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Yonggwang Nuclear Power Plant, South Korea. (Photo: IAEA)
The demand for current force and the growing difficulty at new nuclear power plant sites are tough incentives for the nuclear industry to use existing sites to build new reactor units. Most nuclear power plants involve two or more reactors, and all nuclear power plants have other radiological sources, such as spent fuel tanks and radioactive waste control facilities.
Protecting a nuclear facility would possibly improve if threats related to those services are assessed and maintained at an appropriate level. Probabilistic Security Assessment is an effective tool for generating threat data needed for performance-based and threat-based programs as key elements of a threat control process.
The IAEA webinar – Expanding the assessment of nuclear power plant threats to the multi-unit context, held in July, addressed sustainable nuclear protection efforts by addressing multi-unit interactions for multi-unit sites, with complex technologies such as small modular reactors (MDS). More than three hundred participants attended the webinar, which provided a platform to share their percentage reports and facilitate discussions in the field of threat assessment and the protection of nuclear power plants from multiple reactors.
“Multi-unit threat assessment is a wide-angle goal that allows us to read about protecting reactors at the level,” said Greg Rzentkowski, Director of the IAEA’s Nuclear Facilities Safety Division. “It is vital to perceive these new perspectives in the context of the protection of functioning nuclear power plants and those that are still on a drawing board.”
George Apostolakis, director of the Japan Nuclear Risk Research Center and former commissioner of the U.S. Nuclear Regulatory Commission, Marina Rawekamp, chairwoman of the OECD/NSA Risk Assessment Task Group from 2014 to 2020, and Karl Fleming, a member of the U.S. National Academy. EngineeringArray were the main speakers of the webinar. They shared their experiences, demanding situations and more productive practices, as well as the classes learned so far and the implementation of this three-year IAEA assignment from December 2016 to December 2019.
The webinar also provided a forum to summarize the effects of the IAEA’s recent Probabilistic Protection Assessment (MU) allocation through the IAEA’s Nuclear Facilities Safety Division. “The IAEA’s method for the probabilistic assessment of the safety of several units is a significant step towards advancing prior art and hopefully assessing protection in this area,” Apostolakis said.
Particular emphasis has been placed on the method for the probabilistic assessment of multi-unit protection developed at the IAEA, which can be applied to multi-module AND/or multi-unit MDRs, and the IAEA is in a position to assist Member States in this area. The IAEA method demonstrates how to manage the maximum complexity of probabilistic protection assessment in a multi-unit context, taking into account various combinations of interactions between units, adding the variety of initial events, modeling complex sequences of target turns, the remedy of correlations between units and human errors, taking into account the exchange of systems and resources between sets. The IAEA method was tested by conducting a realistic case review that illustrated how it works for a site with 4 sets and suggests that more sets can also be managed.
“The IAEA has provided a method as a tool that can be used in case a probabilistic assessment of um protection is required through the national regulator,” said Shahen Poghosyan, IAEA director of nuclear protection. Explaining other facets of the project, he said, “For a realistic assessment of the protection of multi-unit sites, consideration should be given to the positive and negative facets of sharing systems and resources between units.”
Speakers discussed demanding situations and multi-unit threat assessment, adding threat-based decision-making. “In terms of protection improvements, the placement of a multi-unit probabilistic protection assessment framework gives you a balanced view, especially with respect to external threats,” Fleming said. “This maximizes and minimizes threats related to the exchange of systems and resources between units.”
“There is a desire to continuously expand probabilistic protection tests at the site level and corresponding rules at the foreign level, sharing the results, lessons learned and cooperation between the IAEA and OECD/NEA,” R-wekamp said.
The test tests of safety were carried out largely on the basis of a single unit, considering that each unit is absolutely independent. Acceptance criteria and threat measures are also implemented in unit tests. This assessment can also be implemented in a multi-unit facility, for example, the likelihood of preventing and mitigating a shift in the target on a unit cannot be evaluated without taking into account the condition of other assemblies and facilities on site, adding spent fuel garage facilities.
Co-located reactors and radiological resources have a percentage of an unusual electrical grid and a final heatsink and, in some cases, a percentage of structures and systems that provide important protection purposes. Each site can be characterized through a set of internal and external hazards that can cause a number of occasions that continue to challenge important protection purposes and cause injuries involving one or more units. Internal start-up occasions are due to human error and curtain defects. Internal occasions come with internal fires and floods. Examples of external hazards come with herbal occasions, such as seismic occasions, external flooding due to tsunamis, river floods, waves of typhoons, strong winds and wind-generated missiles, and man-made occasions, such as commercial and transport injuries.
The IAEA is assisting Member States in their security processes through strategies and equipment to decorate the nuclear protection of countries that envisage a multi-unit context. These efforts will also help develop the feasibility of deploying complex force reactors to reduce the CO2 footprint.
Webinar recording is available here.