05000390/LER-2017-013

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LER-2017-003, 1 OF 5
Watts Bar Nuclear Plant, Unit 1
Event date: 09-06-2017
Report date: 01-24-2018
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3902017003R01 - NRC Website
LER 17-013-01 for Watts Bar Nuclear Plant, Units 1 and 2 Regarding Incorrectly Adjusted Auxiliary Building Gas Treatment System Damper Leads to a Condition Prohibited by Technical Specifications
ML18024A360
Person / Time
Site: Watts Bar Tennessee Valley Authority icon.png
Issue date: 01/24/2018
From: Simmons P
Tennessee Valley Authority
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML18024A360 (7)


Infocollects Resource@nrc gov, and to the Desk Officer, Office of Informahon 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

I PLANT OPERATING CONDITIONS BEFORE THE EVENT Watts Bar Nuclear Plant (WBN) Unit 1 was at 100 percent rated thermal power (RTP) WBN Unit 2 was also in Mode 1 at 100 percent power.

II DESCRIPTION OF EVENT

A Event Summary On September 6, 2017, Watts Bar Nuclear Plant (WBN) identified that the vacuum relief line airflows did not meet acceptance criteria for the Auxiliary Building Gas Treatment System (ABGTS){EIIS VF} for Train A during the performance of 0-S1-30-7-A, ABGTS Pressure Test Troubleshooting of the low airflows identified an Auxiliary Building Secondary Containment Enclosure (ABSCE) Unit 2 General Ventilation intake damper 2-FCO-30-108 {EllS:CDMP} with approximately one inch gaps in the blade seals with the damper in the closed position Preliminary investigation found that the damper linkage appeared to not be adjusted correctly to allow full closure of the damper blades following maintenance in May of 2017 The low vacuum relief line airflows resulted in the Train A ABGTS being inoperable, based on identified open ABSCE breaches, from July 7, 2017 at 2030 Eastern Daylight Time (EDT) to September 5, 2017 at 1645 EDT This time period is longer than that allowed by Technical Specification (TS) 3 7.12 for ABGTS, and is therefore a condition prohibited by TS This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

B Inoperable Structures, Components, or Systems that Contributed to the Event No inoperable equipment contributed to this event C. Dates and Approximate Times of Occurrences Date Time Event 5/19/17 Actuator associated with damper 2-FCO-30-108 replaced to address air leaks. A visual inspection of the damper by inspecting the blade seals through the ventilation manway was not performed Only external checks were performed 7/07/17 2030 ABSCE breach exceeds 63.9 square inches for Train A.

9/05/17 1645 ABSCE breach is less than 63.9 square inches for Train A .

9/06/17 During performance of 0-S1-30-7-A, Auxiliary Building Gas Treatment System Pressure Test Train A, the vacuum relief line airflows obtained did not meet the required acceptance criteria of greater than or equal to 1370 cubic feet per minute (cfm) 9/19/07 1609 Damper issue corrected by Work Order 119015649 10/06/17 A Past Operability Evaluation (POE) performed for this event determined that the A Train of ABGTS was inoperable from July 7, 2017 at 2030 EDT until September 5, 2017 at 1645 EDT.

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

3. LER NUMBER

2017 - 01 013 D Manufacturer and Model Number of Components that Failed During the Event The damper that failed was provided by Pacific Air Products, Part OB1001 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 issue was identified during periodic testing of the ABGTS required by TS.

G Failure Mode and Effect of Each Failed Component The cause of the equipment issue was an incorrectly adjusted damper linkage

H. Operator Actions

No actual event was ongoing related to this report.

I Automatically and Manually Initiated Safety System Responses Not applicable

III CAUSE OF THE EVENT

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

The cause of this event was an incorrectly adjusted damper linkage after replacement of the damper actuator in May 2017, which subsequently resulted in linkage slippage and incomplete damper closure.

B The cause(s) and circumstances for each human performance related root cause Individuals adjusting the damper linkage in May 2017 made a skill based error that resulted in linkage slippage due to linkage tightness during travel, and subsequent incomplete damper closure

IV ANALYSIS OF THE EVENT

The ABGTS and ABSCE serve a specified safety function when either WBN Unit 1 or Unit 2 are in Modes 1 through 4 by (1) providing a secondary containment barrier maintained under negative pressure during certain postulated accidents involving airborne radioactivity, and (2) providing contaminant removal sufficient to keep radioactivity levels in the air released to the environment low enough to assure compliance with the requirements of 10 CFR 100 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 The ABGTS consists of two 100 percent redundant air cleanup units (ACUs), located in separate rooms in the Auxiliary Building (AB) adjacent to each reactor building This system consists of two parallel ducts originating from exhaust ducting that normally serves the fuel handling and waste packaging areas Each of these ducts leads directly to an ABGTS ACU and fan combination, which then exhausts the building air directly to the shield building exhaust vent Following an accident, potential radioactivity releases within the AB are processed by the ABGTS units prior to release to the environment ABGTS performs the primary safety-related function of maintaining the AB at a minimum negative pressure of -0 25 inches water gauge (wg) to assure that the guidelines in 10 CFR 100 and General Design Criteria (GDC) 19 are not exceeded. Sufficient air is drawn from the ABSCE to establish and maintain the desired building negative pressure. The negative pressure chosen for post-accident operation is sufficiently low to ensure that airborne contamination in the AB is not released to the environment without being processed by the ABGTS units. Although the maximum permissible ABSCE leakage rate is 9900 cubic feet per minute (cfm) at -0.25 inches wg with respect to the outside environment, ABGTS will maintain a minimum fan capacity of 9300 cfm at all times. This will allow for adequate airflow for a maximum allowable ABSCE infiltration rate of 7930 cfm, and margin for a postulated one inch service air line break (1370cfm) due to a Safe Shutdown Earthquake (SSE), at a negative differential pressure of -0 25 inches wg The inability of ABGTS Train A to meet the required greater than or equal to 1370 cfm total vacuum relief line airflow required by the design does not necessarily render ABGTS Train A incapable of performing its specified safety function during a Loss of Coolant Accident (LOCA) (maintaining ABSCE at a negative pressure, -0.25 inches wg and -0 5 inches wg) The difference between the actual vacuum relief measured value (corrected for pressure) and 1370 cfm (from a postulated one inch air line break) provides the margin for ABSCE breaching permits during plant operation The ABSCE breach margin is calculated using ABGTS total flow, vacuum relief line flow, and AB pressures Therefore, once either train of ABGTS's breach margin is exceeded that unit of ABGTS becomes inoperable and unable to perform its specified safety function.

Testing performed on September 6, 2017 showed the failure of damper 2-FC0-30-108 to fully close impacted the ability to accommodate the postulated one inch service air line break when the calculated breaches through the ABSCE exceeded 63 9 square inches for Train A. This breach margin was exceeded between July 7, 2017 at 2030 EDT and September 5, 2017 at 1645 EDT. Following correction of damper 2-FC0-30-108, the ABSCE breach margin increased to over 170 square inches.

V. ASSESSMENT OF SAFETY CONSEQUENCES

As described in the previous section, the ABGTS Train A was not able to perform its safety function for a design basis accident with a one inch service airline failure The postulation of a seismic event and a Design Basis Event (DBE) are not assumed to occur concurrently, but are considered for the purposes of design and operability. The consequences of this event are judged to be low, and are not modeled in the plant Probabilistic Risk Assessment (PRA) A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event Train B of ABGTS remained operable during this time period 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

3. LER NUMBER

2017 - 01 013 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 Train B of ABGTS remained operable during this time period.

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 Train A of ABGTS was operable based on ABSCE breaches in effect when the condition of damper 2-FC0-30-108 was identified. The condition identified on September 6, 2017 was corrected on September 19, 2017

VI. CORRECTIVE ACTIONS

This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under Condition Report (CR) 1335791 A Immediate Corrective Actions The improperly adjusted damper was corrected after identification.

B Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future A training needs analysis will be performed to evaluate training solutions for damper linkage adjustments. Damper preventative maintenance activities will be revised to address smooth operation and absence of mechanical binding.

VII PREVIOUS SIMILAR EVENTS AT THE SAME SITE

that the closure of non-safety ventilation dampers may have masked the performance of safety related dampers In addition, as part of this report, two failures of a temporary boundary door used to facilitate Unit 2 construction were reported Corrective actions included revising procedures to ensure that non- safety dampers could not mask the performance of safety related dampers during testing. The event described in LER 390-2017-013 is different in that it is related to performance of post maintenance inspections, not surveillance procedures.

VIII. ADDITIONAL INFORMATION

None

IX COMMITMENTS

None