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The human factor in licensing and operating the next generation of nuclear plants
As human factors specialists working at the intersection of human performance and nuclear operations, we are witnessing one of the nuclear sector’s most significant transitions in decades. The emergence of small modular reactors, microreactors, and other advanced designs is reshaping the industry’s landscape. Digital instrumentation and controls, passive safety systems, and increased automation are creating opportunities for greater safety margins and more flexible operation. These same features also fundamentally redefine what it means to “operate” a nuclear plant. Interactions among human roles, automation, and passive systems shape how people maintain awareness, exercise judgment, and intervene when necessary. These developments affect both operational realities and the regulatory foundations on which nuclear safety is built.
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.
