Exploration of Neutron Counting Techniques Applied to Nuclear Reactivity Measurements (GREEN CDT)

GREENCDT The potential to infer reactor-borne contributions to anthropogenic plutonium-239 in the environment from the 244Pu/239Pu ratio.

The short half-life of the plutonium isotopes, relative to the age of the solar system, results in all primordial plutonium in the environment on Earth being anthropogenic. This arises, globally, from the fallout from atmospheric nuclear weapons tests and, locally, from nuclear facilities and localised fallout from reactor accidents. It is important that local contributions to trace plutonium in the environment are identified and quantified because this can confirm or discount the insight from often incomplete historical records of once permitted discharges, and it can inform decisions concerning the clean-up of contaminated land and help quantify anticipated waste arisings from land quality activities.

One approach to obtain this local proportion is to attempt to derive it from the anticipated isotopic ratios of 240Pu/239Pu of the local (reactor) and global (fallout) components, but these are not always available from records nor sufficiently distinct from one another to render this feasible. To address this limitation, plutonium-244 offers the potential for an alternative approach: this isotope (half-life 80 million years) is only formed in high-flux neutron scenarios, nuclear weapons tests and supernovae, and hence it can be a robust indicator of the global contribution to plutonium abundance in the environment.

For example, where the 244Pu/239Pu ratio is anomalously low because of an elevated proportion of 239Pu since the 244Pu contribution is fixed as per the contribution from stratospheric weapons tests, it may serve as a quantitative indicator of the local plutonium contribution allow local plutonium contamination levels to be inferred: this study is focused on this possibility.