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Description
The European Spallation Source (ESS) is a next-generation neutron research facility currently under construction in Lund, Sweden. Its rotating tungsten target wheel will be cooled by gaseous helium supplied by the Target Primary Cooling System (System 1010). During beam operation, spallation reactions will generate both gaseous and particulate radioactive contaminants, while locally increasing the temperature of tungsten bricks to values approaching 500 °C (at the nominal beam power of 5 MW). Maintaining high helium purity is therefore essential to prevent oxidation of target materials and to ensure that the concentration of radioactive isotopes, in particular tritium, remains within specified operational limits.
To remove particulate contamination, System 1010 incorporates a high-efficiency filter assembly located downstream of the target wheel. This filter includes multiple cartridges with nominal ratings of 5 µm and 1 µm. However, the removal of sub-micron particles, oxidising impurities, and tritium requires a dedicated purification solution.
To address this need, the Target Primary Cooling Purification System (System 1015) has been developed as an auxiliary system connected to the primary helium cooling loop. The project was initiated in 2014 and the system was installed in 2024. It is designed for continuous purification of a helium side-stream flow of approximately 2 g/s. System 1015 consists of two gas purifiers incorporating chemical getters and ultra-fine filtration elements with nominal retention capability down to 3 nm, together with a dedicated valve and instrumentation panel enabling safe integration, operation and maintenance.
Preliminary functional tests with dummy gas purifiers were successfully completed in 2025. Installation of the real gas purifiers is planned for Q3 2026, followed by the remaining verification and performance validation activities. Full purification commissioning is foreseen shortly after Beam on Target, when the circulating helium inventory will begin to contain radioactive contaminants.
This paper presents the design rationale of System 1015, key technical characteristics, selected engineering solutions, verification activites, and the planned operational strategies for helium purification during target operation.