Relevance of biotic pathways to the long-term regulation of nuclear waste disposal: Phase 2, Final report

Abstract

The results reported here establish the relevance and propose a method for including biotic transport in the assess111ent and 1 icensing process for commercial low-level waste disposal sites. Earlier work identified the biotic transport mechanisms and process scenarios linking biotic transport with does to man, and developed models for assessment of impacts. !n this, the second phase of the project, we focused on a review of the sub-models of the B!OPORT computer code and scenarios that were developed in Fhase I. Also site specific assessments of the relevance of biotic transport were conducted for two commercial low-level waste disposal facilities. The resulting Case calculotions indicate that the current BIOPORT/f•1AXI1 models predict lower doses than the previous ordPr-of-magnitude estimates developed in Phase I. However, the resulting doses, depending on model and scenario assumptions, range from the same order-of-magnitude to an order-of-magnitude lower than the doses from the comparable intruder-agriculture scenaric. The efforts to review and enhance the BIOPORT model resulted in the following: • no change in the sub-model representing waste package form de campo~. it ion 4.4.1 Cover Cor1figuration 4.4.2 Erosion Rates. .. . 4.4.3 Plant Populations. . 4.4.4 Animal Populations o o 0 0 4o4o5 ~Jaste-Package Form Integrity \' 1 •i iii 1.1 1.1 2.1 2 .I 2.2 2.4 2.5 2.5 2.7

Summary of Conceptual Models and Data Needs to Support the INL Remote-Handled Low-Level Waste Disposal Facility Performance Assessment and Composite Analysis

“…INL site-specific sampling of harvester ant nests at the Materials and Fuel Complex ponds suggests that ants redistribute radionuclides in soil but the effect is seen mainly in the mound material (Blom et al 1991b). Harvester ants tend to exhibit a preference for disturbed conditions similar to those found in the RWMC SDA (Fitzner et al 1979;McKenzie et al 1985), and it is likely that the engineered cover design will deter burrowing. In the screening analysis for the RWMC PA (DOE-ID 2007) biointrusion analysis, it was assumed that ants can burrow as deep as 2.7 m (9 ft) during the institutional control and compliance periods.…”

Performance assessment for continuing and future operations at solid waste storage area 6

“…Although biotic intrusion and its consequences have been studied, using largely generic models (see, e.g., McKenzie et al 1982aMcKenzie et al , 1982bMcKenzie et al , 1983McKenzie et al ,1984McKenzie et al , 1985McKenzie et al , and 1986Kennedy, Caldwell, and McKenzie 1985), the magnitude of such releases from near-surface waste disposal units as compared to releases due to infiltrating water or inadvertent human intrusion has not been firmly established, nor has the importance of these releases for exposures of humans, especially for units constructed with engineered barriers. However, the following arguments can be made to indicate that radionuclide releases due to biotic intrusion would probably be relatively unimportant for SWSA 6 and, thus, need not be considered explicitly in the PA.…”

Second performance assessment iteration of the Greater Confinement Disposal facility at the Nevada Test Site

“…Exposure can occur at any time during the first 10,000 years after burial, excepting the first hundred years in which it is assumed that the public is barred from the site by active institutional control. The third and fourth pathways constitute what can be described as an "intruderagriculture" scenario [ McKenzie et al, 1982]. This scenario imagines an individual establishing a farm at the site, growing and eating crops, and raising livestock on cultivated feeds.…”

“…Each of these activities involves ingestion of isotopes and consequent exposure. McKenzie et al, [1982] considered this scenario for a low-level site in an arid western states setting and suggests the parameters in Table 3.5.…”