Three dimensional effects in analysis of PWR (Pressurized Water Reactor) steam line break accident. Final report

A steam-line-break accident is one of the possible severe abnormal transients in a pressurized water reactor. TITAN, a coupled code with state-of-the art neutronics and thermal-hydraulics models, is therefore modified and applied to steam-line-break accident simulations. The capabilities that are added to the code for a steam line break analysis include multi-region core-inlet temperature forcing function, total-inlet-coolant flow rate boundary condition, total inlet coolant flow rate transient simulation capability, boron tracking equations, flow/coolant temperature transient plus control-rod transient option, and one-dimensional, fully implicit numerical scheme for thermal-hydraulics calculations. The modifications to TITAN are tested with a ten-channel PWR model. For inlet coolant temperature transients test calculations lead to the conclusion that there is no significant difference between the results of closed- and open-channel calculations until boiling occurs.