Since the discovery of technetium (in 1937, by Perrier and Segre), technetium-99 and technetium-99m have become most familiar in the specialised literature, the behaviour of the former being of concern regarding its health impact, the latter having been used intensively in medical tests for many years. The knowledge of the characteristics and behaviour of this element in nature is currently increasing exponentially. It has become clear, however, that there is still a serious shortage of information needed to assess properly its burden and impact on man and his environment. Technetium may indeed be released from nuclear installations or as a waste product from medical applications. It is generally considered to be highly mobile as the anion TcOi, but it is also suspected to be readily reduced in soils and metabolised in living beings into lower oxidation states. The seminar was planned to analyse thoroughly the experimental results obtained up to now and to make recommendations of specific issues requiring further research. This book presents the papers of the different sessions in the order of presentation, and the conclusions drawn by three discussion groups which dealt separately with: problems of sources and distribution of man-made technetium and its radiological consequences; the chemical behaviour of technetium in different ecosystems; biochemical reactions and binding with macromolecules in various life systems. vi Preface The editors, together with the Programme Committee of the Seminar, wish to express their gratitude to the chairmen of the different sessions for their summary of the group discussions.

Technetium (99Tc, half-life = 2.13 x 105 years,?-emitter) is one of the radionuclides of major concern for nuclear waste disposal. This concern is due to the long half-life of 99Tc, the ease with which pertechnetate, TcO4−, migrates in the geosphere, difficulties in incorporating technetium into glass waste forms, and the corresponding regulatory considerations. The problem of mobility of pertechnetate in the environment is compounded by the fact that pertechnetate is the thermodynamically stable form of technetium in oxidizing environments. These factors present challenges for the separation and immobilization of technetium. The objective of this research project is to provide new knowledge about the chemical behavior of technetium so that the factors underlying technetium speciation in nuclear waste and in waste forms can be understood and the problems can be addressed. In particular, the behavior of technetium and rhenium in glass will be examined since rhenium is ofte n used as a non-radioactive surrogate to predict the behavior of technetium. In this project, glasses containing both rhenium and technetium will be prepared, so that the behavior of both metals can be compared under identical conditions.