Contamination densities

Figures 4.1 to 4.8 show the model predictions for contamination density at the outdoor locations (Locations 4 (Region 1) and 5 and 6 (Region 2), as shown in Appendix V, Figs V.3 and V.4) for ⁶⁰Co for deposition in the summer. The tabulated results for ⁶⁰Co and ²³⁹Pu, including the predicted contamination density for deposition in the winter, are given in Appendix VII (Tables VII.1 to V11.5). Figures 4.1 to 4.5 provide comparisons of the predictions made at all outdoor locations for each model separately. Figures 4.6 to 4.8 provide intercomparisons of all model predictions for ⁶⁰Co for each outdoor location and set of initial conditions (dry, light rain and heavy rain). Only two sets of model predictions (METRO-K and ERMIN) were submitted for deposition during the winter; there was no difference between predicted deposition during the summer and during the winter for either of these models, and therefore, the results are not shown (see Appendix VII, Tables VII.1 and VII.2 for tabulated results). For CPHR, predictions were submitted only for dry conditions and light rain. For CHERURB, predictions were submitted only for Locations 4 and 6 and the predicted contamination density was the same.

LE 4.3. SUMMARY OF ENDPOINTS MODELLED BY EACH PARTICIPANT lling endpointModel METRO-KERMINCPHRRESRAD-RDDCHERURB amination density (outdoor locations 4.1–4.5 (by model) 4.6–4.8 (by location) Summer and wintera Co-60 and Pu-239 dry, light rain, heavy rain Locations 4–6 Summer and wintera Co-60 and Pu-239 dry, light rain, heavy rain Locations 4–6 Summer Co-60 and Pu-239 dry, light rain Locations 4–6 Summer Co-60 and Pu-239 dry, light rain, heavy rain Locations 4–6

Summer Co-60 and Pu-239 dry, light rain, heavy rain Locations 4 and 6 nal dose rates, Co-60 (indoor and or locations) s 4.9–4.13 (by model) s 4.14–4.19 (by location)

Summer and winter dry, light rain, heavy rain Locations 1–6 Summer and winter dry, light rain, heavy rain Locations 1–6 Summer dry, light rain Locations 1–6 Summer dry, light rain, heavy rain Locations 1–6

Summer dry, light rain, heavy rain Locations 2, 4, 5 nal dose rates, Pu-239 (indoor and or locations) ndix VII, TablesVII.6 to VII.10Not doneSummer and winter dry, light rain, heavy rain Locations 1–6

Summer dry, light rain Locations 1–6

Summer dry, light rain, heavy rain Locations 1–6Not done faces contributing to external dose rate ontributions) oor and outdoor locations) 4.20–4.21 (by location) 4.22–4.26 (by model)

Summer and winter Co-60 dry, light rain, heavy rain Locations 1–6 Summer and winter Co-60 and Pu-239 dry, light rain, heavy rain Locations 1–6 Summer Co-60 and Pu-239 dry, light rain Locations 1–6

Summer Co-60 and Pu-239 dry, light rain, heavy rain Locations 1–6Not done ernal doses, Co-60 t year and first 5 years . 4.27 (by region)

Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer dry Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2 nal doses, Co-60 t year and first 5 years . 4.28 (by region)

Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer dry Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2 nal doses, Pu-239 t year and first 5 years . 4.29 (by region)

Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer dry Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2

Summer dry, light rain, heavy rain Regions 1 and 2 ernal doses, Pu-239 t year and first 5 years ndix VII, Tables VII.15 to VII.19 egion)Not doneSummer and wintera dry, light rain, heavy rain Regions 1 and 2

Summer dry Regions 1 and 2

Summer dry, light rain, heavy rain Regions 1 and 2Not done termeasure effectiveness , external dose t year and first 5 years les 4.3–4.5

Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer dry Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2

Summer dry, light rain, heavy rain Regions 1 and 2 termeasure effectiveness, Pu-239, nal dose t year and first 5 years les 4.6–4.8

Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer and wintera dry, light rain, heavy rain Regions 1 and 2 Summer dry Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2 Summer dry, light rain, heavy rain Regions 1 and 2 er predictions are not shown for indicated endpoints.

Most models produced the same or similar predictions for Locations 4 and 6; however, the predictions differed for Location 5. Location 5 is on a dirt pathway in a park area, while Locations 4 and 6 are both on pavements (see Appendix V, Figs V.3 and V.4). ERMIN (Fig. 4.2) used different characterizations or descriptions for Locations 4 and 6 (a street near buildings for Location 4 and a car park for Location 6), resulting in differences between results for the two locations. In contrast, METRO-K (Fig. 4.1), RESRAD-RDD (Fig. 4.4), and CHERURB (Fig. 4.5) each used the same characterization for both paved locations, therefore giving the same results for both Locations4 and 6. CPHR (Fig. 4.3) produced similar results for all three locations under dry conditions and for Locations 4 and 6 under conditions of light rain.

The predicted rate of decrease in contamination densities predicted using METRO-K, ERMIN, and RESRAD-RDD was smaller for Location 5 than for Locations 4 and 6, likely reflecting higher loss rates from the paved surfaces (or greater retention in the unpaved area).

METRO-K (Fig. 4.1), ERMIN (Fig. 4.2), and RESRAD-RDD (Fig. 4.4) all produced higher contamination density predictions for Location 5 than for Locations 4 and 6. The initial contamination densities between Location 5, and Locations 4 and 6, under dry conditions, differed by approximately a factor of 8 for METRO-K, and by approximately 3 fold for ERMIN and RESRAD-RDD. This difference decreased under wet conditions, with similar initial depositions at all three locations for a given model. CPHR (Fig. 4.3) showed a very steep loss of the initial contamination density at Location 5 (on dirt), compared to Locations 4 and 6 (on pavement), under light rain conditions, indicating different assumptions about initial loss rates on the two surfaces.

The predicted initial deposition did not depend on the specific radionuclide considered; for all models except for CPHR, the predicted initial contamination densities for ⁶⁰Co and ²³⁹Pu did not differ; differences were less than a factor of 2 for CPHR. However, changes in contamination density over time did depend on the radionuclide being considered, with ⁶⁰Co generally showing a slightly faster loss rate (steeper slope) than ²³⁹Pu, consistent with the shorter half-life of ⁶⁰Co and the higher mobility in the environment of ⁶⁰Co compared to ²³⁹Pu.

Predicted loss rates were similar for METRO-K, ERMIN, and RESRAD-RDD (Figs 4.6 to 4.8), especially for wet initial conditions. CHERURB showed the slowest loss rate for paved surfaces (Locations 4 and 6), indicating a different removal rate was used in CHERURB.

Under dry conditions, the initial contamination density predicted using four of the models (METRO-K, ERMIN, RESRAD-RDD, and CHERURB) was approximately 10 MBq/m² (ranging by about a factor of 4 from 7 MBq/m² to 30 MBq/m²) for either radionuclide at Locations 4 and 6; an initial contamination density of approximately 50 MBq/m² was predicted at Location 5 by all models (Figs 4.6 to 4.8). Predicted initial contamination densities at all locations were about 2–3 GBq/m² for either radionuclide (⁶⁰Co or ²³⁹Pu) for light rain and about 10 GBq/m² for either radionuclide for heavy rain. When comparing between models, the contamination densities predicted both during light and heavy rain varied by about a factor of 2.

These predictions clearly showed the importance of initial weather conditions in determining the initial deposition of radionuclides.

FIG. 4.1. Contamination densities (Bq/m²) of ⁶⁰Co at three outdoor locations, as predicted by METRO-K for a summer release under different initial weather conditions as a function of time (1 day, 1 week, 1 month, 3 months, 1 year, 2 years, 5 years).

FIG. 4.2. Contamination densities (Bq/m²) of ⁶⁰Co at three outdoor locations, as predicted by ERMIN for a summer release under different initial weather conditions as a function of time (1 day, 1 week,

FIG. 4.3. Contamination densities (Bq/m²) of ⁶⁰Co at three outdoor locations, as predicted by CPHR for a summer release under different initial weather conditions as a function of time (1 day, 1 week, 1 month, 3 months, 1 year, 2 years, 5 years).

FIG. 4.4. Contamination densities (Bq/m²) of ⁶⁰Co at three outdoor locations, as predicted by RESRAD-RDD for a summer release under different initial weather conditions as a function of time (1 day, 1 week,

FIG. 4.5. Contamination densities (Bq/m²) of ⁶⁰Co at two outdoor locations, as predicted by CHERURB for a summer release under different initial weather conditions as a function of time (1 day, 1 week, 1 month, 3 months, 1 year, 2 years, 5 years).

FIG. 4.6. Comparison of model predictions for the contamination density (Bq/m²) of ⁶⁰Co at Location 4 under different initial weather conditions as a function of time (1 day, 1 week, 1 month, 3 months, 1 year,

FIG. 4.7. Comparison of model predictions for the contamination density (Bq/m²) of ⁶⁰Co at Location 5 under different initial weather as a function of time (1 day, 1 week, 1 month, 3 months, 1 year, 2 years, 5 years).

FIG. 4.8. Comparison of model predictions for the contamination density (Bq/m²) of ⁶⁰Co at Location 6 under different initial weather conditions as a function of time (1 day, 1 week, 1 month, 3 months, 1 year,