Yes, radioactive radiation will be formed inside the facility. However, the radiation levels will not pose any danger to employees, guest researchers or local residents.
Radioactivity does in fact occur naturally, above all in background radiation and inside the human body. The radioactive radiation that ESS will expose the local environment to will be an order of magnitude of one-thousandth of the natural background radiation.
Experiences from other neutron sources and particle accelerators show very little impact on the local environment. The radiation that the enormous CERN research facility in Geneva has exposed the local environment to for the duration of its 53-year lifetime is completely negligible according to the calculations of the French and Swiss radiation protection authorities.
During normal use, the threshold limit value that ESS must stay under is 1 millisievert (mSv) per year. In reality, however, ESS will need to plan for considerably lower radiation; an order of magnitude of a few microsievert (i.e. an order of magnitude of a thousandth). This can be compared to the natural background radiation, which is 4 millisievert in Sweden and 3 millisievert in Denmark, thus, an order of magnitude 1000 times more than what ESS will supply in practice.
The radiation from CERN is around 0.01 mSv (millisievert) per year, which is less than one per cent of background radiation.