Investigating leakage and bypass flows in an HTR using a CFD methodology

An area that has been identified as significantly important in the development of a high temperature reactor (HTR) is the prediction of leakage and bypass flows. It is therefore essential to understand the influence of leakage and bypass flows on the thermal performance of an HTR.A methodology was developed to conduct an integral thermal analysis of a reactor using a CFD approach. One of the main objectives was to include leakage and bypass flow paths in order to provide a capability for simulating these very detailed flows.This paper investigates leakage and bypass flows through the PBMR reactor unit. It was found that, although these flows are dependent on the pressure drop through the pebble bed, a change in pebble bed pressure drop does not result in a similar change in the predicted leakages flows. It is also shown that the ability to account for leakage and bypass flows in an integral manner can help designers to focus their efforts on the specific regions that need to be targeted for the improvement of the life expectancy of the graphite blocks. Furthermore, leakage and bypass flows were found to reduce the pressure drop across the reactor unit while increasing the peak fuel temperatures.

► Establishment of a modeling capability to simulate the integral thermal operation of an HTR.
► Leakage and bypass flow is considered to have a crucial influence on the operation of an HTR.
► The combination of an integral approach, including leakage flows, allows for an improved analysis methodology.
► This approach has resulted in new insights into the mechanism of leakage and bypass flows.
► This paper presents findings on the influence of leakage and bypass flow on an HTR.