05000423/LER-2016-004

LER-2016-004, Manual Reactor Trip Due to Low Hydrogen Gas Pressure In Main Generator

Millstone Power Station Unit 3
Event date:	05-15-2016
Report date:	07-13-2016
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
4232016004R00 - NRC Website

LER 16-004-00 for Millstone Power Station Unit 3 RE: Manual Reactor Trip Due to Low Hydrogen Gas Pressure In Main Generator

ML16208A057
Person / Time
Site:	Millstone
Issue date:	07/13/2016
From:	Olsen C T Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 16-004-00
Download: ML16208A057 (6)

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

Send comments regarding burden estimate to the FOIA, Privacy 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 May 15, 2016, with Millstone Power Station Unit 3 (MPS3) operating in MODE 1 at 74% power, the operators observed decreasing hydrogen pressure in the main generator. The operators added hydrogen but it continued to decrease. Operators in the field identified a hydrogen leak from the main generator.

Due to the active hydrogen leak, at 0645 hours0.00747 days <br />0.179 hours <br />0.00107 weeks <br />2.454225e-4 months <br /> eastern daylight time (EDT), the operators manually tripped the reactor and vented the hydrogen from the main generator to the atmosphere. The auxiliary feedwater (AFW) pumps started as designed on low steam generator level and operators maintained steam generator level. The reactor trip was uncomplicated.

The actuation of the reactor protection system was reported in accordance with 10 CFR 50.72(b)(2)(iv)(B), as an event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation. The automatic start of the AFW pumps was reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed in 10 CFR 50.72(b)(3)(iv)(B). (Event Number: 51929) The actuation of the RPS and the automatic start of the AFW 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 active hydrogen leak was the direct cause of the manual reactor trip. The hydrogen leak was caused by a dislodged plug from a port on the main generator. MPS procedures did not contain adequate procedural guidance in that there was no specific direction for installation of the plug, i.e.; torque value and verifications.

3. ASSESSMENT OF SAFETY CONSEQUENCES

The operating crew responded to decreasing hydrogen pressure in the main generator as directed by approved procedures. The reactor was at 74% power. All control rods fully inserted into the reactor and all emergency systems functioned as designed. There were no radiological challenges as a result of the event. There were no detrimental effects to station equipment. No safety limits were exceeded. The operator actions and plant mitigating equipment responded as expected with no safety system failures.

There were no challenges to any fission product barrier. Therefore, there were no safety consequences as the result of the reactor trip.

4. CORRECTIVE ACTION

The plug was properly re-installed. Maintenance procedures will be revised to include specific direction to install the outer end shield pipe plugs and sealant and include direction to tighten the plugs and applicable verifications (i.e., torque value, peer checking). Additional corrective actions are being taken in accordance with the station's corrective action program.

Millstone Power Station Unit 3 05000423 Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy 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-10802, (3150-0104), Office of Management and Bpdget, 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.

NONE

6. Energy Industry Identification System ,(EllS) codes

• Reactor Coolant System — AB

• Auxiliary/Emergency Feedwater System — BA

• Main Generator System — TB

• Main Generator Hydrogen Cooling System — TK

• Turbine — TRB

• Pump — P

• Valve — V Millstone Power Station Unit 3 05000423