The Callaway Energy Center is still not operating after a non-nuclear generator issue occurred sometime during the plant's scheduled refueling shutdown at the turn of the year.
During the refueling, one-third of the plant's fuel assemblies were replaced and 800 additional workers assisted with the refueling and maintenance projects.
On Jan. 13, Ameren Missouri explained in a news release the center is not operating while the company investigates a non-nuclear operating issue related to its generator. No additional information was provided in that release, and the company has not yet submitted its licensee event report to the United States Nuclear Regulatory Commission.
The company declined to provide additional information about when the plant would return to service. According to the news release, the company does not anticipate any challenges meeting customer needs or significant financial impacts.
As of Jan. 19, the NRC was still reporting the plant's power level as zero.
The plant is required by the NRC to report maintenance issues and shutdowns, which are also known as scrams or trips. The current shutdown report has not yet been submitted.
NRC records indicate six events, or operating issues, occurred in 2020 for the Callaway plant. That isn't an unusual number of reports - the NRC database includes eight reports in 2019, six in 2018 and five in 2017. None of the recent reports included high safety risks.
Two of the reports included reactor trips. Adding the current shutdown brings the total to three trips or scrams over the past year.
The first event that occurred in 2020 was reported April 27 and discovered in February. According to the report, on Feb. 18, the plant discovered an emergency exhaust system train had been inoperable for months due to fan belt degradation and failure.
The fan belt was replaced. The report claims the inoperable train did not significantly degrade plant safely as another emergency exhaust system train was operable during the period. This did not include a shutdown.
On April 4, a reactor trip and auxiliary feedwater actuation occurred following the malfunction of a main feedwater regulating valve. According to the report, plant safety functions responded as designed during the shutdown.
On Sept. 9, a makeup water supply control valve was replaced. This was not safety significant according to the report. On Sept. 18, an event of minor safety significance was caused by a loose fuse.
The second shutdown occurred Sept. 27, when a generator fault lead to a turbine and reactor shutdown. According to the report, safety systems functioned as designed, and there was no actual nuclear, radiological or personnel safety impacts.
Every 18 months, the center plans a regular refueling and maintenance outage. One such period began in October. On Nov. 2, during the plant's scheduled refueling shutdown, an improper connection seal on a power operated relief valve was found. The report lists this as not safety-significant.
Other than the current shutdown, a search of the NRC's database for event reports from the Callaway plant containing the term "trip" indicates the April 4 and Sept. 27 reactor trips were the only other unplanned shutdowns over the past year.
Though a number of event reports are submitted by the plant each year, events that include a reactor trip or extended shutdown are more unusual.
The reactor tripped after the last refuel in May 2019 while restarting but was quickly back on track. Before that, the last reported trip occurred in August 2015 due to a transmission line fault.
Unplanned reactor shutdowns are one of the performance indicators the NRC uses to assess plants.
A look at the NRC's performance indicators for the Callaway plant show that as of the third quarter of 2020, the plant was still in the "green" threshold, indicating performance within an expected performance level.
Performance indicators from the third quarter of 2020 can be found online at nrc.gov/reactors/operating/oversight/docket-pi.html?docket=call#IE01.