Transient analysis of OSU-MASLWR with RELAP5

The present paper deals with the assessment of the original and a modified version of RELAP5/MOD3.3 against the OSU Multi Application Small Light Water Reactor (OSU-MASLWR). The new implemented features regard suitable correlations for the heat transfer coefficient evaluation in helical geometry. Furthermore, two different modelling of the Helical Coil Steam Generator (HCSG) are assessed. In the first approach, HCSG's primary and secondary sides are collapsed in a single pipe component. In the second model, three equivalent pipes are conceived for the simulation of the three ranks composing the HCSG. Two different power manoeuvring experiments are reproduced. The simulations highlight a satisfactory agreement in both the transients. Nevertheless, the modified code shows enhanced capabilities in the prediction of the HCSG operation. This is due to the improvements adopted in the modified version of RELAP5/MOD3.3 that allows a better modelling of the dryout phenomena occurring within helical tubes, as well as a better estimation of the primary side heat transfer coefficient. The better agreement of the heat exchange is propagated to the primary system, resulting in a more accurate prediction of the inlet and outlet core temperatures, and primary flow rate.