Migration of 239, 240PU and 233U from a low-level radioactive waste site
Loading...
Date
2022-11-23
Journal Title
Journal ISSN
Volume Title
Publisher
South Pacific Environmental Radioactivity Association
Abstract
Low-level measurements of 239,240Pu and 233U have been used to investigate the migration pathways of these radionuclides in the vicinity of a legacy waste site near Sydney, Australia. Between the years of 1960 to 1968 mixed wastes, including laboratory waste, were disposed at the site in shallow, unlined trenches, and disposal records indicate that the waste contained small masses of plutonium (several grams) and other long-lived radionuclides, including 233U.
Measurements of 239,240Pu and 233U in environmental matrices of soil, sediment, water, and vegetation have been made using a combination of accelerator mass spectrometry and alpha spectrometry techniques. Both 239,240Pu and 233U concentrations and 240/239Pu atom ratios have been used to assess the migration of these actinides.
A site specific 240/239Pu atom ratio has been established (0.084) which is distinctly different from the ratio found elsewhere in the Sydney Basin due to nuclear weapons testing fallout thereby providing an indicator of plutonium originating from the site. 233U has very low abundance in nuclear weapons test fallout therefore the only plausible source of elevated 233U in the environment at and around this site is uranium migration from the disposal site.
The concentrations of 239,240Pu and 233U typically decrease with distance from the disposal trenches. The 239,240Pu concentrations in soils and sediments at distance are within the range seen elsewhere in Australia due to atmospheric nuclear weapons fallout. However, the presence of 233U and the influence of the site specific 240/239Pu atom ratio on the local plutonium isotopic signature indicates that these actinides are persistent in soils, sediments and waters hundreds of metres away and vegetation tens of metres away from the disposal trenches.
Multiple migration mechanisms have been considered for actinides derived from the site, including surface water flow from the disposal trenches, particulate transport during heavy rainfall events, vegetation uptake, contamination which may have occurred during disposal operations and airborne particulate transport.
Description
Keywords
Plutonium 239, Plutonium 240, Uranium 233, Radioisotopes, Radionuclide migration, Radioactive wastes, Radioactive waste disposal, Underground disposal, Spectroscopy, Records management, Soils, Sediments
Citation
Harrison, J., Payne, T., Child, D., Hotchkis, M., Johansen, M,m Thiruvoth, S., & Zawadzki, A. (2022). Migration of 239, 240PU and 233U from a low-level radioactive waste site. Paper presented to SPERA 2022 - Connecting People, developing solutions for a Changing Environment, 28-30 November 2022, Chrischurch, New Zealand, (pp. 40). Retrieved from: https://au-admin.eventscloud.com/file_uploads/baa6bb17538b457fbd436f1552075bea_SPERA2022e-handbook.pdf