Category Archives: Nuclear Reactor Design

Nuclear Design

The core characteristics are both neutronic and thermal. Neutronic characteristics are obtained by the core nuclear design. In the nuclear design, the core configura­tion, the refueling plan and the plutonium enrichment are determined so that the core safely generates the designed thermal power, based on the plant and fuel basic specifications, throughout the plant life. Also, the core reactivity, breeding […]

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Fuel Burnup and Reactivity Control

Shigeo Ohki Abstract Nuclear fuel burnup and reactivity control are important points in the core design of nuclear reactors. The fuel burnup analysis generally evaluates the time-dependent core power distribution and reactivity by solving burnup equations for the atomic density change of nuclides contained in the fuel as well as solving multi-group diffusion equations for neutron flux distribution and effective […]

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Application of Perturbation Theory: Reactivity Worth of Partially Inserted Control Rod [26]

An application of the one-group first-order perturbation theory is discussed here. A bare cylindrical reactor of extrapolated radius R and height H is considered, in which a central control rod of radius a is partially inserted, as shown in Fig. 1.15. The insertion depth of the control rod from the origin in the top of the cylindrical reactor is denoted […]

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Fuel rod behavior calculation

The fuel rod behavior caused by irradiation of fuel pellets and cladding is complicated for investigation in an analytical method. Fuel rod behavior calculation codes were developed from various experiments and operational experiences. FEMAXI-6 [30] as an open code developed in Japan is a general analysis code for fuel rod behavior at normal operation or abnormal transients in LWRs. It […]

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Reload core design

Nuclear reactor operation management is based on a long-term operation plan of 3-5 years. The plan includes startup date of each operating cycle, shutdown period for periodic inspection, and load factor in operation. It also includes intermediate shutdown planned in each operating cycle. After the long-term operation plan, the cycle burnup is obtained from reactor operating days and load factor […]

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Fuel block

The fuel type of the HTTR is the pin-in-block type where the fuel rods are inserted in a hexagonal graphite block as shown in Fig. 4.18. The coated particle fuels are mixed with graphite powder and pressed into an annular cylinder, which is called a fuel compact. Fourteen fuel compacts are inserted into a graphite sleeve to form a fuel […]

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Burnable Poison

A substance which has a large neutron absorption cross section is loaded into the reactor core or is directly mixed in fuel to suppress the large excess reactivity at the initial burnup. This neutron absorber is converted into a nuclide with a low absorption cross section as the result of neutron absorption. Thus, the increase in reactivity accompanying the burnup […]

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Homogenization and group collapsing

In the core calculations with a huge amount of space-dependent data (cross section and neutron flux), the effective cross sections are processed, with a little degradation in accuracy as possible, by using the results from the multi-group lattice calculation. There are two processing methods. One is homogenization to lessen the space-dependent information and the other is group-collapsing to reduce the […]

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