|학술대회||2011년 봄 (05/26 ~ 05/27, 제주 휘닉스 아일랜드)|
|발표분야||E. Structural Materials and processing Technology(구조재료 및 공정기술)|
|제목||New boron compound, silicon boride ceramics for capturing thermal neutrons (Possibility of the material application for nuclear power generation)|
|초록||As you know, boron compounds, borax (Na2B4O5(OH)4･8H2O) etc. were known thousands of years ago. As for natural boron, it has two naturally occurring and stable isotopes, boron 11 (11B) and boron 10 (10B). The neutron absorption 10B is included about 19-20% with 81-80% 11B. Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. The mass difference results in a wide range of δ values between the 11B and 10B.
The 10B isotope, stable with 5 neutrons is excellent at capturing thermal neutrons. For example, it is possible to decrease a thermal neutron required for the nuclear reaction of uranium 235 (235U). If 10B absorbs a neutron (1n), it will change to 7Li + 1α (α ray, like 4He) with prompt γ ray from 11B 11B (equation 1).
10B + 1n → 11B → prompt γ ray (478keV), 7Li + 4α (4He)･･･ (1)
If about 1% boron is added to stainless steel, it is known that a neutron shielding effect will be 3 times the boron free steel. Enriched boron or 10B is used in both radiation shielding and in boron neutron capture therapy. Then, 10B is used for reactivity control and in emergency shutdown systems in nuclear reactors.
Furthermore, boron carbide, B4C, is used as the charge of a nuclear fission reaction control rod material and neutron cover material for nuclear reactors. The B4C powder of natural B composition is used as a charge of a control material of a boiling water reactor (BWR) which occupies commercial power reactors in nuclear power generation. The B4C sintered body which adjusted 10B concentration is used as a charge of a control material of the fast breeder reactor (FBR) currently developed aiming at establishment of a nuclear fuel cycle.
In this study for new boron compound, silicon boride ceramics for capturing thermal neutrons, preparation and characterization of both silicon tetraboride (SiB4) and silicon hexaboride (SiB6) and ceramics produced by sintering were investigated in order to determine the suitability of this material for nuclear power generation. The relative density increased with increasing sintering temperature. With a sintering temperature of 1923K, a sintered body having a relative density of more than 99% was obtained. The Vickers hardness increased with increasing sintering temperature. The best result was a Vickers hardness of 28GPa for the SiB6 sintered at 1923K for 1 h. The high temperature Vickers hardness of the SiB6 sintered body changed from 28 to 12GPa in the temperature range of room temperature to 1273 K. The thermal conductivity of the SiB6 sintered body changed from 9.1 to 2.4W/mK in the range of room temperature to 1273 K.
|소속||Department of Materials Science|
|키워드||silicon boride ceramics; thermal neutrons; control rod|