|River Bend Station - Unit 1|
|Reporting criterion:||10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications|
10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
|4582017005R00 - NRC Website|
|Person / Time|
|From:||Vercelli S P|
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17156A615 (5)|
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by 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.
a LER NUMBER
On April 5, 2017, during a scheduled surveillance test, it was discovered that the Division 1 main control room ventilation filter train [VI] was inoperable due to the flow rate being below the lower limit. The initial investigation found that a manually-operated damper (**CDMP**) in the flow path for that filter train was not correctly positioned. Work documents from the recent refueling outage that started on January 28 were reviewed, and it was found that the damper had been closed as part of establishing a system configuration needed for repairs to other dampers. It was concluded that the as-left condition of the damper after restoration from the maintenance was such that it vibrated in the closed direction upon the first start of the filter train fan, and that the filter train had thus been inoperable since the return to service on February 26, 2017.
The plant was restarted at the end of the refueling outage on March 8. On March 10, an unplanned manual reactor scram was initiated due to a steam leak in the turbine building. The leak was repaired and the plant was restarted on March 11. Since the filter train was inoperable on both occasions, those mode changes were made in violation of Technical Specifications. These conditions are being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as operations prohibited by Technical Specifications.
The investigation of this event also found that during one 8-minute period when the Division 1 filter train was inoperable, the Division 2 main control room fresh air system was inoperable for planned testing. This condition is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D) as a potential loss of safety function of the main control ventilation system.
The manually-operated damper was closed as part of establishing a work boundary for maintenance being performed in other sections of the system. The normal position of the damper is partially open, as established when the system was originally flow balanced. The operating mechanism includes a bolted linkage to lock the damper in place. A match mark is on the mechanism indicating the correct position of the damper.
The documentation for the restoration of the system to its operating configuration was reviewed and it was found that there were no instructions regarding the need to torque the bolts in the damper locking mechanism. It was concluded that the damper was re-opened to align with the match mark, but that the locking bolts were not torqued. It could not be determined from the documentation who had re-opened the damper, so the actual as-left condition of the locking bolts could not be determined.
The damper was correctly locked into position on April 6.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to NEOB-10202, (3150-0104). Office of Management and Budget, Washington, DC 20503. If a means 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.
River Bend Station — Unit 1 05000-458 2017 005 00
CORRECTIVE ACTION TO PREVENT RECURRENCE
The applicable surveillance test procedures will be revised to include instructions on proper torqueing of the locking bolts of the manually-operated dampers. This action is being tracked in the corrective action program.
PREVIOUS OCCURRENCE EVALUATION
No similar events have been reported by River Bend Station in the last three years.
During the 8-minute period when both divisions of the main control room fresh air system were inoperable on March 15, the Division 2 subsystem was under the direct control of a dedicated operator as part of planned testing. That subsystem was thus available for service had it been necessary. At all other times, the Division 2 subsystem was operable and able to fulfill its design safety function. This event, therefore, did not constitute an actual loss of safety function. This event was of minimal significance to the health and safety of the public.
(NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (**XX**) and [XX], respectively.)