Maria V. Zamoryanskaya

Behavior of 238 Pu-Doped Cubic Zirconia under Self-Irradiation

To investigate the resistance of cubic zirconia to accelerated radiation damage, which simulates effects of long term storage, 238 Pu-doped polycrystalline samples of cubic zirconia, (Zr,Gd,Pu)O 2 , were obtained and studied using X-ray diffraction analysis (XRD), electron probe microanalysis (EPMA), optical and scanning electron microscopy (SEM), and modified MCC-1 static leach test. The ceramic material was characterized by the following chemical composition (from EPMA in wt.% element): Zr = 50.2, Gd = 15.4, Pu = 12.2. This corresponds to the estimated formula, Zr 0.79 Gd 0.14 Pu 0.07 O 1.99 . The content of 238 Pu estimated was approximately 9.9 wt.%. The XRD measurements were carried out after the following cumulative doses (in alpha decay/m 3 × 10 23 ): 3, 27, 62, 110, 134, 188, 234, and 277. Even after extremely high self-irradiation, cubic zirconia retained its crystalline structure. All XRD analyses showed no phases other than a cubic fluorite-type structure. The following results of normalized Pu mass loss ( NL , in g/m 2 , without correction for ceramic porosity) were obtained from static leach tests (in deionized water at 90°C for 28 days) for 4 cumulative doses (in alpha decay/m 3 × 10 23 ): The results obtained confirm the high resistance of cubic zirconia to self-irradiation. This allows us to consider zirconia-based ceramic as the universal material that is suitable for actinide transmutation and geological disposal.

Unstable Luminescence of Nitrides under Electron-Beam Irradiation

The aim of the work was to study the nature of unstable luminescence of nitride bulk layers and heterostructures under stationery electron beam irradiation. During irradiation increasing of intensity of luminescence was observed. Typical times of this effect are tens up to hundreds of seconds. Details of the effect were studied. It was noticed that in several cases the irradiated by electron beam area was characterized by different luminescence properties even after 24 h at room temperature in vacuum. Several mechanisms leading to increasing of the intensity of luminescence were discussed.

Behavior of Actinide Host-Phases Under Self-irradiation: Zircon, Pyrochlore, Monazite, and Cubic Zirconia Doped with Pu-238

Crystalline ceramics are the most prospective materials suggested for the immobilization of long-lived radionulcides, in particular, weapons grade Pu and other actinides. The immobilization might include: (1) transmutation (burning) followed by geological disposal of irradiated materials or (2) just direct geological disposal of actinide matrices. Different durable host phases have been suggested for actinide (An) incorporation in the form of solid solutions. These are: different polymorphs of zirconia, (Zr,An,. . . )O2, in particular, one of cubic fluorite-type structure (Carroll, 1963; Heimann and Vandergraaf 1988); zircon, (Zr,Hf,An,. . . )SiO4 (Burakov, 1993; Ewing et al., 1995); monazite, (La,An,. . .)PO4 (Boatner et al., 1980; Boatner and Sales 1988); Ti-pyrochlore, (Ca,Gd,Hf,Pu,U)2Ti2O7 (Ebbinghaus et al., 1998) etc. To investigate the resistance of actinide host phases to accelerated radiation damage, which simulates effects of long term storage the 238Pu-doped samples of cubic zirconia and plutonia, zircon, La-monazite, Pu-monazite and Ti-pyrochlore have been repeatedly studied using X-ray diffraction analysis (XRD) and other methods. Main goal of this chapter was to summarize in comparison the principal features of different actinide host materials under self-irradiation from 238Pu. All results described in this chapter have been obtained during last several years in Laboratory of Applied Mineralogy and Radiogeochemistry of the V. G. Khlopin Radium Institute.

Cathodoluminescence study of americium incorporation into calcite single crystals

In order to study americium incorporation into calcite, CaCO 3 , under conditions of crystal growth, two samples of single crystal Am-doped calcite were synthesized and studied by cathodoluminescence (CL) spectroscopy in comparison with undoped and Eu-doped artificial calcite. Americium contents in calcite crystals were (in kBq/g): 1) 6.9; 2) 1.9(E+4). The CL emission of undoped and Am-Eu-doped calcitesamples was characterized by three broad bands at 2.03; 2.47 and 2.96 eV. Weak CL lines related to typical transitions 5 D 0 7 F1,2,4 of Eu 3+ and Am 3+ ions were observed at 1.68; 1.99, 2.06 eV and 1.60; 1.98 eV, respectively. Degrading of calcite structure under irradiation has been studied using CL emission of high power electron beam.

A Cathodoluminescence Investigation of Pyrochlore, (Ca,Gd,Hf,U,Pu) 2 Ti 2 O 7 , Doped with 238 Pu and 239 Pu

Crystalline ceramic based on the pyrochlore structure [(Ca,Gd,Hf,U,Pu) 2 Ti 2 O 7 ], has been proposed in the U.S. as a candidate waste form for the immobilization of weapons grade plutonium. Several samples of synthetic polycrystalline pyrochlore doped separately with 238 Pu and 239 Pu were studied using cathodoluminescence (CL) and electron probe microanalysis (EPMA) immediately after synthesis and then after 175, 245 and 405 days. The CL spectra of pyrochlore doped with 239 Pu and 238 Pu obtained immediately after ceramic synthesis and 175 days later were nearly the same and characterized by a typical broad band emission with a maximum peak centered at 2.5 eV. New CL peaks with maximum intensities at 2.0 and 2.3 eV in the emission spectra of 238 Pu-and 239 Pu-doped pyrochlore were observed 245 days later. It was determined that this newly formed CL peak at 2.3 eV is similar to one in CL spectrum of artificial standard glass doped with the uranyl ion, (UO 2 ) 2+ . It was suggested that CL band with maximum at 2.0 eV is caused by the U tetrahedral complex (UO 4 ) 2- . Also, the same peaks were observed in the CL spectrum of natural U-rich pyrochlore containing approximately 23 wt.% U (mainly in the form of uranyl ion). The results obtained allow us to conclude that the radiation damage of pyrochlore-based ceramic waste form is accompanied with conversion of tetravalent uranium incorporated into pyrochlore structure to the mobile uranyl ion, (UO 2 ) 2+ , and complex (UO 4 ) 2- .