[en] A repository heat transfer analysis is being performed by the Pacific Northwest Laboratory (PNL) for the US Department of Energy's Performance Assessment Scientific Support Program. The objective of this ongoing study is to evaluate near-field host rock and waste package surface temperatures for a spent fuel repository system located in a tuff geologic medium. A spent fuel logistics model of the waste management system was used to evaluate the thermal characteristics of spent fuel emplaced in the repository. A three-dimensional heat conduction model of the underground repository facility was used to evaluate near-field host rock temperatures throughout the 10,000-year isolation period. The spent-fuel thermal characteristics and near-field host rock temperatures were then used to estimate waste package surface temperature histories and distributions for the repository system. The resulting temporal and spacial distributions provide key input to repository source term model evaluations of waste isolation performance. 15 refs., 7 figs., 1 tab