Rapid Assessment of Atmospheric Releases for Nuclear Emergency Response Planning

Abstract

Two codes developed to assist in safety assessments and nuclear emergency response planning are described and demonstrated. The atmospheric dispersion code PEARL uses an established consequence matrix developed using a unit source term methodology for a given set of atmospheric and release conditions. Solutions for specific source terms are established by multiplying this matrix by vectors of modifying factors characterizing the particular source term and dispersion parameters. This approach has a number of advantages, such as the ability to model time-dependent release characteristics of heat content and isotopic composition as well as the simultaneous evaluation of source terms over the full series of weather patterns in a single run; capabilities not previously available: Using site specific weather information, results can be structured in a number of different deterministic and probabilistic formats, permitting the direct identification of higher risk areas. Output generated by PEARL is used by the complementary computer code NERP to evaluate the effectiveness of specific countermeasures. By calculating the pathway doses and dose rates as a function of downwind distance and elapsed time from the start of release, NERP can represent any conceivable response scheme comprised of distance and time-dependent application and relaxation times for mitigating actions. The doses avoided by the response scheme can be readily determined for easy comparison against measures of effectiveness. Both codes employ menu-driven user interfaces to facilitate code use and run on a 486DX under MS-DOS.