NSUF 24-5145: Natural zirconolites and pyrochlores as test cases for wasteform matrices
Minerals with zirconolite or pyrochlore structures have been proposed as host phase matrices suitable for use as the containment material for high level nuclear waste wasteforms. The aim of this study is to further validate the suitability of these materials for purpose via testing the radiation tolerance of these matrices. The objective of monitoring the test materials’ response to irradiating ions is to attain a quantifiable characteristic; the critical fluence of irradiating ions required to facilitate a transition from a crystalline to amorphous state, Fc. This provides a means of quantitatively comparing the radiation response between the materials of interest. Also by measuring the Fc at various temperatures and plotting the response we attain a second quantity; the critical temperature of crystallinity, Tc, (the temperature above which the rate of crystalline structure recovery is greater than the rate of defect accumulation). This gives us another means of comparing material response to ion-irradiation along with testing at temperatures applicable to the dedicated storage environments. Using an experimental approach such as in situ ion irradiation allows for a controllable and reproducible set of constraints. This will allow for direct comparison with those results determined from natural samples where there is uncertainty in the history of thermal and composition alteration.
Methods A series of natural zirconolite and pyrochlore minerals are exposed to high energy ions (Kr 1 MeV) whilst being monitored in situ using the transmission electron microscope (TEM) (IVEM-tandem facility). Collection of bright field images (BF) and electron diffraction patterns (SADP) are used to monitor the crystalline to amorphous phase transition. The TEM specimens consist of finely ground fragments dispersed on TEM specimen grids. TEM characterisation involves monitoring fragments via the collection of BF and SADPs. Selected ion fluence steps followed by BF and SADP collection are continued until there are no observable Bragg diffraction maxima left in the SADP. This approach is used to quantify the irradiating ion fluence required to cause amorphisation. The critical fluence of amorphisation gives a quantitative approach for comparing radiation response between different test materials. This same experimental approach is repeated for the test material whilst holding it at a range of temperatures. The duration of each critical fluence measurement is dependent on both the fluence of ions required to render the sample amorphous and the time it takes to cool or heat the sample.
Potential Impact to state-of-the Knowledge Natural, actinide containing, zirconolite and pyrochlore minerals have undergone numerous radiation response and aqueous alteration based studies with the stated purpose of validation of potential host matrix materials for high level nuclear wasteforms. Whilst these studies provide invaluable information on the long-term stability of the minerals they are, by their very nature, uncontrolled experiments. The proposed minerals consist of wasteform relevant structure-types. The use of a controlled experimental environment, on exactly the same natural minerals that have been studied allows for control of temperatures, flux, and fluence, in a fast and reproducible approach. The proposed radiation response study will have considerable impact on the decision making process of the best candidates for further development as wasteform matrices.
Period of performance
On average 1 critical fluence measurement takes approximately 2 hours. 3 to 5 specimens are tested per day. There are 10 samples, each requiring multiple runs. The proposed experiments will require approximately 1 day per sample. This proposal is requesting the maximum 10 days.
Scientific Outcome
Peer reviewed publications, conference presentations.
추가 정보
| 필드 | 값 |
|---|---|
| Award Announced Date | 2024-09-23T12:17:17.853 |
| Awarded Institution | Australian Nuclear Science and Technology Organisation |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | Intermediate Voltage Electron Microscopy (IVEM)-Tandem Facility |
| PI | Robert Aughterson |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |