Natural convection tests with the In-Core-Structure Test Section (T2) of the Helium Engineering Demonstration Loop (HENDEL)

Natural convection tests were carried out with the use of In-Core Structure Test Section (T2) of the Helium Engineering Demonstration Loop (HENDEL) with helium gas pressure from 1.0 to 3.0 MPa to investigate thermal hydraulic characteristics inside the reactor pressure vessel of Modular High Temperature Gas cooled reactor (MHTGR) under the condition of loss of forced coolant flow accidents. The HENDEL-T2 is a simulated model of the core bottom structure (CBS) of HTGR. Analytical code -Thermal Analytical Code for Test of Passive Cooling System by HENDEL-T2 (THANPACST2)- was applied to the natural convection test. The analytical results were compared with the test data to verify the validity of analytical method and model. Thermal hydraulic characteristics of the transients were investigated by the experimental and the analytical studies. The results are summarized as follows. (1) Analytical results in consideration of the leakage of helium gas through the CBS graphite blocks reveal that: Pressure difference between cold and hot helium gas agrees with the test results, Temperature distribution on the pressure vessel after 17 hours from the onset of natural circulation is estimated in the range of -11% - +29%, compared with the test data, The maximum temperature differences of hot plenum block and core support plate are estimated to be +27% and +44%, compared with the test data, respectively, after 20 hours. (2) Temperature transients of components were affected by the leakage flow of helium gas through the CBS graphite blocks, helium gas pressure and heat losses from high temperature components such as a hot gas duct between HENDEL and T2 test section. (author)