The development of technologies of safety analysis for LMR ('03)

The developmental objectives of the project, 'The development of safety analysis techniques in LMR', are the code development for the subchannel blockage analysis, the code development for the system transient analysis, the code development for the HCDA(Hypothetical Core Disruptive Accident) analysis, the preliminary safety analysis for KALIMER-600 equipped with the components of new concepts, and the establishment of data base. The purpose of the analysis for subchannel blockage in the subassembly of LMR is to represent quantitatively that the maximum damage due to the accident is within the safety criteria. The computational program should be developed to simulate the thermal hydraulic phenomena and to verify the safety of LMR for the accident. For the purpose, the hybrid scheme has been implemented into the MATRA-LMR code based on the upwind scheme to analyze the various flow fields occurred in the subchannel blockage accident. The turbulent mixing models using the CFX code were assessed to compute more precisely the heat transfer between subchannels. Through this assessment, empirical correction factors of 1.7 for the heat conduction, 0.006 for the turbulent mixing coefficient were obtained. The distributed resistance model instead of wire forcing function has been developed to represent the more exact flow field due to wire-wrap. Other models, such as heat conductor model and various turbulent mixing model, have been implemented into the MATRA-LMR. The ORNL THORS 19-Pin FFM-5B tests have been assessed to validate above new models using the improved MATRA-LMR. The results using MATRA-LMR were well agreed with the experimental data. The subchannel blockage accidents which assumed to be occurred at the three locations for the conceptual plant of KALIMER-600 have been analysed according to blockage size using the MATRA-LMR code. The results of calculations for the design basis events which 6 subchannels were blocked showed the margins of the 290 7.dog. C up to the sodium boiling point, of the about 100 7.dog. C up to the limit of long term cladding damage. On the other hand, the case of the beyond design basis event which 54 subchannels were blocked at the middle location was calculated to violate the limit of long term cladding damage. The flow field at the exit region of subassembly has been analysed using the CFX code to detect subchannel blockage. As a results of the calculations, the detector to identify the subchannel blockage accident should be installed within 30 cm from the exit of subassembly. It is most important in the safety assessment for a metallic fueled liquid metal fast reactor in contrast with a light water reactor or a heavy water reactor, not only to evaluate the fulfillment of the safety criteria but also to analyse the inherent safety characteristics with taking into account the reactivity feedback effect under accidents, for instance, reactivity insertion or loss of heat sink accidents. The SSC-K, the system transient analysis code, has been developed for the new components of KALIMER-600. The reactivity feedback effect of control rod drive line is generated because of the displacement difference between the control rod drive line and reactor vessel. Since above 9.5 m from the bottom in the KALIMER-600 was submerged into the hot pool, the thermal expansion model of the control rod drive line has been improved to consider the temperature of hot pool. The KALIMER-600 equip with PVCS(Passive Vessel Cooling System) as well as PDRC(Passive Decay heat Removal Circuit) while the KALIMER-150 only equip with PVCS. The governing equations that sodium coolant assumed to be incompressible fluid have been setup to model the PDRC into the SSC-K code. Solving these equations decided the sodium flow rate, the temperature distribution, and heat transfer rate in the DHX(Direct Heat Exchanger) and in the AHX(Air Heat Exchanger). The preliminary assessment using the improved SSC-K code has been performed for the KALIMER-600. UTOP accident is occurred by the insertion of the positive reactivity due to the withdrawal of control rod. The calculation results showed that the maximum temperatures for both of coolant and clad satisfied the safety criteria. The calculation results for ULOF accident which lose the injection flow into the core revealed that the core power was maintained 15 % of rated power and 8.5 % of rated power was also maintained after the end of pump coastdown. The fuel rod temperature was increased due to the unbalance of the power and coolant flow at the early of the transient, however, after that period, it was slowly decreased to fulfill the safety limit. The results for the capability of long term cooling also represent that the key parameters do not violate the safety limit. HCDA analysis model has been developed and the development has been focused on the improvement of the structure and the model of MELT-III which was the mechanistic code used to analyse HCDA initial phase and the application of state equation of metallic fuel to VENUS-II. The analysis model of SIEX-II in the MELT-III/STEADY has been improved and carried out the steady state calculation for the KALIMER-150. The reactivity feedback model of MELT-III/TRANSIENT has been improved, modularized the code structure, and developed the GUI(Graphic User Interface) program. SWEEP(Scoping Work Energy Evaluation Program) of the integrated analysis program has been developed to calculate the generation of work energy potential due to the vaporization of fuel and sodium. Using the SWEEP, the mechanistic work energy potential has been estimated in the HCDA accident, the results has been compared to the result of SOCOOL-II of the detail analysis code. The design database and project management system has been established as well