Calculation of Dose Rates at the Surface of Storage Containers for High‐Level Radioactive Waste
Abstract In several countries, the high‐level radioactive waste that will be disposed of in deep geological formations has to be retrievable for a certain time. Since 2010, retrievability is required for the operation phase of a repository also in Germany. Depending on the effort and the feasibility of remote handling, a certain exposure of the involved employees to ionising radiation is caused. The estimation of the exposure requires the knowledge of the inventory of radionuclides and the radiation field around the storage containers. This paper focuses on German concepts for final storage casks for the drift emplacement in rock salt for both spent fuel rods and high‐active waste (HAW) coquilles. Calculations of dose rates at the surfaces of the casks are presented. The calculations show that the gamma radiation of fission and activation products can be efficiently shielded by materials like cast iron or low‐alloyed steel. Ductile cast iron, however, has a positive influence on the neutron moderation because of the high carbon content. The shielding of the neutron radiation strongly depends on the quantity and position of the polyethylene (PE) rods which are used as neutron moderator. PE has unfavourable features at elevated temperatures that can be reached in a repository for high‐level waste. The simulations show that TiH2 is a promising alternative material for the shielding of neutron radiation. The current assumption that a final storage cask for HAW coquilles has the same outer dimensions as the cask for spent fuel rods will lead to unacceptable dose rates at the side wall. An increase of the diameter is necessary to provide sufficient shielding. Graphite insets in the cask interior lead to a considerably lowered dose rate.
Das Konzept des Safety Case und die Endlagerung wärmeentwickelnder radioaktiver Abfälle in Deutschland
The article covers the developments leading to the concept of the safety case for repositories of radioactive waste. It outlines the basic principles of the concept. In the authors' opinion, the concept has proved to be an effective tool in decisionmaking processes in a number of repository programs abroad. In Germany, a description of the present state of exploration, research and development based on this concept as well as of the questions still open could clarify the scientific and technical reasoning underlying options of final storage of heat-producing waste and, in this way, help overcome the present stalemate. Given the research and development findings already in place, and also given the tools developed in Germany, the authors estimate that a safety case as indicated in this article could be established within two or three years.
A botanical biography of Professor Paul Richards C.B.E.
AbstractPaul Westmacott Richards (19 December 1908–4 October 1995) was for 75 years a member of ‘the Society’ (the Moss Exchange Club, MEC, later to become the British Bryological Society, BBS) and was, by some very considerable margin, its longest standing member (Figs 1–4). He was President of the BBS on two occasions (1950–51 and 1978–79), an office that no one else has held twice. He was elected an Honorary Member in 1970. From 1949 until 1976 he was Professor of Botany at the University College of North Wales (now University of Wales, Bangor).