Neutron absorbing material

These assemblies are made of a spider on which 2,5 to 4 m long rods are welded. These rods (16 to 24 per assembly) contain neutron-absorbing material. The rod envelope is made of 0,5 to 1 mm thick steel. The rod diameter is approximately 10 mm. 

Hafnium is obtained as a by-product of the production of hafnium-free nuclear-grade 2irconium (see Nuclear reactors Zirconiumand zirconium compounds). Hafnium s primary use is as a minor strengthening agent in high temperature nickel-base superakoys. Additionally, hafnium is used as a neutron-absorber material, primarily in the form of control rods in nuclear reactors. 

Control of the nuclear chain reaction in a reactor is maintained by the insertion of rods containing neutron absorbing materials such as boron, boron carbide, or borated steel. In state-of-the-art high temperature reactor designs, such as the Gas... 

The central wire, made of a neutron-absorbing material, absorbs a neutron and undergoes beta decay. 

While each of the above technologies offers certain unique advantages, those common to ceramic immobilization include a relative ease in fabrication, a high capacity for actinides or heavy metals compared to other technologies, the capacity for flexibility of feedstock, the ability to add neutron absorber materials for nuclear waste applications, and the ability to control the properties of the final waste form. 

Another application concerning the liquid-metal-cooled fast breeder reactors (LMFBR) was studied as development of advanced control rod materials for FBR (22). Fabrication tests and out-of-pile measurements were made of B4C/Cu cermet to obtain high-performance neutron absorber materials for LMFBR. A coating layer of Cu was formed on the surface of B4C/Cu powder, and then the coated B4C... 

Tlte control element assembly, shown in Fig. 15. consists of 0.8-inch (2-ceiuimeler) outside diameter Inconel tubes containing boron carbide pellets as the neutron absorbing material. A gas plenum is provided in order to limit the maximum stress due to generation of internal gas pressure. 

Boron carbide is a relatively inexpensive hard material, which is used for its mechanical properties of strength and extreme hardness in armor-plates for body protection, in sandblast nozzles, and as an abrasive for grinding and cutoff wheels. In nuclear plants, boron carbide is used as the neutron absorbing material of the control rods. 

A. E. Pasto, C. S. Morgan, Status and Potential of Eu-Based Fast Neutron Absorber Materials, Report ORNL-TM-5244, Oak Ridge National Laboratory, Oak Ridge, TN, February 1976. 

The total breeding ratio in the Creys-Malville reactor was 1.24. In BN-350 a breeding ratio of 1.5 can be obtained because it has less neutron absorbing materials. Still higher breeding gain can be achieved in fast reactors at some sacrifice of safety control. 

Metal borides and boron carbides of different compositions were used as neutron absorber materials—see patents (Hortman and Naum 1981 Lipp et al. 1981 McMurtry et al. 1981, 1982 Naum et al 1979 Owens 1980 Storm 1980 Wieczorek 1988)—and in the control rods of power reactors as well—see patents (Andrews 1987 Dixon et al. 1990). 

Provide sufficient neutron absorbing material to ensure that the core shutdown margin is met... 

Insertion of neutron absorbing materials to shut down the reactor... 

A storage hopper fill tube is provided to refill the hopper at the Reactor Equipment Service Facility after the neutron absorber material has been released into the core. 

The fast (E > 0.18 MeV) neutron flux exiting the active core is attenuated by the graphite reflectors. The attenuation of the total neutron flux exiting the permanent side reflector is enhanced by inclusion of borated steel pins (a neutron absorber material) in the outer portions of the reflector. The shielding poisons are located as far as practical away from the active core boundary to limit their impact on the core reactivity. 

---