The direct cause of the 'B' RCP trip, which resulted in an automatic reactor trip due to partial loss of forced reactor coolant flow, was due to the failure of one of the three RCP motor capacitors. Failure of the capacitor provided a short to ground.

3. ASSESSMENT OF SAFETY CONSEQUENCES:

Final Safety Analysis Review (FSAR) Section 15.3.1 presents an analysis of a Partial Loss of Forced Reactor Coolant Flow (one RCP). The analysis presented spans 10 seconds from the onset of the flow coast down to beyond the time of minimum Departure from Nucleate Boiling Ratio (3.6 seconds).

The event as presented in the FSAR contains conservative assumptions typical of safety analysis.

These include rapid coast down characteristics, maximum trip delay times, most adverse time in cycle reactivity feedbacks, etc.

Plant computer data and log entries were examined to verify that the actual plant response was bounded with respect to that in the safety analysis. Examination of the plant response showed that the January 25th partial loss of forced reactor coolant flow due to the loss of 'B' RCP transient was well bounded by the FSAR analysis.

The event was considered uncomplicated as defined by the Reactor Oversight Process. In addition, all equipment designed to remove decay heat was available prior to the event and functioned properly during the event. The event was not a significant operational event. Therefore, the event posed no actual or potential hazard to public health and safety.

4. CORRECTIVE ACTION:

The failed motor capacitor was replaced on the 'B' RCP.

Additional corrective actions are being taken in accordance with the Millstone Corrective Action Program.

5. PREVIOUS OCCURRENCES:

Millstone Power Station Unit 3 has no previous occurrences.

6. Energy Industry Identification System (EIIS) codes:

• Reactor Coolant System — AB

• Pump — P

• Auxiliary Feedwater System — BA

• Steam Generator- SG

• Capacitor- CAP

7. MANUFACTURER/PART NUMBER

• Capacitor: Westing house/6060B7H01N