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Description
The European Spallation Source (ESS) is a next-generation neutron research facility currently under construction in Lund, Sweden. The rotating tungsten target wheel will be cooled by gaseous helium supplied by the Target Primary Cooling System (System 1010). During operation, the process helium will be continuously purified by the Target Primary Cooling Purification System (System 1015).
To prevent oxidation of target materials and minimise the potential release of radioactive isotopes, in particular tritium, stringent operational requirements have been imposed on the helium cooling loop. Contaminated helium inventory must remain fully confined, while the concentration of oxidising impurities (oxygen, carbon dioxide and moisture) must be maintained below 5 ppmV and the tritium concentration below 0.2 ppmw.
Leak-tightness verification of the cooling loop was performed during commissioning, confirming compliance with the specified allowable leak rate. However, continuous monitoring of contaminant concentrations during operation requires dedicated measurement capability.
For this purpose, the Target Primary Cooling Contaminant Measurement System (System 1017) has been developed as an auxiliary system connected to the primary helium cooling loop. The system incorporates instrumentation for measuring the concentrations of oxygen, carbon dioxide, moisture and tritium in circulating helium. In addition, it includes a gas sampling unit enabling the collection of representative helium samples for further analysis of additional contaminants, such as activation products (e.g. iodine-125), in the ESS Radiation Protection laboratory or external accredited laboratories.
This paper presents the design rationale of the measurement system, its key technical characteristics, selected engineering solutions adopted to ensure safe and representative sampling, and the planned operational strategy for contaminant monitoring during target operation.