the uk approach - the initial radiological assessment methodology laura newsome scientist –...
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The UK Approach - the Initial Radiological Assessment MethodologyLaura Newsome
Scientist – Environment Agency
September 2009
Structure
Background to UK situation
The Environment Agency’s responsibilities
Summary of Initial Radiological Assessment Methodology
Answers to questions
Who does what in the UK?
Legislation for UK regulation
Radioactive Substances Act 1993
Euratom Basic Safety Standards Directive 1996
Ionising Radiation Regulations 1999
Radioactive Substances (Basic Safety Standards) (England and Wales) Direction 2000
Principles document 2002
Summary of criteria for public exposure
Public dose limitfuture and historical discharges and future
direct radiation from the site and other sources excluding medical and natural
1.0 mSv/yr
Site constraintfuture discharges from a site with more than
one operator0.5 mSv/yr
Source constraintfuture discharges and future direct radiation
from a facility or group of facilities0.3 mSv/yr
Threshold of optimisation
future discharges and future direct radiation from a facility
0.02 mSv/yr
Potentially of no regulatory concern
future discharges and future direct radiation
from a facility
<0.01 mSv/yr
Who do we regulate?
How do we regulate discharges?
Use of permit system under RSA 93. Part of permit determination involves radiological assessmentInitial Radiological Assessment Methodology is used to complete prospective assessments and set authorisation limits
Spreadsheet based toolEasy to useCautious but consistent assumptions
PC CREAM used for detailed site assessments
Initial Radiological Assessment Methodology
100 radionuclidesCritical Group – members of the public
Seven different groups of the publicFour age groups (offspring, infant, child, adult)
Releases via air, estuary/coastal water, river/stream, public sewer
Example model – release to air
Exposure Group
Exposure Pathways Default model assumptions
Release to air
Local resident family
Inhalation of radionuclides in the effluent plume
Release at ground level
Local resident is located 100m from the release point
Food is produced at a distance of 500m from the release point
External irradiation from radionuclides in the effluent plume and deposited on the ground
Consumption of terrestrial food incorporating radionuclides deposited to the ground
Initial Radiological Assessment Methodology
Dose Per Unit Release (DPUR)
Assessment of continuous uniform releases
Dose assessed in 50th year of release
Ingrowth of progeny included if significant ingrowth likely to occur in 50 year period
Also includes assessment to non-human biota
Initial Radiological Assessment Tool
Critical group <0.02 mSv/yr
Critical group >0.02 & <0.3 mSv/yr
Critical group <0.02 mSv/yr
Critical group >0.02 & <0.3 mSv/yr
Critical group >0.3 mSv/yr
Step by step method
Refine assessment or undertake site
specific assessment
Further refinements or site specific assessment
Initial source assessment - simple & cautious assessment
of critical group dose
Refine assessment more realistic by
using scaling factors and habits data
Permit may be acceptable on RP grounds.
Permit unlikely to be acceptable on RP grounds
Critical group >0.3 mSv/yr
No further assessment required on Radiation Protection grounds.
Permit likely to be acceptable.
Critical group >0.02 & <0.3 mSv/yr
Limitations
Inflexible - fixed locations and critical groups
Conservative approach – overestimation
Not suitable for < 1yr releases
Does not apply to the disposal of radioactive waste to land or discharge to lakes
Dose Per Unit Release factors are not appropriate for the direct external radiation dose pathway
Answers to questions that I haven’t yet covered
Transfer co-efficientsDatabases of PC CREAMStandard compilations such as IAEA TRS & ICRP publicationsOther robust compilationsScaling, analogues, one-off analytical calculations
Atmospheric modellingDPUR for atmosphere derived using PC CREAMGaussian plume modelMost parameters fixed
