ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Division Spotlight
Materials Science & Technology
The objectives of MSTD are: promote the advancement of materials science in Nuclear Science Technology; support the multidisciplines which constitute it; encourage research by providing a forum for the presentation, exchange, and documentation of relevant information; promote the interaction and communication among its members; and recognize and reward its members for significant contributions to the field of materials science in nuclear technology.
Meeting Spotlight
2024 ANS Winter Conference and Expo
November 17–21, 2024
Orlando, FL|Renaissance Orlando at SeaWorld
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
Latest Magazine Issues
Aug 2024
Jan 2024
Latest Journal Issues
Nuclear Science and Engineering
October 2024
Nuclear Technology
Fusion Science and Technology
August 2024
Latest News
New laws offer nuclear industry incentives for existing power plant uprates
This year, the U.S. nuclear industry received a much-needed economic boost that could help preserve operating nuclear power plants and incentivize upgrades that extend their lifespan and power output.
Signed into law in 2022, the Inflation Reduction Act offers production tax credits (PTCs) for existing nuclear power plants and either PTCs or investment tax credits (ITCs) for new carbon-free generation. These credits could make power uprates—increasing the maximum power level at which a commercial plant may operate—a much more appealing option for utilities.
M. Segev
Nuclear Science and Engineering | Volume 81 | Number 2 | June 1982 | Pages 151-160
Technical Paper | doi.org/10.13182/NSE82-A20082
Articles are hosted by Taylor and Francis Online.
Let the lattice consist of an infinite uniform distribution of clusters in an (external) moderator, and let the cluster consist of a uniform distribution of absorber lumps in an (internal) moderator. The lattice is characterized by the parameters: cluster mean chord length, L; probability of neutrons leaving a cluster to collide in the external moderator prior to crossing a cluster, Γ; adjustable Bell factor for the clusters, A; lump mean chord length, I; probability of neturons leaving a lump (in an infinite cluster) to collide in the internal moderator prior to crossing a lump, γ; adjustable Bell factor for the lumps, a; internal moderator volume fraction in the cluster, υm; internal moderator macroscopic cross section, Σm. The flux in (or resonance integral of) the absorber lump is equivalent to the flux in (or resonance integral of) an infinite medium consisting of the lump material, homogenously mixed with a moderator of cross section Σe, given by where The expression for Σe is quite general, the only restriction on the lattice structure being that a cluster contain many lumps. The factor β can be termed the “double heterogeneity” factor abbreviated “doublet.” In the limit of an infinite single cluster β → 1, yielding the correct single heterogeneity expression for Σe. In the limit of small lump volume fractions, the expression for Σe reduces to the expression of Goldstein, as derived from the work of Lane et al. Goldstein's formulation was successfully compared with the experimental data of Lewis and Conolly. The WIMS formulation for a single cluster is almost equivalent to the above formulas with a difference that becomes significant only if the cluster contains a small number of lumps. The equivalence formulations by Tsuchihashi et al., as well as by Stamatelatos, yield results which are discrepant with those of the formulations discussed above and, therefore, have to be judged unsatisfactory.