Preparation and study of the critical-mass-free plutonium ceramics with neutron poisons Hf, Gd and Li

• Published in: Journal of nuclear science and technology 2002-11, Vol.39 (sup3), p.729-732
• Main Authors: Timofeeva, L.F., Nadykto, B.A., Orlov, V.K., Malyukov, E.E., Molomin, V.I., Zhmak, V.A., Semova, E.A., Shishkov, N.V.
• Format: Article
• Language: English
• Subjects: ceramics; neutron poison; nuclear safety; plutonium oxide; properties; structure
• ISSN: 0022-3131; 1881-1248
• DOI: 10.1080/00223131.2002.10875570

Powder sintering was used to produce homogeneous type oxide ceramics of Pu with Hf, Gd and Li 6 . In all the ceramics, there is the number of neutron poison (Hf, Gd and Li) atoms per plutonium atom needed, according to the physical calculation, for them to be free of critical mass. PuO 2 stabilizes high-temperature modifications of cubic HfO 2 or hexagonalGd 2 O 3i however, at the ratio given by the physical calculation, the plutonium is insufficient for their full stabilization. Addition of yttrium oxide as an additive stabilizing the fee phase of HfO 2 resulted in cubic solid solution (Pu,Hf,Y)O 2-x . Pu/Li/Hf and Pu/Li/Si ceramics produced by sintering of PuO 2 and compound Li 2 HfO 3 or 6 Li 4 SiO 4 powders is characterized with presence of two phases. The method of differential thermal analysis demonstrated the phase stability of (Pu-Hf, Pu-Gd, Pu-Li-Hf) oxide ceramics in the 20-1500°C temperature range. Ceramic (Pu/Li/Si) has several endothermal effects. Tests in boiling water solutions of various composition suggest that the specimens of Pu, Hf oxides and ternary oxides (Pu, Hf, Y) O 2 are less stable in weakly acidic media than in weakly alkaline medium and distilled water. The obtained results were used as a basis to estimate the assumed solid solution region boundaries for binary Hf, Pu and ternary Hf, Pu,Y oxides on the side of HfO 2 .