Nuclear Accident Magnitude Scale

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The Nuclear Accident Magnitude Scale according to David Smythe is a measure of the severity of a nuclear accident . It seeks to correct the shortcomings of the International Nuclear Event Scale (INES) by, unlike INES:

  • is continuous and open to the top
  • is linked to an objective variable
  • Separates magnitude from intensity (see the two earthquake scales - one evaluates the physical strength of the earthquake, the other considers the effect of the earthquake, which depends on geological and structural factors, among other things)
  • is better geared towards the consequences of the accident (compare, for example, the almost inconsequential meltdown in the Lucens research reactor in 1969 without the release of radioactive material and the fire in Windscale in 1957, both of which are rated INES level 5)

definition

The NAMS is based on the amount of radioactivity that is released into the atmosphere and pollutes the environment outside the reactor site.

NAMS = log 10 (20 * R)

where R is the radioactivity released in terabecquerel , converted to the equivalent dose of iodine -131. The factor of 20 ensures that both scales, INES and NAMS, are roughly in the same region. It should be emphasized that an atmospheric release of radioactivity on the INES scale is generally classified as 4, 5, 6 or 7, while the NAMS is open to the bottom in this regard.

Examples

bad luck INES released radioactivity
in TBq		 NAMS
Chernobyl (1986) 7th 5.2 million 8th
Fukushima (2011) 7th 1.592 million 7.5
Windscale (1957) 5 1786 4.6
Kyschtym (1957) 6th 1 million 7.3

There are clear differences between the two scales. An accident of severity 7 according to INES has so far happened every approx. 30 years - but one of grade 7 according to NAMS every around 12 to 15 years.

Literature and Sources