Transcript ICRP Guidelines: `the effective dose equivalent from all sources

Sources of Radiation in the Environment
Ground Zero (New Mexico)
Working Framework
ICRP Guidelines:
‘the effective dose equivalent from all
sources, excluding background radiation
and medical procedures, to
representative members of a critical
group, should not exceed 1 mSv in any
one year; effective dose equivalents of up
to 5 mSv are permissible in some years
provided that the total does not exceed 70
mSv over a lifetime’.
ICRP Website:
http://www.icrp.org/
Natural Sources:
(a) Cosmic radiation
(high energy protons and  particles from the sun and other stars)
• Direct interaction - dose received depends on altitude and latitude
• Interaction with stable molecules
e.g. 14N + 1n
15N
14C
+ 1p
14C
14N
+
1n
12C
production of radionuclides
14CO
+
2
global geochemical cycle
3H
3H
2O
global hydro-geological cycle
National Radiological Protection Board (NRPB) estimate effective dose from
cosmic radiation at about 300 Sv.y-1
Natural Sources:
(b) Terrestrial  radiation
Earth originated from stellar material
crust contains radioisotopes
40K
3 mg.kg-1
232Th
10-15 mg.kg-1
234U
+ 235U + 238U
3-4 mg.kg-1
NRBP estimates annual effective  dose equivalents from these sources
and their daughters to be around 400 Sv.y-1 . Local variations due to
locations and building materials.
(c) Radon and its Daughters
220Rn
and 222Rn arise from natural decay of 238U and 232Th
Gaseous radioisotopes percolate through soil and are trapped in
modern buildings
adsorption on dust particles
lung tissue
potential for short-range  and  irradiation
NRPB estimates around 800 Sv.y-1 from this source
Natural Sources:
(d) Radioactivity in Food and Water
mainly 226Ra (and daughters 222Rn and 218Po) and 40K.
NRPB estimate total effective dose to individuals at  200 Sv.y-1
Examples:
fish - Ra absorbed in partial replacement of Ca (Pacific salmon)
plants - both 210Po and 210Pb enter food from soil and by wet and dry
deposition from the atmosphere
[tobacco leaves can absorb Ra decay products
cigarettes
 activity 6-7 mSv.y-1 from this source]
uptake of 40K
 activity in plants and animals (0.2% body tissue)
(NRPB 170 Sv.y-1 from this source)
Medical Applications
• X-rays
20 Sv per chest X-ray
•
bone and brain scans
99mTc
Need to balance potential benefits from potential hazards
e.g. anti-cancer treatments can involve high dose rates of X and 
radiation in addition to internally administered radio-nuclides, e.g. 131I
Nuclear testing
• since 1945 but predominantly 1954-8 and 1961-2
• >1000 documented tests
Atmospheric and (latterly) underground testing. Moratorium but testing
still continues
Atmospheric testing:
tests in Australia, Pacific, etc
high atmospheric dispersal of subsequent fallout globally
Hiroshima bomb: 14 ktonne
8 x 1024 Bq of activity
including: 106Ru, 137Cs, 140Ba, 144Ce, 85Kr, 89Sr, 90Sr, 99Tc, and
biologically significant 89,90Sr, 131I, 137Cs
3H + fission products
Thermonuclear devices (hydrogen bombs)
Activity from tests > 1020Bq:
2x10-5 Gy (northern hemisphere)
2x10-6 Gy (southern hemisphere)
Activation of surrounding materials
other nuclides, e.g. 14C
Natural background
1 x 1015 Bq.y-1
From testing
5 x 1015 Bq.y-1
Transuranics
Most significant:
239Pu
238U
239U
+ 1n
(t½ = 24,360y)
239Np
239Pu
+ 
+
Estimated 239Pu activity of 1.5x1016Bq: NRPB estimate average effective
dose today in the UK from weapons testing to be around 10 Sv.y-1. This
was around 8 times higher in the 1960’s.
Nuclear Reactor Operations
Production of Fuel
• mining (exposure to miners and contamination of water courses)
• purification, enrichment and fabrication of fuel elements
Reactor processes
• PWR with 100 tonnes of 3.5% enriched 235U fuel contains
0.25 TBq of 235Uand 1.1 TBq of 238U
• unless an accident occurs, no fuel release expected
• gaseous products, 85Kr (t½ 10.8y) leakage to atmosphere
• activation products, 3H
• fuel storage (cooling)
water contamination (<350 Sv.y-1)
NRPB estimates equivalent doses of 100 Sv.y-1 to populations
close to reactors
Fuel Reprocessing
Separation of neutron absorbing fission products from unburnt fuel
highly radioactive wastes