To minimize the use of highly enriched uranium (HEU) fuel in the civil nuclear fuel cycle, the operators of research reactors worldwide have joined in an effort to reduce the enrichment of their fuels. To support these international non-proliferation efforts, the European High-Performance Research Reactors (HPRRs) aim to convert their fuels to low enriched uranium (LEU). The reactors involved in this program are BR2 (Belgium), FRM II (Germany), RHF and JHR (both France). Further the European fuel fabricator Framatome-CERCA participates in this effort.
The development of a new fuel for this conversion is based on a metallic uranium-molybdenum alloy (U-Mo) with very high density, investigated as both a dispersed and monolithic fuel. In the years since the start of this development, much progress has been made towards a qualifiable fuel. The final goal of establishing U-Mo as an accepted and approved standard fuel for HPRRs is much nearer, but still a couple of steps away. The HERACLES-CP project continues the efforts made in the past and is paving the way for the following projects LEU-FOREvER and EU-QUALIFY. To optimize resource utilization, over recent years the considerable work-load involved in developing the new U-Mo plate-type fuel has been split between Europe and the US: The American partners have been focusing on the development of monolithic U-Mo, while Europe has dedicated larger efforts towards dispersed U-Mo solutions. Of course, contributions have been made vice-versa and also by other countries. Accordingly, HERACLES-CP puts more weight on the development of the dispersed branch, but also covers important aspects of monolithic fuel development.
Even though there is extensive data available on U-Mo, there have been several fundamental knowledge gaps to be filled before the qualification of the fuel itself. Therefore, experiments and measurements necessary to fill these knowledge gaps were identified and conducted during the so-called Comprehension Phase within the HERACLES-CP project.
Furthermore, R&D is required for the fabrication technology for both development branches: U-Mo powder production, powder coating and plate fabrication for dispersed fuel, and foil coating and plate production for the monolithic fuel branch. While in-pile experiments are indispensable to fill the knowledge gaps, many questions related to the metallurgical aspects of radiation damage in the fuel assembly can be well or even better studied by out-of-pile heavy ion irradiation experiments.
The objectives of the HERACLES-CP project were:
For dispersed fuel:
- To fill the knowledge gaps identified by performing the necessary experiments and measurements,
- To conclude on the most promising fuel design,
- To develop the necessary fabrication techniques,
- To prepare and launch the SEMPER-FIDELIS irradiation test to verify the theory and to fill the gaps,
- To perform the Post-Irradiation Examinations (PIE) of SEMPER-FIDELIS.
For monolithic fuel:
- To develop the technology and knowledge necessary for fabrication,
- To prepare test samples for the EMPIrE irradiation test (originally foreseen for SEMPER-FIDELIS).
The project has been successful in meeting these objectives. Based on this knowledge and the results of the in-pile irradiation tests SEMPER-FIDELIS and EMPIrE, two further irradiation tests, currently titled “E-FUTURE-3” for dispersed and “FUTURE-MONO-1” for monolithic fuel, will be designed to advance towards the successful qualification of U-Mo as an HPRR fuel. Even though these two irradiation tests themselves are not in the scope of HERACLES-CP, a number of items required for the preparation of the tests in terms of fabrication and irradiation performance have been accomplished within HERACLES-CP.
The general project objective which has been completed can be summarized as: the establishment of the technical and scientific foundations to enable the successful qualification of U-Mo fuel.
Following this stage, the fuel will be qualified in a series of generic and reactor-specific irradiations and examinations, then finally used in the facilities according to their specific conversion plans.
