|River Bend Station - Unit 1|
|Reporting criterion:||10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident|
|4582017006R00 - NRC Website|
|Person / Time|
|From:||Maguire W F|
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17200C938 (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 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.
006 2017 00 05000-458 alLER NUMBER
On May 15, 2017, an engineering investigation determined that a modification installed in 2014 on two of the four safety-related main control building chillers (**CHU**)had a design error. The nature of that error was such that the performance of a regularly scheduled preventative maintenance (PM) task to draw an oil sample from the chiller gearbox inadvertently caused the chiller to be incapable of responding to an automatic start signal. A review of the history of the PM found that, on three occasions since the modification was installed, the task was performed on the operable chiller that was in the standby condition. The inadvertent inoperability of the standby division of the main control building chillers causes the loss of safety function of the supported electrical distribution systems in the building.
The control building chilled water system [VI] provides cooling to the equipment rooms housing the battery chargers and inverters for the safety-related onsite electrical distribution systems. The loss of cooling to the various equipment rooms in the control building requires that the supported equipment in those areas be declared inoperable. The Technical Specifications for the Division 3 DC distribution system requires that the high pressure core spray (HPCS) system be immediately declared inoperable. This condition potentially causes the HPCS system to be incapable of performing its safety function, and is, thus, reportable in accordance with 10 CFR 50.73(a)(2)(v)(D).
The subject modification was installed on the Division 1 "C" chiller in August 2014, and on the Division 2 "D" chiller in April 2014. (Each division has a redundant chiller that has yet to be modified.) The purpose of the modification was to upgrade the chiller controls to a digital system. An error occurred in the development of the modification design that involved the controls for the motor-driven chiller oil pump. The switch for the oil pump is on the main control room panel, and is normally in the "AUTOMATIC" position. The work instructions in the PM require that the control switch be placed in the "RUN" position to start the pump. The effect of the design error is that the automatic start feature of the chiller is disabled when the switch is in the "RUN" position.
The review of the PM history found that the "C" chiller was sampled on February 2nd and August 3rd in 2015. The "D" chiller was sampled on March 21, 2017. In each case, the subject chiller was operable and configured for an automatic start should the operating chiller in the opposite division unexpectedly trip. The execution of the PM step to place the oil pump control switch in "RUN" rendered the chiller inoperable.
IMMEDIATE CORRECTIVE ACTIONS
When this condition was discovered, the oil pump control switches on the "C" and "D" chillers were "CAUTION" tagged to prohibit taking the switch to the "RUN" position if the chiller is in the standby configuration.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE
The error in the subject modification is considered a legacy issue since its design was completed and approved in July 2012. Since that time, a comprehensive root cause analysis on the issue of quality in engineering products was conducted in 2015, which resulted in numerous programmatic changes. Therefore, no new causal analysis was 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 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.
05000-458 2017 006 00 performed for this event.
The PM task will be revised to preclude its performance on chillers in the standby configuration.
tracked in the corrective action program.
This action is being
PREVIOUS OCCURRENCE EVALUATION
River Bend Station has reported no similar events in the last three years.
At no time during the three performances of the PM on the operable standby chiller was there an actual demand for its automatic start. This condition was, thus, of minimal significance with respect 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.)