Plutonium crystalline forms

Plutonium peroxide was investigated by Hamaker and Koch, (0 Hopkins, (2) and Koshland, et al. (3) in the 19 0 s and Leary (h) in the early 1950 s. This work showed that the composition of the precipitate varied and often incorporated anions from the solution from which it was precipitated. These investigations, as well as other work (5), also showed that the peroxide precipitate exists in both hexagonal and cubic crystalline forms. Although both forms are compounds of Pu(lV), they have slightly different O /Pu ratios (6). The cubic form can be colloidal and therefore is less suitable for process application than the hexagonal form. The acidity of the solution has an effect on the... 

The difference between the forms involves either (1) crystalline structure (2) the number of atoms in the molecule of a gas or (3) the molecular structure of a liquid. Carbon is a common example of (1), occurring in several crystal forms (diamond, carbon black, graphite) as well as several amorphous forms. Diatomic oxygen and diatomic ozone are instances of (2) and liquid sulfur and helium of (3). Uranium has three crystalline forms, manganese four, and plutonium no less than six. A number of other metals also have several allotropic forms which are often designated by Greek letters, e.g., a-, y-, and A-iron. 

The only crystalline phase which has been isolated has the formula Pu2(OH)2(SO )3(HaO). The appearance of this phase is quite remarkable because under similar conditions the other actinides which have been examined form phases of different composition (M(OH)2SOit, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction influences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate compounds, however, i.e., the existence of double hydroxide bridges between metal atoms. This structural feature persists from zirconium through plutonium for compounds of stoichiometry M(OH)2SOit to M2 (OH) 2 (S0O 3 (H20) i,. Spectroscopic studies show similarities between Pu2 (OH) 2 (SOO 3 (H20) i, and the Pu(IV) polymer and suggest that common structural features may be present. 

Ewing RC, Weber WJ, Lutze W (1995a) Crystalline ceramics waste forms for the disposal of weapons plutonium. In Disposal of Weapon Plutonium Approaches and Prospects. Merz ER, Walter CE (eds) Kluwer Academic Publishers, Dordrechf The Netherlands, p 65-83 Ewing RC, Weber WJ, Chnard FW, Jr (1995b) Radiation effects in nuclear waste forms for high-level radioactive waste. Progress Nucl Energy 29 63-112... 

The baseline chemical composition of the ceramic form used for plutonium immobilization is a titanite-based crystalline ceramic. Table 1 provides the elemental baseline composition, which indicates that the ceramic form consists of about 65 weight percent (wt%) ceramic precursors and about 35 wt% actinides. This ceramic form has the following special features ... 

A sphere of plutonium metal (one of the five crystalline modifications) 7.4 cm in diameter weighs 3.92 kg. What is the density of this form of plutonium ... 

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