05000293/LER-2014-001
| Pilgrim Nuclear Power Station | |
| Event date: | 05-06-2014 |
|---|---|
| Report date: | 07-07-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2932014001R00 - NRC Website | |
The basic function of all primary containment isolation valves is to provide necessary isolation of the containment in the event of accidents or similar critical conditions when the free release of containment atmosphere cannot be permitted.
The containment isolation valves are listed on Updated Final Safety Analysis Report Table 5.2-4. This table also defines the valve status (normally open or normally closed) during normal reactor operation and shows the signals required to initiate their desired operation. The primary containment isolation valves are grouped into three basic classes.
Class A valves are on process lines that communicate directly with the reactor vessel and penetrate the primary containment. These lines require two valves in series, one inside the primary containment and one outside the primary containment. They are located as close to the primary containment boundary as practical. Except in the case of check valves, both valves shall close automatically on isolation signal. Both valves shall receive the isolation (closure) signal even if normally closed during reactor operation. Since check valves close on reverse process flow, they are used to isolate some incoming lines. All Class A valves except check valves are capable of remote manual control from the control room.
Class B valves are on process lines that do not directly communicate with the reactor vessel, but penetrate the primary containment and communicate with the primary containment free space. These lines require two valves, in series, both of them located outside the primary containment, and as close to the primary containment boundary as practical. For process lines that have a water seal (such as Core Standby Cooling System pump suction lines), one isolation valve without an automatic isolation signal closure, in addition to the water seal is adequate to meet isolation requirements.
Except in the case of check valves or valves in water sealed process lines, both valves close automatically on isolation signal, both valves receive the isolation closure signal even if normally closed during reactor operation. All Class B motor operated or solenoid operated valves are capable of remote manual control from the control room.
Class C valves are on process lines that penetrate the primary containment but do not communicate directly with the reactor vessel, with the primary containment free space, or with the environs. Class C lines require only one valve located outside the primary containment which closes automatically by process action (i.e., reverse flow) or by remote manual operation from the control room
EVENT DESCRIPTION
On May 6, 2014, with Pilgrim Nuclear Power Station (PNPS) in the RUN Mode operating at 100 percent power, the NRC Resident Inspector raised a concern about the PNPS method of complying with PNPS Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.A.2.b when a Primary Containment Isolation Valve is inoperable. TS LCO 3.7.A.2.b.requires that at least one containment isolation valve in each line having an inoperable valve shall be deactivated in the isolated condition. Deactivation means to electrically or pneumatically disarm, or otherwise secure the valve. PNPS interpretation and practice had been that a "Danger" tag on the control switch meets this requirement for a fail-closed valve with no automatic valve opening signal. At the time, Primary Containment Isolation Valves AO- 5042A and AO-5044A were inoperable in the isolated position but were not deactivated.
The apparent cause of this event is failure to properly revise procedures and practices when TS LCO 3.7.A.2.b was revised by the issuance of TS Amendment 113 in 1988. Prior to this amendment, TS LCO 3.7.D.2 stated: "In the event any isolation valve specified in Table 3.7.1 becomes inoperable, at least one containment isolation valve in each line having an inoperable valve shall be placed in the isolated condition." TS Amendment 113 relocated the actions for an inoperable containment isolation valve to TS LCO 3.7.A.2.b and incorporated the requirement to deactivate (not just isolate) a valve in the line in the isolated condition. The basis for requiring deactivation was to provide positive control of an isolation barrier such that the barrier cannot be adversely affected by a spurious single active failure. The PNPS interpretation and practice of placing a "Danger" tag on the control switch for a valve with no automatic valve opening signal does not provide that additional level of protection.
EXTENT OF CONDITION
Seventy-one LCO entries into TS LCO 3.7.A.2.b occurred during the previous three year review period. Deactivation of a valve in the line did not occur for the following three additional LCO TS LCO 3.7.A.2.b entries:
LCO ACT-1-12-0110 Post Accident Sampling System Torus Gas Sample Valves LCO ACT-1-13-0158 Primary Containment Atmosphere Control Valve AO-5035B LCO ACT-1-13-0226 Post Accident Sampling System Valve SV-5065-82 The above valves were in the closed isolated position during the LCO or the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> shutdown TS LCO 3.7.A.5 was entered, if required.
CORRECTIVE ACTIONS
The immediate corrective action was to deactivate Primary Containment Isolation Valves AO-5042A and AO-5044A by isolating the air supply root valve to each of the valve actuators. The valves have been repaired and restored to operable status.
Additional corrective actions are being tracked in the Corrective Action Program under CR-PNP-2014-02008.
SAFETY CONSEQUENCES
This event posed no actual threat to the public health and safety.
During the period that Primary Containment Isolation Valves AO-5042A and AO-5044A were isolated but not deactivated, all safety systems were operable except for short durations to perform required surveillance testing. In the isolated condition, the valves were capable of performing the required safety function. The valves had been declared inoperable due to the closing time from the open position being greater than the surveillance acceptance criteria. Since each penetration has two isolation valves and each valve was closed, the safety function was satisfied, since spurious actuation of both valves would be required to prevent the safety function from occurring.
This report is submitted in accordance with 10CFR50.73(a)(2)(i)(B) — Operation or Condition Prohibited by Technical Specifications. The failure to deactivate a valve in a containment penetration line when one isolation valve in the line is inoperable as required by TS LCO 3.7.A.2.b is a condition prohibited by the PNPS Technical Specifications.
PREVIOUS EVENTS
A review for similar events reported by Licensee Event Reports (LERs) submitted to the NRC was conducted. The review focused on LERs involving a failure to properly implement a TS amendment change resulting in "Operation or Condition Prohibited by Technical Specifications". The review did not identify the occurrence of any similar events.
ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES Not Applicable
REFERENCES
Condition Report CR-PNP-2014-02008 — Primary Containment Isolation Valves Not Deactivated Resulting in a Condition Prohibited by Technical Specifications