Undersökning av ledarkonstruktion vid bränsletest : Teoretisk konceptframtagning av ledarkonstruktion

In nuclear power plants, during operation at high temperatures, there can occur a steam build-up around the fuel rods at an increasing rate. This inhibits the water’s effectivity in removing heat from the rods. When this occurs and reaches a critical point, the temperature in the fuel rods surges, which can lead to them being damaged. This is called critical heat flux (CHF). During operation, the reactor always keeps a safety margin to the point where CHF can occur. The margin to CHF is one of the factors that limits the nuclear power plant’s ability to produce electricity. With the help of the tests that Westinghouse runs, the safety margin to the CHF can be more accurately determined, so that the reactor can safely be closer to the critical point.Westinghouse uses rods that are heated with electricity instead of nuclear fuel. In Westinghouse’s test facility, a problem has been identified, where the uppermost part of the rod has a risk of breaking due to the high temperatures. The temperatures are so high due to the rod being unable to conduct the large amount of current (max. 300kW) through the grid plate, situated at the top. The rod has a tapered end and is hammered into the grid plate’s tapered holes during assembly. The rod’s end is hollow and is attached from above using screws.To find a solution, two theoretical concepts have been developed and an eventual change of rod material has been evaluated. The purpose of the concepts is to limit the risk of problems occurring due to heat increase during operation. Both concepts have reduced hole size and length, to avoid hollow areas around the warmest part of the construction. For concept evaluation, Pugh’s concept selection method has been used. The most appropriate concept has been evaluated to be a reduced hole width, and a deeper hole with a thread insert