05000445/LER-2011-003
| Comanche Peak Nuclear Power Plant Unit | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(V) |
| Initial Reporting | |
| ENS 47352 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition |
| 4452011003R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
This event is reportable per 10CFR50.73(a)(2)(i)(B) as a condition that was prohibited by the plant's TS and 50.72(b)(3)(ii)(B) as an unanalyzed condition that significantly degrades plant safety.
B. PLANT CONDITION PRIOR TO EVENT:
On October 18, 2011 at 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br />, Comanche Peak Nuclear Power Plant (CPNPP) Unit 1 was in Mode 5 and Unit 2 was in Mode 1 at 100% power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO THE
EVENT
This condition occurred since original licensing and startup of Units 1 and 2.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE
TIMES:
On September 14, 2011, at approximately 1600, during performance of a self- assessment for 50.59 reviews, the assessor (Utility, Non-licensed) reviewed an open technical evaluation replacement item (TERI) on the personnel airlock. Since the evaluation was open, the assessor provided feedback to Procurement Engineering regarding a potential issue with the material of an installed valve on the containment side of the hydraulic system for the personnel airlock (1 BS-0053). The Master Equipment List was checked and it indicated that the installed valve was of an appropriate material. Therefore, a Condition Report was not initiated at that point.
On October 3, 2011, at approximately 1421 subsequent to examination with an alloy analyzer of the actual installed valve, it was determined that the Unit 1 hydraulic valve for the containment side of the personnel airlock [EllS: (NH)(AL)(V)] has an aluminum body which is not appropriate for use in containment. The containment personnel airlock hydraulic system on Unit 2 is different than Unit 1, and since this valve is not part of the Unit 2 containment boundary, this was considered a Unit 1 issue only. This valve is currently installed in Unit 1, location 1BS-0053, CNTMT PERS AIRLOCK 1-01 was in mode 5 prior to startup from the 1RF15 refueling outage, it was determined that the valve may not complete the 30 day mission time for containment isolation and the event was determined to be reportable per 50.72(b)(3)(ii)(B) as an unanalyzed condition that significantly degrades plant safety (NRC event 47352). At that time, Unit 1 was in Mode 5 and Operability of the Personnel airlock was not required. The airlock hydraulic system achieves containment integrity by being a closed system inside containment. A loss of pressure boundary integrity of 1BS-0053 would open the hydraulic system to containment and would no longer meet General Design Criteria 57 (GDC-57) for a closed system.
As a compensatory measure, the personnel airlock hydraulic system valve (1BS- 0053) inside containment was encased in stainless steel and filled with an approved sealant (to prevent exposure of the valve body to the sodium hydroxide in the containment spray) prior to entering Mode 4 during startup (when the personnel airlock is required to be operable). This protection of the valve body will assure that the mission time for containment isolation would be met.
On October 19, 2011, at approximately 1100, an extent of condition review of the components and appurtenances associated with the Personnel airlock and Emergency airlock for both Unit 1 and 2 was completed. Two pressure gauges on the Unit 1 Personnel and Emergency airlocks (1-PI-AL012 and 1-PI-AL027) and two pressure gauges on Unit 2 Personnel and Emergency airlocks (2-PI-AL012 and 2-PI- AL027), located inside the Reactor Containment Buildings, were found to have an external epoxy coated aluminum casing. The casing is not a pressure boundary part; however, failure of the casing would expose the internals to containment spray. The pressure sensing element and brazing material used to connect the sensing element to the gauge process connection is being evaluated. The pressure gauges in all 4 airlocks have been isolated by closed ASME Class 2 isolation valves. On October 19, at approximately 2002, it was determined that pressure instrumentation may not complete the mission time for containment isolation and the event was determined to be reportable per 50.72(b)(3)(ii)(B) as an unanalyzed condition that significantly degrades plant safety (NRC event 47357). Exposure of these pressure instruments to Design Basis Accident environment (Containment Spray containing sodium hydroxide) could compromise their integrity. This loss of integrity would violate the redundancy of the Containment pressure boundary integrity of the Reactor Buildings. The outer isolation barrier would still provide isolation from the safeguards building.
The pressure gauges in all 4 airlocks have been isolated by closed ASME Class 2 isolation valves to restore the redundancy of the Containment personnel airlock and Operability. Subsequently, the airlock pressure gauges inside containment were removed and replaced with a stainless steel plug to prevent a loss of the redundancy of the containment pressure boundary during and after a LOCA.
Based on subsequent conclusion that the containment airlock was inoperable due to the inner door materials, this condition is reportable per 10CFR50.73(a)(2)(i)(B) as a condition that was prohibited by the plant's TS for exceeding the Completion Times and 50.72(b)(3)(ii)(B) as an unanalyzed condition that significantly degrades plant safety.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE,
OR PROCEDURAL PERSONNEL ERROR
During performance of a self-assessment for 50.59 reviews, the assessor (Utility, Non-licensed) reviewed an open TERI evaluation on the personnel airlock. Since the evaluation was open, the assessor provided feedback to Procurement Engineering.
This feedback led to the review that identified an issue with the valve material of the existing installed valve. The valve has an aluminum body and is not appropriate for use in containment. This valve is currently installed in Unit 1, location 1BS-0053, CNTMT PERS AIRLOCK 1-01 INT DOOR SWING DUAL FCV. The extent of condition review for the issue found that two pressure gauges on the Unit 1 personnel airlocks (1-PI-AL012 and 1-PI-AL027) and two pressure gauges on Unit 2 personnel airlocks (2-PI-AL012 and 2-PI-AL027), located inside the Reactor Containment Buildings, were found to have materials which may be unsuitable for the application.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable - No component failures were identified during this event.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Not applicable - No component failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE
OF COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable — No component or system failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable — No component or system failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable — No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
The identified conditions are legacy issues. The inappropriate valve material condition existed since 1990 in Unit 1. The pressure instrumentation potentially (February 8, 1990) and Unit 2 (February 2, 1993).
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
The Unit 1 airlock valve's safety function is to provide containment pressure boundary integrity as part of a closed system inside containment.
The Unit 1 airlock hydraulic system penetrates the containment pressure boundary.
The airlock hydraulic system achieves containment integrity by being a closed system.
A loss of pressure boundary integrity of 1BS-0053 would open the hydraulic system to containment and would no longer meet General Design Criteria 57 (GDC-57) for a closed system. This valve can be isolated by closing 1BS-0038 and 1BS-0037 outside containment. These containment isolation valves are normally maintained closed except when the airlocks are in use. If they were open at the time of the accident, it is likely that they would be accessible and be closed by an operator prior to 15 days.
The function of the pressure instruments on Units 1 and 2 are to indicate differential pressure across the doors during manual operation of the airlock.
Exposure of these pressure instruments to Design Basis Accident environment (Containment Spray containing sodium hydroxide) would compromise their integrity as they are principally constructed of materials which may be unsuitable for the application. This loss of integrity would violate the redundancy of the Containment pressure boundary integrity of the Reactor Buildings. The outer isolation barrier would still provide isolation from the safeguards building.
In either scenario described above, approximately 15 days after a LOCA event, the containment radiological and pressure conditions would significantly be reduced. Out- leakage from the pressure instrumentation would be mitigated by the outer airlock boundary. Out-leakage from the Unit 1 airlock hydraulic valve would not be expected because containment pressure would have to be sufficient to evacuate the hydraulic fluid past the closed containment isolation valves and overcome the static head pressure in the hydraulic reservoir. Any out-leakage would still be filtered through the plant ESF ventilation system.
Based on the above, there were no actual safety consequences and the health and safety of the public was not affected and this event has been evaluated to not meet the definition of a safety system functional failure per 10CFR50.73(a)(2)(V).
IV. CAUSE OF THE EVENT
The personnel airlock valve and pressure gauges material was installed during original construction and discovered as a result of a licensee self-assessment. In 1990, it was discovered that the Unit 1 personnel airlock (PAL) was not being tested or operated in accordance with the design and technical specifications. The ASME isolation valves were being operated normally open instead of normally closed. The corrective action changed the design of the hydraulic system from Non-Nuclear Safety to ANSI Safety Class 2 and allowed the ASME isolation valves to remain normally open. Review of the design specification for the PAL indicates specific material requirements were not applied to components/subcomponents outside of the ASME boundary, such as is the case with 1BS- 0053. This condition was caused by a failure to properly assess the ANSI Safety Class 2 reclassification of aluminum containing components inside containment.
V. CORRECTIVE ACTIONS
As a compensatory measure, the personnel airlock hydraulic system valve (1BS-0053) inside containment was encased in stainless steel to prevent exposure of the valve body to the sodium hydroxide in the containment spray. In accordance with the CPNPP Corrective Action Program, the airlock pressure gauges inside containment have been removed and replaced with a stainless steel plug to prevent a loss of the redundancy of the containment pressure boundary during and after a LOCA. Permanent corrective action will assure these parts are replaced with those made of suitable materials.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.