Introducing radiation target level for the shielding design of a nuclear-powered container ship and its determination process using MCNP6 code

As the International Maritime Organization strives for net-zero emissions in the maritime sector by 2050, nuclear-powered ships offer a viable solution due to their zero greenhouse gas emissions, long operational lifespan, and high energy density. However, the implementation of nuclear propulsion raises concerns regarding crew radiation exposure and national security, issues that necessitate optimal radiation shielding. This study proposes the concept of radiation target level (RTL) to inform the radiation shielding design of nuclear-powered ships. To maximize economic viability while ensuring safety, the reference ship, a 15,000 TEU container ship, is divided into a shielding zone, which encloses the reactor and the primary shielding, and a non-shielding zone, which includes crew living and work areas. Radiation exposure in the non-shielding zone is managed by controlling the time spent in different areas of this zone, referred to as stay time, adhering to the ALARA principle. Using MCNP6 code, radiation levels are analyzed at key locations and permissible stay times are evaluated against ICRP dose limits. As a result, this study determined an optimal RTL of 8.92 μSv/hr, ensuring compliance with an annual dose limit of 1 mSv for all personnel on board. This result provides a reference for shielding design, radiation zone classification, and crew exposure management, contributing to the safe and economically viable operation of nuclear-powered ships.