Like any other industry, basic nuclear installations (BNIs) generate by-products, whether or not radioactive, and despite the efforts made for recycling or reuse. These by-products can be treated before disposal as waste or, when their characteristics so allow, discharged into the environment in the form of effluent. After efforts are made to reduce these by-products at source, the choice between effluent discharge and production of waste is the result of an optimisation process specific to each installation. It in particular depends on the feasibility of recovering the radionuclides present in the effluent. The process of containment in the form of waste becomes increasingly cumbersome and costly as the radionuclide concentration diminishes. Below a certain level, the radionuclides cannot be reasonably recovered and they are then discharged into the environment if their impact is acceptable. The radioactivity discharged in effluent represents a marginal fraction of that which is confined in the waste.

At the end of this process, the choice of the form of discharge (liquid or gaseous) also plays a part in the approach designed to minimise the overall impact of the nuclear installation. The actual discharges from the installations are presented in the corresponding chapters.

Until 1995, liquid and gaseous radioactive discharges from nuclear installations were regulated separately by interministerial order. The chemical characteristics of these discharges were regulated by prefectoral order.

The first authorised discharge limits had been set in such a way that they were lower than the health effect values in force.

The optimisation efforts required by the authorities and made by the operators, led to these emissions being reduced. For example, liquid discharges from the Flamanville nuclear power plant, concerning radionuclides other than tritium and carbon 14, fell from 151 GBq in 1986 to 1.2 GBq in 2003. One particular consequence of this reduction was that the former regulatory limits were no longer representative of the actual discharges situation.

For these two reasons, new effluent discharge regulations became necessary:
– concerning procedural aspects, decree 95-540 of 4 May 1995 concerning liquid and gaseous effluent discharges and water intake by BNIs;
– for discharge limits, monitoring conditions and ASN information procedures, with the order of 26 November 1999 setting the general technical requirements concerning the limits and procedures for water intake and effluent discharges subject to authorisation and carried out by basic nuclear installations.

The above-mentioned decree of 4 May 1995 defines the conditions in which discharge and water intake licence applications must be examined. It in particular stipulates that:
– the operator's licence application must be backed up by an impact assessment;
– this application is the subject of a public inquiry;
– examination of this application provides for consultation of the parties concerned (administrative conference, opinion of the local authorities, of the departmental health council, etc.).

After this procedure, a single order issued by the ministers for Health, Industry and the Environment, now regulates all effluent discharges and water intakes.

The above-mentioned decree of 4 May 1995 also enables the administration to revise existing licences at any moment, without any request from the operator being necessary. Finally, this decree confirms the ASN as the body with competence for examination of the licence applications submitted by the operators.

This decree constituted a key step improving control of the administrative procedures regulating BNI effluent discharges into the environment. Its application to all BNIs is gradually leading to a clearer picture of BNI impacts on their environment and how they are understood by the public.