Original subtitles

[Music]

the arac

which stands for atmospheric release

advisory capability

supports the department of energy and

the department of defense

by providing real-time assessments of

the consequences that may result

from an atmospheric release of

radioactive material

iraq is an integration of professional

staff numerical models

and computer systems

the arach contributed to the assessments

of the global effects of the chernobyl

reactor accident

by using a three-dimensional hemispheric

scale transport and diffusion model

in conjunction with wind fields from the

air force global weather central

which were obtained at 12 hour intervals

computations were made of the evolution

of the radioactive cloud over 11 days

and an estimate of the adult inhalation

dose patterns due to cloud passage over

europe and the northern hemisphere was

made

in case of a release at a nuclear site

accident information is transmitted

to the assessors in the arac central

facility for evaluation and processing

concurrently meteorological data are

collected

and topographical and geographical

databases are accessed

model input parameters will be prepared

by the assessors

and the arac computer models are run

model output is once more screened by

the assessors before distribution to the

accident site

and local state and federal agencies

this is a view of the arac central

operations room

on the right-hand side the assessors are

engaged in evaluating both incoming

and outgoing data for the event in

progress

while on the left-hand side computer

operators are busy with the acquisition

of data

and processing of input and output files

as well as running the a-rack assessment

models

in what follows the temporal and spatial

evolution of the simulated chernobyl

reactor accident cloud

will be depicted in terms of the motion

of the marker particles

from the particle in cell arac

assessment model

these marker particles represent the

radioactive cloud

and are used to compute the surface air

concentrations

and subsequently the adult inhalation

dose patterns over europe

and the northern hemisphere

for orientation this map of europe is

displayed

and some key countries from which data

were collected are highlighted

sweden which gave the first report of

the chernobyl radioactive cloud

finland poland west germany

italy france and great britain

the display is now a polar projection of

the entire northern hemisphere

with the north pole at the center the

legend on the right explains the color

code for the heights of the particles as

they simulate the release of

radioactivity

the white particles will represent the

elevated release of the initial

explosion

while the yellow particles represent the

release due to the extended fire period

of the accident

also greenwich date and time is

displayed

as the simulated cloud pattern evolves

as the particles are released they are

transported by 12

hourly wind fields for 14 levels to 10

kilometers in altitude

in addition the particles are diffused

both in the vertical

and in the horizontal directions by the

eddy diffusion parameters of the model

the computations indicate that the cloud

became segmented during the first day

with the lower section heading towards

scandinavia and the upper part heading

in a southeasterly direction

during the second day april 27th the

radioactive cloud became

caught up in a low pressure system

causing further deformation of the cloud

with the lower part continuing to travel

in a northwesterly direction towards

scandinavia

passing over the northeastern part of

poland

by april 29th the counterclockwise

rotation of the low pressure system

had spun off three major arms from the

radioactive cloud

one continued its expansion into

scandinavia

and moving at the same time

southwesterly towards eastern and

central europe

another moving towards the arabian

peninsula and a third towards siberia

these segments of the cloud continued to

expand in those three directions

until by may 1st the surface activity

had spread into central

western and southern europe as far as

france and italy

while activity was reported in kuwait

from the second segment

and the third segment was on its way

across china towards japan

where upper air measurements agreed well

with the modeled arrival time on the 2nd

of may

by the third of may the cloud had

reached great britain on the one extent

while the other part was being dispersed

all over asian russia and china

and was passing over japan and route to

the aleutians

the fifth of may saw the cloud dispersed

over most of the northern hemisphere

the activity was receding southeasterly

from western europe

while arriving on the jet stream over

the northwestern united states

continued dispersion on the following

days resulted in almost complete

coverage of the northern hemisphere

by some activity from the chernobyl

release cloud with a stream of particles

even advancing northwesterly

toward greenland topography and

deposition by precipitation are not

included in this model simulation

following will be the contour lines for

the 50-year unmitigated committed dose

due to the effects of inhalation of the

passing radioactive cloud

in micro grey one micro gray being the

equivalent of one tenth of a millirad

this dose does not include contributions

from other pathways

and is mostly due to the radionuclides

iodine 131

and cesium 137

the dose distribution shows a region

exceeding 100 micrograys

extending over the western ussr

northeastern poland

and up into sweden while extending

southward over the ukraine

and parts of eastern europe because of

spatial averaging

inherent in gridded models radiation

doses closer to the chernobyl area are

greatly underestimated

most of central europe parts of northern

scandinavia

and the remainder of eastern europe

received from 10 to 100 micrograys the

remainder of europe

received less than ten micrograys the

dose within japan

is about one tenth of a microgray and

that for the u s

around one thousandth of a micro gray

which is negligible compared to

background

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