(182a) Study of Plenum to Plenum (P2P) Natural Circulation Phenomena in a Dual Channel Scaled Module of Very High Temperature Reactor Design By Using CFD

A dual channel module was designed to mimic the core of prismatic VHTR (Very High Temperature Reactor) by considering one horizontal layer of a group of seven blocks, with one central block surrounded by six blocks. Two vertical cylindrical channels will be used (one for upward flow in the central block and one for downward flow in one of the six outer blocks) with a diameter similar to OSU HTTF coolant channel (0.625 inch). Length of the channel is identical to 1/4 the length of the channels in the OSU-HTTF (reactor core diameter of one foot). In this study, CFD code STAR-CCM+ and general purpose code COMSOL are used to simulate the flow and thermal conditions in the dual channel scaled model of VHTR design. These preliminary simulations are being carried out using existing models in the codes to help in the design and instrumentation of the scaled facility of dual-channel, which is being constructed to understand flow conditions under accidental scenarios as well as to gather data for code validation. Simulations have been carried out at two different system pressure values of 0.8 MPa and 4.2 MPa using STAR-CCM+ and general purpose COMSOL code. Reynolds number for the 0.8 MPa case is near the transition value, and therefore the density distributions through the two channels and in the two plena lead to the same trend when using the laminar or (k-ε) turbulence models. However, heat transfer rates on the top surface and in both channels predicted when using the k-ε turbulence model are a little smaller than the values predicted when using the laminar flow model. Under the 4.2 MPa condition, average velocities in the two channels are higher and the density is 5 ~ 7 times higher than in the 0.8 MPa case. Total heat transfer rate is consequently about nine times higher than that in the 0.8 MPa case. Velocity fields and temperature distributions are being used to guide the instrumentation placement in the experimental setup. Velocities and temperatures are within expected ranges. Locations for high velocities and temperatures as well as locations where the gradients are high have been identified. This information is useful in placement of instruments in the experimental facility. Selection of appropriate locations for the sensors, informed by a prior simulation of the expected conditions, will help in judicious use of sensors and thus acquiring reliable benchmark data for code validation.

 KEYWORDS

CFD; OSU-HTTF; Prismatic core; Natural circulation; VHTR