2.15.1 Introduction

Almost all the commercial nuclear power plants operating currently utilize uranium oxide fuel. These reactors, sometimes referred to as Generation II or Generation III reactors, produce ~15% of the world’s electricity supply. Production of the uranium oxide fuel required for these reactors is a mature industry and it annually requires more than 68 000 tU.1

Fuel design differs according to the reactor types, which include the advanced gas cooled reactors (AGRs), pressurized water reactors (PWRs), boiling water reactors (BWRs), PWRs developed in the for­mer Soviet Union (Vodo-Vodyanoi Energetichesky Reaktor, VVERs), and CANadian Deuterium Uranium (CANDU) reactors. There are some differences in the production processes to fit each fuel design.

Plutonium utilization within the closed fuel cycle is essential to utilize natural uranium resources effi­ciently. Plutonium recycling demonstrations have been conducted in light water reactors (LWRs) and heavy water reactors (HWRs).2 Industrial utilization of MOX in LWRs has commenced in some countries.

The use of MOX in fast neutron reactors has many attractive features. Plutonium breeding in fast breeder reactors (FBRs) leads to drastically increased energy output from uranium resources. Nuclide transmutation by fast neutrons to incinerate minor actinides (MAs) has the potential to reduce the long­term radio-toxicity of spent nuclear fuel.

2.15.2 Summary of Oxide Characteristics

2.15.2.1 Thermal and Mechanical Properties of Oxides

The starting material for oxide fuel production is oxide powder. It is fed to a powder preparation process and then to a pelletizing process to get powder compacts, which are called green pellets. The green pellets undergo a dewaxing and sintering process to get sin­tered oxide pellets. Certain characteristics of the oxide powder and the sintered pellets are very important for fuel production. A brief summary of their important characteristics is presented in this section. As a com­prehensive review of the characteristics of actinide oxide has been given in Chapter 2.02, Thermody­namic and Thermophysical Properties of the Acti­nide Oxides, most of the data presented here are those dealt with in Chapter 2.02, Thermodynamic and Thermophysical Properties ofthe Actinide Oxides.