EXERCISE

JOINT STATEMENT

by RSMC MONTREAL (CA) and RSMC WASHINGTON (US)

on environmental emergency response for an incident at the

Grand Gulf nuclear facility at 1200 UTC 14 February 2008

Issued: 1630 UTC 10 February 2008

________________________________________________________________________

RADIOLOGICAL EVENT DETAILS

Source:

Grand Gulf, MS, USA

Location:

30.01 degrees North latitude , 91.07degrees West longitude

Release date‑time:

From: 1200 UTC 14 February 2008

To: unknown

Comments:

Exercise

METEOROLOGICAL DISCUSSION

Surface weather:

High pressure area was found over the southeastern USA while a complex low pressure area covered much of the southwestern USA with the deepest center over western Kansas. During Friday, the high will move off the east coast while the low consolidates over Arizona. Meanwhile a new high will slide southeastward from the Canadian Prairie region into the Central Plains Region then eastward. A weak frontal trough will move into the Lower Miss. Valley (LMV) between the highs and bring increased cloudiness and perhaps a little bit of rain. The low will strengthen as it moves eastward into the LMV by Sunday with considerable rain and embedded thunderstorms over the weekend. Winds over the LMV will be light SE into tonight, then NE 5 to 10 knots Friday into Saturday before shifting to S and increasing to 10 to 20 knots with few higher gusts by Sunday.

Weather near 500 hPa:

An upper-level ridge over the southeastern USA will prevail but weaken through Friday and into Saturday. An upper-level trough over the southwestern USA will move into the LMV by Sunday. Winds near 500 hPa will be west to southwest at 25 to 40 knots into Saturday then become more southerly and increase to near 70 knots during Sunday. Meanwhile, a large upper-level trough will cover the Great lakes and Northeast Regions.

Dispersion and transport:

Light clockwise circulation around the departing high should cause particulates originating from Grand Gulf to drift northward up the Miss. Valley then northeastward up the Ohio River Valley into Friday. A stable atmosphere should hinder vertical transport of particulates. Eventually, they should get caught by the circulation around the base of the upper-level trough over the northeast

USA.METEOROLOGICAL FORECAST MODEL DETAILS

US: GFS (Global Forecast System, 100 km grid spacing)

0600 UTC cycle, 3‑h forecast intervals

CA: GEM (Global Environmental Multiscale Model, 33 km grid spacing)

0000 UTC cycle, 3‑h forecast intervals

DISPERSION MODEL PARAMETERS

US: HYSPLIT (includes dry and wet deposition)

1.0 Bq Cs‑137 over 6 hours, uniform between surface‑500 m agl

CA: CANERM (includes dry and wet deposition)

1.0 Bq Cs‑137 over 6 hours, uniform between surface‑500 m agl

TRAJECTORY AND DISPERSION RESULTS

Both models show similar trajectories for the first 36 hours, then the CA 500 and 1500 trajectories move farther to the northeast. The 3000m trajectories are fairly similar with US trajectory being somewhat faster and arriver closer to the southern tip of Greenland by 72 hours.

The exposure patterns overall are quite similar, however the CA exposures are about 1 order of magnitude less than the US up to 48 hours; at 72 hours exposures are roughly the same intensity however the US surface plume extends further to the North towards Greenland. These differences are possibly due to stronger vertical mixing in the CA model and more transport in the upper layers of the atmosphere. That hypothesis is supported by the great similarity in the deposition patterns, both in shape and intensity. In the CA modeling, there is deposition occurring from a plume aloft while no surface plume is present.

Both models show general similarities in terms of spatial patterns. However, at a particular location any model dispersion/deposition differences can be attributed to differences in the flow driving meteorological models and differences in the formulation of the dispersion models. Until updated meteorological data and sufficient radiological monitoring information become available, it is suggested that the higher comparative values of the time-integrated concentrations and total depositions presented above be considered.

Note: Trajectories represent material released from discrete levels. The limited number of trajectories displayed may be used to evaluate the general material flow beginning at each level, but should not be used to determine pollutant time-integrated concentration patterns or total deposition patterns, since these levels may not be representative of all interacting levels where pollutants are being transported, diffused, and deposited. The concentration/deposition model results and comparisons are a more appropriate guide for decision making.

END

EXERCISE