Masters Theses

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Laurence F. Miller

Committee Members

Peter G. Groer, Robert E. Uhrig, Lawrence W. Townsend

Abstract

In order to determine the risk associated with the contamination of a site and the necessary remediation needed to reduce the risk to acceptable levels, a radiological assessment is performed. Radioactive contaminants of concern and possible exposure pathways are identified using sampling results and site characteristics for use in the assessment. These parameters are then used in approved analytical or computer model methodologies for determination of the potential dose to a current or future receptor. Typically, single values are used for each of the input parameters and bounding assessments are performed using the minimum and maximum values of the parameters. However, single values may not be appropriate for many of the parameters; rather, a range and distribution of values are more appropriate. The use of distributions for the input parameters gives results at statistical confidence levels. Therefore, the results of the radiological assessment will provide dose levels to a potential receptor that will not be exceeded with a certain level of confidence.

The goal of this thesis is to perform a radiological assessment and uncertainty analysis of the St. Louis Downtown FUSRAP site using latin hypercube sampling to determine the maximum expected dose at the 90% confidence level to a critical future receptor. To achieve this objective, Argonne National Laboratory's computer code RESRAD (Version 5.6) will be used along with an add-on module called RESRAD-Probabilistic for the uncertainty analysis. After a baseline assessment is performed using site characterization data from earlier assessments, a sensitivity analysis will determine the input parameters that are most sensitive in the assessment. The ranges and distributions for the sensitive parameters will be determined from site data or applicable literature for use in the uncertainty analysis. The results of the uncertainty analysis, in the form of dose to source ratios, will be compared to analytical calculations using simplified transport models for the plant ingestion and soil inhalation exposure pathways. An analytical assessment of the dose to an off-site receptor will also be performed. The results from the uncertainty analysis will be used with current generic soil concentration guidelines as well as the site specific guidelines for the DOE and the NRC in order to determine the site remediation necessary to meet those guidelines.

The results of the uncertainty analysis show that the maximum dose to source ratios at the 90% confidence level for all included pathways are (all values in [mrem/yr]/[pCi/g]): 14.4 for Ra-226; 1.5 for Th-230; 16.3 for Th-232; and 0.2 for U-238. In order to meet the DOE's basic dose limit to the critical receptor of 100 mrem/yr at the 90% confidence level, the specific soil guidelines for the contaminants of concern are: 7 pCi/g for Ra-226; 67 pCi/g for Th-230; 6 pCi/g for Th-232; and 500 pCi/g for U-238.

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