TNAG-1776-FCO40-2530-Daya-Bay-nuclear-power-station-project-safety-concerns-in-Ho-1988 — Page 188

10

EMERGENCY REFERENCE LEVELS

10.1 Emergency Reference Levels

In the event of a major accidental release of radioactive material into the environment, consideration needs to be given to limiting any resultant exposure to the public by the introduction of the countermeasures discussed in Chapter 9. The introduction of any countermeasures interferes, to some extent, with normal living conditions, and therefore there is a social cost and in some cases risk associated with the introduction of countermeasures. The introduction of any countermeasures must achieve a net positive benefit and therefore countermeasures should not be introduced to try to avoid trivial doses which may be associated with very minor releases of radioactivity into the environment, (see Section 5.6). This principle is found in most contingency planning.

When making contingency plans for incidents involving radioactivity, different countermeasures will have different costs and risks. Countermeasures which may be beneficial when the potential doses to the public are relatively large will almost certainly be inappropriate when the potential doses to the public are relatively small.

Another feature of countermeasures for restricting doses to the public is that the costs and risks of their introduction will, to some extent, depend upon local conditions at the time of their introduction and this may have an influence upon the decisions as to when to introduce countermeasures. It follows therefore that there is not a single level of predicted dose which will trigger the introduction of a countermeasure but there will be a range of values of predicted dose over which the introduction of a given countermeasure will be considered. The level of predicted dose at which a particular countermeasure should be introduced is known as the 'Emergency Reference Level' (ERL). The predicted dose at which consideration starts to be given to the introduction of a particular countermeasure is called the lower ERL and the predicted dose at which the countermeasure will almost certainly have been introduced is called the upper ERL. Numerical values of upper and lower ERLs have been recommended by a number of organisations. The tables 10.1, 10.2 and 10.3 gives the values recommended by the International Commission on Radiological Protection (ref 15) and these are generally consistent with other international expert opinion.

TABLE 10.1 EMERGENCY

REFERENCE

LEVELS FOR

PLUME

COUNTERMEASURES

Countermeasure

Sheltering and stable iodine

administration

Upper dose level

Lower dose level

Evacuation

Dose Equivalent (mSv)

Lung, thyroid

Whole Body

and any single organ preferentially irradiated

50

S

Upper dose level

500

Lower dose level

50

70

500

50

5 000

500