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Abstract
The Super Critical Water Reactor (SCWR) is a next generation reactor concept with system simplification and high thermal efficiency. The current study develops analysis capability for the US Reference SCWR design by extending existing LWR analysis codes and studies SCWR behaviors under steady state, burnup and transient conditions.
An extended version of PARCS that can analyze SCWR in steady state is developed first. A single assembly model simulating an infinite lattice of assemblies is used in this study. The results show that the moderator heating leads to a more axially symmetric effective moderator density, and has a significant impact on the axial power shape. Sensitivity calculations are performed to show how the assembly responds to perturbations in assembly power, mass flow rate, bypass ratio and heat transfer coefficient.
To study flow distribution between assemblies and transient in SCWR, a coupled PARCS/RELAP5 code package specialized for current SCWR design is developed used in the rest of the study with a whole core model.
Flow reversal in downward flowing moderator channels is discovered in steady state, bumup and transient scenarios. It is due to the positive flow rate feedback to flow density change necessary for pressure balance. Choosing different orifice sizes based on corresponding assembly powers can prevent the reversal. The results show that the reversed moderator flow accompanies a large axial power peak at the bottom of the core and reduces the core reactivity.
A burnup calculation shows that under the current design parameters, the reactor cannot sustain criticality during full cycle and a moderator flow reversal can develop during burnup.
A SCWR system model is developed which adds the balance-of-plant to the core model. Three transients are studied: loss of feedwater, loss of off-site power and loss of turbine load without scram. The results show that the maximum cladding surface temperatures satisfy the material limit. The location of maximum cladding surface temperature is not in the maximum power assembly, suggesting that normal hot channel analysis methods may not applicable for SCWR.
Future work on sub-channel analysis, full cycle burnup and more safe analyses is proposed.
