[en] A real time reactor system analysis code, ARTIST, based on drift flux model has been developed to investigate the transient system behavior under low pressure, low flow and low power conditions with noncondensable gas present in the system. The governing equations of the ARTIST code consist of three mass continuity equations (steam, liquid and noncondensable), two energy equations (gas and mixture) and one momentum equation (mixture) constituted with the drift flux model. The capability of ARTIST in predicting two-phase flow void distribution in the system has been validated against experimental data. The results of the ARTIST axial void distribution at low pressure and low flow, are far better than the results of both the homogeneous model of TASS code and the two-fluid model of RELAP5/MOD3 code. Also, RELAP5/MOD3 calculation shows the large amplitude of void fraction oscillations at low pressure. These results imply that interfacial momentum transfer terms in the two-fluid model formulation should be carefully constituted, especially for the low pressure condition due to the big density differences between steam and water. Thermal-hydraulic state solution scheme is developed when noncondensable gas exists. Numerical consistency and convergence of obtaining equilibrium state is tested with the ideal problems for various situations including very low partial pressure conditions. Calculated thermal-hydraulic state for each test shows consistent and expected behaviour. A new multi-layer back propagation network algorithm for calculating the departure from nucleate boiling ratio (DNBR) is developed and adopted in ARTIST code in order to have real-time DNBR evaluation by eliminating the tandem procedure of the transient DNBR calculation. The algorithm trained by different patterns generated by latin hypercube sampling method on the performance space is tested for the randomly sampled untrained data and the transient DNBR data. The uncertainty of the algorithm is quantified by the generalization ratio and the one-sided 95/95 tolerance limit. Results show that the accuracy depends on the axial flux shape characterization method. And the computation time is so small that it can be neglected compared to those of DNBR calculation code. ARTIST code can be utilized as a practical analysis tool in analyzing the nuclear reactor transients and accidents occurring at low pressure, low flow and low power conditions which usually contains the noncondensable gas by significantly reducing oscillations which require a long computation time in the two-fluid model system codes

[en] TASS 1.0 is consisted of two parts. First part analyze the reactor transients and calculates system parameters during the transients. This part comprises the program of the primary and secondary thermal hydraulic model, the core model, the transfer model, the protection and the control system. The second part is the TASS executive routine. This part provides an operating system for TASS. The user can execute TASS with above models interactively through the TASS executive routine. But TASS executive routine is very large and the function is restricted. The development of GRIS( Graphical Routines for Interactive Simulation) was initiated to overcome the limitation of the TASS executive routine. TASS-NPA was developed based on GRIS. TASS-NPA simulation can be performed on Windows 95 and Window Nt of IBM Pc. The verification of the TASS-NPA function was performed with the Feed Water Line Break of Kori 3/4. (Author). 6 refs., 3 tabs., 26 figs

[en] The state-of-the-arts for the integral reactor was performed to investigate the safety features. The safety and performance of SMART were assessed using the technologies developed during the study. For this purpose, the computer code system and the analysis methodology were developed and the safety and performance analyses on SMART basic design were carried out for the design basis event and accident. The experimental facilities were designed for the core flow distribution test and the self-pressurizing pressurizer performance test. The tests on the 2-phase critical flow with non-condensable gas were completed and the results were used to assess the critical flow model. Probabilistic Safety Assessment(PSA) was carried out to evaluate the safety level and to optimize the design by identifying and remedying any weakness in the design. A joint study with KINS was carried out to promote licensing environment. The generic safety issues of integral reactors were identified and the solutions were formulated. The economic evaluation of the SMART desalination plant and the activities related to the process control were carried out in the scope of the study

[en] During LOCA Iodine is leaked from RCS along with the coolant in the form of CsI and finally collected in the sump. When the iodine in the sump is regasified, the material of the containment vessel is likely to be damaged, and the iodine is highly likely to be leaked to the outside due to the cracks in the containment vessel or through the vent. So it can threaten the safety of the NPP to a considerable degree. Accordingly, to prevent the regasification of the iodine inside the sump solution, it is stipulated that the pH of the sump solution should be 7.0 or greater and 8.5 or less. The pH of the sump solution is determined by the boric acid-neutralizing additive (referred to as TSP hereinafter) reaction, organic reaction, and the chemical equilibrium of fission products. Accordingly, correct pH estimation in consideration of them is necessary As the pH calculation method considering only the boric acid-TSP reaction is presently used in Korea, the results are not accurate and calculation was complicated. Accordingly, this study intends to take other compounds affecting the pH of the sump solution into consideration, and to use the free minimization, a theory of chemical equilibrium, and the Lagrange Multiplier Technique to establish a simple and accurate method of calculating the pH. The first-year study investigated the correlation of the pH-Iodine behavior and the substances affecting pH. In this year's study the program for calculating the pH of the sump solution will be established by improving the SOLGASMIX-PV code, the chemical equilibrium calculation program

[en] We construct classical solutions for magnetic monopole operators in N = 6 superconformal Chern-Simons-matter theories. In particular, we explicitly find solutions with unequal magnetic flux contents in the two U(N) gauge groups, whose existence has been known only indirectly. We also study the ground state degeneracies of the U(2) × U(2) monopoles by quantizing the moduli of the solution.

[en] SMART is an integral type reactor of 330 MW, which enhances its safety by adopting inherent safety design features. Thermal hydraulic characteristics of transients in heat removal by a secondary system for the SMART have been carried out by means of the TASS/SMR and MATRA codes. The primary, secondary, and passive residual heat removal systems RHRS of the SMART were modeled properly. Then, a set of transients for the whole system was investigated. The results of the analyses using the conservative initial and boundary conditions showed that the safety features of the SMART design carried out their functions well and there was a strong moderator temperature coefficient due to the soluble boron free reactor affected by the transient behavior. The natural circulation was well established in the primary and passive residual heat removal systems during the transients and was enough to ensure a stable plant shutdown condition after a reactor trip

[en] SMART was an integral type reactor of 330 MWt, which enhanced safety by adopting inherent safety design features. Thermal hydraulic characteristics on transient of heat removal increase by the secondary system for the SMART have been carried out by means of TASS/SMR code. The primary, secondary, and residual heat removal systems of the SMART were modeled properly. Then, a set of transients for the whole system was investigated. The results of the analyses using the conservative initial and boundary conditions showed that the safety features of the SMART design well carried out their functions and large moderator temperature coefficient due to the soluble boron free reactor affected on the transient behavior

[en] The present study is to assess the applicability of the best-estimate thermal-hydraulic codes, MARS 1.4, for analysis of thermal-hydraulic behavior in PWRs during natural circulation conditions. The code simulates a BETHSY test 4.1a, which was conducted in the integral test facility of BETHSY. The test represents the cooling states of the primary cooling system under two-phase natural circulation and reflux condensation mode with conditions corresponding to the residual power, 2 % of the rated core power value, and a constant pressure of 6.8 MPa at the secondary system. Based on MARS calculations, the major thermal-hydraulic behavior during natural circulation is evaluated and the differences between the experimental and calculated results are identified

[en] Thermal hydraulic analysis for the helically coiled steam generator has been carried out by means of the MARS code for a full range of reactor operating conditions. A selected event is an increased main steam flow under nominal conditions. Under forced convection condition, a dominant heat transfer in the steam generator is a nucleate boiling mode, which transfers 72% of total generated heat. For natural convection condition, 40% and 60% of the total energy is extracted in the steam generator by single-phase liquid and a nucleate boiling heat transfer, respectively. And 80% and 20% of the extracted energy is exhausted at the heat exchanger by a condensation and single-phase liquid heat transfer. The flow shows an oscillating behavior due to instability in the two-phase natural convection

[en] An analytical model was developed to simulate behavior of the liquid film formed on the outside surface of the steel containment vessel of PCCS including the ellipsoidal dome and the vertical wall. The model was coupled with CFX code using the user subroutines provided by the code, and a series of numerical calculations were performed to evaluate the evaporative heat transfer coefficient at the interface. Numerical results for Sherwood number and evaporative heat transfer coefficient were compared with the experimental data. The results were in good agreement with the experimental data. The calculated liquid film thickness showed good agreement with that of Sun except an upper portion of the channel. The model was applied to the full scale of PCCS to investigate the effects of dome and chimney on the evaporation rate. The results showed that the heat transfer coefficient in the dome region, where the flow cross-sectional area decreases and the swirling occurs, was lower than that of the vertical annulus region. The calculated evaporative heat transfer coefficient was about 20 times larger than that of the dry cooling. Sensitivity studies on the gap size and the wall temperature were also performed to figure out their effects on the heat transfer coefficient and inlet air average velocity. Through the analysis of the dryout point, the minimum liquid film flow rate to cover the entire surface of the vessel was estimated