The ESS Monolith Vessel design and possibilities to introduce a UCN/VCN source

The ESS ERIC neutron source design includes a helium cooled tungsten spallation target and a liquid hydrogen moderator, enclosed in a vacuum vessel (the monolith vessel – spallation source vacuum chamber). The neutron source and moderator are shielded by stainless steel and casted iron to block neutron and gamma radiation emitted in directions outside of the neutron guide lines. After the ESS concept design was approved, discussions were raised if it was possible to introduce a UCN/VCN (Ultra Cold Neutron / Very Cold Neutron) source into the ESS design. Since the shielding concept of the monolith vessel is to 100% fill the monolith void, outside of the proton and neutron path, there are no cavities in the monolith vessel to easily introduce an UCN/VCN source. In addition, pipe routing supporting the UCN/VCN cooling media, will also challenge the possible UCN/VCN positions. However, some of the shielding blocks and monolith components are removable and could possibly be redesigned, enabling a UCN/VCN source feature. The article presents a feasibility study how to physically introduce a UCN/VCN source in the present ESS design, and focus on the geometrical possibilities. Four possible locations for the UCN/VCN source are identified and presented in the article. The locations are selected considered reasonable impact to the existing design. Pros and cons are discussed. All of the four presented locations are feasible but will, to some extent, require redesign of the monolith vessel shielding.