Nuclear hydrogen production systems as a next generation energy resource are under development, which are faced with a new nuclear safety issue that takes place in the interface between a nuclear system and a hydrogen production system. Potential risks of a nuclear system from hydrogen production have been investigated according to a two-step probabilistic safety assessment (PSA) approach, i.e., (1) an identification of the potential factors of a hydrogen production system threatening the nuclear system and (2) an assessment of the impacts on the nuclear system from the identified factors. In the first step, a large scale hydrogen leakage from the hydrogen storage system and its explosion has been identified as a key potential factor. The second step has investigated the related impacts on the nuclear system by a PSA approach. From this investigation, the potential risks of the nuclear system from the hydrogen production system have been identified as (1) an impact of hydrogen explosion and (2) an impact from explosion fragments. As a result of the present study, the obtained insights provide useful information to resolve the new safety issue, which will address the interface between the nuclear system and hydrogen production system. (C) 2014 Elsevier B.V. All rights reserved.