[en] The CNAP Phase III project was carried out following identification of the requirement to support ongoing laboratory and modelling efforts on the potential reaction of the bentonite buffer with cementitious leachates in the repository EBS. Although it is known that the higher pH (12.5 to 13) leachates from OPC cement will degrade bentonite, it is unclear if this will also be the case for the lower pH (10 to 11) leachates typical of low alkali cements. Ongoing laboratory and URL programmes which are currently investigating this face the obstacle of slow kinetics and the production of short-lived metastable phases, meaning obtaining unambiguous results may take decades. This is exacerbated by the limitations of the thermodynamic databases for minerals of interest to models of bentonite/low alkali cement leachate reaction. It was therefore decided to implement a focussed NA study on bentonite/low alkali cement leachate reaction to provide indications of likely long-term reaction products and reaction pathways to provide feedback on the existing short-term investigations noted above and to ascertain if any critical path R and D needs to be instigated now. The results of the analyses presented here suggest that there has been very limited alkaline groundwater reaction with the bentonite. This is generally supported by both the geomorphological evidence and the natural decay series data which imply groundwater groundwater/rock interaction in the last 10⁵ a. When integrated with the novel data currently being produced in the BIGRAD project, the CNAP data tend to indicate that any long-term bentonite reaction in low alkali cement leachates is minimal. (orig.)