Topic 7 - Dose Limits
Example calculations using internal dose conversion
factors |
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Annual Limit on Intake
- Activity of a radionuclide, which if taken in alone, would irradiate
an individual to the limit set by the ICRP for each year of occupational
exposure
- Intake rate: quantity per year
- Pure parent assumption
- Can have an ALI each year
- No time constraint set on exposure period
- (rate can be instantaneous or up to a year)
- Two limits – stochastic and nonstochastic considered.
- Secondary limit
- designed to meet the basic limits for occupational exposure
- derived from the previous two relationships.
- The ALI is the greatest value of the annual intake, I, which
satisfies both of the following inequalities:

- Where
- I (Bq) is the annual intake of the specified radionuclide (by
ingestion or inhalation).
- S = stochastic limit
- N = nonstochastic limit
- HT,50 per unit intake (Sv Bq-1) is the
committed dose equivalent in tissue (T) from the intake of unit
activity of the nuclide by the specified route.
- If Is not exceeded, then stochastic limits met
- If In not exceeded, then nonstochastic limits met
- Select value of I which satisfies both inequalities to determine
limiting value.
Calculating an ALI inhalation- example 239 Pu intake by inhalation
Tissue |
H50,T Sv Bq-1 |
WT |
H50,T Sv * WT |
Lungs |
3.2 * 10-4 |
0.12 |
309 * 10-5 |
Red Marrow |
7.6 * 10-5 |
0.12 |
9.1 * 10-6 |
Bone surfaces |
9.5 * 10-4 |
0.03 |
2.9 * 10-5 |
Liver |
2.1 * 10-4 |
0.06 |
1.2 * 10-4 |
Sum |
8.9 * 10-5 Sv Bq-1 |
ICRP 30
Calculating ALI (stochastic)
Calculating ALI (nonstochastic)
Calculating ALI: 239Pu
- Stochastic limit
- Nonstochastic limit
- Uncertainites in metabolic models result in listed ALI at one significant
figure:
Derived Air Concentrations
- Revised version of ICRP 2 MPCair
- Maximum permissible concentration (air)
- Old MPCs were misused.
- They were maximum permissible concentrations intended
to control exposure over prolonged periods (> 3 mos).
- They have been used to infer over-exposure for even short exposure
times.
- The limit for inhalation of a radionuclide is the appropriate
ALI.
- The concentration of a radionuclide in air during any year is
limited as follows:
- That concentration of a radionuclide in air, which if breathed for
one working year, would result in one ALI by inhalation:
- 2000 hrs per working year
- 1.2 m3 h-1 working breathing rate
- Note: ALI is the main limit and the DAC is a derived limit.
DAC’s, alternate calculation
- Calculated based on annual breathing rate:
- 2400 m3 annual breathing rate
- Again Note: ALI is the main limit and the DAC is a derived
limit.
Use of Dose Conversion Factors
- Tables generated based on ICRP methodologies
- Printed by several agencies
- Units may vary (SI vs standard)
- Methodology may vary
- ICRP 2
- ICRP 26/30
- ICRP 60
- Example to follow
50-Yr committed dose equivalent factors -- rem/ƒΚCi
intake: 239Pu
Class |
Ingestion |
Inhalation |
f1 |
D |
W |
Y |
Lungs |
|
|
|
|
1.2 * 10+3* |
|
|
|
|
|
0/0/100 |
Gonads |
9.6 * 10-1* |
9.6 * 10-3* |
|
1.2 * 10+2* |
|
|
|
|
|
25/33/42 |
|
R Marrow |
5.9 * 100* |
5.9 * 10-2* |
|
7.4 * 10+2* |
2.8 * 10+2* |
|
|
|
|
25/33/42 |
7/2/91 |
Bone Surf |
7.8 * 101* |
7.8 * 10-1* |
|
9.3 * 10+3* |
3.5 * 10+3* |
|
|
|
|
25/33/42 |
7/2/91 |
Liver |
1.6 * 101* |
1.6 * 10-1* |
|
2.0 * 10+3* |
7.8 * 10+2* |
|
|
|
|
25/33/42 |
7/2/91 |
ULI Wall |
|
6.3 * 10-2* |
|
|
|
LLI Wall |
|
2.0 * 10-1* |
|
|
|
C.E.D.E. |
4.3 * 100* |
5.8 * 10-2* |
|
5.1 * 102* |
3.3 * 102* |
* Indicates that <90% of total dose is
received in year of intake
GI Absorption & Lung Retention
Element/Symbol |
Atomic Number |
Compound |
f1 |
Lung Retention Class |
Neptunium (Np) |
93 |
All forms |
1E-3 |
W |
Nickel (Ni) |
28 |
Oxides, hydroxides |
5E-2 |
W |
All others (vapor) |
-- |
D |
Niobium (Nb) |
41 |
Oxides, hydroxides |
1E-2 |
Y |
All others |
1E-2 |
W |
Osmium (Os) |
76 |
Oxides, hydroxides |
1E-2 |
Y |
Halides, nitrates |
1E-2 |
W |
All others |
1E-2 |
D |
Palladium (Pd) |
46 |
Oxides, hydroxides |
5E-3 |
Y |
Nitrates |
5E-3 |
W |
All others |
5E-3 |
D |
Phosphorus (P) |
15 |
Phosphates |
8E-1 |
W or D; dependent upon associated element |
Platinum (Pt) |
78 |
All forms |
1E-2 |
D |
Plutonium (Pu) |
94 |
Oxides, hydroxides |
1E-5 |
Y |
Nitrates |
1E-4 |
W |
All other
(Note: Use same values for ingestion) |
1E-3 |
W |
Class examples to work
- Show how CEDE obtained
- Demonstrate particle size correction
Respiratory Model
Limits for Intakes of Radionuclides by Workers |
|
Class |
D |
W |
Y |
Region |
Compartment |
T day |
F |
T day |
F |
T day |
F |
N-P
(DN-P = 0.30) |
a |
0.01 |
0.5 |
0.01 |
0.1 |
0.01 |
0.01 |
b |
0.01 |
0.5 |
0.40 |
0.9 |
0.40 |
0.99 |
T-B
(DT-B = 0.08) |
c |
0.01 |
0.95 |
0.01 |
0.5 |
0.01 |
0.01 |
d |
0.2 |
0.05 |
0.2 |
0.5 |
0.2 |
0.99 |
P
(DP = 0.25) |
e |
0.5 |
0.8 |
50 |
0.15 |
500 |
0.05 |
f |
n.a. |
n.a. |
1.0 |
0.4 |
1.0 |
0.4 |
g |
n.a. |
n.a. |
50 |
0.4 |
500 |
0.4 |
h |
0.5 |
0.2 |
50 |
0.05 |
500 |
0.15 |
L |
i |
0.5 |
1.0 |
50 |
1.0 |
1000 |
0.9 |
j |
n.a. |
n.a. |
n.a. |
n.a. |
infinity |
0.1 |
Fig. 5.2. Mathematical model used to describe clearance from the respiratory
system. The values for the removal half-times, Ta-1 and compartmental
fractions, Fa-1 are given in the tabular portion of the figure
for each of the three cleasses of retained materials. The values given
for DN-P, DT-B and DP (left column) are
the regional depositions for an aerosol with an AMAD of 1 μm. The
schematic drawing identifies the various clearance pathways from compartments
a-i in the four respiratory regions, N-P, T-B, P and L.
n.a. = not applicable.
Fig. 5.1. Deposition of dust in the respiratory system. The percentage
of activity or mass of an aerosol which is deposited in the N-P, T-B and
P regions is given in relation to the Activity Median Aerodynamic Diameter
(AMAD) of the aerosol distribution. The model is intended for use with
aerosol distributions with AMADs between 0.2 an 10 μm and with geometric
standard deviations of less than 4.5. Provisional estimates of deposition
further extending the size range are given by the dashed lines. For an
unusual distribution with an AMAD of greater than 20 μm, complete
deposition in N-P can be assumed. The model does not apply to aerosols
with of greater than 20 μm, complete deposition in N-P can be assumed.
The model does not apply to aerosols with AMADs of less than 0.1 μm.
Particle Size Correction
Where DN-P, etc are the deposition probabilities in the respiratory region
for a given AMAD (see fig 5.1), and fN-P etc are the fraction of the committed
dose in the reference tissue arising from deposition in the N-P, T-B,
and P regions (see conceptual model).
Tissue Weighting Factors
Tissue |
ICRP26
Wt |
Gonads |
0.25 |
Breast |
0.15 |
Lung |
0.12 |
RBM |
0.12 |
Thyroid |
0.03 |
Bone Surfaces |
0.03 |
Remainder* |
0.3 (0.06/tissue) |
Sum Total |
1 |
*To use in calculating the effective dose equlivalent,
calculate the dose to the remain g organs, and apply the value of
0.06 to the 5 most-dosed of the remainder, then throw out the rest.
You are then calculating the HE to include up to 11 tissues. |
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