LABORATORI NAZIONALI DI LEGNARO
In the context of the ESS project, cryogenic cooling is essential for various equipment of the facility that will be provided with both liquid nitrogen and liquid helium; in particular the superconducting section of the accelerator containing 21 High Beta cryomodules, 9 Medium Beta cryomodules and 13 Spoke cryomodules. A total of 146 superconducting radio frequency (SRF) cavities operating at 2 K will be housed in those cryomodules. Additionally, cryogenics will also be used for the cold hydrogen moderator surrounding the target as well as for some neutron instruments. In order to achieve a proper cooling, different facilities will be built to house the future cryogenic installation but will be subject to ODH (Oxygen Deficiency Hazard). Two factors make ODH so dangerous. The first is the large volume ratio between a cryogenic liquid and its gaseous state at room temperature and pressure. As an example 1 liter of liquid nitrogen will result in 700 liters of nitrogen gas at room temperature and pressure. Thus, it takes a small amount of cryogenic liquid vented into a space to reduce the oxygen concentrations to dangerous levels. Second, in low enough oxygen concentrations the first physiological symptoms of a problem can be unconsciousness, coma and death. Unconsciousness can occur in less than 30 seconds. In order to address this large cryogenic safety issue ESS wide, a preliminary long-term strategy has been prepared based on the selection of a calculation model, the definition of an ODH safety process as well as the clarification of the roles and responsibilities and the list of control measures. At this early stage, some preliminary ODH assessments have been carried out in various areas such as the accelerator tunnel and the compressor building using simple calculation models. The presentation will introduce the different methodologies adopted and some examples of ODH assessment carried out at ESS, and finally the long-term strategy chosen to address the ODH issues.

DATA: 26-05-2015