05000395/LER-2011-003
| Virgil C. Summer Nuclear Station Unit 1 | |
| Event date: | 05-27-2011 |
|---|---|
| Report date: | 09-27-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3952011003R01 - NRC Website | |
PLANT IDENTIFICATION
Westinghouse - Pressurized Water Reactor
EQUIPMENT IDENTIFICATION
XVM02801C-MS, "C" Main Steam Isolation Valve (MSIV)
IDENTIFICATION OF EVENT
At 1201 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.569805e-4 months <br /> on 5/27/2011, a Safety Injection (SI) occurred on High Steam Line Differential Pressure due to opening XVM02801C-MS ('C' Main Steam Isolation Valve) with the downstream header depressurized. The resulting steam flow caused 'C' Steam Line pressure to decrease to greater than 97 psid below the 'A' and 'B' Steam Lines, satisfying the condition for an SI on both Engineered Safety Feature (ESF) Trains.
EVENT DATE
May 27, 2011 Condition Report CR-11-03001 was generated to address this violation.
REPORT DATE
September 27, 2011
CONDITIONS PRIOR TO EVENT
MODE 3, 0% Power
DESCRIPTION OF EVENT
On May 25, 2011, at 1103 hours0.0128 days <br />0.306 hours <br />0.00182 weeks <br />4.196915e-4 months <br />, the plant entered Mode 3 (HOT STANDBY) during plant start up from Refueling Outage 19. Operations began Main Steam header warming and made preparations for surveillance testing over the next two days.
On May 27, 2011, at approximately 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br />, Operations commenced MSIV Full Stroke Testing. 'C' MSIV failed its stroke test due to an out-of-tolerance stroke time, and was subsequently closed pursuant to TS 3.7.1.5, "Main Steam Line Isolation Valves," Action Statement 'a.' Shortly after the stroke test the Main Steam header was isolated to restore RCS temperature. This action depressurized the Main Steam header downstream of the MSIVs. Prior to the event, the Control Room was requested to stroke the 'C' MSIV to allow the Instrument and Controls (I&C) technicians and the System Engineer investigating the 'C' MSIV failure to observe the valve locally. At 1201 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.569805e-4 months <br />, the 'C' MSIV was then opened.
With the downstream header depressurized an SI actuation occurred due to 'C' Steam Line Pressure decreasing to greater than 97 psid below Main Steam Lines 'A' and 'B.'
CAUSE OF EVENT
A root cause analysis was conducted to determine the reason(s) for the inadvertent safety injection event of May 27, 2011. It was determined that the root cause of this event was the failure to follow procedures while manipulating a plant system.
After the stroke test failure of the "C" MSIV, the Control Room Supervisor (CRS) directed the Reactor Operator (RO) to leave the MSIVs closed and to close the three MSIV bypass valves. A Removal & Restoration Sheet (R&R) was issued due to "C" MSIV being closed as required by the Technical Specification Action Statement. The Operations crew did not discuss or recognize which procedure was maintaining configuration control of the MSIVs and bypass valves. Instrument and Controls (I&C) technicians called the RO requesting that "C" MSIV be stroked. The RO asked and received permission from the Shift Supervisor (SS) to stroke open the "C" MSIV. Operations stroked open the "C" MSIV resulting in a Safety Injection due to excessive steam line differential pressure.
ANALYSIS OF EVENT
The consequences of this event were minimal. The Reactor Protection System responded to the Hi Steam Line Differential Pressure condition by initiating a Safety Injection. The RCS responded with a temperature decrease from 557.7°F to approximately 538.5°F, a pressure decrease from 2234 psig to approximately 2180 psig, followed by a pressure increase to 2243 psig following the SI actuation. The SI initiated 320 gpm of injection flow into the RCS, resulting in an increase in pressurizer level from 25.6 percent to 86.2 percent at SI termination.
CORRECTIVE ACTIONS
The following corrective actions to prevent recurrence were identified by the Root Cause Analysis and have been entered into the corrective action program:
Revise operating guidelines to address procedural guidance to control the manipulation of plant components to support maintenance activities.
Revise station administrative procedures to better describe procedural expectations when manipulating plant components, and require a stand down with Operations prior to entering Mode 4 to reinforce expectations of increased rigor for control of work activities during changing plant conditions.
Evaluate the feasibility of developing an engineering solution to prevent opening MSIVs under a high differential pressure.
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