Pyrochemical method of salvaging weapons plutonium in oxide for fabricating mixed fuel for fast reactors

Abstract

Experimental results of investigations of pyrochemical conversion of weapons plutonium into plutonium oxide for fabricating fast-reactor fuel are presented. Weapons plutonium was hydrogenized by hydrogen at 220°C, after which the plutonium hydride obtained was acidified at 550-560°C with the formation of PuO 2 . To increase fire and explosion safety of the process, a mixture of oxygen with nitrogen, helium, or argon was used or nitriding with nitrogen and oxidation of plutonium mononitride were introduced. The particle size of the plutonium oxide powders obtained was less than 15 µm. The powders showed poor flowability, but after granulation they were suitable for fabricating kernels with mixed fuel. The gallium was removed by reduction of Ga 2 O 3 by hydrogen to Ga 2 O, which was sublimated. The mixed-fuel kernels sintered at 1600-1700°C in a hydrogen atmosphere contained <0.001 wt.% gallium, and their density was 94-97% of the theoretical value.Two variants of the technology were studied to obtain ceramic type plutonium dioxide: pyrochemical with only gallium removed from the plutonium in the process and combining the pyrochemical process of converting weapons plutonium into a disperse powder of plutonium hydride or plutonium mononitride by dissolving them in acids and extraction removal of gallium and americium. The simplest, most cost-effective and efficient method of converting weapons plutonium into plutonium oxide is the pyrochemical method with pre-hydrogenation followed by oxidation of plutonium hydride [1].In connection with the decision to use mixed fuel in BN-800 and other reactors, the conversion of weapons plutonium into a disperse plutonium oxide powder, which is suitable for fabricating mixed fuel, becomes urgent [2]. The initial plutonium and uranium oxide powders, from which after mixing, granulation, and pressing blanks kernels were sintered in a hydrogen-containing atmosphere at 1600-1750°C. Gallium can be removed in this variant of fuel fabrication [3,4].Americium is removed from plutonium oxide in order to bring excess plutonium into the fuel cycle and use it to fabricate mixed fuel for power reactors, first and foremost, thermal reactors, provided that the process is radiologically safe [2,5].

Sintering and characterization of ZrN and (Dy,Zr)N as surrogate materials for fast reactor nitride fuel

“…In addition, the prepared nitrides readily react with moisture and oxygen [8,9]. The incorporation of these impurities can have adverse effects on the structural integrity of the reactor, as high concentrations of O and C impurities might lead to internal cladding corrosion or carburization [10,11]. Moreover, it has been shown that a significant O concentration in (Pu,Zr)N leads to the segregation of PuO 2 phase [12], which complicates the reprocessing of nitride fuels, otherwise shown to be compatible with the industrially established technology [13,14,15,16].…”