The challenge
While vitrification is now commonly used for waste treatment, there remains a need for more detailed data about the retention and release of radionuclides during the process. Understanding the extent of emissions is key to maintaining a total inventory of radioactive material on nuclear licenced sites, and to making waste treatment processes safer and more effective for the future.
Facilitated by NNUF-EXACT’s specialist expertise and equipment, this project aimed to generate new information about emissions from glass powder, with varied waste-loadings using two types of waste, at high temperatures.
The researcher conducted phase one of their study at Sheffield Hallam University using non-radioactive isotopes and their own self-built furnace. Collaboration with us was essential for the next step: validating the findings using radioactive materials.
This project was funded by the Nuclear Decommissioning Authority, National Nuclear Laboratory and Transcend consortium, with supportive funding from the National Nuclear User Facility.
The research
We worked with the researcher to custom-design an experimental setup to simulate intermediate-level waste thermal treatment. It utilised the NNUF-EXACT’s Pyrolyser-Trio furnace, which we specially adapted for the purpose. This enabled the interrogation of off-gas emissions from simulated waste glasses, focusing on caesium (Cs-137) and iodine (I-129). The study also looked at the effects of additives, including carbon sources, on radionuclide retention.
This validated the findings of the earlier tests on non-radioactive isotopes, producing a reliable and reproducible set of data and filling the knowledge gap in this area.
- The Pyrolyser unit was used to capture volatile Cs and I emissions and determine the retention of these elements from simulated waste-loaded borosilicate glasses at temperatures up to 950°C, simulating intermediate-level waste thermal treatment. Conditions above the melt were controlled with compressed air and nitrogen gas.
- Capture solutions or resultant glasses were then measured by inductively coupled plasma mass spectrometry (ICP-MS), gamma spectrometry or liquid scintillation counting to determine the retention of both stable and active isotopes of Cs and I. Active and non-reactive reagents were used to gain an understanding of the accuracy of non-active simulants.
- The trials investigated the retention of Cs and I from low-temperature borosilicate glass melts with waste loadings of either clinoptilolite or simulated Magnox sludge (CMS) at concentrations of 10 to 50 wt% in comparison to baseline measurements (no waste loading).
- The effect of adding carbon sources such as xanthan gum (used as a deflocculating agent in waste treatment) to the waste-loaded glasses was also studied to better understand impact of redox reactions on emissions.
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Specialist facilities
- NNUF-EXACT enabled a crucial stage of the study – validation of test results with radioactive isotopes.
- Working with us gave the researcher access to the Pyrolyser furnace at GAU-Radioanalytical Laboratories (one of NNUF-EXACT’s supporting facilities). Using an adapted purpose-built furnace enabled them to produce reliable and reproducible data.
- The researcher was also able to take advantage of advanced analysis instrumentation and techniques for active isotopes, including gamma spectrometry and liquid scintillation counting, as well as cross-validation with stable isotopes using ICP-MS.
Expert input
Our expert team shared their specialist knowledge and experience in the release and trapping of volatile radionuclides, advising on the experiment design and equipment adaptations.
Research support
- Working with us on the experiment design helped the researcher secure funding from the NNUF-EXACT access fund, demonstrating the need for the study and how it aligns with national strategy.
- We took care of the practicalities, enabling the researcher to focus on their project. This included carrying out the necessary radiological risk assessments, active material handling, spiking test materials with radioactive solutions, and storing and disposing of all produced samples.
Flexible approach
- Flexibility was built into the experiment plan, with the researcher accessing our facility over five visits and amending the plan based on the results of each visit.
- We tailored the furnace setup to meet the project’s requirements, ordering add-ons and bespoke components.