The exemption from regulatory control of practices with very low level activity materials has an historical legal acceptance. The aim of the paper is to present some personal considerations linked with the application of the exemption criteria stated in the new ICRP recommendations. The report analyses and tries to clarify the apparent contradiction between the optimisation process and the practical threshold that a de minimis policy implies. Some practical cases that could appear now or in the near future are commented on.

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Decommissioning nuclear power plant causes an enormous amount of radioactive waste with very low level of contamination. A risk optimisation analysis would indicate that some of these residual materials need not to be handled, processed or disposed of with any reference to their radioactivity content, in order to allow more beneficial allocation for the limited social resources. This analysis could also be applied to the site liberation once a particular facility is decommissioned, remedial or restoration actions should be subjected to an optimisation process for selecting the best strategy of remedial measures. In order to make this release from regulatory control possible, it is necessary to establish conditions for the site or for these materials to be managed during their later reuse or final disposal. Authorisation for this release or clearance of control is a responsibility of the competent authority and, in the case of Spain, is carried out by the CSN (Spanish Nuclear Safety Council) on an “ad hoc” case by case analysis. Some personal considerations linked with the exemption policy and the application of radiological protection principles and criteria to the release authorisation of sites and solid materials generated within a regulated facility are presented in the paper. The main aim of this paper is to present the management options for very low level waste materials that are considered in the case of the Dismantling and Closure Plan authorisation granted for Vandellós 1 NPP decommissioning project. A framework consisting of three basic possibilities to apply clearance appears in the mentioned authorisation: • A first set of unconditional clearance levels N1 expressed in terms of gross activity concentration and surface contamination has been issued for unrestricted release of materials. Derived unconditional generic clearance levels, based on published international guidance, are also accepted. • Generic use of derived conditional clearance levels N2, based on “ad hoc” internationally published guidance, has been established for particular waste streams managed in well defined non regulated practices (metallic scrap recycling and concrete demolition debris). • The applicant may also propose candidate materials for other non-regulated route management practice, for which specific conditional clearance levels N3 can be issued by the Nuclear Safety Council. In all cases, control procedures have to be imposed to the licensee producing the residual materials that can be verified by the Safety Authority. They are based on the certification of the radionuclide content supported by quality controls and maintenance of records. There is not an official criterion, until now, for the remediation of land and liberation of the site, but probably the same radiological analysis will be used when evaluating the restoration plan application. A kind of “rubblization” is being considered by the licensee, using the above-mentioned third possibility for conditional clearance of the rubble produced in the dismantling of some particular buildings.