05000370/LER-2012-001
| Docket Number Sequential .Drev• | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3702012001R00 - NRC Website | |
BACKGROUND
The following information is provided to assist readers in understanding the event described in this LER.
Applicable Energy Industry Identification [EllS] system and component codes are enclosed within brackets.
McGuire unique system and component identifiers are contained within parentheses.
The Reactor Coolant System (NC) [AB] consists of four heat transfer loops connected in parallel to the reactor vessel [RCT]. Each loop contains a reactor coolant pump (RCP) [P], steam generator [SG] and associated piping and valves. In addition, the system includes a pressurizer, a pressurizer relief tank, and interconnecting piping.
Reactor Coolant System pressure is controlled by the use of the pressurizer [PZR] where water and steam are maintained in equilibrium by electrical heaters or water sprays. Steam can be formed (by the heaters) or condensed (by the pressurizer spray) to minimize pressure variations due to contraction and expansion of the reactor coolant. Pressurizer spray is provided from branch lines off of reactor coolant loops A and B downstream of the respective RCPs. Additional auxiliary pressurizer spray can also be provided from the Residual Heat Removal (ND) [BP] system and Chemical and Volume Control (NV) [CB] system for use during plant cool down when the RCPs are not operating.
Technical Specification (TS) 3.6.3 requires containment isolation valves (CIVs) to be operable in Modes 1 through 4. Per TS 3.6.3 Condition A, if a penetration flow path with two CIVs has one of two CIVs inoperable, the penetration flow path shall be isolated within four hours.
TS 3.6.3 Bases states that normally closed isolation valves are considered operable when manual valves are closed, automatic valves are closed and de-activated, blind flanges are in place, and closed systems are intact.
The TS 3.6.3 Actions are modified by a Note stating that penetration flow paths may be unisolated intermittently under administrative controls. These controls consist of stationing a dedicated operator at the valve controls, who is in continuous communication with the control room. In this way, the penetration can be rapidly isolated when a need for containment isolation is indicated. For valve controls located in the control room, an operator may monitor containment isolation signal status rather than be stationed at the valve controls.
EVENT DESCRIPTION
On October 26, 2012, while in Mode 5 during a scheduled Unit 2 refueling outage, an emergent issue was identified associated with the 2A RCP. After the 2A RCP was started, No. 1 seal leak-off flow would not remain above the minimum flow limit at low NC system pressures. Operations and Engineering decided that the 2A RCP should be secured and not restarted until Unit 2 NC system pressure increased to greater than 700 psig. This issue rendered pressurizer spray associated with the 2A RCP/NC loop unavailable at NC system pressures less than 700 psig.
was to remain in Mode 4 at low NC system temperatures and pressures due to the ongoing refueling outage Turbine Generator work.
On November 1, 2012, Engineering requested that Operations secure the 2B RCP due to a known generic industry concern of potential RCP shaft cracking during extended operation at low NC system temperatures. Per Westinghouse, the RCP manufacturer, counter clockwise NC system loop flow makes older RCP shafts susceptible to this concern. The 2B and 2D RCPs are contained in such loops.
Due to the unavailability of both the 2A and 2B RCPs at the current NC system parameters, Operations determined that pressurizer spray would need to be provided by either the NV or ND system auxiliary pressurizer spray feature.
Operations identified a concern using the NV system auxiliary pressurizer spray feature due to a differential temperature restriction between the pressurizer and NV system. The "Heat-up to 350 F" Operating Procedure also contained a note stating that NV system auxiliary pressurizer spray flow is only effective if the ND system is not in residual heat removal mode. Unit 2 was currently in residual heat removal mode.
The ND system auxiliary pressurizer spray containment penetration consists of an inside containment check valve and two outside containment valves; manual valve 2NV-1053 and air operated valve 2NV-840. Valve 2NV-1053 is the credited outside CIV. Both 2NV-840 and 2NV-1053 needed to be open to establish ND auxiliary pressurizer spray.
In order to establish ND system auxiliary pressurizer spray, Operations reviewed the Test Acceptance Criteria (TAC) design basis guidance document for valve 2NV-1053. The TAC document, which contains Operability guidance, states in part that in Modes 1 through 4: "If 2NV-1053 is open and incapable of closing or incapable of isolating, the valve and associated containment penetration is inoperable." Operations considered valve 2NV 1053 to be operable because the valve was capable of manual closing and isolating. TAC design basis documents are developed, checked, and approved by Engineering. The "Cool Down to 240 F" Operating Procedure was also reviewed and it did not restrict the use of ND auxiliary pressurizer Spray in Mode 4.
TS 3.6.3 was also reviewed. Since the TAC document led Operations to believe that valve 2NV-1053 was operable as long as it could be closed, they did not think that the TS 3.6.3 Actions needed to be considered or entered. Nor did they believe the Note concerning administrative controls to open a CIV needed to be applied.
This determination of valve 2NV-1053 operability included several Senior Reactor Operators (SROs) and the on duty Operations Shift Manager (OSM).
On November 2, 2012, Operations established ND auxiliary pressurizer spray by opening valve 2NV-1053 and then secured the 2B RCP. A "TS Action Log" tracking entry was made for TS 3.6.3 so that the Control Room Operators were aware that a manual CIV had been opened in Mode 4.
On November 4, 2012, an Operations individual questioned the opening of valve 2NV-1053 during Mode 4.
Subsequent investigation determined that TS 3.6.3 Condition A should have been entered when valve 2NV-1053 was opened because it should have been considered inoperable per the TS Bases. The Bases states in part:
"normally closed isolation valves are considered operable when manual valves are closed, automatic valves are closed and de-activated.
On November 4, Operations entered TS 3.6.3 Condition A which required valve 2NV-1053 closed within four hours. Operations restarted the 2B RCP re-establishing normal pressurizer spray, then closed 2NV-1053 within four hours and exited Technical Specification 3.6.3 Condition A.
After returning Unit 2 to Mode 5, ND auxiliary pressurizer spray was re-established since there are no restrictions with opening valve 2NV-1053 in Mode 5. The 2B RCP was again secured due to the generic industry concern of potential RCP shaft cracking during extended operation at low NC system temperatures.
REPORTABILITY DETERMINATION
With one CIV inoperable in Modes 1 through 4, TS 3.6.3 Condition A requires isolation of the affected flow path within four (4) hours. Manual CIV 2NV-1053 was open (thus inoperable) for approximately 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> from November 2, 2012 to November 4. Since the Condition A Completion Time of four hours to close the CIV was not met on November 2, this condition represented an "Operation or Condition Prohibited by Technical Specifications" reportable under 10 CFR 50.73(a)(2)(i)(B).
CAUSAL FACTORS
The cause of this event was incorrect design basis operability and procedure guidance which allowed Operations to wrongly interpret that they could open a manual containment isolation valve in a Mode prohibited by Technical Specifications.
Use of TAC design basis documents for operability guidance is common for SROs since they contain more specific system and component operability guidance than described in Technical Specifications. The 2NV-1053 TAC document states that in Modes 1 through 4, if this valve is open and incapable of closing or incapable of isolating, the valve and associated containment penetration is inoperable. The operability requirements are incorrect based on the TS 3.6.3 Bases which state that normally closed isolation valves are considered operable when manual valves are closed. The TAC operability wording led the SROs to consider 2NV-1053 operable in the ND auxiliary pressurizer spray alignment since it was capable of closing and isolating.
Similar incorrect guidance in the "Cool Down to 240 F" Operating Procedure validated the TAC document operability guidance.
CORRECTIVE ACTIONS
Immediate:
1. Operations entered TS 3.6.3 Condition A (declared 2NV-1053 inoperable) which required valve 2NV-1053 closed within four hours.
2. Operations restarted the 2B RCP re-establishing normal pressurizer spray, then closed 2NV-1053 within four hours and exited Technical Specification 3.6.3 Condition A.
Subsequent:
1.The Unit 1 and 2 "Cool Down to 240 F" Operating Procedures were placed on "Technical Hold" until revisions could be completed.
2. Operations issued an "Immediate Information Package" to all personnel regarding this event.
3. The instructions for all manual CIVs listed in the Operations Tag-out program were revised to state:
"If this valve is open in Modes 1 through 4, the valve and associated penetration is inoperable.
Refer to TS 3.6.3 for additional guidance.
Planned:
1.Revise the 2NV-1053 TAC design basis document to state: "If this valve is open in Modes 1 through 4, the valve and associated penetration is inoperable. Refer to TS 3.6.3 for additional guidance.
2. Revise the Unit 1 and 2 "Cool Down to 240 F" Operating Procedures to remove the option to use ND auxiliary pressurizer spray in Mode 4.
SAFETY ANALYSIS
The Unit 2 ND system auxiliary pressurizer spray containment penetration consists of an inside containment check valve and two outside containment valves; manual valve 2NV-1053 and air operated valve 2NV-840. Valve 2NV-1053 is the credited outside CIV.
Per the McGuire UFSAR, this penetration and CIVs are not required to be local leak rate tested because they qualify as Leak Class 1 a. Leak Class 1a is characteristic of valves which would not release containment atmosphere during a loss of coolant accident (LOCA) if valve leakage were to occur. This is because the piping and equipment external to the outer isolation valve (2NV-1053) are seismically designed. The piping is also protected from pipe whip, missiles, and jet forces.
During the period that CIV 2NV-1053 was open in Mode 4, the Operators in the Control Room were aware of its status and knew to close this valve if a containment isolation signal was received. Although it would have taken some amount of time to close this manual valve, air operated valve 2NV-840 could have been closed quickly from the Control Room.
Valve 2NV-1053 is a CIV whose applicable fUnction is to provide containment isolation to prevent a containment release. The auxiliary spray to pressurizer penetration is a water solid penetration, which is a tortuous path and is insignificant with respect to containment release consequences. The penetration pathway remained water solid and pressurized during the entire exposure period. Therefore, the risk associated with this event is considered to be of no significance with respect to the health and safety of the public.
ADDITIONAL INFORMATION
To determine if this event was recurring, a search of the McGuire Problem Identification Process (PIP) database was conducted for a time period covering five years prior to the date of this event (TS violation) using the corresponding cause codes, "Technical inaccuracies" and "Other intended or required verification not performed." The search brought back three potential similar events. A thorough review of these three events concluded that none were similar enough to call this event recurring.