Durability and natural mineral studies carried out to support development of waste forms for immobilisation of plutonium interim report: April 30, 1999

Hart, K.P.; Lumpkin, G. R.; Zhang, Y; Loi, E.; Leung, S

doi:10.2172/15007249

Cited by 4 publications

(8 citation statements)

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“…Data from Appendix 1 and Hart et al, 1999a. Single-phase brannerite appears to be significantly less durable than either zirconolite or pyrochlore based on the 70 o C SPFT data shown in Fig. 5c (Hart et al, 1999a). This is consistent with the MCC-1 test results of brannerite-rich multiphase ceramics (Bakel et al, 1999b) which show increased release rates of U release relative to brannerite-poor ceramics.…”

Section: Single Phase Test Resultssupporting

confidence: 75%

“…No difference in durability between the pure and impure ceramic was found. Similar tests of impure ceramics containing additional Ni, Nd, Zn, La, Si, Na, Mg, Fe, Al, Cr, K, Mo, Ta, W, Sn, Ba, and P also show no measurable difference in dissolution rates (Hart et al, 1999a). These data suggest that at these levels of impurities, the added elements either: (1) fit into existing lattice sites in the major phases of the ceramic without significant destabilization; (2) form a separate, relatively durable phase that dissolves no faster than the titanate matrix; or (3) form a relatively non-durable phase that does not contain any of the actinides or neutron absorbers.…”

Section: Effects Of Impuritiesmentioning

confidence: 72%

“…Also shown are the data for the pyrochlore-based Ce-U and Pu-U ceramics tested at 25 o C, data at 70 o C for brannerite and a pyrochlore-based ceramic, and data at 90 o C for two multi-phase ceramics at two different flow rates given in the legend. Data from Appendix 1 and Hart et al, 1999a. Single-phase brannerite appears to be significantly less durable than either zirconolite or pyrochlore based on the 70 o C SPFT data shown in Fig. 5c (Hart et al, 1999a).…”

Section: Single Phase Test Resultsmentioning

confidence: 99%

“…We can better evaluate diffusion of ions through a leached layer as a potential rate-limiting mechanism by comparing our dissolution rate measurements over time with model Grail et al, 1999, andHart et al, 1999a). predictions based on the equations which describe diffusion.…”

Section: Release Rate Behavior Over Timementioning

confidence: 99%

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Interim Report on Development of a Model to Predict Dissolution Behavior of the Titanate Waste Form in a Repository

Bourcier¹

1999

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Dissolution testing performed to date on a titanate waste form under development for plutonium immobilization reveals the following: (1) The wasteform is very durable. Many of the test results have shown the dissolution rate to be below detection or less than background levels of the constituent elements; (2) elemental release is non-stoichiometric with Pu, U, Ca, and Gd released faster than Ti and Hf at most pH conditions; (3) dissolution rates measured in flow-through tests sometimes show a continuous decrease with time in tests of up to two years duration; (4) attempts to model the dissolution as a transport-controlled process with diffusion through a leached layer as the rate limiting mechanism show reasonable agreement at low pH conditions but poor agreement at neutral to alkaline pHs.Based on present uncertainties in our understanding of rate control, we have provided conservative estimates of radionuclide release rates based on the fastest observed release rates measured in short-term tests. These dissolution rates under repository-relevant conditions are in the range of 10 -3 to 10 -6 g/m 2 /day.

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Section: Single Phase Test Resultssupporting

confidence: 75%

Section: Effects Of Impuritiesmentioning

confidence: 72%

Section: Single Phase Test Resultsmentioning

confidence: 99%

Section: Release Rate Behavior Over Timementioning

confidence: 99%

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Interim Report on Development of a Model to Predict Dissolution Behavior of the Titanate Waste Form in a Repository

Bourcier¹

1999

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“…The data in Figure 3.15 show that rates with respect Ca and Mo are greater than the U rate by a factor of ~10X. Recent reports show that release of Ca to solution is typically faster than rates based on other elements in the specimens (Strachan et al 2000 andHart et al 1999a). Dissolution rates based on Mo release are also faster (~10X) compared to the U release rates.…”

Section: 10mentioning

confidence: 88%

The Status of Radiation Damage Experiments

Strachan¹,

Scheele²,

Icenhower³

et al. 2001

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SummaryThis is a status report on the progress of the radiation damage experiments that are being performed at the Pacific Northwest National Laboratory in support of the Plutonium Immobilization Program (PIP) to dispose plutonium that is surplus to the defense needs of the US. This report covers the progress of radiation damage from the decay of 238 Pu to the titanate phases that comprise the PIP ceramic. With the exception of brannerite, all the phases are represented in the specimens we are testing and characterizing. The phases appear to damage faster than anticipated from the information in the literature. Pyrochlore appears to become metamict 2 to 3 times faster. Zirconolite is more resistant, but this depends on what impurities are present.Radiation damage results in swelling of the specimens. After 650 days, the trend in the data suggest that swelling will continue as the damage process appears to be incomplete (it has not yet "saturated" or reached a steady-state condition). The decrease in density from swelling is between 8 % and 15%, based on measurements of the pyrochlore baseline and a zirconolite-rich ceramic. The linear expansion of the specimen dimensions is between 2% and 5%.The dissolution rate appears to be between 500 -1000 times greater for a 238 Pu-bearing pyrochlore baseline sample than for the corresponding 239 Pu specimen. Although we believe that this increase in rate is due to radiation damage, we cannot be absolutely certain because we did not manage to obtain SPFT data on these specimens before damage started to accumulate. It is possible that the increased rate is due to some effect related to the higher dose rate and radiation field near the 238 Pu specimens that we don't understand.

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THE CRYSTAL CHEMISTRY, STRUCTURE AND PROPERTIES OF A SYNTHETIC CARNOTITE-TYPE COMPOUND, Ba2[(UO2)2Ti2O8]

Wallwork¹,

James²,

Carter³

2006

The Canadian Mineralogist

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The crystal structure of the carnotite-type compound Ba 2 [(UO 2) 2 Ti 2 O 8 ] has been determined by ab initio methods from synchrotron X-ray and neutron powder-diffraction data. We describe the first reported structure of a uranyl titanate; it was solved in the monoclinic space-group P2 1 /c and has the lattice parameters a 6.4463(1), b 8.5999(1), c 10.2532(1) Å, b 75.936(1)°, V 551.36(1) Å 3 , D calc 6.253 g/cm 3 and Z = 4. A multiple histogram approach was used to refine the structure from synchrotron and neutron-diffraction data, giving quality factors of R B 0.032 and 0.039, R wp 0.090 and 0.063, and R p 0.070 and 0.049, respectively. The compound forms a layered structure in which sheets of uranyl pentagonal bipyramids share edges with dimers of TiO 5 square pyramids. These are separated by layers of 11-fold-coordinated barium atoms. Because of the potential presence of Ba 2 [(UO 2) 2 Ti 2 O 8 ] in ceramic waste-forms for the immobilization of radioactive wastes, the leach rate of uranium and barium were determined. The normalized rates of leaching from Ba 2 [(UO 2) 2 Ti 2 O 8 ], averaged over seven days, are 1.3 3 10-5 g/m 2 /day for uranium, a significantly lower rate than that observed from pyrochlore waste-forms, and 1 3 10-4 g/m 2 /day for barium. Keywords: Ba 2 [(UO 2) 2 Ti 2 O 8 ], crystal structure, uranyl titanate waste-form, synchrotron data, neutron-diffraction data, powder diffraction.

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Durability and natural mineral studies carried out to support development of waste forms for immobilisation of plutonium interim report: April 30, 1999

Cited by 4 publications

References 0 publications

Interim Report on Development of a Model to Predict Dissolution Behavior of the Titanate Waste Form in a Repository

Interim Report on Development of a Model to Predict Dissolution Behavior of the Titanate Waste Form in a Repository

The Status of Radiation Damage Experiments

THE CRYSTAL CHEMISTRY, STRUCTURE AND PROPERTIES OF A SYNTHETIC CARNOTITE-TYPE COMPOUND, Ba2[(UO2)2Ti2O8]

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