05000423/LER-2016-003

LER-2016-003, Loss of Safety Function- Supplementary Leak Collection and Release System

Docket Number
Event date:	04-09-2016
Report date:	06-08-2016
Reporting criterion:	10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
LER closed by
IR 05000245/2016002 (25 July 2016)
4232016003R00 - NRC Website

LER 16-003-00 for Millstone Power Station, Unit 3, Regarding Loss of Safety Function-Supplementary Leak Collection and Release System

ML16165A488
Person / Time
Site:	Millstone, Docket Number
Issue date:	06/08/2016
From:	Daugherty J R Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
16-207 LER 16-003-00
Download: ML16165A488 (6)

On April 9, 2016, while in MODE 1 and reducing power to enter a scheduled refueling outage (RFO), Millstone Power Station Unit 3 (MPS3) performed the 'B' train Supplementary Leak Collection and Release System (SLCRS) Negative Pressure Verification Surveillance. This test was completed at approximately 1521 hours0.0176 days <br />0.423 hours <br />0.00251 weeks <br />5.787405e-4 months <br /> and did not meet the acceptance criterion of -0.4 inches water gauge..

Technical Specification (TS) Limiting Condition for Operation (LCO) 3.6.6.1 states "With one Supplementary Leak Collection and Release System inoperable, restore the inoperable system to OPERABLE status within 7 days or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

Later, on April 9, 2016, at approximately 2141 hours0.0248 days <br />0.595 hours <br />0.00354 weeks <br />8.146505e-4 months <br /> with the reactor in MODE 1, MPS3 operators conducted the 'A' train SLCRS Negative Pressure Verification Surveillance and it also did not meet the acceptance criterion of -0.4 inches water gauge. Because both trains of SLCRS failed the required surveillances, TS LCO 3.6.6.2 was entered (SLCRS directly affects the operability of Secondary Containment). The LCO states that "Secondary Containment shall be OPERABLE in MODEs 1, 2, 3, and 4, and with Secondary Containment inoperable, restore Secondary Containment to OPERABLE status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />." Operations continued with the planned plant shutdown associated with the RFO and entered COLD SHUTDOWN, MODE 5 at 1241 hours0.0144 days <br />0.345 hours <br />0.00205 weeks <br />4.722005e-4 months <br /> on April 10, 2016.

Since both trains of SLCRS failed to meet TS acceptance criteria, this condition is reportable pursuant to 10CFR50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of a safety function for systems or structures to control the release of radioactive material, and 10CFR50.73(a)(2)(v)(D) to mitigate the consequences of an accident.

2. CAUSE:

SLCRS did not meet the acceptance criteria of -0.4 inches water gauge due to the aggregate impact of a number of dampers not providing effective isolation.

3. ASSESSMENT OF SAFETY CONSEQUENCES:

Although the SLCRS draw down tests did not meet the acceptance criterion of -0.4 inches water gauge, the test results and the consideration of conservatisms in the design basis radiological consequences analyseS support a conclusion of low safety significance.

SLCRS is designed to mitigate the radiological consequences of postulated accidents by filtering the exhaust air from the Secondary Containment. SLCRS is comprised of two redundant trains of exhaust fans and filter units. The safety function of SLCRS is to maintain a negative pressure in the secondary containment to ensure there is no unaccounted, unfiltered leakage to the outside environment from these areas in the event of a loss of coolant accident.

The SLCRS system and the auxiliary building filtration portion of the auxiliary building ventilation system start on receipt of a Safety Injection Signal. SLCRS is required to draw down the secondary containment to a negative pressure within 120 seconds after the accident.

The negative pressure provided by SLCRS ensures the containment releases occur through the release pathways modeled in the design basis analysis. As long as negative pressure is maintained in all the buildings associated with SLCRS, then the dose consequences are consistent with the analyzed results, which are within the regulatory limits for control room (5 REM TEDE) and offsite doses (25 REM TEDE).

The test acceptance criterion is based primarily upon developing sufficient negative pressure to counteract a relatively high wind speed. The as-tested values of negative pressure from either of the SLCRS trains would have been sufficient to develop negative pressure for the majority of the wind conditions during Cycle 17 operation.

Additionally, there are other conservatisms in the design basis dose calculation relative to expected (i.e., best-estimate) dose consequences. Notably, atmospheric dispersion factors would be significantly less adverse than those used in the design basis dose consequences analysis if the relatively high wind speeds considered in the development of the test acceptance criterion were actually occurring at the site. An additional conservatism is that the containment integrated leak rate testing performed in 2011 showed a leakage rate nearly 1/5th of that assumed in the design basis dose consequences analysis.

4. CORRECTIVE ACTION:

Following troubleshooting and maintenance of both SLCRS trains, the surveillance test was performed satisfactorily on both trains prior to entering MODE 4 when starting back up from RF017.

Detailed procedural steps are being developed for verifying the closed position of SLCRS isolation dampers following maintenance. The master post maintenance testing matrix for dampers is being updated to refer to these detailed procedural steps. Associated surveillance procedures are being revised to improve monitoring program for SLCRS isolation dampers.

5. PREVIOUS OCCURRENCES:

There have been no previous occurrences within the last three (3) years with the same underlying reason or consequences.

6. ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES:

• Damper- DMP

• Containment Leakage Control- BD