Results 1 - 10 of 96
Results 1 - 10 of 96. Search took: 0.017 seconds
|Sort by: date | relevance|
[en] Highlights: • Power density profile effects to the reactor safety feature. • Uniform power density in a core enhances the passive safety margin of core. • A smaller-sized reactor could be designed without degrading safety performance to achieve an economic gain. - Abstract: Reactor designs with passive safety features have been actively developed ever since the Fukushima Daiichi Nuclear Power Plant accident in 2011. In our previous works, we investigated the design of a small, prismatic HTGR for passive decay heat removal and the relations of parameters for successful decay heat removal. For the power density distribution of the HTGR, the Bessel function was used in the radial direction and the cosine function in the vertical direction, assuming a barrel-type cylindrical core. In practice, the power density distribution is usually flattened by introducing burnable poisons or control rods during operation to prevent non-uniform power production throughout the core. The power density profile might have an effect on the passive safety features of the HTGR. Therefore, the influence of a flat power distribution on the passive safety features of a prismatic HTGR was investigated in the present study. Results showed that flattening the power density profile allowed greater thermal power with the same safety performance without changing the reactor dimensions or calculation conditions. On the other hand, a same-power reactor could be designed with a smaller size without worsening its passive safety features, which is highly advantageous from an economical point of view. Hence, it was confirmed that reactor safety characteristics could be improved by implementing uniform power density in the design.
[en] Highlights: • Transient analyses in super-critical condition were performed for multiple-region tank system. • The neutronic coupling between the tanks was taken into account in analysis. • Total released energy in two-fuel-solution-tank system can be predicted based on the released energy in single-tank system. - Abstract: A calculation code was developed for transient analysis of the total released energy in a criticality accident with two fuel-solution tanks. The calculation method was confirmed to be effective for transient analysis in a fuel-solution-tank system. The verification of the code was performed by comparing the calculation results with those of TRACY experiments. In the code, neutronic coupling between the tanks is treated. Using this code, transient analyses were performed for a two-tank system using different feedback models. The analyses confirmed that the total energy released in criticality accident with two fuel-solution tanks can be estimated using the knowledge of the total energy released in a single-fuel-solution-tank system.
[en] Highlights: • Improvement of pebble bed reactor using the accumulative fuel loading scheme as a fuel management method. • Optimization of fuel composition by varying the HM/pebble and "2"3"5U enrichment. • By using the optimum fuel composition, large excess reactivity occurred in the BOL condition. • Low "2"3"5U enrichment was used in the BOL to reduce the excess reactivity. - Abstract: Innovative nuclear power plant designs and high-efficiency utilization of nuclear fuel are important issues in the field of nuclear power. Pebble bed reactors with an accumulative fuel loading scheme have been introduced to obtain high burnup and efficient uranium utilization. Monte Carlo codes, MVP/MVP-BURN, were used to perform the neutron transport and burnup calculation. Optimum fuel composition was obtained in the finite geometry using 6-g HM of uranium per pebble ball with 20% "2"3"5U enrichment. The results show that the maximum burnup was 223 GWd/t with 10.2 years of operation. However, a large amount of excess reactivity occurred in the initial condition. One of the options for minimizing this was to reduce the enrichment of "2"3"5U from 20% to 3.42%, only for the initial condition. The result showed a relatively small amount of excess reactivity during the operation period. However, the maximum burnup decreased to 199 GWd/t with 8 years of operation.
[en] Highlights: • A 300 MW_t Small Pebble Bed Reactor with Rock-like oxide fuel is proposed. • Using ROX fuel can achieve high discharged burnup of spent fuel. • High geological stability can be expected in direct disposal of the spent ROX fuel. • The Pebble Bed Reactor with ROX fuel can be critical at steady state operation. • All the reactor designs have a negative temperature coefficient. - Abstract: A pebble bed high-temperature gas-cooled reactor (PBR) with rock-like oxide (ROX) fuel was designed to achieve high discharged burnup and improve the integrity of the spent fuel in geological disposal. The MCPBR code with a JENDL-4.0 library, which developed the analysis of the Once-Through-Then-Out (OTTO) cycle in PBR, was used to perform the criticality and burnup analysis. Burnup calculations for eight cases were carried out for both ROX fuel and a UO_2 fuel reactor with different heavy-metal loading conditions. The effective multiplication factor of all cases approximately equalled unity in the equilibrium condition. The ROX fuel reactor showed lower FIFA than the UO_2 fuel reactor at the same heavy-metal loading, about 5–15%. However, the power peaking factor and maximum power per fuel ball in the ROX fuel core were lower than that of UO_2 fuel core. This effect makes it possible to compensate for the lower-FIFA disadvantage in a ROX fuel core. All reactor designs had a negative temperature coefficient that is needed for the passive safety features of a pebble bed reactor
[en] Highlights: • The concept of a small pebble bed reactor with ROX fuel is proposed. • Optimization of UO_2-ROX fuel composition was performed by cell calculation. • The ROX fuel pebble bed reactor with OTTO cycle could achieve high burnup and FIFA. • The peak power density could be reduced by decreasing reactor power. • The reactor design showed a negative temperature coefficient. - Abstract: The conceptual design of a small rock-like oxide fuel pebble bed reactor with once-though-then-out (OTTO) cycle is proposed here. TRISO-coated particles based on AGR-1 design were used to achieve a target burnup larger than 100 GWd/t-HM without any failure of spent fuel. In the first step, optimization of fuel composition was implemented by cell calculations. After that, whole core calculations were performed with and without movement of the fuel pebbles. With a heavy metal amount of 2 g per pebble and 20% uranium enrichment, the pebble bed reactor with OTTO cycle could achieve maximum burnup of about 145 GWd/t-HM and fissions per initial fissile atom (FIFA) of 75%. The results show that the core height can be reduced due to the fact that the impact of bottom core on burnup performance is insignificant. Also, the peak power density of the reactor exceeded the limit of that for the PBMR design. Therefore, subsequent optimizations of the core design were carried out by decreasing the core height and reactor power to reduce the construction cost as well as the peak power density. A reactor with 6-m core height and 120-MW_t_h reactor power was ultimately determined as the optimal design for a pebble bed reactor with ROX fuel. This optimal design also has a negative temperature coefficient, and the peak power density was less than the limit of 10 W/cm"3.
[en] The α-particle pulse-height distribution measured from irradiated LBE is determined from the polonium distribution in it. The unfolding of vertical polonium distribution in irradiated LBE ingot is performed with the unfolding code UFOQ. The code uses quadratic programming to consider the constraint that polonium distribution does not have negative values. The response function defined as normalized α-particle pulse-height distributions caused by α-particles emitted from polonium in surface region, which is divided vertically to thin layers, of LBE ingot is calculated by Monte Carlo method. The polonium distribution around surface of irradiated LBE ingot is obtained clearly with the response function calculated for the surface region divided narrowly. Also, the polonium distribution in deeper layer of the surface region is obtained consistently with the response function calculated for the surface region divided widely
[en] Highlights: • The melt refining (MR) method was applied to solve fuel integrity problem in CANDLE. • The fuel element was assumed cut into several melt-and-refining-regions (MRRs). • Nuclide composition was homogenized in the 9 MRR, 5 MRR and 3 MRR at each cycle. • The CANDLE burning can be achieve if a proper number of MRR is selected. • The fuel volume fraction can be reduced if fission products are removed in MR. - Abstract: The application of melt and refining procedures has demonstrated great potential to solve the fuel integrity problem in the high-burnup condition of CANDLE reactors. However, if the melt and refining procedures are applied during operation, the reactor might lose all the nuclide distribution in the fuel pins and CANDLE burning becomes impossible to achieve. In this study, the application of melt and refining was simulated in two cases to overcome the cladding limitation at ⩾200 dpa. It became clear that if the number of axial regions for the melt and refining procedure is chosen properly, CANDLE burning is possible to achieve even if each region is homogenized by the procedure. In addition, the fission products released by the melt and refining procedure increase the burnup performance of the CANDLE core remarkably. It is also possible to improve the engineering design by reducing the fuel volume fraction to a minimum at 48%.
[en] Highlights: • The melt and refining process with cooling time was applied to the CANDLE burning. • The effect of the cooling during melt and refining process was investigated for one, two, four and eight years cooling. • The change of effective multiplication factors in the equilibrium condition depends on the cooling time. • If the cooling time is equal to or less than 4 years, it will give little effects on the effective multiplication factor. • Burnup performance and neutron flux has not changed a lot by the cooling. - Abstract: The effects of cooling during the melt and refining process in a CANDLE burring reactor was investigated. The introduction of cooling time during the melt and refining process had an impact on the CANDLE burning. A cooling time of one, two, four and eight years were simulated at each melt and refining cycle. The effects of cooling on excess reactivity varied with the cooling time. A longer cooling time may reduce the excess reactivity of a CANDLE burning reactor in the equilibrium condition to negative. In this case, the core design of the CANDLE might need to be optimized to compensate for the decrease of excess reactivity due to the accumulation of Am-241 during the cooling period.
[en] Nuclear-pumped laser is produced by pumping laser active medium with kinetic energy of fission fragments. In this pumping process, the kinetic energy of fission fragments is transferred to laser active medium by collisions of fission fragments with laser active medium. The energy is converted to optical energy with the transition of energy levels of the laser active medium. Experimental and theoretical study on nuclear pumped laser has been performed in IPPE using a coupled reactor. The coupled reactor consists of a twin-core pulse reactor with highly enriched metallic uranium and a subcritical laser module with highly enriched metallic uranium. The purpose of study is to design a low enriched uranium coupled reactor for nuclear-pumped laser which consists of pulse reactors and a subcritical laser module. Neutronic calculations were performed for a coupled reactor with highly enriched metallic uranium and low enriched metallic uranium to show the possibility of low enriched uranium coupled reactor for nuclear pumped laser
[en] This report is presented on a reactor laboratory course for graduate students using large facilities in national laboratories in Japan. A reactor laboratory course is offered every summer since 1990 for all graduate students in the Nuclear Engineering Course in Tokyo Institute of Technology (TIT), where the students can choose one of the experiments prepared at Japan Atomic Energy Research Institute (JAERI), Power Reactor and Nuclear Fuel Development Corporation (PNC) and Research Reactor Institute, Kyoto University (KUR). Both JAERI and PNC belong to Science and Technology Agency (STA). This is the first university curriculum of nuclear engineering using the facilities owned by the STA laboratories. This type of collaboration is promoted in the new Long-Term Program for Research, Development and Utilization of Nuclear Energy adopted by Atomic Energy Commission. Most students taking this course reported that they could learn so much about reactor physics and engineering in this course and the experiment done in large laboratory was a very good experience for them. (author)