Investigation of the Environmental Fate of Tritium in the Atmosphere

More documents

Recommendations

Info

INVESTIGATION OF THE ENVIRONMENTAL FATE OF TRITIUM IN THE ATMOSPHERE There remains a high level of uncertainty regarding the impact of climate change on the dispersion and behaviour of tritium in the atmosphere. One of the reasons is that climate change modeling currently does not reliably predict effects on short-term (day-to-day) weather variance, which plays a significant role in tritium dispersion. Also, the resolution of current climate change models is regional, which is beyond the more localized effects of subregional features (shorelines, topography, etc.) that surround individual facilities. Thus, more detailed work on climate change downscaling techniques is needed to fully understand the influence of climate change on the atmospheric dispersion of tritium at nuclear facilities. BACK TO TABLE OF CONTENTS 44
INVESTIGATION OF THE ENVIRONMENTAL FATE OF TRITIUM IN THE ATMOSPHERE 4.0 DYNAMIC BEHAVIOUR OF TRITIUM IN THE HYDROLOGICAL CYCLE This section outlines the partitioning of tritium from air to soil water and surface water, tritium migration from soil water to groundwater, and tritium behaviour in lake and river plumes. The transfers between air, soil water, surface water and groundwater are highlighted in Figure 4.1. For context, this figure also illustrates the full set of transfers between environmental compartments, relevant to human exposure and dose assessment. 4.1 Partitioning from Air to Soil and Surface Water As noted in Section 3.1.3, tritium may be transferred by vapour exchange and by precipitation between the air and the surface of the earth, i.e. to soil porewater and to surface water bodies. The vapour exchange is continuous, and is the dominant process for plumes near the ground (Bunnenberg et al., 1986). This exchange is augmented by transfer of tritium in precipitation during rainfall and snowfall events. For snowfall, the transfer is completed when the snow melts (Davis, 1997). Light rainfall events are more effective than heavy ones in scavenging tritium from a local air plume (Bolin, 1961; Sejkora, 2006). It is difficult, and generally unnecessary, to separate the transfer of tritium that occurs via precipitation, from that which occurs via direct water vapour exchange. Tritium concentrations in a body of surface water or in soil porewater respond to the recent history of tritium inputs and reflect a dynamic equilibrium between air and water. The relevant historical period depends on the residence time of water in the water body or the surface soil. Water residence times in surface soil are on the order of months. Those in deeper sub-soils can range from years to thousands of years. Residence times in ponds and lakes range from weeks to hundreds of years, depending on their volumes and discharge rates. The transfers from air to soil water, or to small surface water bodies such as ponds, are best represented by specific activity models. These models apply when there is rapid isotopic exchange between environmental compartments, so that if one compartment is initially contaminated, the other compartment will tend to have the same tritium to hydrogen (T/H) ratio, except for any dilution effects. The T/H ratio is referred to as the specific activity of tritium. BACK TO TABLE OF CONTENTS 45
Page 1 and 2: Investigation of the Environmental
Page 3 and 4: TABLE OF CONTENTS INVESTIGATION OF
Page 5 and 6: LIST OF TABLES INVESTIGATION OF THE
Page 7 and 8: EXECUTIVE SUMMARY INVESTIGATION OF
Page 9 and 10: 1.0 INTRODUCTION INVESTIGATION OF T
Page 11 and 12: INVESTIGATION OF THE ENVIRONMENTAL
Page 19 and 20: Table 2.2: Estimated Rates of Gener
Page 25 and 26: 2.4.2.5 Airborne Tritium Releases f
Page 27 and 28: 2.4.3 Fuel Reprocessing Plants INVE
Page 49: INVESTIGATION OF THE ENVIRONMENTAL
Page 73 and 74: s) bg th (m p e D INVESTIGATION OF
Page 75 and 76: 5.1.2 Shield Source Incorporated IN
Page 85 and 86: ) Modelled (Bq/m 6 5 4 3 2 1 0 y =
Page 101 and 102:
INVESTIGATION OF THE ENVIRONMENTAL
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
show all

Investigation of the Environmental Fate of Tritium in the Atmosphere

Create successful ePaper yourself

Delete template?

Save as template?