05000285/LER-2008-002
| Telephone Number (Include Area Code) | |
| Event date: | 03-15-2008 |
|---|---|
| Report date: | 08-15-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2852008002R01 - NRC Website | |
U.S. NUCLEAR REGULATORY COMMISSIONNRC FORM 366A� LICENSEE EVENT REPORT (LER)�(9-2007) CONTINUATION SHEET Fort Calhoun Station 05000285 2� OF� 3
BACKGROUND
The Fort Calhoun Station Technical Specifications Section 2.6(1)a, "Containment Integrity" requires that containment integrity shall be maintained unless the reactor is in a cold or refueling shutdown condition.
Containment integrity is maintained through normally locked or sealed-closed valves during power operation. Without containment integrity, it must be restored within one hour or the plant must be in at least hot shutdown within the next six hours, or be subcritical and less than 300 degrees F within the next six hours 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 />. Normally locked or sealed-closed valves (except for PCV-742A/B/C/D) may be opened intermittently under administrative control without constituting a violation of containment integrity.
EVENT DESCRIPTION
On March 15, 2008 at 0833 CDT, following a plant trip from 85% power (described in FCS LER 2008- 001), a "Relief Valve CH-223 Discharge Temperature High Alarm" was received in the control room due to a closure of HCV-204, "Letdown Heat Exchanger CH-7 Inlet Valve", from a letdown system pressure transient. At 0903, with the plant in hot shutdown (mode 3), operators restored the letdown system in accordance with station procedures. At 1315 operators noted a two to three gallon per minute (gpm) reactor coolant system (RCS) leak and entered procedure AOP-22, "Reactor Coolant Leak". An investigation revealed that valve CH-223, "Regenerative Heat Exchanger CH-6 Letdown Relief Valve to Pressurizer Quench Tank", lifted and had not reseated. This allowed RCS leakage through CH-223 into the pressurizer quench tank, which is located within the containment building. Several attempts were made to manually seat CH-223, but leakage past the seat continued. On March 16, 2008 at 0115, operators secured the letdown system by closing the upstream isolation valve, TCV-202, "RCS Loop 2A Letdown Temperature Control Valve", and began intermittent charging to maintain pressurizer level.
TCV-202 is the inboard isolation valve located in the containment, and HCV-204 is the outboard isolation valve located in the auxiliary building. HCV-204 was left in the open position.
CH-223 is located within a branch connection between automatic isolation valves HCV-204 and TCV-202 and is classified as part of the containment boundary.
On March 16, 2008 at 1355, operators determined that CH-223 is a containment boundary valve and AOP-12, "Loss of Containment Integrity" and Technical Specification 2.6(1)a, "Containment Integrity" were entered.
�NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER U.S. NUCLEAR REGULATORY COMMISSIONNRC FORM 366A LICENSEE EVENT REPORT (LER)(9-2007)
CONTINUATION SHEET
2008 - 0020 - 01- At 1401 valve HCV-204 was closed restoring containment integrity. This was a conservative action since the automatic containment isolation valves were operable. Since containment integrity was not restored within the technical specification requirements this event is reportable per 10 CFR 50.73(a)(2)(i)(B).
CONCLUSION
The root cause of the event was determined through an in-depth investigation. The Technical Specifications, licensing and design basis, and related procedures were reviewed. The Fort Calhoun Station Final and Updated Safety Analysis Reports section 5.9.5 states, "Branch connections between the containment and the isolation valves are only included when necessary for system functioning or to enhance reliability, testing, or leak tightness. Such branch lines are equipped with valves to provide isolation integrity equal to at least that of the main system." The investigation concluded that since relief valve CH-223 is located on a branch line between two containment isolation valves, this valve is part of the containment boundary. This was not identified as such in plant procedures. Therefore, the root cause I of this event is that containment integrity design requirements were not adequately translated from the Final and Updated Safety Analysis Reports into appropriate plant operating procedures and guidance.
CORRECTIVE ACTIONS
Upon discovery that CH-223 is part of the containment boundary, containment isolation valve HCV-204 was closed to re-establish containment integrity.
The Updated Safety Analysis Report (USAR) Section 5.9, "Structures Containment Penetrations" and associated figures and drawings will be reviewed and modified to uniquely identify containment penetration valves that are required for containment integrity, including annotation of automatic or non automatic functioning. In addition, plant operating procedure 01-00-5, "Containment Integrity," will be modified to reflect the results of the USAR review.
These corrective actions and other enhancements to plant documents will be controlled by the corrective action system.
SAFETY SIGNIFICANCE
Containment integrity is established to preclude the release of radioactive nuclides to the environment in the event of a design basis loss of coolant accident (LOCA). During the period when containment integrity was degraded, no event occurred to challenge the containment envelope. In addition, the outside containment isolation valve (HCV-204) was capable of closing on an automatic containment isolation actuation signal (CIAS). The closure of HCV-204 would maintain total containment leakage rate less than 1 La (leakage allowable) as described in Technical Specification 5.19.a. Therefore, this event had very minimal impact on the health and safety of the public.
SAFETY SYSTEM FUNCTIONAL FAILURE
This event does not constitute a safety system functional failure as described in NEI-99-02.
PREVIOUS SIMILAR EVENTS
Fort Calhoun Station reported a similar loss of containment integrity event in LER 2006-01.
_NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER