The American Electric Power (NYSE:AEP) D.C. Cook 2 nuclear unit in Michigan went offline unexpectedly around 1 a.m. on July 6 due to an “unanticipated explosion” associated with a steam leak in the turbine building, according to a report filed with Nuclear Regulatory Commission (NRC).
“On July 6, 2016, at 0038 [EDT], DC Cook Unit 2 Reactor was manually tripped and at 0050 [EDT] an Unusual Event (N-7 ‘Unanticipated Explosion’) Emergency Declaration was made due to steam leak and associated damage to the turbine building,” according to the report filed with NRC.
The NRC report goes on to say that the “unusual event” was terminated shortly after 2 a.m. An unusual event is the least serious emergency plan classification.
“Unit 2 is being supplied by offsite power. All control rods fully inserted. Decay heat is being removed via Steam Generator PORVs [Power Operated Relief Valve]. Preliminary evaluation indicates all plant systems functioned normally following the Reactor Trip. DC Cook Unit 2 remains stable in Mode 3 while conducting the Post Trip Review. No radioactive release is in progress as a result of this event,” according to the report filed with NRC.
The Cook nuclear plant, located in Bridgman, Michigan and operated by AEP’s Indiana Michigan Power, consists of two pressurized water reactors (PWRs) that each have a capacity rating of roughly 1,100 MW.
Cook Unit 1 remains at 100% power. Causal analysis and repair estimates are under development, the company said in its own July 6 news release. AEP does not release return-to-service information for generation units.
The utility said that an expansion joint bellows on a Moisture Separator Reheater ruptured. “That component provides non-radioactive steam to the low pressure turbines. The expansion joint bellows is roughly 48 inches in diameter. The rupture released pressurized, high-temperature steam to the surrounding area causing damage to an adjacent Turbine Building exterior wall. No one was in the area at the time and there were no injuries,” Indiana Michigan said in the news release.