05000338/LER-2016-002

LER-2016-002, , Chemical Addition System Outside of Technical Specification Due to Excessive Unseating Thrust on MOVs

North Anna Power Station, Unit 1
Event date:	03-09-2016
Report date:	05-05-2016
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3382016002R00 - NRC Website

LER 16-002-00 for North Anna, Unit 1, Regarding Chemical Addition System Outside of Technical Specification Due to Excessive Unseating Thrust on MOVs

ML16133A335
Person / Time
Site:	North Anna
Issue date:	05/05/2016
From:	Bischof G T Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
16-171 LER 16-002-00
Download: ML16133A335 (5)

1.0 DESCRIPTION OF THE EVENT On March 9, 2016, with Unit 2 at 0 percent power in Mode 6, the Unit 2 Chemical Addition Tank Outlet Valve, 2-QS-MOV-202B (EIIS System-BE, Component-V) failed to open when functionally tested. The actuator was unable to unseat the disc under normal bus voltage. This resulted in tripping the thermal overload for breaker, 2-EE-BKR-2J1-2S-B3 (EIIS System-EE, Component-BKR), due to excessive unseating thrust. The actuator stall thrust was estimated to be approximately 25,000 lbs. The valve would not have been able to open if called upon in a Design Basis Accident (DBA). - In support of continued troubleshooting of 2-QS-MOV-202B, an extent of condition review and an engineering evaluation was conducted on Unit 2 Chemical Addition Tank Outlet Valve, 2-QS-MOV-202A. Periodic Test, 2-PT-212.34H, "Valve Inservice Inspection (2-QS-MOV-202A)", had been performed prior to evaluation. Therefore, initial unseating thrust was unknown prior to testing. Based on 2-QS-MOV-202A successfully opening during the performance of 2-PT-212.34H, subsequent test data, and engineering evaluation it was determined that 2-QS-MOV-202A would have opened and performed its function if called upon in a DBA. Design Change (DC) NA-16-00021 was implemented to modify the gear ratio to increase the unseating thrust margin to the motor operated valves (MOVs) and valve stroke was changed to limit controlled seating, instead of torque controlled.

On March 25, 2016, at approximately 0805 hours0.00932 days <br />0.224 hours <br />0.00133 weeks <br />3.063025e-4 months <br />, with Unit 1 at 100 percent power' in Mode 1, the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Required Action for Technical Specification (TS) 3.6.8 was entered to perform an extent of condition review and as-found diagnostic testing on the Unit 1 Chemical Addition Tank Outlet Valves. While both valves exhibited higher than expected unseating thrust, they both opened on demand. Based on functional testing and engineering evaluation, it was determined that 1-QS-MOV-102B would have performed its function. Engineering could not definitively- determine that 1-QS-MOV-102A would have performed its function if called upon in a DBA; therefore, it is considered not capable of performing, its function. DC NA-16-00023 was implemented to modify the gear ratios to increase the unseating thrust margin for the valves and valve stroke was changed to limit controlled seating, instead of torque controlled. The Required Action for Unit 1 was cleared on March 26, 2016, at approximately 0055 hours6.365741e-4 days <br />0.0153 hours <br />9.093915e-5 weeks <br />2.09275e-5 months <br />.

While only one of the valves is needed in order for the system to perform its function, Technical Specification (TS) 3.6.8 requires both valves to function in order to be considered operable.

The function of the Chemical Addition System was maintained for both Units 1 and 2. Because 1-QS-MOV-102A and 2-QS-MOV-202B were unable to perform their function, the requirements of TS 3.6.8 were not met. Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), as a condition prohibited by TS.

2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS There is assurance that the function of chemical addition was maintained. The CAT MOVs are parallel full flow trains. Only one valve is required to open for chemical addition to occur. Based on as-found testing and engineering, evaluation of the design calculations, NaOH injection would have been supplied in the event of a DBA.

3.0,CAUSE The apparent cause of 2-QS-MOV-202B exhibiting excessive unseating' thrust, resulting in a failure to open during functional testing, was due to mechanical binding internal to the valve body and/or actuator. This is considered to be the cause for the excessive unseating thrust exhibited in 2-QS-MOV-202A, 1-QS -MOV-102A, and 1-QS-MOV-102B.

4.0 IMMEDIATE CORRECTIVE ACTION(S) Troubleshooting was performed, an extent of condition review- was conducted, and prior operability review performed on Unit 1 and Unit 2 Chemical Addition System valves 1-QS- MOV-102A, 1-QS-MOV-102B, 2-QS-MOV-202A and 2-QS-MOV-202B.

5.0 ADDITIONAL CORRECTIVE ACTIONS Design Changes (DC). (DC NA-16-00023 for Unit 1 and DC NA-16-00021 for Unit 2) were implemented to change the actuator gear set to provide more unseating capability for the valves.

In addition, the valve stroke was changed to limit controlled verses torque controlled seating, allowing valve seating to be adjusted to lighter loads providing even more margin.

-002 more frequently, every 6 months of operation (plus grace). This is to ensure that the valve design with the new gearing is acceptable for long term operation following implementation of DCs NA 16-00021 and NA 16-00023.

6.0 ACTIONS TO PREVENT RECURRENCE DCs were implemented to increase overall gear ratio in order to provide additional valve operating margin and allow greater unseating capacity.

7.0 SIMILAR EVENTS None 8.0 MANUFACTURER/MODEL NUMBER Component:

1-QS-MOV-102A, 1-QS-MOV-102B, 2-QS-MOV-202A, and 2-QS-MOV-202B Manufacturer: Velan Valve Corp.

Model: B14-0054B-13PSN 9.0 ADDITIONAL INFORMATION None