[en] The 4th NUCEF seminar was held at JAERI Tokai Establishment on 18 February 2000. The NUCEF seminar aims at the promotion of effective researches and the encouragement of research cooperation through the discussions and information exchanges by researchers in the field on the nuclear fuel cycle back-end. This seminar was divided in the following sessions: Criticality Safety, Reprocessing/Partitioning and Radioactive Waste Management. Especially, considering highly regrettable impact of the criticality accident at JCO, the Criticality Safety session including the Dose Evaluation focused on the evaluation of JCO Criticality Accident. This report compiles the papers presented and the related discussions. The 13 of the presented papers are indexed individually. (J.P.N.)