RAMI analysis of the helium refrigeration system of HL-2M tokamak

•The first domestically made helium refrigeration system independently developed in China.•The first application of RAMI analysis in the helium refrigeration system of HL-2M Tokamak•A general RAMI analysis method is proposed, which can be used as reference and citation. The 500 W@4.5 K helium refrigeration system operated in HL-2M Tokamak is the first domestically made cryogenic system independently designed and manufactured in China. It is expected to cool down HL-2M cryousers for the first time around June 2021. In the requirement document of helium refrigeration system, the mean time between failures (MTTF) should be at least 8000 hours, and the inherent availability of the subsystem should be 60%. This paper presents the RAMI (Reliability, Availability, Maintainability and Inspectability) analysis of the failure modes of the HL-2M helium refrigeration system as well as the corresponding effects and criticality to guide the design of the components and the preparation for operation and maintenance. The description of the risk mitigation actions regarding the design, testing, maintenance and operation in order to reach the expected targets of enhancing the reliability and availability of the refrigeration system.