Conference Agenda

In this study, systematic methodology for small modular reactor fuel assembly optimization using multi-objective simulated annealing was proposed, considering various uranium enrichment conditions. Using a reference 17×17 fuel assembly design with 1/8 symmetry, 194 neighbor solutions were generated by exchanging the positions of fuel rods and absorbers while preserving the number of each component and the symmetry constraint. The nuclear characteristics of each candidate configuration were evaluated using the KARMA code across enrichment levels of 4.2%, 4.4%, 4.6%, and 4.8%. Performance indices, the maximum infinite multiplication factor (KINF_EQ) and peaking factor(FXY), were evaluated. Through multi-objective simulated annealing, an optimal design that balances safety and economic performance was achieved.

An integral pressurized water reactor is a type of small modular reactor (SMR) whose operational safety is based on the use of passive safety systems. The SMRs are currently one of the most important energy options in the introduction of new reactor systems. The analyses, presented in the paper, will be carried out for the IRIS (International Reactor Innovative and Secure) reactor, an integral, medium power (1000 MWt), light water reactor. IRIS consists of eight internal cooling loops. It has eight small, spool type, reactor coolant pumps and eight modular, helical coil, once through steam generators. The pressurizer is located in the reactor pressure vessel (RPV) upper head.

There are several passive safety systems and features in the IRIS reactor used for mitigating consequences of an accident: the emergency heat removal system (EHRS), the automatic depressurization system (ADS), emergency boration tanks (EBT), the pressure suppression system (PSS), the long-term gravity make-up system (LGMS) and the injection from the reactor cavity after it is filled with discharged water. They are used for decay heat removal, controlling the reactor pressure, the high pressure and the low pressure water injection. These systems do not require electrical power, but in order to be operable, it is necessary that natural circulation conditions are ensured, that the pipelines are correctly aligned, and that other components, such as check valves, are reliable. The ADS, EHRS and EBT systems are actuated at the very start of the transient and they represent the primary safety measure to mitigate the consequences of an accident. Water injection from the containment tanks (LGMS tanks, PSS pools, reactor cavity) is actuated later, after primary pressure drops below the containment pressure. The pressure difference between the containment and the RPV acts as a driving force for the water discharge. The goal of the paper is to evaluate importance of each safety system by performing calculations with accurately adjusted boundary conditions. The results can be used in determining the optimal accident management strategy. Using the coupled code RELAP5-GOTHIC, the analyses will be conducted in a way that some of the passive safety systems will be considered unavailable. In the worst case, the consequences will lead to a severe accident, when it will no longer be possible to successfully cool the core. The impact of early and late safety measures will be specifically addressed.

Interest in heat-only small modular reactors (SMRs) is growing due to the urgent need for economically viable decarbonization of residential and industrial heating sectors. Heating accounts for more than half of global energy consumption, with the majority still reliant on fossil fuels. While renewable energy sources such as solar, geothermal, and biofuels have demonstrated promising techno-economic potential to replace outdated fossil-based heating systems, their availability is often limited—especially in regions distant from energy consumption centers. Moreover, these renewable sources are subject to natural limitations and generation uncertainties, making them less reliable for meeting the continuous and high-demand heating needs of both residential and industrial applications. This highlights the pressing need for carbon-neutral, reliable, economically competitive, and location-flexible heat supply technologies—needs that heat-only SMRs are well-positioned to meet. From this perspective, the present study investigates the heating energy requirements of both residential and industrial sectors, categorizes the temperature ranges involved, and evaluates the potential deployment of heat-only SMRs, along with the challenges they may face.