MELCOR 2.2 iPWR LOCA type accident analysis, PART I: Thermal-hydraulics

One of the coming Small Modular Reactor (SMR) designs is the integrated Pressurized Water Reactor (iPWR), which merges years of knowledge and experience in light water reactors with new demands from the market, such as flexibility, construction optimization, and reliability. Generally, SMRs are considered to be inherently safe and, in many cases, safer than generation III designs. Most of the SMR designs rely on passive safety systems at different levels of passive operation. One of the ways to examine new concepts is a numerical simulation using a reliable tool. However, when new features come up, there are also new challenges for existing tools, even though they are continuously updated following the technology’s evolution. To investigate if implemented new features give expected results and to increase knowledge about SMRs modeling and simulations, accident transients of iPWR were calculated using MELCOR 2.2 code and analyzed. The work aims to understand better numerical simulations of the analyzed iPWR accident scenarios and code reliability. To do so, the paper is divided into two parts; in Part 1, the authors present MELCOR 2.2 iPWR input deck description, including nodalization and steady-state conditions as well as the analysis of an iPWR LOCA-type scenario in the design basis accident domain. In addition, design basis accident progression is compared to beyond design basis scenario in which safety systems are postulated partly failing. The analyses of beyond design basis scenarios in which core degradation is observed are published separately in second part of that paper. The obtained results indicate that MELCOR2.2 can simulate the thermal–hydraulic response of an iPWR in accident scenarios. Values received in this study in steady state and accident simulations are mostly expected and coherent with general knowledge of accident progression.