Such a nuclear fuel product can be particularly used as a primary target to produce elements such as molybdenum-99 (hereafter referred to as “Mo99”), which can in turn serve as a source of technetium-99 which is a standard beta emitter and therefore used for instance for equipment calibration, and in particular of metastable nuclear isomer of technetium-99 (Tc99m) used as radioactive tracer in nuclear medicine and biology.
Such a nuclear fuel product can also be used as nuclear fuel for research nuclear reactors.
The nuclear fuel product generally takes the shape of a plate or a cylinder with a core sealed by a cladding. It is intended to be put in a nuclear reactor to be irradiated, in order to recover Mo99 as a fission product of enriched uranium or to provide neutrons for research applications.
In the prior art, highly enriched uranium (hereafter referred to as “HEU”), that is to say with a content of U235 above 20 wt % and for instance around 93 wt %, is generally used. Particles of UAlx alloys, mostly containing UAl3 and UAl4 phases, are produced and mixed with an aluminium powder. The mix is then pressed to produce a core comprising UAlx particles within an Al matrix, the UAlx particles representing around 20-30% of the final core volume. The core is then hot-rolled along with cladding plates to seal it. As a result, its length is increased by a factor of about 400 to 600%, such plasticity coming from its high aluminium powder content. In case of cylindrical shape, after hot-rolling the plate is bent and welded for instance by arc welding such as Gas Tungsten Arc Welding (GTAW) also known as Tungsten Inert Gas (TIG) welding, by resistance welding . . . .
Due to growing concerns about potential misuse of HEU, there is a need for switching from HEU to low-enriched uranium (referred to as “LEU”), that is to say with a U235 content below 20 wt %, usually around 19.75%. However, nuclear fuel product with LEU leads to less U235 content than HEU nuclear fuel product and thus to a lower Mo99 recovery in primary targets and lower neutron emission of nuclear fuel for research reactor.
For this reason, the particles of mostly UAlx, with x above or equal to 3, are replaced by particles mostly containing the UAl2 phase, which provides a higher uranium-alloy density than both UAl3 and UAl4, hence a higher U235 content to compensate the lower U235 enrichment of the uranium. The UAl2 particles represent about 20-30% of the initial core volume. The nuclear fuel product, after being rolled, undergoes a thermal treatment in order to convert the UAl2 phase into UAlx in the core, with x above or equal to 3 by using part of the Al matrix. The UAlx particles represent about 30-40% of the final core volume, the UAl2, UAl3 and UAl4 phases amounting in total to about 50 wt % of the core and the aluminium phase and the other aluminium compounds amounting to about 50 wt %. This thermal treatment generates huge geometrical deformations leading to additional flattening steps with subsequent risks of cladding failures or delamination.
The obtained uranium loading in the core ranges approximately from 2.7 to 3.0 gU/cm3, 3.0 gU/cm3 being the technological limit achievable for nuclear fuel products made of UAlx alloy, with the described prior art manufacturing processes.