Scaling Analysis and Test Facility Design for Steam Ingress Accident in MHTGR

High-temperature Gas-cooled Reactors (HTGRs) are attractive due to their inherent safety features and
high power conversion efficiency. Due to low technical risks, the steam Rankine cycle is being
considered as one of the power cycle options for near-term deployment of commercial HTGRs. In the
proposed HTGR steam Rankine cycle designs, the feedwater/steam pressure on the secondary side is
typically much higher than the helium pressure on the primary side, which may lead to water/steam
ingressing into the primary side during a steam generator tube rupture accident. The ingressed
moisture could result in positive reactivity to affect the control of the reactor. In addition, chemical
reactions of the ingressed moisture and graphite in the reactor primary system could weaken the
graphite structures and produce flammable gas, such as H2 and CO. Although some numerical analyses
have been carried out in the literature, these models/analyses have not been validated against qualified
experimental data. Therefore, the objective of our current research is to experimentally study the steam
ingress accident in a scaled-down test facility. The steam Rankine cycle Modular High Temperature
Gas-cooled Reactor (MHTGR) is chosen as the prototype for this study. The three-level scaling
analysis methodology developed at Purdue University has been adopted for designing the test facility.
Following the scaling analysis, a steam ingress test facility capitalized on an existing air ingress test
facility has been developed, which has a height ratio and area ratio of 1/20 and 1/10, respectively to
the prototypic reactor design.