III. THE FOUR HEDR DOCUMENTS

Report PNWD 1983, HEDR Modeling Approach, is a letter report for the TSP and CDC that details the conceptual approaches that the HEDR project is planning to use in calculating radiation doses to people. It considers major environmental transport pathways, including atmosphere, surface water, and groundwater. A different sequence of modeling techniques is projected for each transport pathway. The model chosen for each pathway depends on the available dose data, the degree of confidence justified by existing data, and the level of sophistication deemed appropriate for the particular pathway and period being considered.

Because the largest releases of radionuclides to the air occurred in the mid-1940s, a very fine temporal resolution is required for that period to account for the transport and deposition of these radioactive materials and to propagate properly the uncertainties associated with the data. Less-detailed modeling efforts were justified for the middle and later periods of operations at Hanford because environmental monitoring became more detailed and more reliable during 1973 to 1991. The original reactors and their reprocessing plants were shut down in 1972; however, the N reactor continued to operate until 1987. The fineness of grids for the receptor locations depended on the source term and transport temporal resolutions. Beyond the Hanford site boundaries, a 10- by 10-km (6- by 6-mile) grid was used for the early and intermediate release periods. After 1972, a more general approach was proposed because use of a fine grid was considered to be excessive. For considering the source and amount of food eaten by people, agricultural production at a county or subcounty level was used and a high resolution was proposed for the counties closest to Hanford for the early period. For the later period, initial calculations will be based on local production of all foods, an overestimate but a reasonable approach, since foods will contribute very little to the overall dose.

Releases to the Columbia River are not transported as quickly through the environment as those in air, so a weekly time resolution was proposed for most of the



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THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS III. THE FOUR HEDR DOCUMENTS Report PNWD 1983, HEDR Modeling Approach, is a letter report for the TSP and CDC that details the conceptual approaches that the HEDR project is planning to use in calculating radiation doses to people. It considers major environmental transport pathways, including atmosphere, surface water, and groundwater. A different sequence of modeling techniques is projected for each transport pathway. The model chosen for each pathway depends on the available dose data, the degree of confidence justified by existing data, and the level of sophistication deemed appropriate for the particular pathway and period being considered. Because the largest releases of radionuclides to the air occurred in the mid-1940s, a very fine temporal resolution is required for that period to account for the transport and deposition of these radioactive materials and to propagate properly the uncertainties associated with the data. Less-detailed modeling efforts were justified for the middle and later periods of operations at Hanford because environmental monitoring became more detailed and more reliable during 1973 to 1991. The original reactors and their reprocessing plants were shut down in 1972; however, the N reactor continued to operate until 1987. The fineness of grids for the receptor locations depended on the source term and transport temporal resolutions. Beyond the Hanford site boundaries, a 10- by 10-km (6- by 6-mile) grid was used for the early and intermediate release periods. After 1972, a more general approach was proposed because use of a fine grid was considered to be excessive. For considering the source and amount of food eaten by people, agricultural production at a county or subcounty level was used and a high resolution was proposed for the counties closest to Hanford for the early period. For the later period, initial calculations will be based on local production of all foods, an overestimate but a reasonable approach, since foods will contribute very little to the overall dose. Releases to the Columbia River are not transported as quickly through the environment as those in air, so a weekly time resolution was proposed for most of the

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THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS operating period of the reactors, and that was changed to an annual scale after reactor shutdown. Movement of groundwater plumes to the Columbia may be very slow; once the contaminated water reaches the river it is diluted, depending on seasonal flow, and moves downriver rapidly. PNWD 1983 indicates that the HEDR project plans to calculate doses to individuals at only a dozen sites or selected locations along the river's length, and perhaps into the coastal areas. Report PNWD 2023 is a letter report that explains the parameters used in the DESCARTES and CIDER models. It documents the environmental accumulation and dose-assessment parameters used to estimate the impacts of airborne releases of iodine-131 from the Hanford site. The purpose of report PNWD 2033, Volume 1, was to document the releases of iodine-131 to the atmosphere from Hanford in 1944 to 1947. The selection of iodine-131 and that period was based on preliminary results of the HEDR project that confirmed that iodine-131 released during 1944 to 1947 was responsible for over 90% of the effective dose of the historical Hanford-related dose (Napier, 1991). In Phase I of the HEDR project, a preliminary estimate of iodine-131 releases was made on a monthly basis (Heeb and Morgan, 1991). The more recent process of determining the iodine-131 exposure to anyone person as a result of the Hanford operations uses a series of computer models designed to work together under the collective name Hanford Environmental Dose Reconstruction Integrated Codes (HEDRIC). Four computer models were used: Source Term Release Model (STRM), a model based on production and fuel reprocessing at Hanford that estimates the amount of iodine-131 that was vented to the atmosphere through the plant stacks. Regional Atmospheric Transport Code for Hanford Emission Tracking (RATCHET), a model to show the geographic deposition of iodine-131 after its release by combining release data with information on wind direction and speed.

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THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS Dynamic Estimates of Concentrations and Radionuclides in Terrestrial Environments (DESCARTES), a model to use the distribution of iodine-131 to calculate its progress through the food chain and to calculate concentrations in foods available to the population in the area covered by the HEDR project. Calculation of Individual Doses from Environmental Radionuclides (CIDER), a model that uses time, location, and diet information to calculate how much of the iodine-131, released hourly, according to plant operations, affected the offsite population. Report PNWD 2033, Volume 2, contains the detailed data that were used in the calculations reported in volume 1. The document details iodine-131 released daily by the B, D, and F reactors and presents tables of material processed by separation plants B and T. This document also includes a transcription of the computer-generated Jaech report (Jaech, 1957).