Byung Chul Lee

Prediction of major transient scenarios for severe accidents of nuclear power plants

It is very difficult for nuclear power plant operators to predict and identify the major severe accident scenarios following an initiating event by staring at temporal trends of important parameters. In this regard, a probabilistic neural network (PNN) that has been applied well to the classification problems is used in order to classify accidents into groups of initiating events such as loss of coolant accidents (LOCA), total loss of feedwater (TLOFW), station blackout (SBO), and steam generator tube rupture (SGTR). Also, a fuzzy neural network (FNN) is designed to identify their major severe accident scenarios after the initiating events. The inputs to PNN and FNN are initial time-integrated values obtained by integrating measurement signals during a short time interval after reactor scram. An automatic structure constructor for the fuzzy neural network automatically selects the input variables from the time-integrated values of many measured signals, and optimizes the number of rules and its related parameters. In cases that an initiating event develops into a severe accident, this may happen when plant operators do not follow the appropriate accident management guidance or plant safety systems do not work, the proposed algorithm showed accurate classification of initiating events. Also, it well predicted timings for important occurrences during severe accident progression scenarios, which is very helpful to perform severe accident management.

Development and characteristics of the HANARO neutron irradiation facility for applications in the boron neutron capture therapy field

The HANARO neutron irradiation facility for various applications in the boron neutron capture therapy (BNCT) field was developed, and its characteristics were investigated. In order to obtain the sufficient thermal neutron flux with a low level of contamination by fast neutrons and gamma rays, a radiation filtering method was adopted. The radiation filter was designed by using a silicon single crystal, cooled by liquid nitrogen, and a bismuth crystal. The installation of the main components of the irradiation facility and the irradiation room was finished. Neutron beam characteristics were measured by using bare and cadmium-covered gold foils and wires. The in-phantom neutron flux distribution was measured for flux mapping inside the phantom. The gamma-ray dose was determined by using TLD-700 thermoluminescence dosimeters. The thermal and fast neutron fluxes and the gamma-ray dose were calculated by using the MCNP code, and they were compared with experimental data. The thermal neutron flux and Cd ratio available at this facility were confirmed to be 1.49 x 10(9) n cm(-2) s(-1) and 152, respectively. The maximum neutron flux inside the phantom was measured to be 2.79 x 10(9) n cm(-2) s(-1) at a depth of 3 mm in the phantom. The two-dimensional in-phantom neutron flux distribution was determined, and significant neutron irradiation was observed within 20 mm from the phantom surface. The gamma-ray dose rate for the free beam condition was expected to be about 80 cGy h(-1). These experimental results were reasonably well supported by calculation using the facility design code. This HANARO thermal neutron facility can be used not only for clinical trials, but also for various pre-clinical studies in the BNCT field.

In-core fuel management practice in HANARO

Abstract The HANARO (High-flux Advanced Neutron Application Research reactOr) is a newly created research reactor. Its initial criticality was achieved on February 8, 1995. In its design stage, the HANAFMS, which is the nuclear analysis and fuel management code system for the HANARO, was verified using the results from the MCNP4A full core model because there was no similar research reactor in the world. It was needed to verify the HANAFMS with reactor physics experiments, which were performed during the reactor commissioning and power operation. The calculated results for the criticality, power distribution and control absorber rod (CAR) worth were compared with the measured ones. In the criticality calculation, the clean and depleted cores were applied and in the comparison of power distribution, the gamma scanning data of the fuel assemblies were used. The CAR worth was calculated following the measurement positions and then compared with the measurements. The calculated results for verifying the HANAFMS are in good agreement with the measured ones.

A Conceptual Design of I-125 Generator at the HANARO

A simple I-125 generating device at the research reactor, HANARO, is developed. Xenon-124 gas circulates continuously in the generator producing I-125 by neutron capture and the I-125 is adsorbed at the upper part of the generator, which is to be chemically recovered in a hot-cell. The continuous xenon circulation technology is devised by the design of the generator structure with the consideration of thermal hydraulics and neutron physics involved. A computational fluid dynamics technique is used for the conceptual design of the generator.Copyright