A Study of optimal design for Neutron Transmutation Doping in HANARO

The Neutron Transmutation Doping (NTD) is a production technique of the semi-conductors using a nuclear reaction between isotopes and thermal neutrons. The interest in NTD stems from two of its advantages over the conventional metallurgical methods of impurity incorporation. The first advantage is high-precision doping, because the concentration of impurities introduced at a constant neutron flux is proportional to irradiation time, which can be controlled with a high accuracy. The second advantage is the high homogeneity of dopant distribution, which is determined by a random isotope distribution, small neutron capture cross section, and the uniformity of the neutron flux. HANARO (High-flux Advanced Neutron Application Reactor) with the maximum available thermal neutron flux of 5x1014n/cm22·sec is a unique research reactor in the world and has two NTD irradiation holes. To produce the NTD-Si in 2002, KAERI has been setting up the irradiation facility for NTD. The optimization analyses have been conducted to finalize the irradiator design to produce the high quality NTD-Si grown by floating zone. The device that flats the axial neutron flux distribution in silicon ingot is very important in NTD process because the neutron screen is the sole method to achieve the uniform irradiation. The high quality NTD-Si must meet the requirement that the axial and the radial uniformity should be less than ±5% and ±1.7%, respectively. In this thesis, the optimal methods for uniform irradiation at silicon ingot in NTD hole are studied. The MCNP4B was used to simulate the neutron screen. The results show that the optimized neutron screen is sure to satisfy the requirements. The uniformity of the axial neutron flux distribution is below ± 1.5% and also the best vertical location of the silicon ingot during irradiation was analyzed because the critical control rod position greatly affects the axial flux distribution