Evidence of sharp features in the Fukushima plume over Southwestern British Columbia Réal D’Amours, Alain Malo, Jean-Philippe Gauthier et Gilles Mercier (CMC) and Ian Hofman (Health Canada)
Jul 13, 2015
Evidence of sharp features in the Fukushima plume over
Southwestern British Columbia
Réal D’Amours, Alain Malo, Jean-Philippe Gauthier et Gilles Mercier (CMC)
and Ian Hofman (Health Canada)
Introduction
• Several studies on the radioactive releases from Fukushima nuclear power plant already exists
• The Fukushima plume provide nice opportunities to test radioactivity detection capabilities
• This study focusses on the arrival of the plume over SWRN BC
NRCAN aerial survey March 20 18:00 – 19:00 UTC
Other detections: Health Canada’s radiation monitoring network: 15-minutes time resolution
PNNL Richland, Washington: 12-hours time resolution
Detections on Health Canada’s radiation monitoring network in BC
Sampling every 15 minutes
Sidney & PNNL Observations
What is going on?
• In all likelihood, the plume originates from Japan, ~8000km away
• Naively one could expect a diffuse and well-mixed plume reaching the West Coast, especially in the boundary layer
• Nevertheless important small scale features are observed in the plume
Look at (Lagrangian) dispersion modelling results
• We use CMC’s dispersion model MLDP01 together with CMC’s operational analyses
• Make minimal hypotheses about the source of emission: – It is located at the Fukushima Power Plant – Sometimes after the tsunami hit (~ March 11 06 UTC) – A release rate of 1 Bq of 133Xe / hour – Assume 10 6-hour realeases from March 11, 12UTC,
ending March 14, 00 UTC – 2 000 000 particles for each of the 10 simulations
1R. D’Amours, A. Malo, R. Servranckx, D. Bensimon, S. Trudel, and J.-P. Gauthier-Bilodeau. Application of the atmospheric Lagrangian particle dispersion model MLDP0 to the 2008 eruptions of Okmok and Kasatochi volcanoes. J. Geophys. Res., 115, 10 2010.
11-12H 11-18H 12-00H 12-06H 12-12H 12-18H 13-00H 13-06H 13-12H 13-18H
0.38 0.80 0.60 0.58 0.65 0.94 0.35 0.44 0.76 0.59
Correlations with observed concentrations
Results for Sidney
Position of Model particles Release March 12 18UTC
Only particles in the layer SFC – 2000m are shown
March 19 18:00 UTC March 20 00:00 UTC
March 20 06:00 UTC March 20 12:00 UTC
March 20 1800 UTC
In principle the observed concentration at a point should be a combination of the resulting modelled concentrations using sources with a « unit released rate », the (sensitivity factors) scaled by the real release rate:
Where the amn are the sensitivity factors and the Sn , the source scaling factors Here we assume a constant release rate…
Total sensitivity
Along Vancouver Island March 20 18-19 UTC
Estimating a « constant » release rate
Averarge Sens. factor
Average Obs Concentratio
n
Release rate Bq / 6 hours
Aircraft 1.44 X 10-16 46.7 3.2 X 1017
Sidney 9.05 X 10-17 58.0 6.4 X 1017
PNNL 1.59 X 10-16 21.6 1.4 X 1017
Average release rate: 3.6 X 1017 /6 hours => 17 000 GBq s-1
Conclusions • Dispersion modelling indicates that there are indeed
small scale / sharp features in the plume even after several days travel times
• The accurate timing of the plume arrival is a good
indication of the high quality of CMC wind analyses over the Pacific
• « Horizontal » diffusion does not play a major role in
the horizontal spread of the plume