Safety and reliability assessment of CO2 refrigeration system for underground applications below -50 °C.

A new CO$_2$ refrigeration concept is evaluated to cool the ATLAS and CMS experiments installed close to 100 m underground, at the Large Hadron Collider (LHC) at CERN. The first prototype unit produced to validate the conceptual design and to assess safety and reliability of the system has been commissioned. This paper presents results obtained, discusses the safety and reliability of the system and discourses on the list of recommendations for the future final units to cover the cooling loads of 380 kW for ATLAS and 750 kW for CMS at -53 °C evaporation temperature.