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Essay Question - Very High Radiation Area

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Rain Man:

--- Quote ---different plants seem to have different ways of deciding what is VHRA.

--- End quote ---
Plants can establish any level for a VHRA as long as it at least is equal to or more restrictive than the 10CFR20 or 10CFR835 definition:  >500 Rads (5 Grays) in 1 hour @ 1 meter from the source.  Facilities are only obligated to at a minimum meet the federal limits.  For numerous reasons (many legal) they have opted to be more conservative.  Hence, different facilities-different definitions.

SloGlo:
i hate it when this stuff gets started on my friday!  let's go with a layman's approach.  roetgens are in air.  rems are based on a conversion factor, rems/roetgen, based on photon energy in mev.  so you go from r to rem.
rad is a measure of energy deposited in matter, a little more technically known as the quotient of the deposited energy by the mass.  but a rad is not necessarily a rad, as some radiations cause more damage than others, neutrons vs xrays for example, due to the linear energy transfer.  the rbe referenced earlier is used to describe this.  thus begat the "q", quality factor which is used to determine the biological injury according to the present conditions.  q is a function of the let and is based on the kev/um.  this begat the hsubt....yadda, yadda, yadda.  why do the regs go to rads at vhra?  because they want the personnel involved to be aware of the damage that may be involved!

'n i won't know yer beating me up until i get back frum my weekend adventures!   ;)

bsdnuke:
Dose rates are in rad per hour for the VHRA because it is outside of the ranges normally considered in radiation protection that use quality factor for the types of radiation and give us rem (rad times QF = rem). So here the 500 rad is just energy absorbed per gram without the quality factor.

sammoyers:
Everyone has been dancing around the answer as it was explained to me back in '92.
  If my failing memory serves... the VHRA regulatory posting was not originally considered a posting for the "Commercial Power" nukes, but for the research end of the Nuclear industry. Excelerators(sp?) are concerned more with absorbed dose in matter, rather than the biological effects, ergo RAD/hr instead of REM/hr.

Or so it was splained to me when I was but a wee lad, back in the old country....

Phideaux:
It appears that Slo Glo is pretty close.

It has something to do with the fact that the NRC did not feel it necessary to have to bother with Quality Factors at such high dose rates because, at these dose rates, the biological effects are non-stochastic (the dose can cause serious effects in a short time and the severity of the effects are directly dependent on the dose). I don't know how they arrived at the 500 Rad number, but I guess they HAD to have a number.

At lower (than 500 Rad) doses, the biological effects are supposedly more stochastic (there is a varying chance of a biological effect). The RBEs were used as the basis for the development of QFs because, as we know, different types of radiation, measured in Rads, cause different amounts of biological effect, measured in Rems.

That's the short answer. You'll have to talk to somebody smarter than me for a longer explanation.

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