This paper studies the U.S. reference Supercritical Water Reactor (SCWR) design with the newly extended coupled codes PARCS/RELAP5. Steady-state, burnup, and loss-of-feedwater transients are simulated. A possible flow reversal in moderator channels is found in the simulations, and the impact of this reversal on power peaking and reactivity is observed. The transient results show that the assembly with the maximum cladding surface temperature (MCST) and the assembly with the maximum power are different and that the MCST is within the material limit under the current design.