Effect of Remediation Parameters on in-Air Ambient Dose Equivalent Rates When Remediating Open Sites with Radiocesium-contaminated Soil

Abstract

Calculations are reported for ambient dose equivalent rates [H˙*(10)] at 1 m height above the ground surface before and after remediating radiocesium-contaminated soil at wide and open sites. The results establish how the change in H˙*(10) upon remediation depends on the initial depth distribution of radiocesium within the ground, on the size of the remediated area, and on the mass per unit area of remediated soil. The remediation strategies considered were topsoil removal (with and without recovering with a clean soil layer), interchanging a topsoil layer with a subsoil layer, and in situ mixing of the topsoil. The results show the ratio of the radiocesium components of H˙*(10) post-remediation relative to their initial values (residual dose factors). It is possible to use the residual dose factors to gauge absolute changes in H˙*(10) upon remediation. The dependency of the residual dose factors on the number of years elapsed after fallout deposition is analyzed when remediation parameters remain fixed and radiocesium undergoes typical downward migration within the soil column.

The Effect and Effectiveness of Decontaminating a Pond in a Residential Area of Fukushima

“…1 and 2) demonstrated the most reduction. This is consistent with the observation that covering a decontaminated area is more effective at reducing ADR than leaving it uncovered (Cresswell et al, 2016; Malins et al 2016) because the covering material shields the underlying gamma rays.…”

“…The decontamination factor (and percentage reduction) was lowest at P in with a value of 2.04 (51% reduction), followed by P edge at 2.30 (56% reduction), then P center at 10.29 (90% reduction), and P out with the highest at 15.13 (93% reduction). It appears that lower decontamination factors were obtained from areas where radiocesium had penetrated more deeply, which is consistent with the finding of Malins et al (2016). The apparent deviation of P center and P out from this trend is attributable to the comparatively higher total inventory (and concentration) at P center , which yielded higher residual values resulting in its lower decontamination factor.…”

“…An experiment reported by Cresswell et al (2016) demonstrated that forest dose rates could be further reduced by 10–15% if cleared areas were covered with woodchips. This is similar to soil decontamination where removal of the top layer (usually 5–10 cm) and recovering with a fresh clean layer was deemed most effective at reducing ADR (Malins et al 2016).…”

External Dose to Recovery Teams Following a Wide-area Nuclear or Radiological Release Event

“…A separate hypothetical RDD event in an urban environment produced a calculated contamination of ~800–4,000 kBq m −2 (Kamboj et al 2009), resulting in 8 μGy h −1 fields. Depositions due to the Fukushima reactor accident range to > 3,000 kBq m −2 and extending >20 km from the reactor site (Malins et al 2016). Thus, the assumptions of this study and its results can be confidently extrapolated to a variety of release events with corrections of less than an order of magnitude.…”