Session: 05-01: Waste Conditioning, Stabilization and Encapsulation Studies

Paper Number: 118501

118501 - Radiation Stability and Durability of Magnesium Phosphate Cement for the Encapsulation of Radioactive Reactive Metals 

Large amounts of radioactive reactive metallic waste (RRMW), such as aluminium, beryllium, and tungsten, are produced in nuclear facilities. Besides being radioactive by neutron activation, they represent a source of concern because of their reactivity in alkaline media, such as Ordinary Portland Cement matrices. Corrosion-driven  production leads to deleterious effects, namely safety concerns, embrittlement, swelling, and premature cracking. A stable protective layer forms on RRMW at the lower pH values of Magnesium Phosphate Cement (MPC) matrices, making these materials promising for the encapsulation of RRMWs.

In this study the radiation stability of a reference formulation is carried out at 100, 200, and 500 kGy. Moreover, compliance with some waste acceptance criteria (WAC) is assessed by means of leaching and compression tests.

Two series of samples, one of which containing representatives of fission and activation products (Sr, Cs, Co, and Eu), were irradiated with a -60 source after 28 days of curing at relative humidity above 90%. Afterwards, the specimens underwent a 90 days leaching test according to the ANSI/ANS-16.1-2003 protocol. Unirradiated samples were used as reference. The release of both matrix constituents (K, P, and Mg) and contaminants was measured using inductively coupled plasma-optical emission spectroscopy and inductively coupled plasma-mass spectrometry, respectively. Eventually, compressive tests were performed on all the samples, and characterization through X-ray powder diffraction, X-ray fluorescence, and mercury intrusion porosimetry was carried out. Leachability indices derived from the leaching tests and compressive strengths overcome the minimum reference values, 6.0 and 10 MPa respectively, imposed by Italian regulators with a solid margin. Moreover, no major differences attributable to radiation damages have been pointed out, thus confirming the stability of the MPC matrix up to 500 kGy. Further studies involving low-cost formulations, different contaminants such as actinides, incorporation of surrogate RRMW, and thermal fatigue are ongoing to provide a more complete assessment of the durability of these matrices.

Acknowledgements:

This work was conducted within H2020-PREDIS project, which has received funding support from the Euratom research and training program 2019-2020 under grant agreement No. 945098. The authors thank Gammatom S.r.l. for the support to irradiation.

Presenting Author: Fabio Fattori Politecnico di Milano, Department of Energy

Presenting Author Biography: I have a degree in Nuclear Engineering as of May 2023. Currently involved in the development and testing of novel cementitious materials for the encapsulation of challenging radioactive waste, in particular radioactive reactive metallic wastes encapsulated in magnesium phosphate cement matrices.