The Eurobitum bituminised waste produced by the former EUROCHEMIC reprocessing plant in Mol-Dessel (Belgium) contains a lot of salts, mainly NaNO3. This NaNO3 may possibly affect significantly the evolution of a radwaste repository through redox and ion exchange reactions with Boom Clay, which in Belgium is studied as a reference host formation. Yet, the leaching behaviour of NaNO3 from the Eurobitum and its migration in the Boom Clay is rather unclear. Therefore, some scoping numerical calculations have been performed. In a first phase, we calculated the water flux towards the disposal gallery to assess the timescale of the saturation process of the disposal galleries. In a second phase, the leaching rate of NaNO3 out of the drums is compared with its diffusive removal through the Boom Clay.
The water flux to the gallery was calculated at approximately 100 ml/day per metre gallery, based on the natural pressure gradient observed around the HADES Underground Research Laboratory. Different approaches were elaborated to find a NaNO3 source term for the diffusion calculations. For various ways of characterising the nitrate release, the numerical calculations generally show that the NaNO3 concentrations in the first decimetres of Boom Clay will not be much higher than 1 M. Moreover, a sensitivity analysis showed that if the nitrate is released from the bituminised waste product within 10 000 years, the Boom Clay controls the concentration profiles; if the release is slower, the source term has a more pronounced effect on the near field concentrations.