ML15324A302
| ML15324A302 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 11/19/2015 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Brown, Tony, NRR/JLD 415-1924 | |
| References | |
| Download: ML15324A302 (2) | |
Text
The purpose of this communication is to: 1) discuss the status of Dominions response to Westinghouse Technical Bulletin (TB) 15-1, and 2) provide supplemental information regarding the unlikely failure of both Refueling Water Storage Tanks (RWSTs) due to tornado generated missiles at North Anna Power Station.
Westinghouse Technical Bulletin 15-1, Reactor Coolant System Temperature and Pressure Limits for the No. 2 Reactor Coolant Pump Seal Westinghouse Technical Bulletin (TB) 15-1 was issued on March 17, 2015 and recommended implementation of an additional extended cooldown of the Reactor Coolant System (RCS) to less than 350 degrees within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to maintain the integrity of the No. 2 reactor coolant pump (RCP) seal following a loss of all RCP seal cooling event. Dominion reviewed the TB and entered the information into the Corrective Action system for further evaluation.
Dominion has been assessing the recommendations of TB 15-1 with the understanding that Westinghouse is evaluating less stringent cooldown requirements and intends to issue a revision to the TB. Additionally, Dominion has been working closely with Westinghouse and the Pressurized Water Reactor Owners Group to determine the best solution that could qualify the No. 2 seal for higher temperatures and allow for relaxation of the cooldown time and temperature requirements.
North Anna Power Station intends to implement the vendor recommendations of the revised TB to ensure integrity of the RCP seal package while avoiding concerns of unintended consequences with TDAFW pump operation associated with the original TB recommendations.
Supplemental Information Regarding the Likelihood of Failure of Both North Anna Power Station RWSTs due to a Tornado Generated Missile The Refueling Water Storage Tanks (RWSTs) at North Anna Power Station are safety related structures that are seismically designed and protected from high winds, but are not protected from tornado generated missiles. In the responses to ISE CI 3.2.1.9.A, SE
- 8, and SE #11, Dominion has stated that the loss of both site Refueling Water Storage Tanks (RWSTs) is highly unlikely. But, even so, the North Anna Power Station FLEX strategies can conservatively accommodate the loss of both RWSTs.
The loss of both RWSTs due to a tornado generated missile is highly unlikely based on the following: 1) the two RWSTs are approximately 450 feet apart and are located on opposite ends of the power block; separated by the Auxiliary Building and the Containment buildings, 2) a portion of the Auxiliary Building and the entire Containment buildings are tornado generated missile protected structures and the RWST top elevations are below the top elevations of the Auxiliary Building and Containments, 3)
each RWST is further shielded by several other structures (including the Safeguards Buildings, Emergency Condensate Storage Tanks (ECSTs), the AFW Pumphouses, the Main Steam Valve houses, and the Service Building) on three of four sides. All of these structures except the Service Building are protected from tornado generated missiles, and 4) the side of each RWST that is not shielded by other structures is exposed to tornado generated missiles coming from opposite directions, thus inherently ensuring that one of the two RWSTs would not be vulnerable to tornado generated missiles.
Therefore, it is highly unlikely to consider that tornado generated missiles are capable of damaging both RWSTs and it is reasonable to conclude that one of the two RWSTs would remain available as a borated water source following a tornado generated missile event.
The purpose of this communication is to: 1) discuss the status of Dominions response to Westinghouse Technical Bulletin (TB) 15-1, and 2) provide supplemental information regarding the unlikely failure of both Refueling Water Storage Tanks (RWSTs) due to tornado generated missiles at North Anna Power Station.
Westinghouse Technical Bulletin 15-1, Reactor Coolant System Temperature and Pressure Limits for the No. 2 Reactor Coolant Pump Seal Westinghouse Technical Bulletin (TB) 15-1 was issued on March 17, 2015 and recommended implementation of an additional extended cooldown of the Reactor Coolant System (RCS) to less than 350 degrees within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to maintain the integrity of the No. 2 reactor coolant pump (RCP) seal following a loss of all RCP seal cooling event. Dominion reviewed the TB and entered the information into the Corrective Action system for further evaluation.
Dominion has been assessing the recommendations of TB 15-1 with the understanding that Westinghouse is evaluating less stringent cooldown requirements and intends to issue a revision to the TB. Additionally, Dominion has been working closely with Westinghouse and the Pressurized Water Reactor Owners Group to determine the best solution that could qualify the No. 2 seal for higher temperatures and allow for relaxation of the cooldown time and temperature requirements.
North Anna Power Station intends to implement the vendor recommendations of the revised TB to ensure integrity of the RCP seal package while avoiding concerns of unintended consequences with TDAFW pump operation associated with the original TB recommendations.
Supplemental Information Regarding the Likelihood of Failure of Both North Anna Power Station RWSTs due to a Tornado Generated Missile The Refueling Water Storage Tanks (RWSTs) at North Anna Power Station are safety related structures that are seismically designed and protected from high winds, but are not protected from tornado generated missiles. In the responses to ISE CI 3.2.1.9.A, SE
- 8, and SE #11, Dominion has stated that the loss of both site Refueling Water Storage Tanks (RWSTs) is highly unlikely. But, even so, the North Anna Power Station FLEX strategies can conservatively accommodate the loss of both RWSTs.
The loss of both RWSTs due to a tornado generated missile is highly unlikely based on the following: 1) the two RWSTs are approximately 450 feet apart and are located on opposite ends of the power block; separated by the Auxiliary Building and the Containment buildings, 2) a portion of the Auxiliary Building and the entire Containment buildings are tornado generated missile protected structures and the RWST top elevations are below the top elevations of the Auxiliary Building and Containments, 3)
each RWST is further shielded by several other structures (including the Safeguards Buildings, Emergency Condensate Storage Tanks (ECSTs), the AFW Pumphouses, the Main Steam Valve houses, and the Service Building) on three of four sides. All of these structures except the Service Building are protected from tornado generated missiles, and 4) the side of each RWST that is not shielded by other structures is exposed to tornado generated missiles coming from opposite directions, thus inherently ensuring that one of the two RWSTs would not be vulnerable to tornado generated missiles.
Therefore, it is highly unlikely to consider that tornado generated missiles are capable of damaging both RWSTs and it is reasonable to conclude that one of the two RWSTs would remain available as a borated water source following a tornado generated missile event.