The Capabilities of HTRs to Burn Actinides and to Optimize Plutonium Exploitation

Abstract

At present, the 125 GWe of nuclear power in the European Union produce about 3000 tons of spent fuel annually, containing about 25 tons of plutonium, 2.5 tons of minor actinides (MA) and about 100 tons of fission products, of which 3.1 tons are long-lived fission products. Actual reprocessing of LWR fuel and a first recycling as mixed plutonium and depleted uranium oxide fuel (MOX) in LWR already contribute to a significant reduction of waste volumes and radiotoxicity. However HTRs have some characteristics which make them particularly attractive: intrinsic safety, cost-effectiveness, reduced thermal pollution, capability of increasing energy availability (with the use of Pu-Th cycle) and of minimizing actinides radiotoxicity and volume of actinides. In this paper particularly the last item is investigated. Symbiotic fuel cycles of LWR and HTR can reach much better waste minimization performances. It happens because of the specific features of HTRs cores that leads to an ultra-high burnup and, last but not least, the ability to accommodate a wide variety of mixtures of fissile and fertile materials without any significant modification of the core design. This property is due to a decoupling between the parameters of cooling geometry and of neutronic optimization. In our calculations we considered a pebble-bed HTR using a Pu-based fuel (deriving from reprocessing of classical LWR fuel and/or weapons grade plutonium) at the maximum technological discharge burnup. As results, we find, at EOL (End Of Life), a relatively small amounts of residual Pu and MA produced in terms of quantities and of radiotoxicities. Furthermore we used in our calculations a different type of fuel based on a mixture of Pu and Th to try to optimize the previous results and to increase energy availability. Calculations have been done using MCNP-based burnup codes, capable of treating 3-D complex geometry and ultra-high burnup

The VHTR and GFR and their use in innovative symbiotic fuel cycles

“…A reactor or fuel cycle has a positive impact on long-term spent fuel management if it reduces the time that the spent fuel takes to reach the radiotoxicity level of the original uranium ore from which is extracted (i.e. the LOM); this time is defined as Level Of Mine Balancing Time (LOMBT) (Cerullo et al, 2004). Because the LOM is substantially the radiotoxicity of a quantity of natural U (U nat ), it is expressed in Sv.…”

A Critical Review of the Recent Improvements in Minimizing Nuclear Waste by Innovative Gas-Cooled Reactors

“…Nevertheless, it is difficult to guarantee the perfect integrity of a human-made confinement beyond 10 • 000 years [3], then in international context the LOM is used as reference parameter. A reactor or fuel cycle has a positive impact on long-term spent fuel management if it reduces the time that the spent fuel takes to reach the radiotoxicity level of the original uranium ore from which is extracted (see [14], level of mine balancing time (LOMBT)). Because the level of mine is the radiotoxicity of a quantity of natural uranium, it is expressed in Sv.…”

“…In order to demonstrate the capability of HTRs to contribute in reducing nuclear waste (actinides in particular), it was decided to analyze Pu-based fuel [14]. In order to validate the used code (namely MONTEBURNS), an international codeto-code benchmark was performed.…”

“…To check the advantages in using different fuel cycles, the radiotoxicity evolution of spent fuel versus time was evaluated. As reference for radiotoxicity, we, as described above, originally defined [14] the LOMBT (level of mine balancing time), that is, the interval of time necessary for the radiotoxicity of the exhausted fuel to return to the values of the mineral extracted from the mine (in this case of uranium) from which the fuel was generated.…”

“…To check the advantages of the chosen fuel cycles, we mainly took into account the radiotoxicity evolution of the spent fuel versus time. As already anticipated, please remember that as reference for radiotoxicity, we defined [14] the level-of-mine balancing time (LOMBT). This value is linked to the LOM definition, value characteristic of the type of fuel cycle and it is not easily defined (due to its oscillation range).…”