ASN Report 2018

∙ ∙ The difficulty in accessing the waste was not taken into consideration in the design (trenches, concrete-lined pits, cramped premises, etc.), necessitating the costly construction of infrastructures in conformity with current safety practices and leading to long retrieval time frames and unforeseen events. ∙ ∙ The deterioration of the containment barriers, for example corrosion of waste drums or pollution of soils resulting from the occurrence of significant events during operation. 3 —  ASN actions concerning research facilities: a graded approach 3.1  ̶  The graded approach according to the risks of the facilities ASN ensures the oversight of facilities undergoing decommissioning, as it does for facilities in operation. The BNI system also applies to definitively shut down facilities. ASN has implemented an approach that is proportional to the extent of the risks or drawbacks inherent to the facility. In this respect, ASN has divided the facilities under its oversight into three categories from 1 to 3 in descending order of the severity of the risks and drawbacks they present for the interests mentioned in Article L. 593-1 of the Environment Code (ASN resolution 2015- DC-0523 of 29 September 2015). This BNI classification allows oversight of the facilities to be adapted and the inspections and depth of examinations conducted by ASN to be proportional to the risks present at the facility. The risks with facilities undergoing decommissioning differ from those for facilities in operation. For example, the risks of significant off-site discharges decrease as decommissioning progresses because the quantity of radioactive substances decreases. The requirements concerning the systems for controlling the risks associated with the decommissioning operations therefore tend to decrease as decommissioning progresses. ASN considers that it is generally not appropriate to undertake as substantial reinforcement work on a facility undergoing decommissioning as on a facility in operation, provided that the decommissioning is effectively carried out and leads to a reduction in the hazard sources in short time frames. 3.2  ̶  Lessons learned from Fukushima To take into account the lessons learned from the nuclear accident that occurred at the Fukushima Daiichi NPP in Japan, ASN asked the BNI licensees to carry out stress tests on their installations, including those undergoing decommissioning. The stress test procedure has been divided into three lots according to the safety risks inherent to the facilities. The facilities being decommissioned are essentially in lots 2 and 3. For the facilities in lot 2, the post-Fukushima assessments have led ASN to request the removal of radioactive substances or the reinforcing of emergency management means on centres that often also have facilities in operation (see introduction to the report and chapters 11 and 12). Schematic of retrieval and packaging of the waste from silo 130 ASN report on the state of nuclear safety and radiation protection in France in 2018  343 13 – DECOMMISSIONING OF BASIC NUCLEAR INSTALLATIONS 13