Relap5-3d model validation and benchmark exercises for advanced gas cooled reactor application

摘要

High-temperature gas-cooled reactors (HTGR) are passively safe, efficient, andeconomical solutions to the world??s energy crisis. HTGRs are capable of generating hightemperatures during normal operation, introducing design challenges related to materialselection and reactor safety. Understanding heat transfer and fluid flow phenomenaduring normal and transient operation of HTGRs is essential to ensure the adequacy ofsafety features, such as the reactor cavity cooling system (RCCS). Modeling abilities ofsystem analysis codes, used to develop an understanding of light water reactorphenomenology, need to be proven for HTGRs. RELAP5-3D v2.3.6 is used to generatetwo reactor plant models for a code-to-code and a code-to-experiment benchmarkproblem.The code-to-code benchmark problem models the Russian VGM reactor forpressurized and depressurized pressure vessel conditions. Temperature profilescorresponding to each condition are assigned to the pressure vessel heat structure.Experiment objectives are to calculate total thermal energy transferred to the RCCS forboth cases. Qualitatively, RELAP5-3D??s predictions agree closely with those of othersystem codes such as MORECA and Thermix. RELAP5-3D predicts that 80% of thermal energy transferred to the RCCS is radiant. Quantitatively, RELAP5-3D computesslightly higher radiant and convective heat transfer rates than other system analysiscodes. Differences in convective heat transfer rate arise from the type and usage ofconvection models. Differences in radiant heat transfer stem from the calculation ofradiation shape factors, also known as view or configuration factors. A MATLAB scriptemploys a set of radiation shape factor correlations and applies them to the RELAP5-3Dmodel.This same script is used to generate radiation shape factors for the code-toexperimentbenchmark problem, which uses the Japanese HTTR reactor to determinetemperature along the outside of the pressure vessel. Despite lacking information onmaterial properties, emissivities, and initial conditions, RELAP5-3D temperature trendpredictions closely match those of other system codes. Compared to experimentalmeasurements, however, RELAP5-3D cannot capture fluid behavior above the pressurevessel. While qualitatively agreeing over the pressure vessel body, RELAP5-3Dpredictions diverge from experimental measurements elsewhere. This difference reflectsthe limitations of using a system analysis code where computational fluid dynamics codesare better suited.