Amoebae

The condenser is a heat exchanger which cools the secondary system with water taken from the river. The older versions of this equipment are made of brass, while the more recent models are made of stainless steel or titanium. Stainless steel and titanium were chosen in place of brass because they entail fewer metal releases through wear than brass, which generates releases of copper and zinc. The Bugey, Chooz, Dampierre (reactors 1 and 3), Golfech, Nogent-sur-Seine and Civaux plants are equipped with stainless steel or titanium condensers. The condensers at the Belleville, Cattenom, Chinon, Dampierre (reactors 2 and 4) and Saint-Laurent-des-Eaux (except reactor B1) plants are still made of brass, while those in Cruas and Saint-Laurent-des-Eaux (reactor B1) are half of them brass and half titanium.

Amoebae do not grow in systems equipped with brass condensers owing to the toxicity for the micro-organisms of the copper present in this material.

Conversely, owing to the development of amoebae in their cooling systems, and in order to meet the limit value set by the health authorities of 100 Nf/l (amoebae of the Naegleria Fowleri type per litre) in the natural environment, the Bugey, Chooz, Dampierre (reactors 1 and 3), Golfech and Nogent sur Seine plants use monochloramine treatment, while the Civaux plant for its part uses UV treatment of the released cooling water owing to the Vienne river's greater sensitivity to chemical treatment discharges.

These measures allow effective compliance with the 100 Nf/l limit. Chemical substance discharges are for their part regulated by interministerial orders which limit the quantities of products released and require periodic forwarding of the measurement results to the ASN and to the health authorities.

EDF is also conducting a study programme to look for alternative solutions to chemical treatment.

Legionella

The legionella concentrations in the secondary systems cooling systems are variable and depend on a variety of factors (time of the year, use of anti-amoeba treatment, etc.). They can be significant, up to several hundred thousand colony forming units per litre (CFU/l), or even more than a million for those plants with no anti-amoeba treatment: Belleville, Cattenom, Civaux, Chinon, Dampierre (reactors 2 and 4) and Saint-Laurent-des-Eaux. They are less than a hundred thousand CFU/l on the other plants concerned: Bugey, Chooz, Dampierre (reactors 1 and 3), Golfech and Nogent-sur-Seine. The monochloramine treatment used against amoebae thus confirms its biocidal effect against legionella.

The ASN and the DGS considered that it was time to adopt a stance concerning the maximum concentrations for secondary system cooling systems in power plants equipped with cooling towers. In its letter of 28 January 2005, the ASN therefore asked EDF not to exceed certain legionella concentration levels in the secondary system cooling systems.

When setting these levels, account was taken of the results of EDF studies in which, for the same concentration in the systems, the large cooling towers (about 150 metres high) generate concentrations in the environment 50 times lower than the towers normally encountered in ICPEs (installations classified under environmental protection regulations). This value was reduced to 5 in the case of the Chinon nuclear power plant, where the cooling towers are of medium size (28 metres).

Thus the legionella concentration levels not to be exceeded in the secondary systems cooling systems are 5.106 CFU/l for nuclear power plants with large cooling towers, and 5.105 CFU/l for the Chinon nuclear power plant. The measurement frequencies are tailored to the measured concentrations. For systems other than the secondary system cooling system (air-conditioning for example), application of the legal current threshold for ICPEs is required.

As of the summer of 2004 and in order to avoid exceeding the level of 5.105 CFU/l, the licensee operating the Chinon nuclear power plant carried out chlorination of the water in the secondary systems cooling systems. Since the end of summer 2005, it has been operating a new monochloramine treatment unit, this time in order to treat legionella. On 17 August 2005, this installation was the subject of an order modifying the water intake and liquid and gaseous effluent discharge licence for operation of the Chinon nuclear site.

For the other plants without specific treatment, the value of 5.106 CFU/l is respected through the preventive servicing measures normally employed by EDF and designed to limit the development of biofilms.

To complement this stance, an expert appraisal of the situation appeared necessary, in particular to allow an assessment of the various studies, especially the health studies, conducted by EDF. The DGS, ASN and the Directorate for the Prevention of Pollution and Risks at the Ministry for the Environment, referred the matter to the French agency for environmental health safety.