Про критерії безпеки та критерії прийнятності в аналізах ядерної безпеки та нормативно-правових актах

• Дата: 2025
• Автори: Khalimonchuk, V., Ovdiienko, Iu., Ieremenko, M., Shepitchak, A.
• Формат: Стаття
• Мова: Ukrainian
• Опубліковано: State Scientific and Technical Center for Nuclear and Radiation Safety 2025
• Онлайн доступ: https://nuclear-journal.com/index.php/journal/article/view/1288
• Назва журналу: Nuclear and Radiation Safety

This paper analyzes the limit established in Regulation 306.2.145-2008 on the permissible rate of positive reactivity insertion into the reactor core ∂ρ(t)/(∂t) < 0.07 β/s, which is based on a similar Soviet document developed back in the 1970s–1980s. It is stated that this limit, along with the rule prohibiting the simultaneous insertion of positive reactivity using two different methods of impact on reactivity, is not presented in documents of the same level from Western countries. The analysis of the literature reveals that the limit that the limit ∂ρ(t)/(∂t) < 0.07 β/s is established to ensure a reactor period T > 10 s when transitioning to the critical state during power operation. Additional calculations show that the limit ∂ρ(t)/(∂t) < 0.07 β/s is also acceptable for reactor start-up. Furthermore, the condition T>10 s is maintained throughout the entire time of the transition process with inserting positive reactivity. It is shown that based on the actual value of ∂ρ(t)/(∂h)  for the VVER-1000 control rods differential efficiency, ∂ρ(t)/(∂t)  does not exceed 0.04 β/s, and the requirement ∂ρ(t)/(∂t) < 0.07 β/s at power is met with a significant margin, which can ensure meeting the criterion  even in simultaneous insertion of positive reactivity using two independent ways, in particular additionally by reducing the concentration of boric acid in the coolant. The justification is presented for the acceptability criterion in the experimental study of the reactivity coefficient based on coolant temperature at reactor power for VVER reactors. The research conducted shows that as an acceptability criterion for the measured aisotherm, it is more appropriate to consider a relevant frame value of the Doppler coefficient rather than a specific value, or its calculated value for the respective reactor state at power. Attention is drawn to the need for adjustment of some terminological definitions in Regulation 306.2.145 2008. Furthermore, it is not appropriate to set numerical limits for the reactor operation in high-level regulatory documents like Regulation 306.2.145‑2008, which should fundamentally establish general requirements, while numerical limits should be defined in the reactor design and justified in the safety analysis report.