Regulatory Issues on the Safety Distance Between a VHTR and a H₂ Production Facility and an Overpressure Prediction Using Correlations and a CFD Analysis for the JAEA Explosion Test in an Open Space

Regulatory issues are discussed to establish Korean regulations on the safety distance between a very high temperature reactor (VHTR) and a hydrogen production facility. The major issues for the regulations concerning a gas explosion are an overpressure criteria, a regulation philosophy, and an overpressure prediction method. The overpressure can be predicted using empirical correlations of the trinitrotuluene (TNT) equivalent method and the multi-energy method (MEM). A comparison work of the predicted values using these correlations and the Japan Atomic Energy Agency (JAEA) explosion test results was performed to evaluate the applicability of these correlations to a VHTR. The MEM predicts the peak overpressure better than the TNT equivalent method because the explosion test results in a deflagration phenomenon. Thus, the MEM may be used effectively to estimate the peak overpressure for the gas explosion simply. A CFD analysis for the explosion test was also performed to establish an analysis methodology for a gas explosion. A spark ignition model to simulate an electric spark of 40 J in the JAEA explosion test was developed based on an energy conservation law. A sensitivity computational fluid dynamics (CFD) calculation was performed to elucidate the optimized pressure, temperature, and radius value of the spark ignition model. The CFD analysis results showed that the peak overpressure and the flame front time of arrival may be predicted better by the CFD analysis than by the MEM if the proper pressure and radius for the spark ignition model are chosen. So, the CFD analysis may be used as an accurate evaluation tool to provide the three-dimensional information of an overpressure and a time history of the overpressure variation. Therefore, it is recommended that the risk-informed regulation, the MEM, and the CFD analysis method should be used together to determine a safety distance.