Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision Page: 6 of 205
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iu sonme cases, cakulated results are desirable to till in experimental data or to extend them.
Where they appear in this report, they are identified as calculations because of the uncer-
tainty associated with them. III general, the 16-group Hansen-Roach cross-section .et r is
used with the ouie-dimensional transport code, DSN," or its modern version, ONEDANT12
in one dimensiotu and TWODANT" in two dimensions. The reason for this choice is
Stratt on's extensive comparison of results of such calculations with experimental data. 14
Where this comparison is unfavorable, part icuilarly for solution or hydrogeneous mixtures
of few-percent =L'tTlenriched uraniutm, the Los Alanios MICNP Monte Carlo code15 and
cross-sect ions based on ENDF-B1 V* are used instead. This combinat ion is also applied in
the few cases where finite-cylinder calculat ions are desired.
('alculated exteio;ions of experimental dat a are iiclided to show the nature of trends, not
to substitute for results of experiments. They should be used with caption.
A fundamental aim of this document is to illust rate relationships among critical data. The
compilation and correlation of dat a for this purpose, from many measurements in a number
of laboratories, require a certain amount of normalization or reduction to common terms.
Frequently, for example, the effects of variations in geometry or density must be removed
to show trends in data. The manner in which these alterations may be made is discussed
in the early section RELATIONS FOR CONVERSION TO STANDARD CONDITIONS.
Reactor mockups and related critical assemblies are generally outside the scope of this
document. Many of those that are appropriate to serve as computational models are fast-
neutron sx stems that are of secondary interest in criticality safety matters.'6 Nevertheless,
fast-reactor mockups which are used as benchmark assemblies (for comparison with calcu-
lations) are instructive, for they illustrate the value of data other than criticality specifi-
cat ions. namely, spectral information, neut ron flux distributions, prompt-neutron lifetime,
and reactivity coefficients. Unfortunately, data for critical assemblies suitable as safety
benchmarks are usually limited to critical compositions, dimensions and masses without
useful supplement ary information.
* Robert C. Little. Los Alamos National Laboratory, Los Alamos, NM 87545, 1986.
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Paxton, H.C. & Pruvost, N.L. Critical dimensions of systems containing /sup 235/U, /sup 239/Pu, and /sup 233/U: 1986 Revision, report, July 1, 1987; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1109879/m1/6/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.