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Objectives European Thorium Cycle Project

The general objectives of this proposal are:

The EU’s Fifth Framework Programme aims at the exploitation of the potential of nuclear energy by making nuclear technology safer and more economical. The aspect of sustainability is strongly emphasised in its full scope addressing environmental compatibility, social acceptance, waste management, disposal and non-proliferation aspects, protection of plant personnel, energy supply diversity, competitiveness etc. Against this background, the exploration of innovative concepts should also contribute to the general programme objectives including conservation and advancement of relevant know-how and its transfer to a new generation of nuclear engineers. New applications of nuclear power are indicated in complementary market segments beyond dedicated electricity production like co-generation of heat and power and incineration of long-lived radionuclides.

The objective of this proposal work is to provide key data for the thorium cycle in the context of limitation of nuclear waste production and prospects for waste burning. The aim is to obtain essential data for the thorium fuel cycle. This project addresses one of the key items in the Work programme 2.3. Safety and efficiency of future systems.

The previous 4th FWP Thorium cycle project has shown that there are important advantages of thorium cycles with respect to the waste issue. Long-lived radiotoxicity of mining waste is expected to be relatively small, which leads to more manageable waste compared to the uranium case. Fabrication of Th fuels is comparable with MOX fabrication methods as long as fresh Th, U and recycled Pu are used. However, recycling of U requires remote handling as well as innovative reprocessing techniques on industrial scale. Open cycles are possible in PWRs, but require additional fissile material, also known as make-up fuel or topping material. To reduce the radiotoxicity of PWR waste, make-up fuel like ²³³U or highly-enriched uranium should be admixed with Th. Advantages are observed during the first 10,000 years of storage. The long-term risk of directly stored fuel in a thorium matrix is not known very well yet, but there are speculations on improved performance. Further experimental work is needed to clarify this issue. Recycling gives a further reduction of radiotoxicity up to 10,000-50,000 years of storage.

Th-assisted Pu burning in a PWR is an attractive option with respect to mass reduction of Pu, which could be twice that of U/Pu MOX in a 100% core loading. In open cycles, a relatively small amount of ²³³U is produced. Recycling of ²³³U together with Pu is feasible in a PWR.

Fast reactors and accelerator-driven systems (ADS), like the Fast Energy Amplifier (FEA), offer the possibility of a closed Th cycle without additional fissile material, reducing mining needs and risks. Full recycling of actinides gives impressively low radiotoxicity results. Initially, these systems could be used for Th-assisted Pu-burning and simultaneous ²³³U breeding, providing fuel for a new generation of low- actinide-waste producing energy systems.

Long-term residual risks of mining waste are reduced by storing in a geological disposal facility. Direct storage of Th-based fuels gives similar residual risks as U-based fuels with the present conservative assumptions.

Long-term radiotoxicity of mining waste is smaller than for the U/Pu cycle in case of fast reactors and ADS. The reactor waste radiotoxicity is smallest if fast reactors or ADS are used with full actinide recycling. Pu burning capacity is high for once-through Th/Pu MOX in PWRs and in fast reactors or ADS.

The general objective of this proposal is to supply key data for application of the Th-cycle in PWRs, FRs and ADS, with respect to Pu and TRU burning as well as reduction of lifetime of nuclear waste. The use of the thorium cycle offers a challenging option for waste reduction, both at the front and at the back-end of the fuel cycle. The front end of the Th fuel cycle, i.e. the mining of thorium, produces less waste than uranium mining. At the back of the thorium cycle, less waste is produced than with the conventional uranium cycle. In addition, very high plutonium consumption rates can be achieved when Th/Pu fuel is used.

The specific objectives of this proposal are:

Behaviour of Th-based fuel at extended burnup under respectively PWR, FR and ADS conditions. When the introduction of the thorium cycle for commercial reactors is considered, the application of a once-through scenario in PWRs is an important initial step. This initial step should focus on the open cycle first, such that additional measures for the realisation of closed cycle (reprocessing, interim storage etc.) do not have to be taken. An interesting possibility is once-through Pu burning with Th in PWRs. This concept allows a much higher Pu-destruction rate being twice as efficient as MOX. Since data for the fuel behaviour of Th-MOX are scarce, irradiation of this fuel type is essential. In order to assess the fuel behaviour of Th-based fuel, irradiation experiments of different thorium targets will be performed. Two irradiations are planned within the Thorium cycle proposal, in the High Flux Material Test Reactor HFR and one in the KWO power reactor. One irradiation of 4 targets will be performed in the HFR at a high thermal flux up to a high burnup of 55-60 MWd/kgHM, and 1 fuel pin will be irradiated in KWO under typical PWR conditions to a burnup of about 35 MWd/kgHM. These experiments should provide sufficient information for a follow-up test in a commercial reactor.
The motivation of the KWO irradiation is outlined in Appendix A.
Core calculations for Th-based fuel, including validation of previous results from 4th FWP work. At present, experimental results on Th-based fuels in PWRs are scarce, and a code-to-code validation referring to a reference fuel bundle and core definition constitutes a first step to validate the accuracy of the results of core calculations. In this context, a sensitivity check for the nuclear data of significant isotopes, like ²³²Th and ²³³U, gives a preliminary impression for the necessity to improve the nuclear data. The full-core level assessments are to validate the conclusions drawn from the pin-cell burn-up results in the 4th FWP and to give more accurate results for the voided core especially at higher burn-ups, i.e. 80 or 100 MWd/kgHM which are envisaged for Th/Pu-MOX fuels in a PWR. Furthermore, the performance parameters for transuranic (TRU)-consumption are to be increased significantly by minor modifications of the fuel. The results shall be compared to those obtained with U/Pu-MOX full-core loads. The output of this research topic are reports on the inter-comparison of the reference fuel bundle and core assessments as well as on the full core Th/Pu MOX assessments including innovative fuel concepts to reduce the TRU discharged.