I've read that it's also called 'hydraulic cement'.

2. Hydraulic cements and aggregates
A hydraulic cement powder mixed with inert aggregates and water reacts with the latter to form a paste that sets and hardens to give a final solid product referred to as concrete.
Three types of hydraulic cements commonly used to make concrete have so far been applied for radioactive waste immobilization purposes. The most currently used are the "portland" varieties although "pozzolanic", "slag" and high alumina cements have also been applied. Hydraulic cements mainly consist of calcium silicate and calcium aluminate mixed in various proportion. Their chemistry is complex but fairly well understood.
Typical compostions of some varieties of such cements are shown in Appendix I.

http://publications.europa.eu/resource/cellar/1cea4edf-0c02-...

There is a variety of matrices that can be used for radioactive waste immobilization, hydraulic cement is most widely used for low level radioactive waste because of its low cost, shielding ability, and easy operation.

https://inis.iaea.org/collection/NCLCollectionStore/_Public/...

Immobilisation of radioactive waste involves a technique that entraps the waste in a stable product in order to reduce the mobility or leachability of the waste into the environment. Generally, this technique has been widely used for low and intermediate level radioactive waste (Glasser 2011). The binders which normally used for the immobilisation of radioactive waste especially for spent ion exchange resins is a hydraulic cement i.e. Portland cement. Cement materials are known to be attractive for solidifying radioactive wastes because of its low water permeability after hardening and the high absorbability of some radioactive species onto hardening materials (Kaneko et al., 2001). Cemented radioactive wastes also are characterised by good compressive strength, thermal, chemical and physical stability (Ojovon et.al. 2011). Besides, the alkaline condition of hydraulic cement helps to maintain the low solubility of many radionuclides in radioactive wastes (Atkins & Glasser). Moreover, the solidified radioactive waste can be safely isolated from the environment for a long time in radioactive waste repository (El-Kamash et al., 2006).

https://inis.iaea.org/collection/NCLCollectionStore/_Public/...