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Nuclear Fuel Fabrication
Published in Kenneth D. Kok, Nuclear Engineering Handbook, 2016
Some reactor fuel also contains material called a burnable poison. This burnable poison material is added to the powder during the blending process. A material such as gadolinium has a large neutron cross section or ability to absorb neutrons when it is in the reactor core. Once it has absorbed a neutron, it is transmuted to a material that no longer acts as a poison. This poison allows more fissile material to be initially loaded into the reactor core and, as the poison material is burned away, more reactivity will be available for ongoing fission reactions. The end result is that the energy production can be more evenly distributed between fuel assemblies, which helps core designers increase the neutron utilization of the core while continuing to meet safety limits. In some cases, the operating time between refueling for the reactor may be extended through the use of such burnable poisons, allowing for a reduction in the number of outages over a period of time. An alternate scheme for reactivity control is through use of integral burnable absorbers, where a coating containing the neutron poison Boron-10 is applied to the pellet prior to fuel rod loading. The transmutation of B-10 produces additional helium gas during operation, which often requires the use of annular blanket pellets to avoid excessive fuel rod pressures.
Advanced MCNP Simulation of the Neutron and Photon Flux and Absorbed Dose Rates for the SLOWPOKE-2 Nuclear Reactor at the Royal Military College of Canada
Published in Nuclear Technology, 2020
J. C. Rook, K. P. Weber, E. C. Corcoran
Added to all models are the use of thermal neutron S(α,β) scattering laws for hydrogen in light water and beryllium metal. Scattering laws are used to account for the molecular and crystalline structure effects of thermal energy neutrons. This is particularly important in the moderating materials as it affects the neutron cross section and the energy and angle distribution of secondary neutrons. As hydrogen in light water and the beryllium metal of the reflector account for a high fraction of material of the thermal reactor core, S(α,B) scattering treatments were included for beryllium (be.20t) and light water (lwtr.01t) (Ref. 22).