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IMPACT ON PEOPLE AND THE ENVIRONMENT
Dose

TO SUMMARIZE THE DOSE MODULE

 

We have now finished the criteria related to exposure, but before we move on, a few comments about how the dose levels should be assessed.
Generally they refer to doses that have been received, but the definitions actually add

or could easily have been received

- have a look at page 18, last paragraph and footnote 4.

Take note that the purpose is not to invent scenarios different than the one that occurred but to consider what doses might reasonably have occurred unknowingly. For example if a source would be found later to be out of its shielding during transport, dose to the driver should be estimated.

The other comment to make is that all these criteria—i.e. not cumulative doses. If an individual is exposed in excess of statutory annual dose limits, that is to be rated under defence in depth. Actually, if you look at the last row of Table 3 on page 22, you will see that very point explained.

If you do need to estimate doses, the calculation should

be based on a realistic scenario,
follow national assumptions for dose assessment and
take account of any protective actions taken.

Generally, the estimates of dose should be undertaken by experts in radiation safety. If you need to calculate the dose from
a source, there are also some on-line tools available such as http://www.radprocalculator.com/Gamma.aspx

The intention here is not to invent scenarios different than the one that occurred but to consider what doses might reasonably have occurred unknowingly. For example if a radioactive source has become separated from its shielding and is transported, doses to drivers and package handlers should be estimated.

TABLE 3. SUMMARY OF RATING BASED ON DOSES TO INDIVIDUALS

Level of exposure

Min rating

Number of individuals

Actual rating

The occurrence of a lethal deterministic effect or the likely occurrence of a lethal deterministic effect as a result of a whole body absorbed dose of the order of a few Gy

Few tens or more ††
Between several and a few tens
Less than several

The occurrence or likely occurrence of a non-lethal deterministic effect

Few tens or more
Between several and a few tens
Less than several

Exposure leading to an effective dose greater than ten times the statutory annual whole body dose limit for workers

100 or more
10 or more
Less than 10

Exposure of a member of the public leading to an effective dose in excess of 10 mSv or exposure of a worker in excess of statutory annual dose limits

100 or more
10 or more
Less than 10

Exposure of a member of the public in excess of statutory annual limits or exposure of a worker in excess of dose constraints

100 or more
10 or more
Less than 10 †††

Cumulative exposure of workers or members of the public in excess of statutory annual dose limits

1 or more †††

Level 6 is not considered credible for any event involving radiation sources.

As explained in Section 2.4, the Level 1 definitions are based on defence-in-depth criteria explained in Sections 4-6, but they are included here for completeness.