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