Chairman F. LANGE
THE RADTRAN 4 COMPUTATIONAL SYSTEM FOR TRANSPORTATION RISK ASSESSMENT: A PROTOTYPE
FOR THE INFORMATION SUPERHIGHWAY*
K.S. NEUHAUSER
Sanaia National Laboratories, Albuquerque, New Mexico, United States of America Abstract
The RADTRAN 4 computer code for transportation risk assessment [Neuhauser and Kanipe, 1992] is the central code in a system that contains both other codes and data libraries [Cashwell, Neuhauser and Kern, 1988; Cashwell, 1989]. Some of these codes and data libraries supply input data for RADTRAN; others perform supplemental calculations. RADTRAN 4 will be released by the IAEA in an international version known as INTERTRAN 2 in 1995. In the United States, RADTRAN 4 and its supporting system may be accessed via the INTERNET, a precursor lo the Information Superhighway. Similar networks arc being contemplated elsewhere in the world, and the RADTRAN System may serve as a prototype for systems on these networks. A system is desirable for the following reasons. Some classes of data and data-handling methods are country-specific and some are not - ancillary codes and data libraries that provide the latter are not affected by national and regional borders while the former must be provided on a country-by-country basis. Making the invariant portions available to all users in an international system would simplify quality assurance (QA) and, therefore, the reliability and consistency of risk results.
Among the classes of data used in RADTRAN 4 (and INTERTRAN 2) and the supplemental calculational capabilities that are essentially invariant for all countries and regions are:
• radionuclide characteristics such as half-life, photon energy, and dose-conversion factors;
• characteristics of radioactive-material packages found in international commerce;
• features of highly standardized international transportation modes (primarily sea and air);
• uncertainty analysis.
We have found in the United States that making these features available in a form that either can be electronically transferred to or is already embedded in a RADTRAN input-data set increases the ease with which risk analyses can be performed, reduces the frequency of data-entry errors, and standardizes to the extent possible the calculation of transportation risk. These features and their related QA benefits are discussed individually in the next paragraphs.
This work was performed at Sandia National Laboratories, a US Department of Energy facility, under contract DE-AC04-94AL85000.
Analysts who redefine the three zones for some special purpose should use the comment-line feature of RADTRAN to make a note of the deviation each time they run the code with the redefined values in order to facilitate comparisons between countries
Meteorological data can be supplied to RADTRAN in one of two ways -either as a single "look-up" table of downwind areas and dilution factors or as a set of six frequencies for the Pasquill atmospheric stability classes A through F [Pasquill, 1960] The latter refers the code to a second set of "look-up" tables, one tor each Pasquill category evaluated at a single release height (ground-level, small-diameter puff) for the minimum wmdspeed in each class As part of the IAEA Coordinated Research Program effort that is producing INTERTRAN 2, France has developed a computer code, TRANSA F, which can supply these data in a form directly usable in
RADTRAN/INTERTRAN [DeOrange et al., 1993]
Making the TRANSAT code available within the system would assist the user lo calculate dispersion values. Good-quality meteorological data often are not available for a particular locale, especially in areas remote from cities and airports that are nevertheless traversed by highways, rail lines, and sea lanes. It is tempting to blindly follow arbitrary rules that yield ostensibly
"accurate" data in these situations — for example, to extrapolate from the nearest weather station, regardless of how far away or how dissimilar the terrain around the station may be - but such practices should be avoided. The result is precision without accuracy. MesoscaJe weather research will ultimately provide more satisfactory methods for handling this problem, but in the meantime, regional averages are often the best that one can do. TRANSAT can be used to produce regional-average dispersion parameters in a form electronically compatible with RADTRAN; but it also can be used to generate locale-specific dispersion parameters for those users who have information on that level of detail and resolution.
Supplemental Calculations
The Transportation Individual Center-Line Dose (TICLD) code fills the needs of risk analyst to respond to questions and regulations based on individual doses while at the same time ensuring that the individual dose estimates are obtained in a manner that is methodologically consistent with population-dose estimates [Enckson, Kanipe and Neuhauser, in preparation].
TICLD also allows dose thresholds !o be correlated with distance and time-integrated concentration. In the United States, for example, there are two thresholds of particular interest.
The first is the Negligible Individual Dose of 1 mrem (.01 mSv) [NCRP.1993]. The downwind distance at which the individual dose estimate drops below 1 mrem can be identified with TICLD and used in an iterative process to refine the original risk estimate by truncating the cumulation of population dose at that distance. The second threshold of interest in the United States is the radial distance within which the 100 mrem (1 mSv) recommended annual dose limit fora member of the public [ICRP, 1990] is exceeded Radial distances within which other, higher dose thresholds are exceeded may, of course, also be identified, although these often either do not occur or occur within a very short distance of the release point. These calculations can assist emergency-response personnel and policy makers by identifying radial distances within which efforts should be concentrated in the event of an accident of the type analyzed
The RADTRAN/TNTERTRAN system is more powerful than the sum of its parts and provides the user with several benefits. The system allows all shipment configurations to be evaluated within a consistent methodological framework while also allowing route-related features to be treated as specifically as the available data permit. Additionally, quality assurance of most of the system components needs only to be done once, or after regular updates, at most. Thus, when a country establishes or joins a network containing the system, their analysts need be concerned only with QA of their own country-specific data Quality assurance thus becomes less time-consuming and expensive than it would be otherwise. With proven risk analysis tools and facilitated QA, RADTRAN- or INTERTRAN-based systems can provide flexible, high-quality transportation risk analysis capabilities to the international community This concept could serve as a prototype for other systems that might be made available on the future network now being referred to as the Information Superhighway.
Literature Cited
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