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
2025 ANS Winter Conference & Expo
November 9–12, 2025
Washington, DC|Washington Hilton
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
Oct 2025
Jul 2025
Latest Journal Issues
Nuclear Science and Engineering
November 2025
Nuclear Technology
October 2025
Fusion Science and Technology
Latest News
OECD NEA meeting focuses on irradiation experiments
Members of the OECD Nuclear Energy Agency’s Second Framework for Irradiation Experiments (FIDES-II) joint undertaking gathered from September 29 to October 3 in Ketchum, Idaho, for the technical advisory group and governing board meetings hosted by Idaho National Laboratory. The FIDES-II Framework aims to ensure and foster competences in experimental nuclear fuel and structural materials in-reactor experiments through a diverse set of Joint Experimental Programs (JEEPs).
Daniel S. Williams, John C. Rommel, Raymond L. Murray
Nuclear Technology | Volume 87 | Number 4 | December 1989 | Pages 1134-1144
Late Paper | TMI-2: Decontamination and Waste Management / Nuclear Safety | doi.org/10.13182/NT89-A27705
Articles are hosted by Taylor and Francis Online.
Criticality safety and adherence to established keff criteria had to be demonstrated for the various defueling operations performed at Three Mile Island Unit 2. This included determination of adequate neutron poisoning for the reactor coolant system (RCS), design of the defueling canisters, the canister-handling devices, the storage racks, and the shipping cask. Tools, equipment, and support systems required for the defueling operation also had to adhere to criticality safety requirements. The keff criterion used to define the poison concentration for the RCS was ≤0.99. This criterion, coupled with an extremely conservative core model, led to a poison concentration that provided an appropriate margin of safety. To define the fixed poison requirements for the defueling canisters, a keff criterion of <0.95 was used for both single canisters and arrays in all credible configurations. For all design analyses, bounding assumptions were made. For each set of analyses performed, the evaluation of keff included an allowance to account for uncertainties in the calculated values. A criticality benchmark study was completed to determine appropriate computer code bias values for both the RCS and canister analyses. A lenticular model, which included the entire fuel inventory, was used to define the RCS boron concentration. Based on the analysis by Oak Ridge National Laboratory, a boron concentration of 4350 ppm was required to meet the keff criterion. Babcock and Wilcox Company performed the design analyses for the defueling canisters. Each type of canister was explicitly modeled and analyzed using the KENO code. The design requirements mandated that the diameter of the canisters be larger than critically safe dimensions; thus, fixed boron poisoning was utilized. The fixed poison used in the canisters was either Boral plates or stacked sintered boron carbide pellets. The quantity and location of the canister poison was determined based on keff limits and operational criteria for the canisters. Analyses were also performed to ensure that keff was ≤0.95 for canisters contained within the canister-handling devices.
