Chlorine-36 data at Yucca Mountain: statistical tests of conceptual models for unsaturated-zone flow.
An extensive set of chlorine-36 (36Cl) data has been collected in the Exploratory Studies Facility (ESF), an 8-km-long tunnel at Yucca Mountain, Nevada, for the purpose of developing and testing conceptual models of flow and transport in the unsaturated zone (UZ) at this site. At several locations, the measured values of 36Cl/Cl ratios for salts leached from rock samples are high enough to provide strong evidence that at least a small component of bomb-pulse 36Cl, fallout from atmospheric testing of nuclear devices in the 1950s and 1960s, was measured, implying that some fraction of the water traveled from the ground surface through 200-300 m of unsaturated rock to the level of the ESF during the last 50 years. These data are analyzed here using a formal statistical approach based on log-linear models to evaluate alternative conceptual models for the distribution of such fast flow paths. The most significant determinant of the presence of bomb-pulse 36Cl in a sample from the welded Topopah Spring unit (TSw) is the structural setting from which the sample was collected. Our analysis generally supports the conceptual model that a fault that cuts through the nonwelded Paintbrush tuff unit (PTn) that overlies the TSw is required in order for bomb-pulse 36Cl to be transmitted to the sample depth in less than 50 years. Away from PTn-cutting faults, the ages of water samples at the ESF appear to be a strong function of the thickness of the nonwelded tuff between the ground surface and the ESF, due to slow matrix flow in that unit.
TR-13-26 Chlorine cycling and fates of 36 Cl in terrestrial environments
This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the authors. SKB may draw modified conclusions, based on additional literature sources and/or expert opinions. Abstract Chlorine-36 (36 Cl), a radioisotope of chlorine (Cl) with a half-life of 301,000 years, is present in some types of nuclear waste and is disposed in repositories for radioactive waste. As the release of 36 Cl from such repositories to the near surface environment has to be taken into account it is of interest to predict possible fates of 36 Cl under various conditions as a part of the safety assessments of repositories for radioactive waste. This report aims to summarise the state of the art knowledge on Cl cycling in terrestrial environments. The view on Cl cycling in terrestrial environments is changing due to recent research and it is clear that the chloride ion (Cl –) is more reactive than previously believed. We group the major findings in three categories below according to the amount of data in support of the findings. From the result presented in this report it is evident that: • There is an ubiquitous and extensive natural chlorination of organic matter in terrestrial ecosystems. • The abundance of naturally formed chlorinated organic compounds (Cl org) frequently exceeds the abundance of Cl – , particularly in soils. Thereby Cl org in many cases dominates the total Cl pool. • This has important implications for Cl transport. When reaching surface soils Cl – will not be a suitable tracer of water and will instead enter other Cl pools (Cl org and biomass) that prolong residence times in the system. • Cl – dominates import and export from terrestrial ecosystems while Cl org and biomass Cl can dominate the standing stock Cl within terrestrial ecosystems. • Both Cl and Cl org pools have to be considered separately in future monitoring programs addressing Cl cycling. Further, there are also indications (in need of confirmation by additional studies) that: • There is a rapid and large uptake of Cl – by organisms and an accumulation in green plant parts. A surprisingly large proportion of total catchment Cl (up to 60%) can be found in the terrestrial biomass. • Emissions of total volatile organohalogens could be a significant export pathway of Cl from the systems. • Some of the Cl org may be very …
Basic Legal Issues of the Management of Natural Resources of the Caspian Sea
Taking into account different interpretations of legal status of the Caspian Sea, the paper focuses on the current and future legal regime of its natural resources. The relevant international instruments are considered and in this context national approaches of the Caspian states to resource management are legally assessed. In conclusion, some basic prerequisites for the developing scope of the legal regime of the Caspian natural resources are suggested.