Abstract

In April 2005 a routine review of the material balance of nuclear materials across the Sellafield Thermal Oxide Reprocessing Plant (THORP) revealed a significant in-balance. This was traced to a large leakage of highly radioactive dissolver liquor from the inlet to an accountancy tank into the cell of the THORP head-end plant. Some 83 cubic metres of liquor had built up in the bottom of the cell and had gone unnoticed for several months. No evidence was found of leakage out of the cell into the environment nor did any person, worker or member of the public receive any significant radiation dose. However, the plant had to be shut down for over a year and a half, the operator was prosecuted and the regulator to re-consider how to address such issues as an operators safety culture. This presentation reviews this incident and its causes and presents it as a case study of lessons for designers, operators and regulators.