Multigroup method

Another source of error inherent in the perturbation approach to sensitivity studies is the inadequacy of multigroup methods based on flux-averaged group constants to allow for the fine-structure effects of the perturbation. A detailed description of this problem and of possible ways of reducing or eliminating the errors are described in Section VII. 

The reactivity usually calculated with multigroup methods corresponds to the definition... 

Here, and distributions calculated with the unperturbed flux-averaged group constants. In the following discussion we shall refer to multigroup methods that calculate the reactivity from Eq. (235) or from Eqs. (236) or (237) as, respectively, the consistent flux (CF) or the flux formulations. 

There are several approaches that can take into account spectral fine structure effects with multigroup methods that use flux-averaged group constants (a) All calculations (flux, adjoint, and perturbation) are performed... 

These statements are, however, only approximate. What is perhaps most relevant, mathematically, for intermediate reactors, is to have a convenient and tractable approximation scheme for computing the energy distribution even when the flux is not separable into energy, space, and angle—in other words, a practical way to find solutions of (11). The commonest such scheme is the so-called multigroup method. This method merely amounts... 

E. SUICH and H. C. HONECK, The HAMMER System Heterogeneous Analysis by Multigroup Methods of Exponentials and Reactors, DP-1064, E. I. du Pont de Nemours and Co., Savannah River Laboratory (1967). 

In preparation for the experiment, extensive calculations and selected critical facility measurements were made. The basic analytical approach is the multigroup method in the Sn and diffusion theory approximations to the transport equation. The fast and epithermal spectra used in computing the multigroup cross sections are calculated using HRO. The thermal spectra are calculated using Battelle Revised THERMOS. ) The NeUdn kernel is used to describe the thermal-neutron scattering in water. 

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