The fuel for a nuclear reactor is both the source of the fission energy that is used to produce electricity and the source of radioactive material during an accident. Ensuring fuel integrity is one of the primary goals of nuclear safety.
Since the inception of nuclear power, there has been substantial experience with the operation of water-cooled reactors – the most prevalent reactor design used for producing energy. This experience has led to the optimisation of the fuel design and reactor operating conditions for energy production while ensuring an adequate margin for safety. Co-operation on research into the criteria for the safe operation of fuel has been conducted under the Committee on the Safety of Nuclear Installations (CSNI) for several decades. First, in conjunction with more general activities on accident analysis, and since the early 2000s, under a separate Working Group on Fuel Safety (WGFS). There are two main types of threat to fuel integrity considered by WGFS. First, there are conditions in which the coolant flow is not sufficient to maintain a safe temperature for the fuel and integrity is lost due to overheating. Second, the control of the nuclear fission reaction may be compromised leading to high rates of energy production in the fuel and loss of integrity.
This task group was set up to carry out a pilot project using the methodology propsed in the final SMAP report published in 2007. In this pilot project, the SMAP methodology was applied to the Zion nuclear power plant in consideration of the US NRC loss-of-coolant accident rulemaking change and a power uprate of 10%.
The main mission of the Working Group on Fuel Safety (WGFS) is to advance the current understanding and address cross-cutting issues related to fuel behaviour in accident conditions, including work on associated aspects of thermal-hydraulics, oxidation, chemistry, mechanical behaviour and reactor physics.
This working group's objective was to advance the current understanding and to address safety issues related to fuel safety margins, in particular to systematically assess the technical basis for current safety criteria and their applicability to high burn-up and to the new fuel designs and materials being introduced in nuclear power plants.