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Re: Re[4]: Patient Release - A Related Question
At 11:24 AM 11/2/99 -0600, Steven D. Rima wrote :
> So, let's see, using the NRC's numbers, if I live near a nuclear power
> plant for its nominal 30 year life, I can legally receive up to 100
> mrem/y x 30 y = 3000 mrem.
No. The optimization of any practice require restrictive protection to
workers and to public by the introduction of the so called dose constraints:
Considering the ICRP 60 and IAEA BSS Safety Series 115, dose constraint means:
A prospective and source related restriction on the individual dose
delivered by the source which serves as a bound in the optimization of
protection and safety of the source. For occupational exposures, dose
constraint is a source related value of individual dose used to limit the
range of options considered in the process of optimization. For public
exposure, the dose constraint is an upper bound on the annual doses that
members of the public should receive from the planned operation of any
controlled source. The exposure to which the dose constraint applies is the
annual dose to any critical group, summed over all exposure pathways,
arising from the predicted operation of the controlled source. The dose
constraint for each source is intended to ensure that the sum of doses to
the critical group from all controlled sources remains within the dose
limit. For medical exposure the dose constraint levels should be interpreted
as guidance levels, except when used in optimizing the protection of persons
exposed for medical research purposes or of persons, other than workers, who
assist in the care, support or comfort of exposed patients.
By Critical group one should consider: A group of members of the public
which is reasonably homogeneous with respect to its exposure for a given
radiation source and given exposure pathway and is typical of individuals
receiving the highest effective dose or equivalent dose (as applicable) by
the given exposure pathway from the given source.
Taking into account the above conception, you can consider an individual,
member of the public, submited to two different sources.
One source, for example, can be from a Power Reactor as you mentioned and
another can be from Nuclear Medical Institution, where the individual is
an employ. So, to avoid the dose limit (1 mSv), the applicability of the
ICRP and IAEA dose constraint, to the area of public exposure, should take
these cases into consideration, as well as other, if the case. Depending
of the practice the relationship between the dose constraint and the dose
limit is is important to be fixed, for calculating 'generalized derived
limits,' as the above example, to ensure that dose or risk limits are not
exceeded. For this reason dose constraint is not a dose limit, and varies
according with practice, geographical situation, o other parameter.
National Authorities, taking into account ICRP recommend the development of
constraints to dose or risk as a powerful mechanism to improve the
optimisation of protection, fixing levels, to be applied to the dose limit.
To give an example, in Brazil, in order to consider the contribution to the
dose received by the critical group due to practices carried out at regional
and global levels, and to count on a proper margin for future practices, the
Regulatory Authority has established dose constraints for a particular
installation. For the case of Power Reactor and Repository, the effective
dose to the critical group shall not exceed 0.3 mSv in a year.
In case of effluent, the authorised discharges into the environment also
the value of 0.3 mSv is applied when it is demonstrated that the effluent
discharge system has been optimised. Otherwise, a more restrictive value is
used that shall not exceed 0.1 mSv per installation.
I recommend to RADSAFERS interested the following NRC site, to provide a
understanding and interesting discussion on this subject. Please GO TO
http://www.nrc.gov/NRC/COMMISSION/TRANSCRIPTS/19950112b.html
** BRIEFING BY ICRP/NCRP ON THE PRINCIPLES OF RADIOLOGICAL PROTECTION AND
THEIR APPLICATION IN SETTING LIMITS AND CONSTRAINTS FOR THE PUBLIC FROM
RADIATION.
J. J. Rozental
josrozen@netmedia.net.il
jjrozental
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