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.
Explore membership for yourself or for your organization.
Conference Spotlight
Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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
Jul 2025
Jan 2025
Latest Journal Issues
Nuclear Science and Engineering
August 2025
Nuclear Technology
Fusion Science and Technology
Latest News
ANS joins others in seeking to discuss SNF/HLW impasse
The American Nuclear Society joined seven other organizations to send a letter to Energy Secretary Christopher Wright on July 8, asking to meet with him to discuss “the restoration of a highly functioning program to meet DOE’s legal responsibility to manage and dispose of the nation’s commercial and legacy defense spent nuclear fuel (SNF) and high-level radioactive waste (HLW).”
Anil Kumar, M. Srinivasan, K. Subba Rao
Nuclear Science and Engineering | Volume 84 | Number 2 | June 1983 | Pages 155-164
Technical Note | doi.org/10.13182/NSE83-A17722
Articles are hosted by Taylor and Francis Online.
The Trombay criticality formula (TCF) has been derived by incorporating a number of well-known concepts of criticality physics to enable prediction of changes in critical size or keff following alterations in geometrical and physical parameters of uniformly reflected small reactor assemblies characterized by large neutron leakage from the core. The variant parameters considered are size, shape, density and diluent concentration of the core, and density and thickness of the reflector. The mass-to-surface-area ratio of the core, is essentially a measure of the product ρr extended to nonspherical systems and plays a dominant role in the TCF. The functional dependence of keff on σ/σc, the system size relative to critical, is expressed in the TCF through two alternative representations, namely the modified Wigner rational form and the exponential form as follows: where is the k∞ of the critical system. The quantity in the square brackets is close to unity and Z is a parameter weakly dependent on both the physical and geometrical properties of the core, where θ = ln[/( - 1)] and ε is a parameter introduced to account for the steep rise in the net leakage probability for highly subcritical cores. The applications of the TCF range from the quick computation of the keff of a lump of fissile fuel having arbitrary shape and density through the study of keff of highly enriched fissile materials during transportation accidents to an estimation of the void and fuel expansion coeffficients of reactivity in high leakage systems.