A computer simulation model has been designed to check the validity of newly-proposed mechanism of self-quenching streamer (SQS) induced by α-rays in gas counters. This com- putation model reproduces the SQS propagation through a series of successive avalanches which are initiated by free electrons created along an ionization track of incident α-ray. In spite of a simple modeling with some approximations, computed results show good agreement with the observed ones in nature. This means the computation model based on the newly- proposed mechanism successfully interprets the essence of the SQS phenomenon induced by α-rays.

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A neural network model is under development to predict the local power distribution in a BWR fuel bundle as a high speed simulator of precise nuclear physical analysis model. The relation between 235U enrichment of fuel rods and local peaking factor (LPF) has been learned using a two-layered neural network model ENET. The training signals used were 33 patterns having considered a line symmetry of a 8×8 assembly lattice including 4 water rods. The ENET model is used in the first stage and a new model GNET which learns the change of LPFs caused by burnable neutron absorber Gadolinia, is added to the ENET in the second stage. Using this two-staged model EGNET, total number of training signals can be decreased to 99. These training signals are for zero-burnup cases. The effect of Gadolinia on LPF has a large nonliniality and the GNET should have three layers. This combined model of EGNET can predict the training signals within 0.02 of LPF error, and the LPF of a high power rod is predictable within 0.03 error for Gadolinia rod distributions different from the training signals when the number of Gadolinia rods is less than 10. The computing speed of EGNET is more than 100 times faster than that of a precise nuclear analysis model, and EGNET is suitable for scoping survey analysis.

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Ion transport from a laser-induced metal plasma in a vapor to a cathode surface has been investigated experimentally using conventional parallel plate electrodes and a new conceptual electrode system, which consists of an anode and two cathodes, designated as"M-type electrodes". Rapid ion transport is possible using the M-type electrodes compared with the parallel plate electrodes and there are two modes of ion transport. One is a mode similar to that seen for parallel plate electrodes, in which the bulk plasma upstreams with a velocity of 1, 160m/s during the ion extraction. The other is a special mode for the M-type electrodes, in which the plasma upstream stops at its origin and ions are transported to the parallel cathodes from both sides of the plasma.

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In the PUREX process, extraction disturbances are caused by the formation, at the aqueous/organic interface, of a cumbersome stable emulsion, called"interfacial crud", stabilized by solid products. These solids are insoluble residues of fission products and precipitates. The effect of insoluble residues, on crud phenomenon, was investigated using submicronic particles of ruthenium (IV) oxide in a 3M nitric acid/30% TBP-dodecane system under electron irradia- tions. It was shown that irradiation strongly modifies the behaviour of these particles which were gradually collected at the aqueous/organic interface with increasing radiation doses. Such a behaviour can be assigned to a chemical modification of ruthenium (IV) into nitrosyl ruthe- nium (III) species which is likely to increase the affinity of the irradiated ruthenium oxide particles for the organic phase. However, these particles were not effective in stabilizing emulsions. Thus, the presence of both ruthenium oxide particles and zirconium precipitates has been studied. In such conditions, a bulky and very stable emulsion, whose characteristics are very similar to those of industrial crud, was for the first time obtained. Therefore, the critical condition of crud formation seems to be the simultaneous presence of precipitates and insoluble residues at the aqueous/organic interface.

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A relation satisfied by an optimum feed point (axial height lopt:a dimensionless height from the bottom), which maximize separation factor (and, then, separative power), was derived based on an approximate column constants in terms of operating condition such as temperature difference between hot and cold walls ΔT, feed flow rate F, pressure P, and cut θ as well as geometrical condition of thermal diffusion column for isotope separation. The value of lopt is obtained through Newton iterative solution of this relation. As for an ordinary cold-wall (Tc=288K) thermal diffusion column separating H2-HT (Tracer level: 7.3×10-10) mixture, the authors got lopt=-0.2 for operating conditions that ΔT=1, 000K, F=5×10-5m3 (i.e. 50cm3)/min (at 0.1MPa, 288K), and θ=0.5. The optimum point obtained through a rigorous two-dimensional analysis by changing parametrically the feed point was lopt=-0.17, and the optimum point can, therefore, be predicted well even by the present simple model. Moreover, the optimum feed position exists closely near the point where the radially averaged HT-concentration coincides with the feed mole fraction.

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A deterministic safety assessment methodology has been developed to evaluate long-term radiological consequences associated with geologic disposal of high-level radioactive waste, and to demonstrate a generic feasibility of geologic disposal. An exposure scenario considered here is based on a normal evolution scenario which excludes events attributable to probabilistic alterations in the environment. A computer code system GSRW thus developed is based on a non site-specific model, and consists of a set of sub-modules for calculating the release of radionuclides from engineered barriers, the transport of radionuclides in and through the geo- sphere, the behavior of radionuclides in the biosphere, and radiation exposures of the public. In order to identify the important parameters of the assessment models, an automated procedure for sensitivity analysis based on the Differential Algebra method has been developed to apply to the GSRW.

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Public acceptance has become an important factor in nuclear power program particularly after Chernobyl accident and recent rapid democratization in Korea. A method reflecting public opinions in order to improve public acceptance is to find out the public preference values for its policy alternatives. In this study, the conjoint analysis was applied to find out the quantitative values of public preferences for twelve policy alternatives to support commu- nities surrounding nuclear power plants in Korea. To implement the analysis, questionnaires of trade-off matrix form were mailed to the science teachers of middle or high school through- out the country who had the experience of visiting nuclear power plant. The quantitative preference values for potential policy alternatives were estimated, which made it possible to forecast the effectiveness of each option. It was revealed that the improvement of reactor safety 100 times and the establishment of civilian monitoring system for nuclear safety would be two best options to improve public acceptance of nuclear power in Korea.

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Using the low electric energy railgun system, dummy pellet acceleration tests have been conducted to investigate the application of the electromagnetic railgun system for high-speed pellet injection intofusion plasmas. The primary objective of the development is to improve the pellet acceleration efficiency and durability of the rail materials. In the system, the pellet is pre-accelerated before railgun acceleration. A laser beam is used to induce plasma armature. The ignited plasma armature is accelerated by an electromagnetic force that accelerates the pellet. As low electric energy was used, rail materials were used for multiple operations. Tungsten-alloy rail provided longer durability and slightly higher energy conversion coefficient than copper rail. The energy conversion coefficient was from 0.3 to 0.5% using a plastic insulator. A ceramic insulator improved the energy conversioncoefficient by 80%. The highest pellet velocity was 1.7km/s using wooden pellets accelerated by 1m-long railgun. Based on the findings, it is estimated that the hydrogen pellet has the potential to be accelerated to 5km/s using a 3m-long railgun.

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This report describes the development and testing of a coolant leak detection system for an inlet feeder pipe of an advanced thermal reactor (ATR) using high temperature-resistant microphones. Such microphones must be resistant to both high temperatures and high radia- tion doses. Leakage sound characteristics, attenuation of the sound level in a heat insulating box for the inlet feeder pipes, and background noise were investigated using the experimental facility and the prototype ATR'FUGEN'. The optimum frequency ranges for the microphone were then determined based on the observed leakage sound and background noise. The ability of the microphone to discriminate between leaks and other burst-type noises was also investi- gated by statistical analyses. Finally, it was confirmed that the present method could detect a leak within a couple of seconds.

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The applicability of the REFLA/TRAC code, which is one of best-estimate codes based on two-fluid model, was assessed for a typical small-break loss-of-coolant accident (SBLOCA) transient of PWR. The main assessment subject was to investigate whether the physical models in REFLA/TRAC can apply to the transient under SBLOCA condition (high pressure/low flow rate) or not. The applicability had been verified under low pressure/low flow rate condition during reflood phase in large-break LOCA transients of PWR. The assessment calculation was performed for Run SB-CL-05 (5% cold leg break SBLOCA test) in the ROSA-IV large-scale test facility. The REFLA/TRAC almost predicted the thermal-hydraulics in primary loops while the hydrau- lic models should be improved for regions at the pump side of loop seal and at the up-flow side of steam generator tube under CCFL condition. The core thermal-hydraulic models in REFLA/ TRAC give better prediction for core full-height differential pressure and the peak clad tem- perature (PCT) than those in original TRAC code. The PCT by the models in TRAC was lower about 100K than the measured one but the PCT by those in REFLA/TRAC was lower only about 40K.

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