Final Technical Progress Report Long term risk from actinides in the environment: Modes of mobility

Kirchner, Thomas B.

New Mexico State University (United States)

关键词: Yucca Mountain Actinides;    Actinides;    Wipp;    Actinides;    Progress Report;   

DOI  :  10.2172/793122
RP-ID  :  NONE
RP-ID  :  FG07-98ER62542
RP-ID  :  793122

美国|英语

来源: UNT Digital Library

【 摘 要 】

The key source of uncertainty in assessing actinide mobility is the relative importance of transport by: (1) wind erosion, (2) water erosion, and (3) vertical migration. Each of these three processes depends on several environmental factors and they compete with one another. A scientific assessment of the long-term risks associated with actinides in surface soils depends on better quantifying each of these three modes of mobility. The objective from our EMSP study was to quantify the mobility of soil actinides by wind erosion, water erosion, and vertical migration at three semiarid sites where actinide mobility is a key technical, social and legal issue. This EMSP project was the first to evaluate all three factors at a site. The approach has been to investigate both short- and long-term issues based on field and lab studies and model comparisons. Our results demonstrate the importance of incorporating threshold responses into a modeling framework that accounts for environmental factors and natural disturbances that trigger large changes in actinide mobility. The study measured erosional losses of sediment and fallout cesium (an actinide analogue) from field plots located near WIPP in 1998. The results highlight the large effect of burning as a disturbance on contaminant transport and mobility via runoff and erosion. The results show that runoff, erosion, and actinide transport are (1) strongly site specific-differences in radionuclide transport between WIPP and Rocky Flats differed by a factor of twelve because of soil and vegetation differences, and (2) are strongly impacted by disturbances such as fire, which can increase runoff, erosion, and actinide transport by more than an order of magnitude. In addition, a laboratory experiment using soil columns was conducted to investigate the vertical transport of contaminants in sandy soils. Nine columns of soil collected from the vicinity of the WIPP site were prepared. The column consisted of a piece of PVC pipe 20 cm in diameter and approximately 22 cm long. A thin ''marker layer'' of white soil was added to the top of each column followed by a thin layer of soil that had been spiked with 137Cs, cerium and lanthanum was applied to the surface. Approximately 900 cm of water (the equivalent of about 30 years of rainfall) was then applied at a rate of 3.2 L d-1. All of the activity contained in the soil core appeared to be in the top few mm of soil, i.e. there was virtually no movement of the 134Cs labeled particles. Finally, a library of object-oriented model components was created using Visual Basic to support the construction of contaminant transport models. These components greatly simplify the task of building 1- to 3- dimensional simulation models for risk assessment. The model components created under this funding were subsequently applied to help answer questions regarding risks from irrigation associated with potential releases from the Yucca Mountain waste repository.