Study of irradiated graphite-bakelite paste

Highlights: • The study of irradiated graphite-bakelite paste from a uranium-graphite reactor was carried out for the first time. • The radionuclide composition and the rate of leaching of radionuclides from graphite-bakelite paste were determined. • Wigner energy value in the irradiated graphite-bakelite paste was estimated. The article is devoted to the study of irradiated graphite-bakelite paste formed during the restoration of graphite stack and the operation of uranium-graphite reactors. It was shown that irradiation of graphite-bakelite paste in the reactor leads to the formation of long-lived radionuclides and the accumulation of Wigner energy. The studies of graphite-bakelite paste extracted from the graphite stack of one of the UGR with a closed primary loop showed that the samples of graphite-bakelite paste are contaminated unevenly with ¹³⁷Cs, ¹⁵⁴Eu, ⁶⁰Co, and ²⁴¹Am radionuclides (fission and activation products and actinides). From the results of experiments on leaching of radionuclides from graphite-bakelite paste, it can be seen that radionuclides ²⁴¹Am and ¹³⁷Cs are more subjected to leaching. The estimation of the stored energy in the selected samples shows that the heat release begins at a temperature of 600–650 ◦C. The largest amount of stored energy is released at a temperature of 750 ◦C. Moreover, the magnitude of this quantity does not exceed 1–6 J/g. It was also shown that the development of the concept and program for decommissioning of UGR, the stack of which was restored using graphite-bakelite paste, requires additional studies to determine the potential danger of irradiated graphite-bakelite paste.