Special Analysis: Atmospheric Dose Resulting from the Release of C14 from Reactor Moderator Deionizers in a Disposal Environment

摘要

The proposed action of disposing of 52 moderator deionizer vessels within the ILV was evaluated in this SA. In particular, a detailed analysis of the release of (sup 14)C via the atmospheric pathway was conducted for these vessels since the major concern has been the nearly 20 Ci of (sup 14)C that is associated with each vessel. The more rigorous evaluation of the atmospheric pathway for (sup 14)C included incorporation of new information about the chemical availability of (sup 14)C when disposed in a grout/cement encapsulation environment, as will be the case in the ILV. This information was utilized to establish the source term for a 1-D numerical model to simulate the diffusion of (sup 14)CO(sub 2) from the ILV Waste Zone to the land surface. The results indicate a peak surface emanation rate from the entire ILV of 1.42E-08 Ci/yr with an associated dose of only 3.83E-05 mrem/yr to the Maximally Exposed Individual (MEI) at 100m. The fact that the atmospheric pathway exposure for (sup 14)C is controlled by chemical solubility limits for (sup 14)C between the solid waste, pore water and pore vapor within the disposal environment rather than the absolute inventory suggests that the establishment of specific facility limits is inappropriate. With the relaxation of the atmospheric pathway restriction, the groundwater pathway becomes the more restrictive in terms of disposing (sup 14)C or (sup 14)C(sub KB) within the ILV. Since the resin-based (sup 14)C of the 52 moderator deionizer vessels is highly similar to the (sup 14)C(sub KB) waste form, the inventory from the 52 deionizer vessels is compared against the groundwater limits for that waste form. The small groundwater pathway fraction (1.14E-05) calculated for the proposed inventory of the 52 moderator deionizer vessels indicates that the proposed action will have an insignificant impact with respect to possible exposures via the groundwater pathway. This investigation recommends that there be no ILV Atmospheric pathway limit for (sup 14)C and (sup 14)C(sub KB). Further, in the absence of an Atmospheric pathway limit it was determined that there are no other applicable ILV limits (Groundwater or Intruder pathway) that would be impacted in any significant fashion should the waste package be disposed within the ILV. Thus, it is concluded that the disposal of 52 moderator deionizer vessels can easily be accommodated within the ILV.