Birch Wood Modification Technology for Creating Neutron Shielding Materials

Abstract

The article considers a method for producing neutron shielding materials based on modified birch wood. It is known that shielding materials based on polyethylene with boron addition are widely used in the nuclear industry, medicine and the military-industrial complex to create protection against neutron radiation. Due to the high hydrogen content, their use makes it possible to protect objects from the effects of fast neutrons, and thermal neutrons are effectively contained due to the presence of boron atoms in the protective screens. Wood is also a hydrogen-containing material, therefore, it is of scientific and practical interest to create and study the properties of neutron shielding materials based on wood. The most expedient is the creation of neutron shielding materials from hardwood, which have a high specific density and, accordingly, a high content of hydrogen per unit volume. It is possible to increase the hydrogen content per unit volume of wood and, accordingly, to reduce the thickness of the protective layer due to the compaction of wood by the method of flat (singleaxis) pressing. The main condition for obtaining high-strength and form-resistant pressed wood is the preservation of its microstructure (without damage) during pressing. It has been theoretically found that the optimal pressing stage, at which the lowest percentage of microfractures in wood is observed, should not exceed 50 %. In the experimental part of the work, birch lumber was used for the production of an experimental neutron shielding material, radial sawn with a length of 200 mm, a width of 100 mm, and a thickness of 80 mm to obtain ready-made neutron shielding materials with a thickness of 40 mm, which is equivalent to a polyethylene shielding thickness of 26.8 mm. It is known that during flat pressing bursting forces occur in wood, which can lead to cracks, destruction of edges, buckling, delamination, and a decrease in the uniformity of the density distribution. The bursting force acts in the direction perpendicular to the action of the applied load. Therefore, in the manufacture of a neutron shielding composite material, it is necessary to use press molds (with side stops) that stop the impact of the bursting force. The design parameters of the press molds and pressing modes are determined taking into account the resistance caused by the friction forces of the wood against the side walls of the press mold. The design of a press mold that provides the production of a neutron shielding material of specified properties from wood is presented.