Магній-калій-фосфатний цемент для інкапсуляції золи від спалювання радіоактивно забрудненої деревини

• Дата: 2024
• Автори: Sayenko, S., Shkuropatenko, V., Svitlychnyi, Ye., Pylypenko, O., Kholomieiev, H., Karsim, S., Zykova, A.
• Формат: Стаття
• Мова: English
• Опубліковано: State Scientific and Technical Center for Nuclear and Radiation Safety 2024
• Онлайн доступ: https://nuclear-journal.com/index.php/journal/article/view/1128
• Назва журналу: Nuclear and Radiation Safety

When wood from Chornobyl radioactively contaminated forests is burned in the Incinerator created in the Chornobyl zone under support of the European Commission, ash with a high content of Cs radionuclides is formed. Recently, magnesium potassium phosphate cements (MKPC) have been proposed as an effective alternative to Portland cement-based protective matrices. In this work, MKPC compositions were optimized for laboratory-scale encapsulation of inactive model ash, used as surrogate of the radioactive ash. The influence of the MgO/KH2PO4 ratio and the amount of added model ash on the temperature and setting time of the MKPC paste were determined. The compressive strength after 28 days of MKPC curing without ash was 22.7 MPa. After adding 20 wt.% model ash, the compressive strength of the MKPC matrix was 34.5 MPa, 40 % model ash was 23.4 MPa and 60 % model ash was 8.3 MPa. Thus, the accepted amount of the added ash that does not initiate the essential strength decrease of the MKPC matrix is 40 %. X-ray diffraction analysis of the MKPC matrix with 40 % model ash shows the presence of the main phase – K-struvite MgKPO4·6H2O. In addition to K-struvite, there are peaks of unreacted MgO and compounds such as calcite CaCO3, quartz SiO2 and potassium chloride KCl, which are parts of the model ash. It has been shown that ash components such as hydroxyapatite Ca5(PO4)3(OH) and calcium oxyphosphate Ca4(PO4)2O are involved in the formation reaction of phosphate cement and it contributes to increasing of the permissible amount of ash encapsulated into the MKPC matrix. SEM images of MKPC samples demonstrate a dense structure with well-connected ash particles. The leaching behavior of the MKPC matrices and their thermal stability were also assessed using immersion tests and thermogravimetric analysis, respectively. The Cs leaching rate of 1.2×10-4 g/cm2·day from the MKPC matrix containing 40 % MA is lower than the rates typical for cement waste forms. The obtained results demonstrate the possibility of using new magnesium-potassium phosphate cement as a matrix for the encapsulation of ash from the combustion of radioactively contaminated wood in the Chornobyl zone.