CERN n_TOF Facility: waste calculations and dose rate simulations of the n_TOF spallation target

The n_TOF facility, a spallation neutron source, uses a pure lead target for production of neutrons with a proton beam extracted from the Proton Synchrotron (PS) of CERN with an energy of 20 GeV. During operation, since 2001, a steady transfer of radioactive spallation products into the cooling water has been observed. From August 2004 on, this transfer has been accelerated. After more than two years of cooling, the present spallation target is considered as damaged and will be moved to its provisional storage place available in the n_TOF service gallery. A new spallation target shall be constructed and will replace the old one. For the removal and the storage of the lead target, isotope production and dose rate calculations were performed. This report presents in a first part the considered technical layout, pictures of the lead target assembly and the actual implementation in the FLUKA simulation. The second part gives detailed results about the activation of n_TOF target and the surrounding installation. The last part refers to the residual dose rates around the target. All results are given for a representative cooling time referring to September 2007 as well as numerous other decay times ranging from one to 100 years.