The inspectors identified a
URI associated with licensees capability to meet their station blackout (
SBO) mitigation strategy. This item remains unresolved pending the inspectors review of the additional information to determine compliance with
10 CFR 50.63, Loss of All Alternating Power. The
reactor coolant pumps (
RCP) No.1 seal leakoff line was designed to recover leakoff volume, at low pressure and temperature, and return it to the chemical and volume control system (
CVCS). The leakoff lines (one per pump) join into a common
header before exiting containment to the
CVCS. In 1992, Westinghouse Technical Bulletin, NSD-TB-91-07-R1, Over-Pressurization of
RCP No.1 Seal Leakoff Line, informed specific licensees (including Harris) of the potential over-pressurization of the No.1 seal leakoff line during high seal leakoff flow conditions as a result of abnormal performance of the No.1
RCP seal. Specifically, the leakoff line pipe segment downstream of the air operated valve (which fails open on loss of instrument air) and upstream of the flow element restriction orifice was designed to 150 psig and could overpressurize and fail under high flow conditions. While Harris had implemented recommendations contained in the bulletin, the licensee did not upgrade the piping for higher pressures nor evaluate the line capability to handle expected seal leakage flow rates associated with loss of seal cooling (LOSC) events documented in Westinghouse Owner Group Report
WCAP-10541 Reactor Coolant Pump Seal Performance Following a Loss of All
AC Power, Rev 2. The technical bulletin specifically stated that the validity of the information in
WCAP-10541 was dependent upon the assumption that the integrity of the leakoff line was maintained. The inspectors reviewed
WCAP-10541 and noted that the leakoff line could experience a pressure
transient between 800-2000 psig during a LOSC event before seal leakage flow rates stabilize at approximately 21gpm and 800psig. The report also indicated that the backpressure provided by the leakoff line (upstream of the orifice) is what limits seal leagage to 21gpm and reduction of this backpressure would result in higher seal leakage flow rates. In 2003,
Information Notice (IN) 2003-19,
Unanalyzed Condition of
Reactor Coolant Pump Seal Leakoff Line During Postulated Fire Scenarios or Station Blackout, informed licensees of specific LOSC events (
SBO and fires coincident with loss of all
AC events) that could over-pressurize and fail the leakoff line. The IN reemphasized the pressures that will be experienced by the leakoff line (800-2000 psig) and that the failure of the line would result in
RCP leak rates in excess of the 21gpm determined by Westinghouse and the 25 gpm assumed in
SBO coping analyses. The inspectors reviewed the licensees evaluation of
IN 2003-19 (
AR #1069790-09) and determined the licensees actions did not adequately address the potential for over-pressurizing the seal leakoff line. The licensee entered the issue into the
CAP as
AR #589248 and indicated that the alternate seal injection (ASI) system, installed in December of 2010 to meet the sites new
fire protection program requirements (
NFPA-805, Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants), automatically starts on a LOSC event (
SBO or fire related) and will maintain seal cooling. By maintaining seal cooling, the
RCP seal leakage flow rates are expected to remain at nominal operating values (2-5 gpm) and prevent seal leakage flow rates that would challenge the integrity of the No.1 seal leakoff line. The inspectors questioned the appropriateness of crediting the ASI system for
SBO events and the systems capability to prevent overpressurization of the leakoff line. Specifically: The inspectors noted that the ASI system was not credited for meeting the current licensing bases for
SBO. The ASI has a delayed start and the inspectors questioned whether seal cooling would be restored before seal leakage increases to the point of challenging the leakoff line. This issue remains unresolved pending the inspectors review of additional information to be provided by the licensee to address the issues described above and determine compliance with
10 CFR 50.63, Loss of All Alternating Power. This issue is being tracked as:
URI 05000400/2013002-04, No. 1
Reactor Coolant Pump Seal Leakoff Line Over-Pressurization.
