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IMPACT ON RADIOLOGICAL BARRIERS AND CONTROLS AT FACILITIES
Radiological barriers and controls

WHAT THE CRITERIA LOOK LIKE

 

Now we move on to

Criteria related to general contamination.

These are equally applicable to reactor facilities and other large facilities.
They are defined at Levels 2 and 3.

 

To rate an event at Level 3 based on this criterion requires
dose rates > 1 Sv per hour in an operating area
or
release of a few thousand TBq of activity into an area not expected by design regardless of probability of overexposure

operating area = areas where worker access is permitted without specific permits. It excludes areas where specific controls are required (beyond the general need for a personal dosimeter and/or coveralls) due to the level of contamination or radiation.

of activity = total activity without any radiological equivalence calculations.

area not expected by design = design basis did not assume it would receive and retain contamination.

The full definitions are given in footnotes 13 and 14 on page 33 of the Manual. Have a look at them now.

 

To rate an event at Level 2 based on this criterion requires
dose rates > 50 mSv per hour in an operating area
or
significant quantities of radioactive material in areas not expected by design, radiologically equivalent to
liquids > 10 TBq 99Mo
solids > 1 TBq 137Cs
airborne > few tens GBq 131I

We will look more at radiological equivalence in a moment. Note that there are three separate forms of the definition: one for liquids, one for solids and one for airborne contamination. In each case, the definitions are in terms of a typical isotope for that physical form. The full definition is on page 34 of the Manual.

13 Areas not expected by design are those whose design basis, for either permanent or temporary structures, does not assume that during operation or following an incident the area could receive and retain the level of contamination that has occurred and prevent the spread of contamination beyond the area. Examples of events involving contamination of areas not expected by design, are:
- Contamination by radioactive material outside controlled or supervized areas, where normally no such material is present, for example floors, staircases, auxiliary buildings and storage areas.
- Contamination by plutonium or highly radioactive fission products of an area designed and equipped only for the handling of uranium.

14 Operating areas are areas where worker access is allowed without specific permits. It excludes areas where specific controls are required (beyond the general need for a personal dosimeter and/or coveralls) due to the level of contamination or radiation

In this context, ‘significant quantity’ should be interpreted as:

  1. A spillage of liquid radioactive material radiologically equivalent to a spillage of the order of ten terabecquerels of 99Mo.
  2. A spillage of solid radioactive material radiologically equivalent to a spillage of the order of a terabecquerel of 137Cs, if in addition the surface and airborne contamination levels exceed ten times those permitted for operating areas.
  3. A release of airborne radioactive material contained within a building and radiologically equivalent to a release of the order of a few tens of gigabecquerels of 131I.