NUCLEAR FUEL TECHNOLOGY
Fuel assemblies, the "heart" of the reactor
Cycle of fuel assemblies
The nuclear fuel in the fuel assemblies constitutes the "heart" of the reactor and provides the energy in the form of heat, which the power plant converts into electrical energy. In operation, the fuel assemblies are subjected to high thermal, mechanical, chemical, and radiological loads. These loads need to be accommodated throughout the entire operating time without damaging the fuel assemblies.
This objective is achieved by emphasising four important issues:
- Carefully designing the fuel assemblies,
- a controlled implementation of the design results during production,
- continuous monitoring of the operating conditions and the operating performance of the fuel assemblies, and
- the feedback from the operation and research results in designing and manufacturing new fuel assemblies.
Comprehensive safety-related analysis throughout the entire life cycle
TÜV NORD Nuclear provides consultancy support in designing, producing, and operating the fuel assemblies and other core components of the reactor. TÜV NORD Nuclear experts inspect whether the safety-relevant requirements for the fuel assemblies are satisfied throughout the fuel assembly life cycle by conducting independent analyses and inspections during manufacture as well as monitoring and assessing the operating performance.
The entire process is comprehensively analysed by evaluating the design analyses with respect to the neutron physical, thermo-mechanical, and thermal-hydraulic design of the fuel assemblies. Such analyses are usually conducted by the licensee and his fuel vendor and are submitted to the regulator to undergo an independent review. TÜV NORD Nuclear would be the reviewer of these analyses. Apart from this, TÜV NORD Nuclear is also charged with verifying independently the product realisation through randomly surveilling the fabrication shop, and checking the operating performance of the fuel assemblies by means of operation surveillance. Experience is gained from analysing the operating behaviour and from the systematic analysis of operational results of comparable fuel assemblies that are also integrated into the manufacturing of next generation fuel assemblies.
Basically, the same process is followed for other components of the reactor core, such as the control rods.
Storage of spent fuel assemblies
After being used in the reactor, the fuel assemblies initially remain in the transport and storage containers located in the dry interim storage. Here, verification must also be provided that the fuel assemblies overcome the entire storage time undamaged. TÜV NORD Nuclear reviews the calculations and measurements performed for this by carrying out independent analyses, e.g. of the temperature distribution and the resulting fuel assembly loads.
During its analyses, TÜV NORD Nuclear relies on qualified analytical processes and programmes that are linked to a comprehensive data management system.
