A Conceptual Study of a Supercritical CO2-Cooled Micro Modular Reactor

Abstract

A neutronics conceptual study of a supercritical CO 2 -cooled micro modular reactor (MMR) has been performed in this work. The suggested MMR is an extremely compact and truck-transportable nuclear reactor. The thermal power of the MMR is 36.2 MWth and it is designed to have a 20-year lifetime without refueling. A salient feature of the MMR is that all the components including the generator are integrated in a small reactor vessel. For a minimal volume and long lifetime of the MMR core, a fast neutron spectrum is utilized in this work. To enhance neutron economy and maximize the fuel volume fraction in the core, a high-density uranium mono-nitride U 15 N fuel is used in the fast-spectrum MMR. Unlike the conventional supercritical CO 2 -cooled fast reactors, a replaceable fixed absorber (RFA) is introduced in a unique way to minimize the excess reactivity and the power peaking factor of the core. For a compact core design, the drum-type control absorber is adopted as the primary reactivity control mechanism. In this study, the neutronics analyses and depletions have been performed by using the continuous energy Monte Carlo Serpent code with the evaluated nuclear data file ENDF/B-VII.1 Library. The MMR core is characterized in view of several important safety parameters such as control system worth, fuel temperature coefficient (FTC) and coolant void reactivity (CVR), etc. In addition, a preliminary thermal-hydraulic analysis has also been performed for the hottest channel of the Korea Advanced Institute of Science and Technology (KAIST) MMR.

Neutronics optimization and characterization of a long-life SCO2-cooled micro modular reactor

“…Another interesting finding is that at the EOL the CVR of the current MMR core is more negative than the one in the preliminary core design (about −1.47 ± 7.48 pcm) . This is because at the EOL the peak radial power of the current core (about 1.174) is higher than that in the preliminary core design (about 1.169), which leads to higher neutron leakage from the central nonfuel region of the current MMR core.…”

“…As shown in Figure 2, the core excess reactivity is very high without any absorber, about 4708 pcm or 6.47 dollars for U 15 N fuel and 5451 pcm or 7.46 dollars for UC fuel. In a previous study [1], this high excess reactivity was reduced to half by introducing a thin layer RFA in the central nonfuel hexagonal duct. This coating-type RFA is installed from the beginning of the operation and removed after 10 EFPYs.…”

The application of supercritical CO2 in nuclear engineering: A review

“…The Massachusetts Institute of Technology (MIT) has investigated a large size (2400 MW) SCO 2 -cooled fast reactor concept combined to direct SCO 2 Brayton cycle. 22 MIT formed an SCO 2 recompression circulation pattern based on the early Feher cycle by removing CO 2 condensation process and replacing the pump with the compressor and other improvements. In order to improve cycle efficiency, they proposed a general scheme of SCO 2 cooling fast reactor (GFR) and set up a recompression compressor and two regenerators.…”

“…The design parameters of KAIST MMR are shown in Table 4. 22 In the KAIST MMR, the SCO 2 power conversion system driven by the coolant is a direct process without intermediate heat exchanger. Due to the design of compact modular, the SCO 2 power conversion module and the reactor core can be integrated into a single reactor vessel.…”

“…Due to the design of compact modular, the SCO 2 power conversion module and the reactor core can be integrated into a single reactor vessel. 22 Supercritical CO 2 -cooled reactor concept of Japan Figure 6. 23 Researchers analyzed that usual spherical fuel and block fuel can still be used in this new SCO 2 -cooled reactor.…”