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Fuel Pins, Fuel Rods, Fuel Assemblies, and Reactor Cores
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
The fuel pellets are then inserted into the fuel rods, which are stacked to the correct height, welded shut, filled with a pressurized gas, and sealed. As we will shortly see, not all of fuel rods or the fuel pellets have the same size, and the actual dimensions can vary considerably from one reactor to the next. As a matter of fact, they can even vary from one PWR or BWR to the next. However, there are still a lot of similarities between the two designs, and we would like to summarize these similarities for you in this chapter. The Canadian CANDU reactor, which is a pressurized heavy water reactor, does not require enriched uranium to operate, but the natural uranium fuel used in CANDU reactors is still combined with two oxygen atoms to create a ceramic material called uranium dioxide (UO2). In fast reactors, plutonium can also be combined with two oxygen atoms to form plutonium dioxide fuel or PuO2. Later in the chapter, we will learn that the physical properties of uranium dioxide and plutonium dioxide are similar in many respects.
Nuclear Fuel Materials
Published in C. K. Gupta, Materials in Nuclear Energy Applications, 1989
It is the general trend for reactor fuel to be developed with an emphasis on the requirements of reactor irradiation. Not much consideration is given to the problems that might be introduced in other parts of the fuel cycle. The MOX fuels, for instance, for thermal reactor systems, are highly inert to water and are preferred in case of leakage of water into the cladding, but the same fuel must be readily dissolved for reprocessing. These fuels present a particular problem in regard to solubility. Plutonium oxide is essentially insoluble in nitric acid. This means that a fuel containing discrete PUO2 partially may present a dissolution problem, although it is entirely satisfactory for in-reactor service. Mechanically blended fuel, containing small enough PUO2 particles and sintered adequately, takes to homogeneity, but plutonium-rich regions may still respond poorly to dissolution. Experimentally, the fuel dissolves satisfactorily in nitric acid if the plutonium content on a microscopic scale does not exceed 4%, but dissolution is increasingly more difficult with segregated plutonium concentration greater than this. Postirradiation processing needs, thus, reinforce the desirability of homogeneous fuel. Use of small-sized PUO2 particles, high temperature sintering, and reactor operation itself, all promote homogenization, and it is desirable to have a general appreciation of all these factors in any reactor fuel-making process development.
The Other Energy Markets
Published in Anco S. Blazev, Global Energy Market Trends, 2021
Following reprocessing, plutonium is transported as an oxide powder since this is its most stable form. Plutonium oxide is transported in several different types of sealed packages, and each can contain several kilograms of material.
Towards a Systematic Requirement-Based Approach to Build a Neutronics Study Platform
Published in Nuclear Science and Engineering, 2023
Alberto Previti, Alberto Brighenti, Damien Raynaud, Barbara Vezzoni
In this type of parametric study, it is necessary to be able to test the impact of the scheme option on a set of conditions and parameters that are representative of the domain on which the calculation scheme should be validated. Three types of fuel have been considered: uranium-based oxide (UOX), mixed uranium and plutonium oxide (MOX), and uranium-based fuel with gadolinium pins (UGD). Their geometries, material compositions, and operating conditions are determined based on the information available in public benchmarks.39,40 These fuel assemblies have been depleted up to 30 GWd/tIHM in nominal conditions by considering a power mass density of 37.5 W/g for UOX and UGD and 36.6 W/g for MOX. Configurations without control rods inserted [all rods out (ARO)] and with the insertion of an absorbent rod cluster [Ag-In-Cd (AIC), B4C] are investigated by modifying the simulation configuration for selected points among the irradiation steps.
Impact Temperature Determination for GPHS Safety Testing
Published in Nuclear Technology, 2020
Jonathan G. Teague, Roberta N. Mulford
Space exploration missions have long relied on the radioisotope thermoelectric generator (RTG) to provide safe, reliable, long-lived power systems to provide electricity and heat to spacecraft and onboard instruments. The RTG reliably converts the heat of nuclear decay into electricity using solid-state conversion, with long life and high reliability. The radioisotopic fuel of choice is 238PuO2, which has a high thermal output and emits little neutron or gamma radiation. Since 1961, these devices have provided power for space missions where solar irradiation is insufficient to power instruments and for missions having demanding power requirements such as the Mars Rover. The current RTG design employs the general purpose heat source (GPHS). The GPHS consists of four plutonium-oxide fuel pellets, each sealed inside DOP-26 iridium alloy cladding. The DOP-26 consists of Ir-0.3%W to which trace levels (60 ppm) of thorium have been added to improve the alloy’s high-temperature impact ductility.
Safety Strategy and Update of the TREAT Facility Safety Basis
Published in Nuclear Technology, 2019
Douglas M. Gerstner, James R. Parry, David J. Broussard, Brandon L. Moon, Anthony W. LaPorta, Charles P. Forshee, Lawrence J. Harrison, Monty L. Conley
Based on a comparison of the estimated inhalation dose contribution from a nine-pin array of high-burnup UO2-based LWR fuel, a seven-pin array of MOX fast reactor fuel, and a minor actinide–bearing fast reactor fuel pin, the updated SAR concludes that a seven-pin MOX fast reactor fuel experiment would provide the bounding inventory for accident analysis. Existing, high-burnup MOX fuel pins preirradiated in the Fast Flux Test Facility have been reserved for future testing. The bounding radiological inventory for an experiment in the updated SAR is assumed to contain 14.2 kg of MOX fuel (25% plutonium oxide and 75% uranium oxide) that has been taken to 10 at. % burnup and decayed for 1 year and then subjected to a transient in TREAT that deposits 5000 J/g of energy into the experiment.