Reactor head replacement brought forward

Tuesday, 22 June 2010

The reactor vessel head at the Davis-Besse nuclear power plant in Ohio will be replaced in 2011 and not 2014 as previously planned, FirstEnergy Nuclear Operating Company (Fenoc) has announced. 

  

Davis-Besse (Image: NRC)

The 908 MWe pressurized water reactor is preparing for a restart following repairs to 24 control rod drive mechanism (CRDM) nozzles in which signs of cracking caused by stress corrosion were found during a scheduled refuelling and maintenance outage.

 

After carrying out repair work, Fenoc had been planning to take operational steps to avoid more cracking until the scheduled vessel head replacement in 2014. This would have included using a shorter operating cycle, a lowered core temperatures and the extensive testing of the nozzles during a planned outage in 2012. However, local media contends the Nuclear Regulatory Commission was not happy with Fenoc's proposed interval between inspections and now it appears that Fenoc has decided that the best solution is to bring forward the vessel head replacement rather than undergo the more frequent inspections that the NRC would likely have demanded.

Fenoc president and chief nuclear officer James Lash said that the company was confident that the modifications to the nozzles undertaken during the current outage had been successful but that bringing forward the vessel head replacement would be the best option in the long run. "Post-modification inspections and tests indicate these nozzles will support continued safe and reliable operations. At the same time, advancing the installation of the new reactor head will provide additional margins of safety and reliability for long-term plant operations," he said.

The new reactor head will be the second such replacement: a new head was installed in 2002 after severe CRDM nozzle cracking occurred following an employee's cover-up of missed inspections. Fenoc acquired the first replacement vessel head as an unused component from a partially completed power plant in Michigan.

The new reactor head, in which the nozzles are made of a different alloy that is less susceptible to cracking, has already been manufactured by Areva and is currently being stored in France. The component is expected to arrive at the plant, on the shores of Lake Erie, in autumn 2010. On arrival at the plant, the new head will undergo a series of pre-service inspections. The reactor will then be taken out of service in the autumn of 2011 for the new head to be installed.

Davis-Besse was taken off line for the refuelling and maintenance outage during which the cracks were discovered in February 2010. It is now preparing to restart, with fuel re-loaded into the reactor core, the reactor vessel head installed and pre-startup testing under way. The plant is expected to return to service by July.

 

Researched and written

by World Nuclear News