Factors affecting dose estimates for long-term performance assessments: case study-Armagosa Valley

Area of Science:

• Environmental Science
• Radiological Protection
• Risk Assessment

Background:

• Assessing public dose from chronic environmental radioactive releases is crucial for nuclear waste repository safety.
• Previous assessments often involve numerous assumptions that can lead to over or underestimation of actual radiation doses.
• Understanding these factors is key to refining dose estimation methodologies for regulatory compliance and public safety.

Purpose of the Study:

• To review and evaluate factors influencing public dose estimates from chronic radioactive releases.
• To illustrate how specific assumptions and input values impact dose estimations and quantify their significance.
• To identify sources of conservatism and non-conservatism in current dose assessment practices.

Main Methods:

• Focused on factors related to receptor location and living habits, rather than environmental transport.
• Analyzed the influence of regulatory requirements for groundwater withdrawal on dose estimates.
• Compared dose estimates based on different individual receptor locations (e.g., EPA site vs. Amargosa Valley).

Main Results:

• Regulatory requirements for groundwater withdrawal were the most significant source of dose overestimation (conservatism).
• The assumed location of the Reasonably Maximally Exposed Individual (RMEI) also contributed significantly to conservatism.
• Effective radionuclide half-lives and specific intake factors (e.g., aquaculture, stable iodine) had lesser impacts.

Conclusions:

• Overall conservatism in dose assessments, due to identified factors, approaches an order of magnitude.
• The application of the RMEI concept, as defined by the U.S. EPA, led to dose underestimation compared to the Critical Group (CG) concept.
• Further rigorous analysis of both RMEI and CG concepts is needed to improve dose estimation methodologies for environmental radionuclide releases.