Abstract
The effects of waste loading in vitrified high-level nuclear waste (HLW) from the reprocessing of high-burnup spent fuel (56 GWd/tHM) on waste volume reduction (i.e., number of HLW canisters produced) and decay heat generation were investigated to minimize the repository footprint. As the waste loading increases, the number of canisters produced decreases; however, the decay heat and subsequent footprint per canister increase. The best estimate waste loading observed was 23 wt% (including 10 wt% Na2O), wherein the repository footprint minimizes to 60.0 m2/tHM. These results are slightly higher than those for standard HLW (55.5 m2/tHM). However, upon comparing the repository footprint with electric power generation, the benefit of optimization was that the footprint for high-burnup HLW (131 m2/TWh) was 13% smaller than that of standard HLW (151 m2/TWh).Graphical abstractRepository footprint of the vitrified HLW as a function of waste loading for different cooling times. a, b Footprint per tons of heavy metal (tHM), c, d footprint per electricity generation (tera watt-hour, TWh). a, c 45 GWd/tHM, b, d 56 GWd/tHM.
Highlights
In view of the safe geological disposal of high-level waste (HLW) in Japan, the properties of standard vitrified HLW in canisters are evaluated assuming a spent fuel burnup of 45 GWd/tHM (Giga Watt-days per metric ton of heavy metal), a spent fuel cooling time of 4 years, and a waste loading of 20.8 wt% [1, 2]
Considering current consumption trends, where nuclear fuel burnup continues to increase owing to the economical operation of nuclear power plants, the rise in nuclear waste inventory, decay heat, and subsequent waste volume poses a challenge with regard to its reprocessing, interim storage, and final disposal
We focused on the spent fuel cooling time because it is an important factor affecting the decay heat of HLW due to the build-up of 241Am from 241Pu decay in spent fuel
Summary
In view of the safe geological disposal of high-level waste (HLW) in Japan, the properties of standard vitrified HLW in canisters are evaluated assuming a spent fuel burnup of 45 GWd/tHM (Giga Watt-days per metric ton of heavy metal), a spent fuel cooling time of 4 years, and a waste loading of 20.8 wt% (including Na2O) [1, 2]. The increase in decay heat generation affects the thermal constraint of the repository, where the temperature of the bentonite buffer surrounding the waste form is limited to below 100 °C; otherwise, the repository footprint would be greater than expected. This study investigated the effects of waste loading on the waste volume and heat generation in the vitrified HLW from the reprocessing of high-burnup spent fuel and optimized the waste loading to minimize the repository footprint under the thermal constraint of the repository. We focused on the spent fuel cooling time (interim storage period) because it is an important factor affecting the decay heat of HLW due to the build-up of 241Am from 241Pu decay in spent fuel
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