Limer LMC, Assessment Calculations for C-14 Labelled Gas and ...

3 EDA-specific AssumptionsThe purpose of this section is to outline those assessment assumptions that are specificto the assessment of the EDA. A distinction is made between those assumptions madefor each of the two gases of interest.3.1 C-14As noted in Limer et al. (2011), to assess the potential impacts associated with gaseousreleases of C-14, it is important to account for factors that may affect the calculatedimpacts of any C-14 entering the soil zone, and also any factors that may determine theinitial release of C-14 labelled gas from the wastes.For the assessment of the EDA, the following uncertainties associated with the initialrelease of C-14 labelled gas from the wastes are considered in a range of near-fieldcalculations which provide the source fluxes for the EDA assessment (Small et al.,2011b).Case 2 groundwater flow with PIER Inventory A, with instantaneous release ofC-14 from all metal wastes and slower release from the graphite matrix, based onelicitations (Case2_InvA) (the reference case);A variant of Case2_InvA case examining the effect of instantaneous C-14 releasefrom all C-14 wastes including the 9.3 TBq anticipated to be present in graphite(Case2_InvA_C14rel);A variant of Case2_InvA case examining the effect of increased flow resulting fromconsidering higher cap infiltration rates (Case2_var1_InvA); A variant of Case2_InvA examining the effect of a slower release from the Stage 3decommissioning metals (Case2_InvA_S3M); andCase 2 groundwater flow with PIER Inventory B (additional volume for newbuild), where the flow model takes account of the increased vault volume, anduses the same C-14 release assumptions as Case2_InvA (Case2_InvB).The PIER A2 and B2 C-14 inventories are given in Table 3-1; the inventory data comesfrom Harper (2011). In the B2 inventory not only is the total anticipated C-14 inventorygreater, more of it is anticipated to be emplaced in the first three EDA vaults (15 to 17).12