Radiocarbon (14C or carbon-14, half-life 5730 yr) is a key radionuclide in the assessment of the safety of a geological disposal facility (GDF) for radioactive waste. In particular, the radiological impact of gaseous carbon-14 bearing species has been recognized as a potential issue. Irradiated steels are one of the main sources of carbon-14 in the United Kingdom’s radioactive waste inventory. However, there is considerable uncertainty about the chemical form(s) in which the carbon-14 will be released. The objective of the work was to measure the rate and speciation of carbon-14 release from irradiated 316L(N) stainless steel on leaching under high-pH anoxic conditions, representative of a cement-based near field for low-heat generating wastes. Periodic measurements of carbon-14 releases to both the gas phase and to solution were made in duplicate experiments over a period of up to 417 days. An initial fast release of carbon-14 from the surface of the steel is observed during the first week of leaching, followed by a drop in the rate of release at longer times. Carbon-14 is released primarily to the solution phase with differing fractions released to the gas phase in the two experiments: about 1% of the total release in one and 6% in the other. The predominant dissolved carbon-14 releases are in inorganic form (as 14C-carbonate) but also include organic species. The predominant gas-phase species are hydrocarbons with a smaller fraction of 14CO (which may include some volatile oxygen-containing carbon-species). The experiments are continuing, with final sampling and termination planned after leaching for a total of two years.

For five years from 1976 to 1980 the archaeology and environment of a block of landscape centred around Shaugh Moor on south-west Dartmoor were analysed prior to the destruction of some of the evidence by china clay working. The investigations began in 1976 with a survey of the field monuments and the initiation of soil, vegetation, small mammal and phosphate studies in addition to the search for peat deposits of sufficient antiquity. From 1977 the programme was determined by the encroachment of the quarries and other works, so that early in that year a group of cairns were excavated (site 10) and subsequently the first of two seasons work on a walled enclosure (site 15) was initiated. The excavation of the enclosure was completed in 1978 and in that year it was also necessary to undertake a small investigation near the northern edge of the project area on the Trowlesworthy cross-dyke (site 202) and near its southern edge on Wotter Playground (site 201). Settlements and field systems were surveyed and excavated on Wotter Common in 1979 and these investigations were completed in 1980 when the Saddlesborough Reave, which crosses the centre of the project area from east to west was also surveyed in detail and sampled by excavation.More field work could have been undertaken on threatened areas and indeed a limited operation was undertaken in 1981 on the Saddlesborough Reave to confirm some points of detail. Instead, it was thought best to conclude the project after five years, to complete the publication of the results and to allow mature consideration of these so as to generate a new set of questions.At an early stage the decision was taken to publish the work as a series of annual reports in theseProceedingsrather than as a single monograph. The first report (Wainwrightet al.1979) set out the simple research design for the project and contained accounts of the 1976 survey and of the excavation of the cairn group.

An interlaboratory comparison experiment for 14C measurements has been organized jointly by the Harwell and British Museum laboratories to include the working radiocarbon laboratories of the United Kingdom. The experiment has been run along the lines of that organized by the IAEA for tritium and has explored the problems of sample preparation, verification of equivalent levels, and presentation of results. Samples of benzene representing 5 age equivalent levels between twice modern and 20,000 years old have been prepared and distributed for measurement either by direct counting (liquid scintillation) or full process tests. Preliminary results received show excellent agreement both between laboratories and in comparison with the known relative activities of the prepared solutions. The possibility of extending the experiment to cover different sample types and a wider distribution of testing laboratories is briefly discussed.