Study on the development of shielding materials using resin, heavy metal and thermal neutron absorber as raw materials

High-performance shielding materials and their production techniques are developed by an ultraviolet curing method and a heat curing method. They are mainly made of resin, lead powder, and a boron compound. As resin materials, single functional monomers are selected. As a practical use, the heat curing method is recommended. In this case, stearylmethacrylate (SMA) is used as a monomer. To get good dispersion of lead and the boron compound in the resin, the viscosity of SMA is increased by adding a small amount of a peroxide into the liquid monomer and heating up to the temperature of about 100degC. The viscous SMA is mixed with a peroxide, lead powder, a boron compound, a three functional monomer, and a curing accelerator, and is cured in an atmosphere of nitrogen after removing bubbles using a vacuum pump. Measured properties of the cured material are as follows. The curing rate of SMA is 97%. The typical densities are between 2 and 3 g/cm3 which stay almost constant in the range from room temperature to 150degC. The weight-change measured by a thermogravimetry is 0.16% in the range from room temperature to 200degC. Details of fragments in the gas released from the material is analyzed by a gas chromatography and a mass spectrometry. The hydrogen content of the material is about 6x1022/cm3. The shielding effect of the curing material is measured for a 252Cf neutron source. Comparison of experimental results with MCNP Monte Carlo calculations indicates a good agreement. The shielding effect is calculated for a fission source by an Sn code ANISN. They are quite excellent. For example, concrete shield of a certain thickness can be replaced by the material having a thickness of less than a half of concrete. The shielding effect of the material is larger than those of the practical shielding materials. Several samples of the material are irradiated an an irradiation facility of the research reactor JRR-4 installed at Japan Atomic Energy Research Institute. At the 14th day after irradiating with the thermal neutron fluence of 6.6x1015/cm2, the radioactivity is less than 4.4 Bq/g. (author)