Mesoscopic structure of cerium waste loaded hydrated cement by SANS

Cementation is one of the most commonly used methods for conditioning radioactive wastes. It provides a cost-effective solution for encapsulation of low and intermediate level radioactive wastes into suitable solid form for long term safety storage. Cerium is used for decontamination of alpha contaminated metallic waste and after this decontamination process, secondary wastes with corrosion products are created, which must be managed properly and cemented for near surface disposal. In the present work, modification of mesoscopic structure in hydrated cement due to addition of simulated cerium waste at different concentrations has been investigated by small-angle neutron scattering (SANS). Structural modifications, in mesoscopic length scale, have been observed. The scattering profiles for three kinds of cement blocks (virgin, 10 g/l and 20 g/l of corrosion product (C.P.) with 4 mm thickness) are shown. Data have been analyzed in the light of polydisperse spherical particles model assuming a log-normal distribution. Widely separated bimodal particle size distributions best represent the present data. Further, it has been observed that the scattering profile obeys power-law (Q-n) behaviour in two domains of Q, which reflects the self-similar/self-affined morphology of the inhomogeneities. Estimated parameters from SANS data are tabulated. A comparison is shown mentioning the value of scattering radius of gyration, exponent values (η) and average particle size for each kind of hydrated cement sample. (author)