Potential defects shipped to Farley reactors and four others

No worries about this reactor coolant system defect; Westinghouse says so, and didn’t even list Vogtle or Diablo Canyon, where Southern Company and PG&E said they were going to install these shields. Nevermind a reactor operator warned us back in January. Westinghouse did list “Beaver Valley Unit 2, Callaway, D.C. Cook Unit 1, Farley Units 1 and 2, and Wolf Creek”.

NRC Event Notification Report for July 29, 2013 Event Number 49217:

POTENTIAL EXISTENCE OF DEFECTS IN SHIELD PASSIVE THERMAL SHUTDOWN SEAL SYSTEM

“The defect being reported concerns an identified inconsistency between the intended design functionality of the SHIELD passive thermal shutdown seal (SDS) and that observed during post-service testing.

“The purpose of the SDS is to reduce current reactor coolant system inventory losses to very small leakage rates for a plant that results in the loss of all reactor coolant pump (RCP) seal cooling. The SDS is a thermally actuated, passive device integral to the RCP Number 1 seal insert and is positioned between the Number 1 seal and the Number 1 seal leak-off line to provide a near leak-tight seal once activated.

“There are two delivered components associated with this report: 1. the SDS hardware, and 2. the Probability Risk Assessment (PRA) SDS model and the assigned SDS reliability. The hardware component is the SHIELD passive thermal shutdown seal. The associated PRA SDS model and assigned reliability basic component is WCAP-17100-P-A, Supplement 1, Rev. 0, ‘PRA Model for the Westinghouse Shut Down Seal Supplemental Information for All Domestic Reactor Coolant Pump Models’ (dated December 2012).

“The SDS has only been delivered and installed in the following plants: Beaver Valley Unit 2, Callaway, D.C. Cook Unit 1, Farley Units 1 and 2, and Wolf Creek.

“Westinghouse has concluded that the hardware itself will not adversely impact safe plant operation.

“Westinghouse has completed a root cause analysis (RCA) and an independent third party review of this RCA is expected to be completed by August 2013. In parallel, SDS design improvements are being considered and may be completed during the third quarter of 2013. Additionally, and if necessary, Westinghouse will revise WCAP-17100 and its Supplements, as needed, to reflect any new information that is developed.

“Affected customers have been informed via their respective Customer Project Managers of the post-service test failure.”

If you’re a Georgia Power customer, you’re a Southern Company customer, and Southern Company owns Farley units 1 and 2. Were you informed?

There’s a picture in here, but it’s copyrighted by Southern Company, in Pressurized Water Reactor Owners Group News, Fall 2011, U.S. NRC Approves PWROG PRA Model for New Westinghouse RCP Shutdown Seal for Referencing in Licensing Applications,

Installation of the SDS at Farley Unit 2 (see photo) along with implementation of the PRA Model took place this October. Scott said that Southern Nuclear also has plans to install the SDS at its Alvin W. Vogtle Electric Generating Plant (Units 1 and 2) near Waynesboro, Georgia (USA).

Pacific Gas and Electric also is scheduled to install the SDS at its Diablo Canyon Power Plant in San Luis, California (USA) in fall 2012, said Mendez.

[Picture redacted due to copyright]

Number 1 Seal Housing with Westinghouse SDS Insert at Farley Unit 2

Southern Company grants Westinghouse permission to use photographs of the SHIELD shutdown seal installation at Farley Unit 2, for the express purposes of Westinghouse’s PRA Model article for the PWROG News. This photograph is copyrighted by Southern Company.

Westinghouse just introduced this seal two years ago, and first installed it at Farley, according to Westinghouse PR 22 June 2011, Westinghouse Introduces SHIELD® Passive Thermal Shutdown Seal,

Westinghouse partnered with Southern Nuclear Operating Company (SNC) to successfully install the first-of-its-kind SHIELD® passive thermal shutdown seal in each RCP at the Joseph M. Farley Nuclear Power Plant (Unit 1) near Dothan, Alabama (USA), during the plant’s fall 2010 refueling outage. SNC has announced plans to apply the product to Farley Unit 2 during its next refueling outage.

The Farley Unit 1 SHIELD® seal installation garnered a 2011 Nuclear Energy Institute (NEI) Top Industry Practice (TIP) Award for Southern Nuclear. The installation of the SHIELD® shutdown seal reduced the estimated risk of core damage by some 40 percent, and the overall plant safety margin also has been improved.

More details by Marsha White, Westinghouse Technical Communications, in Power Engineering 1 September 2011, Passive Thermal Shutdown Seal Successfully Installed at Farley Plant.

Counterpoint by Bob Meyer for Professional Reactor Operator Society, Westinghouse Shutdown Reactor Coolant Pump (RCP) Seal – A PRA Perspective,

Some of the first operating experience at the Farley station raised some conerns for the seal performance within the nuclear community. Southern Company installed the seals at Farley in the plant’s October 2010 outage. The removal of the seal revealed it failed some of the performance objecties for the SDS. The The Farley post-operational SHIELD seal test in July of 2012 prompted forensic investigations and resulted in minor enhancements to improve reliability margins. The results of the forensic investigations concluded that the concept for the Westinghouse SHIELD passive thermal shutdown seal operation remains sound and the benefits remain intact. The analytical models already approved by the NRC in WCAP-17100-P-A, “PRA Model for the Westinghouse Shutdown Seal,” as well as those in this report are still valid for all plants with the enhanced SHIELD seal and for the Farley Units with the original design as long as they are not exposed to a dry oxidizing environment after initial installation and operation.

As I have stated many times, these seals are not operator proof. If an operator restarted an RCP with a warped shaft, the seal packages may exhibit well over 300 gpm leakage. For every solution, there are usually 10 more problems, lets look at some of the issues. One of the problems may be that operators will have a different set of critical, time sensitive actions to ensure these seals function as designed. The time window, available for operator action after these seals reach the “seal trip” setpoint, if not met, may result in a new set of problems. Most of issues with the RCP seals are that the reliability of the polymer rings which are time and temperature dependent. Even in this report only the Model 93A-1 repesented the most challanging sealing conditions. After the pump seal trips, can these pumps be restarted in the functional restoration procedures? What are the consequences if operators do not trip the RCPs in the intended time frames? The loss of seal cooling to the RCP seal trip is significantly lower than the current values used for loss of seal cooling. For non-SBO events, the low leakage characteristics of the SDS are dependent on successful operator action to trip the RCP within a time window as described in this report. However, an assumed failure to trip the RCP will only result in an RCS leakage rate of 19 gpm per pump (at nominal RCS hot standby conditions) if the SDS has actuated.

And that’s the problem with nuclear reactors:

“For every solution, there are usually 10 more problems”

Operator error or seal leakage or fire or lightning or bugs or rats can cause problems with high risk. Ever heard of a solar leak?

-jsq