Priority issues and key findings from evaluation of disposal records for a legacy radioactive waste site

This paper reports on a detailed investigation into the disposal procedures and records from the operational period (1960-1968) of the Little Forest Legacy Site (LFLS) in eastern Australia. The aims of the paper are firstly, to highlight the priority issues which are relevant to the radiological assessment of the LFLS, and secondly, to present key lessons that may help to guide future investigations of the records at similar sites. Particular effort was put into assessing the various types of relevant documents and the relationships between them. A specific objective of this work was to evaluate an inventory of the wastes which was reported shortly after the time of disposals. A major finding of the study is that the original actinide inventory for LFLS relied solely on estimates from a limited number of specific records known as 'Scrap Disposal Reports' (SDRs). For example, the estimated amount of plutonium disposed at the LFLS was based on only seven SDR records. Given that there are approximately 50000 buried items, it is possible that other Pu-contaminated items could make a significant additional contribution to the amount of Pu present at the site. For some waste components (e.g. beryllium) the documentation shows that rough estimates of disposal quantities were made, based on the number of disposed Be-contaminated items in each trench. The use of such approximations casts some doubt on the accuracy of the previous inventory of wastes at the site. In addition, the early summaries of radionuclide disposals, which categorized radionuclides into groups according to their radiological hazard, contained significant underestimates of the radionuclide inventory in the most hazardous category (referred to at the time as 'Group I' radionuclides). This was mainly due to the omission of the Pu (which had been recorded on the SDRs) from the Group I inventory, but was also in part because the Group I radionuclide content of disposed sludge drums (from a wastewater treatment plant) was not taken into account for most of the disposal period. Establishing the disposal history and radionuclide inventory at legacy sites is an important pre-requisite to evaluating their radiological impact and developing management options. The detailed investigation of the LFLS records shows the importance of understanding the operational practices of the period and the derivation of the original inventories. These insights should help guide future efforts to better understand disposal histories and inventories at LFLS and elsewhere.