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
Latest Magazine Issues
Mar 2026
Jul 2025
Latest Journal Issues
Nuclear Science and Engineering
March 2026
Nuclear Technology
February 2026
Fusion Science and Technology
April 2026
Latest News
NRC approves TerraPower construction permit
Today, the Nuclear Regulatory Commission announced that it has approved TerraPower’s construction permit application for Kemmerer Unit 1, the company’s first deployment of Natrium, its flagship sodium fast reactor.
This approval is a significant milestone on three fronts. For TerraPower, it represents another step forward in demonstrating its technology. For the Department of Energy, it reflects progress (despite delays) for the Advanced Reactor Demonstration Program (ARDP). For the NRC, it is the first approval granted to a commercial reactor in nearly a decade—and the first approval of a commercial non–light water reactor in more than 40 years.
J. T. Mihalczo, W. T. King
Nuclear Technology | Volume 84 | Number 2 | February 1989 | Pages 205-223
Technical Paper | Techniques | doi.org/10.13182/NT88-2
Articles are hosted by Taylor and Francis Online.
The method used since 1970 for determining the subcriticality of High-Flux Isotope Reactor (HFIR) fuel elements submerged in water is to add extra reactivity-calibrated uranium fuel plates and neutron absorber strips to a fuel element in order to achieve delayed criticality when it is submerged in water. This quality assurance (QA) verification determines that a fuel element meets reactivity specifications before it is used in the reactor. The use of the 252Cf-source-driven neutron noise analysis method to measure the subcriticality of fuel elements as an alternate to the critical experiment method was investigated by performing experiments with 29 HFIR fuel elements submerged in water. Reactivity was also measured by the break frequency noise analysis method. These measurements have shown that the 252Cf-source-driven noise analysis method can be used to determine whether HFIR fuel elements are fabricated within design specification by measuring the subcritical neutron multiplication factor of the fuel element submerged in water without the need to achieve delayed criticality. These subcritical measurements can replace the existing critical experiments for QA testing of fuel elements before use in a reactor and would be a more accurate and cost-effective method with reduced personnel radiation exposure and increased nuclear criticality safety. In addition, these experiments have shown that (a) measurements can be made with the detectors outside the water reflector tank; (b) the results do not depend on the type of detector used (neutron sensitive, gammaray sensitive, or sensitive to both neutrons and gamma rays); and (c) the method can measure the reactivity of the fuel element partially submerged and has the sensitivity to determine the effects of small uranium mass changes (∼1%) in the fuel element while the element is partially flooded (approximately half submerged) and very far subcritical. Validation of this method on these fuel elements suggests a potential for broad application of the 252Cf-source-driven noise analysis for QA testing of water reactor fuel elements where it is possible to submerge the elements in water without achieving a delayed critical state.
