250
20 Remediation
areas have different uses and occupancy factors. There are 168 h in a week; consider
a person who spends those hours thusly:
• Work 40 h
• Home 100 h
• Commuting 10 h
• Shopping, errands 8 h
• Exercise 10 h.
Now, consider the questions that even this simple list raises:
• Should roads and train tracks have the same cleanup levels as home?
• Should parks, public squares, and related areas have the same cleanup levels as
the workplace (to protect those who work to maintain them) or as the roads (to
reflect the way the typical person uses them)?
• Should alleys have the same cleanup levels as main streets—and should sidewalks
have the same standards as the roadways?
• Should the nature of the surface in each location be considered since they affect
the amount of contamination that is resuspended and might be inhaled?
Determining what should constitute allowable levels of surface contamination
can become hopelessly complex if every type of surface and the use patterns of
every area is taken into account. It might be easier to try to weight all of these
various factors to develop a single cleanup level to use everywhere, accepting the
fact that a large number of residents are likely to spend their time differently than the
averages assumed for the purpose of calculation. As a result, this approach would
require applying a safety factor to account for, for example, stay-at-home parents,
workaholics, nature enthusiasts, train crews, highway workers, and so forth.
Radiation dose rate from contamination on the ground (or floor) is important, but
equally important (possibly even more important) is determining radiation dose rate
from the intake of radioactivity, which is largely the result of resuspended radioactive contamination. This is especially important when the nuclide(s) used are alphaemitting actinides such as plutonium or americium, or bone-seeking elements such
as strontium or radium. Unfortunately, determining resuspension factors is fiendishly
difficult because it depends on the physical and chemical properties of the contaminant, the physical and chemical properties of every surface (asphalt, concrete, brick,
grass, soil, gravel, marble (both polished and varying levels of unpolished), glass,
etc.), the variability in wind speeds (as well as breezes from traffic passing at various
speeds), the orientation of surfaces (horizontal, vertical, various inclines), chemical
reactions between the contamination and the various materials that comprise all of the
different surfaces, and much more. For this reason, determining resuspension factors
and the resultant intake is a problem that, at present, cannot be solved in any meaningful manner. Accordingly, if internal exposure from resuspended radioactivity is
to be considered in developing decontamination standards, it will be necessary to
make a number of simplifying assumptions; such determinations might be better
performed in advance of the need for this information.
20 Remediation
areas have different uses and occupancy factors. There are 168 h in a week; consider
a person who spends those hours thusly:
• Work 40 h
• Home 100 h
• Commuting 10 h
• Shopping, errands 8 h
• Exercise 10 h.
Now, consider the questions that even this simple list raises:
• Should roads and train tracks have the same cleanup levels as home?
• Should parks, public squares, and related areas have the same cleanup levels as
the workplace (to protect those who work to maintain them) or as the roads (to
reflect the way the typical person uses them)?
• Should alleys have the same cleanup levels as main streets—and should sidewalks
have the same standards as the roadways?
• Should the nature of the surface in each location be considered since they affect
the amount of contamination that is resuspended and might be inhaled?
Determining what should constitute allowable levels of surface contamination
can become hopelessly complex if every type of surface and the use patterns of
every area is taken into account. It might be easier to try to weight all of these
various factors to develop a single cleanup level to use everywhere, accepting the
fact that a large number of residents are likely to spend their time differently than the
averages assumed for the purpose of calculation. As a result, this approach would
require applying a safety factor to account for, for example, stay-at-home parents,
workaholics, nature enthusiasts, train crews, highway workers, and so forth.
Radiation dose rate from contamination on the ground (or floor) is important, but
equally important (possibly even more important) is determining radiation dose rate
from the intake of radioactivity, which is largely the result of resuspended radioactive contamination. This is especially important when the nuclide(s) used are alphaemitting actinides such as plutonium or americium, or bone-seeking elements such
as strontium or radium. Unfortunately, determining resuspension factors is fiendishly
difficult because it depends on the physical and chemical properties of the contaminant, the physical and chemical properties of every surface (asphalt, concrete, brick,
grass, soil, gravel, marble (both polished and varying levels of unpolished), glass,
etc.), the variability in wind speeds (as well as breezes from traffic passing at various
speeds), the orientation of surfaces (horizontal, vertical, various inclines), chemical
reactions between the contamination and the various materials that comprise all of the
different surfaces, and much more. For this reason, determining resuspension factors
and the resultant intake is a problem that, at present, cannot be solved in any meaningful manner. Accordingly, if internal exposure from resuspended radioactivity is
to be considered in developing decontamination standards, it will be necessary to
make a number of simplifying assumptions; such determinations might be better
performed in advance of the need for this information.