LWR High Burn-Up Operation and MOX Introduction; Fuel Cycle Performance from the Viewpoint of Waste Management

Abstract

From the viewpoint of waste management, a quantitative evaluation of LWR nuclear fuel cycle system performance was carried out, considering both higher burn-up operation of UO 2 fuel coupled with the introduction of MOX fuel. A major parameter to quantify this performance is the number of high-level waste (HLW) glass units generated per GWd (gigawatt-day based on reactor thermal power generation before electrical conversion). This parameter was evaluated for each system up to a maximum burn-up of 70 GWd/THM (gigawatt-day per ton of heavy metal) assuming current conventional reprocessing and vitrification conditions where the waste loading of glass is restricted by the heat generation rate, the MoO 3 content, or the noble metal content. The results showed that higher burn-up operation has no significant influence on the number of glass units generated per GWd for UO 2 fuel, though the number of glass units per THM increases linearly with burn-up and is restricted by the heat generation rate. On the other hand, the introduction of MOX fuel causes the number of glass units per GWd to double owing to the increase in the heat generation rate. An extended cooling period of the spent fuel prior to reprocessing effectively reduces the heat generation rate for UO 2 fuel, while a separation of minor actinides (Np, Am, and Cm) from the high-level waste provides additional reduction for MOX fuel. However, neither of these leads to a substantial reduction in the number of glass units, since the MoO 3 content or the noble metal content restricts the number of glass units rather than the heat generation rate. These results suggest that both the MoO 3 content and the noble metal content provide the key to reducing the amount of waste glass that is generated, leading to an overall improvement in fuel cycle system performance.

Burning of MOX fuels in LWRs; fuel history effects on thermal properties of hull and end piece wastes and the repository performance

“…Burn-up calculations for UO 2 fuels with 28, 45, and 70 GWd/THM (gigawatt days per ton of heavy metal) were conducted; enrichments of U-235 were chosen to be 2.6, 4.5, and 6.5 wt.%, respectively [4]. The Pu isotopic compositions in initial MOX fuels were calculated from the above UO 2 spent fuel compositions, assuming the cooling periods for UO 2 spent fuels were 4, 30, and 50 years and the storage periods for the MOX fuels before being loaded into a PWR were 2 and 10 years.…”

“…Our previous study demonstrated that the operation of a MOX-LWR increased the number of HLW glass units per GWd by a factor of two in comparison with that of a UO 2 -LWR due to the higher heat generation rate in the MOX HLW [4]. We have also determined the impact of wastes that include transuranic elements (hereafter referred to as TRU waste) on deep geological disposal.…”

“…If the amount of Am-241 included in HLWs is high, the HLW cooling periods required for the use of compacted bentonite after disposal must be extended. Inagaki et al [4] reported that a longer storage period of vitrified waste, over 50 years prior to final disposal, is required if the cooling period of UO 2 spent fuels before reprocessing is extended to 30 years.…”

Impact of Partitioning and Transmutation on High-Level Waste Disposal for the Fast Breeder Reactor Fuel Cycle

“…The waste loading ratio of the conventional glass waste form for the LWR(non-PT) scenario has been determined by considering several constraints: 14) chemical solubility of waste element oxides in a glass matrix, solubility of molybdenum oxide (MoO 3 ), contents of PGMs in a waste form, maximum initial heat of 2.3 kW/package, and maximum heat of 0.35 kW/package after a 50-year storage. The …”

Thermal Impact on Geological Disposal of Hull and End Piece Wastes Resulting from High-Burn-up Operation of LWR and Introduction of MOX Fuels into LWR

“…Both the noble metals and the yellow phase could cause problems with the disposal of high-burn-up UO 2 and MOX fuels. 3,4) The usage of MOX fuel is, inevitably, tied to spent fuel reprocessing. The resulting production of intermediate-level waste, including transuranic elements, is of concern from the viewpoint of waste management.…”