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Release

RADIOLOGICAL EQUIVALENCE: EXAMPLE

 

Now let's look at an example of how we calculate radiological equivalence to rate a release.

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Suppose there was an atmospheric release of 30 TBq of 137Cs.
137Cs

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We need to look up the radiological equivalence factor.

These are contained in Table 2 on page 16 of the Manual and also on the wizard.

The table shows a range of isotopes with a multiplication factor. You will see that 137Cs has a multiplication factor of 40.

This means it is 40 times more radiologically significant than 131I.

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To rate this event we need to multiply the release of 30 TBq by a factor of 40.

30 x 40 = 1 200 TBq of 131I

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We now need to determine the level

Level 5

radiologically equivalent to the order of hundreds to thousands of TBq of 131I

Level 6

radiologically equivalent to the order of thousands to tens of thousands of TBq of 131I

The release seems to fit in both categories, so we now refer to the footnote on page 17...

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It suggests that the boundary between the two levels should be about 5 000 TBq.

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The release here of 1 200 TBq is clearly well below that value.

Click here to see the equivalent value of the release in the context of the definitions of each level.

So the rating is Level 5

 

radiologically equivalent to the order of more than tens of thousands of TBq of 131I

( > 50 000 TBq 131I)

 

radiologically equivalent to the order of thousands to tens of thousands of TBq of 131I

( > 5 000 TBq 131I)

 

radiologically equivalent to the order of hundreds to thousands of TBq of 131I

( > 500 TBq 131I)

 

radiologically equivalent to the order of tens to hundreds of TBq of 131I

( > 50 TBq 131I)

Isotope

Multiplication Factor

a Lung absorption types: S - slow; M - medium; F - fast. If unsure, use the most conservative value

Am-241

8 000

Co-60

50

Cs-134

17

Cs-137

40

H-3

0.02

I-131

1

Ir-192

2

Mn-54

4

Mo-99

0.08

P-32

0.2

Pu-239

10 000

Ru-106

6

Sr-90

20

Te-132

0.3

U-235(S)a

1 000

U-235(M)a

600

U-235(F)a

500

U-238(S)a

900

U-238(M)a

600

U-238(F)a

400

U nat

1 000

Noble gases

Negligible (effectively 0)

 

These criteria relate to accidents where early estimates of the size of release can only be approximated. For this reason, it is inappropriate to use precise numerical values in the definitions of the levels. However, in order to help ensure consistent interpretation of these criteria internationally, it is suggested that the boundaries between the levels are about 500, 5 000 and 50 000 TBq 131I.