Year

2014

Degree Name

Bachelor of Environmental Science (Honours)

ANZSRC / FoR Code

050399 Soil Sciences not elsewhere classified

Department

School of Earth & Environmental Sciences

Advisor(s)

Samuel Marx

Abstract

This study presents an examination of fallout derived radioactivity in soil and alluvial sediment samples from the Sydney Basin. This work was undertaken to add to the growing dataset of published values on radioactivity from sites across Australia and to provide baseline data for the Sydney region. Such data provides further information on fallout patterns in Australia, and enables baseline values of radionuclides such as 240+239Pu and 137Cs to be established for the Sydney Basin in which Australia’s major nuclear facility, with an associated legacy low-level waste site is located.

Samples were collected in an east-west transect across the Sydney Basin and Blue Mountains, resulting in the collection of 10 soil samples and 4 alluvial sediment samples. These were analysed by gamma spectroscopy for caesium-137 and with Accelerator Mass Spectroscopy for plutonium concentrations and 240/239 Pu isotopic ratios.

Plutonium-240+239 concentrations are found to be 0.24 Bq/kg (standard deviation 0.2, range 0.04-0.52 Bq/kg) for the <63 micron fraction. The caesium-137 activities averaged to 11.7 Bq/kg for soils and 2.1 Bq/kg for sediments.

Results from Plutonium-240/239 isotope studies agree with previous data indicating that continental Australia has a 240/239 Pu ratio that is lower than the global average. The average ratio of 0.15 (ranging from 0.11-0.16) for the Sydney Basin is found to be significantly lower than the accepted global mean of 0.176, indicating regional influences on Australian fallout. Similarly to previous studies, the Pu was concentrated preferentially in the finer soil fractions. Levels of caesium were approximately proportional to the plutonium, which suggests that Pu will be a suitable long-term substitute for caesium as an environmental tracer in Australia.

Radionuclide data from various soil and sediment samples collected at the legacy low-level waste site known as Little Forest Legacy Site (LFLS) indicates actinides such as isotopes of Pu are reaching the soil surface as a result of overflowing trenches during rainfall periods. This baseline data will allow for the disentanglement between the contributions of the legacy waste site and global fallout.

In order to explain the variations in caesium-137 and plutonium 240+239 between sites environmental factors were also measured. These include pH, rainfall, elevation, organic content as well as soil moisture. There was no correlation found between the measured environmental factors and the fallout activities.

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