05000391/LER-2017-001

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LER-2017-001, Containment Airlock Function Lost Due to Equalizing Valve Not Closing
Watts Bar Nuclear Plant, Unit 2
Event date: 03-09-2017
Report date: 05-03-2017
Reporting criterion: 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
Initial Reporting
ENS 52618 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material
3912017001R00 - NRC Website
LER 17-001-00 for Watts Bar, Unit 2, Regarding Containment Airlock Function Lost Due to Equalizing Valve Not Closing
ML17123A367
Person / Time
Site: Watts Bar Tennessee Valley Authority icon.png
Issue date: 05/03/2017
From: Simmons P
Tennessee Valley Authority
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML17123A367 (7)


I. PLANT OPERATING CONDITIONS BEFORE THE EVENT

Watts Bar Nuclear Plant (WBN) Unit 2 was at 100 percent rated thermal power (RTP) .

II. DESCRIPTION OF EVENT

A. Event Summary On March 9, 2017 at 0120 Eastern Standard Time (EST), the equalizing valve {El IS:V} for the Watts Bar Nuclear Plant (WBN) Unit 2 upper containment {EIIS:NH} airlock {EIIS:AL} inboard door was found not closed while the outboard airlock door was open. This created a containment bypass with leakage potentially greater than allowed by the design. The operator immediately identified that the pressure equalizing valve for the inner door was not fully closed when the outer door of the elevation 757 airlock was opened. The outer door was promptly shut to isolate the airlock. The inner door was then cycled which closed the equalizing valve. The total time that a containment bypass was present is estimated to be five minutes.

This condition was initially recognized as being potentially reportable on March 9, 2017. However, the assessment performed at the time, based on operator control of the outer airlock door, concluded there was a reasonable assurance of meeting the safety function. An independent review of this condition on March 17, 2017 identified that this should have been reported under 10 CFR 50.72(b)(3)(v)(C) within eight hours of the event. This event was reported on March 17, 2017.

This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of a safety function needed to control the release of radioactive material.

B. Inoperable Structures, Components, or Systems that Contributed to the Event No additional inoperable systems or components beyond the one identified valve contributed to this report.

C. Dates and Approximate Times of Occurrences Date Time Event 3/09/2017 0120 Technical Specification (TS) Limiting Condition for Operation (LCO) EST 3.6.2 Condition C and TS LCO 3.6.1 not met. Inboard equalizing valve of WBN 2 Elevation 757 airlock found leaking with outer airlock door open.

3/09/2017 0125 TS LCO 3.6.2 condition C and TS LCO 3.6.1 met after cycling the hand EST wheel on the inner airlock door (with the outer door closed) which allowed the equalizing valve to fully shut. The outer door was then opened and no leakage to containment was verified.

3/17/2017 1708 Event Notification (EN) 52618 was submitted for a loss of containment EDT airlock function under 10 CFR 50.72(b)(3)(v)(C).

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc goy, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 - 00 001 D. Manufacturer and Model Number of Components that Failed During the Event The three inch Class 2 containment airlock pressure equalizing device was manufactured by Trentec.

E. Other Systems or Secondary Functions Affected

No other systems or secondary functions were affected .

F. Method of discovery of each Component or System Failure or Procedural Error The leaking equalizing valve was found by a plant operator during a routine containment entry.

G. Failure Mode and Effect of Each Failed Component A damaged element of the equalizing valve operating linkage was discovered after this event occurred.

H. Operator Actions

Upon discovery, Operations personnel promptly entered the appropriate TS LCO conditions for the inoperable containment and containment airlock. The inner door mechanism was cycled and the equalizing valve properly seated in the closed position.

I. Automatically and Manually Initiated Safety System Responses There were no safety system responses associated with this issue.

III. CAUSE OF THE EVENT

A. The cause of each component or system failure or personnel error, if known.

The cause of the equalizing valve failing to seat is due to a damaged pin in the equalizing device closure mechanism.

B. The cause(s) and circumstances for each human performance related root cause.

The failure to recognize the need to report this event at the time of occurrence is attributed to not performing a review of operating experience associated with loss of airlock function. The event was subsequently reported on March 17, 2017.

IV. ANALYSIS OF THE EVENT

While entering containment to perform a routine surveillance activity, a plant operator heard the sound of air moving through the equalizing valve for the inboard containment airlock door. The operator then closed the outer door, cycled the inner door to seat the equalizing valve, and then reopened the outer airlock APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

door. No indication of leakage was found after cycling the inner airlock door. An inspection of the equalizing valve closing mechanism identified a part that needed replacement.

As a result of this condition, an unquantified amount of leakage existed through the inner containment airlock door equalizing line which was not closed. An estimated 3-inch open containment penetration was created with the equalizing valve not fully shut and the outer airlock door open for egress into the upper containment.

V. ASSESSMENT OF SAFETY CONSEQUENCES

The event resulted in a bypass of the containment function for approximately five minutes. During the event, the equipment involved was under constant control by a plant operator. In the event of an accident, the operator would have been able to promptly close the outer containment airlock door. The probability of an accident with core damage and a large early release is estimated to be much less than 1E-7, or very small.

A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event The outer containment airlock door remained fully operable at the time of the event.

B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident Not applicable.

C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service The containment bypass condition existed for about five minutes.

VI. CORRECTIVE ACTIONS

This event was entered into the Tennessee Valley Authority (WA) Corrective Action Program and is being tracked under Condition Reports (CRs) 1270608 and 1273873.

A. Immediate Corrective Actions

When the leaking equalizing valve was found, the inner door was cycled and the equalizing valve properly seated. The issue with this seating function has not recurred.

B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future A damaged element of the valve closure mechanism was identified following this event. The airlock remains functional, and an operations caution order was put in place related to use of this air lock.

The airlock will be repaired prior to Unit 2 returning to Mode 4.

Rto,, ) LICENSEE EVENT REPORT (LER)

  • CONTINUATION SHEET comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collecton does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 - 00 001

VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE

No previous events associated with the containment airlocks were identified at WBN.

VIII. ADDITIONAL INFORMATION

None.

IX. COMMITMENTS

None.