**Gamma Uranium Molybdenum Alloy: Its Hydride and Performance**

Enrique E. Pasqualini

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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/63652

#### **Abstract**

The high density metastable gamma uranium molybdenum alloy (γ‐UMo) is being qualified as a nuclear fuel for the conversion of high enriched uranium (HEU) to low enriched uranium (LEU) fuels in research nuclear reactors. γ‐UMo, with compositions between 7 and 10 wt.%molybdenum, has excellent properties to allocate fission gases but unacceptable behavior in contact with aluminum in the matrix of dispersed fuels. Development and processing alternatives are welcome to decide final workingpaths and new nuclear fuels design. A historical introduction on the development of materials testing reactors (MTR) nuclear fuels is presented to illustrate comings and goings to reach desired qualification objectives. Several studies performed on UMo probes, miniplates and full size plates are mentioned to contribute to the knowledge of fuel properties and to incorporate new process technologies. Focus is directed to the discovery of the gamma uranium molybdenum hydride and the hot rolling colamination of monolithic UMo with nonaluminum claddings. A scalable process of hydriding, milling and dehydriding (HMD) to comminute the ductile UMo was developed. Monolithic UMo miniplates with Zircaloy‐4 (Zry4) cladding was colaminated for the first time and under irradiation conditions showed excellent performance after high burn‐up.

**Keywords:** uranium, molybdenum, zircaloy‐4, hydride, comminution, colamination, coverage
