[en] The environmental effects of SECURE-400 MW has been investigated for normal operation and after an accident. When calculating the doses during normal operation it has been assumed that 0.1 % of the fuel elements in the core have fuel cladding damages. The doses after an accident have been calculated only for the cases when there might be an effect on the environment: accidents at change of fuel, fracture of the biggest gas pipe and fracture of the main coolant loop. The result of the investigation is that a core melting accident in SECURE 400 is impossible due to the design of the different systems. Other typs of accidents which might happen will give extremly low doses to the environment. The doses will not differ significantly from doses during normal operation. (K.K.)