US used fuel storage options assessed

It is 'unclear' whether the benefits of an accelerated transfer of used nuclear fuel from storage pools to dry storage at US nuclear power plants would outweigh the risks and costs involved, an updated study by Electric Power Research Institute (EPRI) concludes.

EPRI has updated a 2010 study examining the impacts associated with potential policy decisions that may result from the accelerated transfer of five-year cooled used nuclear fuel from wet storage to dry storage. That study examined the cost impacts associated with procurement of dry storage casks, cask loading operations, dry storage facility construction and/or expansion, and annual operating and maintenance costs. However, it did not include an assessment of the amount of heat decay and radionuclide source term reduction in the used fuel pools due to lower numbers of used fuel assemblies in them.

The 2010 report assumed the transition of five-year cooled used fuel could be accomplished in five years. However, industry feedback indicated a more realistic time frame is ten to 15 years. EPRI has revised the study to evaluate the dose and cost impacts of accelerating transfer of used fuel from storage pools to on-site dry storage for two scenarios - one taking ten years to transfer all the fuel that has been cooled for at least five years, and the other taking 15 years to complete the transfer. Benefits and impacts are determined for a representative boiling water reactor (BWR) plant, pressurized water reactor (PWR) plant, new plant, and for the industry as a whole. Various operational constraints affecting the ability to accelerate the transfer of fuel are taken into account, such as the availability of handling equipment for the used fuel pool and dry storage casks.

Increasing volumes

According to EPRI, there are currently 57 operational independent used fuel storage facilities at US nuclear power plant sites storing used nuclear fuel from 95 nuclear power plants, with several more such facilities that are not located at nuclear power plant sites.

At the end of 2011, approximately 67,300 metric tonnes of uranium (MTU) of used fuel was in storage (both wet and dry) with more than 17,300 MTU of used fuel loaded into more than 1500 dry storage casks. EPRI estimates that there will be 32,000 MTU of used fuel in dry storage by 2020 stored in some 2900 dry storage casks. Total used fuel discharges by 2020 are projected to be some 86,000 MTU. By 2060, by which time all of the currently operating nuclear power plants will reach the end of their renewed operating licences, there will be some 136,000 MTU of used fuel in storage at reactor sites.

"With the near-term prospects for an operational repository fading, it is expected that every nuclear power plant site will need to implement dry storage of used nuclear fuel by approximately 2025 in order to support continued operation of their power reactors," the study notes. "In addition, used nuclear fuel is expected to remain in dry storage at reactor sites for decades."

EPRI noted, "It is unclear whether the potential risk reduction due to lower amounts of decay heat and cesium in used fuel pools would offset the real increase in risks, occupational safety hazards, operational impacts, and costs associated with a policy decision to transfer used nuclear fuel from storage pools at an accelerated rate."

The report concludes that accelerating the transfer of fuel from the used fuel pools to dry storage of all fuel cooled more than five years would reduce pool inventories by an estimated 67% to 78% for a representative PWR plant and by 73% to 78% for a representative BWR plant. This transfer would decrease the decay heat remaining in the pool by an estimated 23% to 32% for a PWR plant and 32% for a BWR plant. The corresponding reduction in potential source term from cesium is estimated to be 43% to 53% for a PWR plant and 47% to 48% for a BWR plant.

The accelerated transfer of used fuel to dry storage would have significant radiological impacts due to loading fuel with higher decay heat and higher dose rates and to loading more packages. The increase in worker dose for the US nuclear industry as a whole is estimated at 1650 person-rem and 2090 person-rem for the ten-year and 15-year scenarios, respectively.

The economic impact to the US nuclear industry is estimated at $3.5 billion to $3.9 billion above current operating costs, which includes costs associated with procurement of dry cask storage systems, cask loading operations, dry storage facility construction, and annual operation and maintenance.

EPRI said that the study - entitled Impacts Associated with Transfer of Spent Nuclear Fuel from Spent Fuel Storage Pools to Dry Storage After Five Years of Cooling, Revision 1 - is "expected to be useful in informing policy and operational decisions regarding the handling and management of used nuclear fuel."

Researched and written
by World Nuclear News