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
2026 ANS Annual Conference
May 31–June 3, 2026
Denver, CO|Sheraton Denver
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
Dec 2025
Jul 2025
Latest Journal Issues
Nuclear Science and Engineering
January 2026
Nuclear Technology
December 2025
Fusion Science and Technology
November 2025
Latest News
AI at work: Southern Nuclear’s adoption of Copilot agents drives fleet forward
Southern Nuclear is leading the charge in artificial intelligence integration, with employee-developed applications driving efficiencies in maintenance, operations, safety, and performance.
The tools span all roles within the company, with thousands of documented uses throughout the fleet, including improved maintenance efficiency, risk awareness in maintenance activities, and better-informed decision-making. The data-intensive process of preparing for and executing maintenance operations is streamlined by leveraging AI to put the right information at the fingertips for maintenance leaders, planners, schedulers, engineers, and technicians.
J. T. Mihalczo, J. J. Lynn, J. R. Taylor
Nuclear Science and Engineering | Volume 130 | Number 1 | September 1998 | Pages 153-163
Technical Paper | doi.org/10.13182/NSE96-121
Articles are hosted by Taylor and Francis Online.
The reactivity worth of a central void region in the Oak Ridge National Laboratory (ORNL) unmoderated and unreflected uranium (93.20 wt% 235U) metal sphere was obtained by replacement measurements in a small (0.460-cm-diam) central spherical region in this 3.4420-in.-radius sphere. The measured central void region worth was 9.165 ± 0.023 ¢ using the delayed neutron parameters of Keepin, Wimett, and Zeigler to obtain the reactivity from the measured stable reactor periods. This value is slightly larger than measurements for GODIVA I with larger cylindrical samples of uranium (93.70 wt% 235U) in the center: 135.50 ± 0.12 ¢/mol for GODIVA I and 138.05 ± 0.34 ¢/mol for the ORNL sphere measurements. The difference could be due to sample size effect. The central worth was also calculated by neutron transport theory methods to be 6.02 ± 0.01 × 10-4 k. The measured and calculated values are related by the effective delayed neutron fraction. The value of the effective delayed neutron fraction obtained in this way from the ORNL sphere is 0.00657 ± 0.00002, which is in excellent agreement with that obtained from GODIVA I measurements, where the effective delayed neutron fraction was determined as the increment between delayed and prompt criticality and was 0.0066. From these ORNL measurements, using the delayed neutron parameters of ENDF-B/VI to obtain the reactivity from the stable reactor period measurements, the central void worth is 7.984 ± 0.021 ¢, and the inferred effective delayed neutron fraction is 0.00754. These values are 14.2% higher than those obtained from use of the Keepin, Wimett, and Zeigler delayed neutron data and produce a value of effective delayed neutron fraction in disagreement with GODIVA I measurements, thus questioning the usefulness of the six-group delayed neutron parameters (fast fission) of uranium from ENDF-B/VI for obtaining the reactivity from the measured reactor period using the Inhour equation.
