New system to keep fuel pools cool

Thursday, 26 May 2011

A stand-alone emergency fuel pool cooling system (EFPCS) developed by Westinghouse would be able to keep used fuel cool in emergencies including the loss of all plant power, the company claims. 

 

A used fuel pool (Image:Westinghouse)

Developed from the company's existing and patented temporary fuel pool cooling system, the new EFPCS includes a permanent primary cooling loop installed inside the reactor building or spent fuel pool building. The secondary cooling loop is designed as a separate mobile system to be stored off-site, complete with support equipment required to drive the system such as diesel generators, air compressors and switchgear.

The secondary loop would be set up outside the reactor or fuel pool building. As well as reducing the time required for system assembly and startup, this also eliminates any need to enter the reactor building which could be particularly advantageous in emergency situations.

According to Westinghouse, its EFPCS is designed primarily as a stand-alone backup system to remove decay heat from spent fuel pools during site emergencies involving a loss of off-site electrical power and on-site emergency diesel power. The system also allows for the addition of make-up water to ensure that safe water levels are maintained in the spent fuel storage pool.

Used nuclear fuel remains hot when it is removed from a nuclear reactor, and is stored underwater in pools at the reactor site until it is cool enough to be transferred for reprocessing or storage and disposal. In normal operation, water circulation keeps the temperature in the spent fuel pool at around 30ºC. However, in emergency situations where power is lost and water circulation fails, the water temperature in the pool gradually increases. If the water boils away, the stored fuel rods can become exposed to air leading to the risk of hydrogen formation and radioactive release.

The issue of emergency cooling of used fuel has been thrown into the spotlight following the natural disasters that hit Japan's Fukushima Daiichi nuclear power plant. The pools for reactors 1-4, situated inside the reactor buildings at that particular plant, all lost cooling capacity in the wake of the 11 March earthquake and tsunami, and keeping the fuel pools at all of the Fukushima Daiichi reactors topped up with water has been a priority.

Westinghouse says that the safety design and features of the system take into account a list of plant requirements including seismic requirements, environmental release limits, fuel pool temperature limits, supplemental cooling mode, remote operating interface, independent diesel power and used fuel pool keep-fill system.

During normal plant operations, the EFPCS can be used to provide temporary pool cooling. For example during refuelling outages, the EFPCS could help to reduce fuel movement delays, which are based on the decay heat in the spent fuel pool, as well as improving working conditions on the refuelling floor by reducing pool temperatures.

Nick Liparulo, Westinghouse Nuclear Services senior vice president, said the new product would serve to provide an added layer of safety for nuclear plants around the world. "Recent industry events have placed increased focus on the need to be prepared for every contingency," he noted.

 

Researched and written

by World Nuclear News