Modeling the outdoor environment--new perspectives and challenges.

Abstract

Assessing risk from manmade and naturally occurring radionuclides in the environment has long been of primary interest in radiation protection. Early investigations and decisions relied on direct measurements of radiation in environmental media; however, these techniques were inadequate for determining exposure to humans and biota from very low levels of radiation and in predicting exposures from future releases. The Plowshare Program in 1957 investigated the use of nuclear explosives for peaceful purposes and created an immediate need for predicting the dispersion and ultimate fate of radionuclides that might be vented to the atmosphere or enter groundwater and expose man. As a result, modeling the behavior of radionuclides in the outdoor environment became a field of vigorous interest, merging disciplines of mathematics, biology and physics, among others. Environmental models and, more specifically, models predicting radiation dose from radionuclides in the environment have evolved rapidly and have increased significantly in sophistication, complexity and scope. Application of these models is commonly known as radiological assessment. This presentation examines the current status, future direction and weaknesses of radiological assessment models used in making decisions about radiation. The trend in recent years has been toward more complex models, which has not necessarily improved the accuracy of dose estimates and, in certain cases, has had the opposite effect. The presentation also discusses the future of model development, with particular emphasis on simple techniques and the expanded use of microcomputers, which will make radiological assessment models widely available for risk assessment and for practical applications such as the design of efficient monitoring programs and engineering calculations on the clean-up of contaminated soils. The screening models developed by the National Council on Radiation Protection and Measurements are offered as an example of a powerful yet simple method for demonstrating compliance with standards. Finally, the paper reviews two major areas of challenge for the future--defining uncertainty associated with radiological assessment models and the potential for converting radiological assessment models for use with nonradioactive environmental pollutants such as chemicals. Modeling radionuclides in the environment is adopting a new perspective. Future models will be less complex than their predecessors and will be adaptable to a much broader range of users. Key challenges remain in applying the techniques used for radionuclides to nonradioactive pollutants.