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IMPACT ON RADIOLOGICAL BARRIERS AND CONTROLS AT FACILITIES
Radiological barriers and controls

RADIOLOGICAL EQUIVALENCE

 

The calculation of radiological equivalence is similar to that used in the criteria for people and the environment.

The table below is almost identical to one you would have seen in the people and the environment module. Can you spot the differences?

Firstly, there are three options for which factor you use, depending on the physical form of the isotope.
Secondly, the factors are different! That’s an important point. Make sure you always use the right table when doing these calculations: Table 2 for people and the environment (radiological equivalence to 131I for releases to the atmosphere), Table 4 for contamination spread (radiological equivalence for facility contamination).

Table 4: RADIOLOGICAL EQUIVALENCE FOR FACILITY CONTAMINATION
Isotope Airborne based on I-131 Solid based on Cs-137 Liquid based on Mo-99
Am-241 2,000 4,000 50,000
Co-60 2 3 30
Cs-134 0.9 1 20
Cs-137 0.6 1 12
H-3 0.002 0.003 0.03
I-131 1 2 20
Ir-192 0.4 0.7 9
Mn-54 0.1 0.2 2
Mo-99 0.05 0.08 1
P-32 0.3 0.4 5
Pu-239 3,000 5,000 57,000
Ru-106 3 5 60
Sr-90 7 11 140
Te-132 0.3 0.4 5
U-235(S)a 600 900 11,000
U-235(M)a 200 300 3,000
U-235(F)a 50 90 1,000
U-238(S)a 500 900 10,000
U-238(M)a 100 200 3,000
U-238(F)a 50 100 1,000
Unat 600 900 11,000
Noble gases Negligible (effectively 0) Negligible (effectively 0) Negligible (effectively 0)

a - Lung absorption types: S - slow, M - medium, F - fast. If unsure, use most conservative value.

The factors are different from that of people and the environment because the scenario of exposure is different. As these events relate to contamination within a facility, it is not appropriate to include long term doses from ground contamination. This is the main difference between the radiological equivalence here and that used in the criteria for people and the environment.

The basis of the radiological equivalence factors is explained in appendix 1 of the Manual.

Appendix 1

CALCULATION OF RADIOLOGICAL EQUIVALENCE

1.1. INTRODUCTION
This appendix shows calculations for multiplying factors that can be applied to the activity released of a specified radionuclide to give an activity that may be compared with those given for 131I. In this analysis, values of inhalation coefficients have been taken from the Basic Safety Standards (BSS), while the dose factors for ground deposition have been taken from IAEA-TECDOC-1162. Both publications are in the process of being updated, but such updates are unlikely to have a large impact on the one significant figure radiological equivalence numbers given in Table 14.
While other parts of this manual makes use of D values to compare the relative significance of different isotopes, this appendix uses another approach. This is because the D value calculations are specifically based on scenarios that are only appropriate for the handling and transport of radioactive sources. The radiological equivalence factors calculated here use assumptions based on scenarios more appropriate to accidents at facilities.

1.2. METHOD
The scenarios and methodology are summarized below. For airborne releases of activity, the following two components were added:
- Effective dose to adult members of the public, Dinh, from inhalation of unit airborne concentration, with a breathing rate of 3.3 × 10-4 m3 ·s -1; and
- Effective dose to adults from ground deposition of radionuclides, integrated over 50 years, including consideration of resuspension, weathering and ground roughness. Ground deposition is related to airborne concentration using deposition velocities (Vg ) of 10-2 m·s -1 for elemental iodine and 1.5 × 10-3 m·s -1 for other materials. The integrated dose over 50 years, from unit ground deposition of each radionuclide is used (Dgnd (Sv per Bq·m-2)).
Ingestion doses are not included in this calculation as the food intervention levels will prevent any significant doses to individuals affected by the accident.
The total dose (Dtot) resulting from an activity release Q and time-integrated, ground-level airborne radionuclide concentration of X (Bq·s·m-3 per Bq released) is:

Dtot = Q.X. (Dinh·breathing rate + Vg ·Dgnd)

For each radionuclide, the relative radiological equivalence to 131I was calculated as the ratios of Dtot/(Q.X).

Facility contamination considers only the inhalation pathway, and the inhalation coefficients are for workers.

1.3. BASIC DATA
The inhalation coefficients for the calculations were taken from the BSS, apart from Unat, which is not listed in that document. Values for Unat were calculated by summing the contributions from 238U, 235U, 234U and their main decay products, using the ratios 234U (48.9%), 235U (2.2%) and 238U (48.9%). Where a radionuclide has a number of lung absorption rates, the maximum value of the inhalation coefficient was used except for uranium where all of them are provided. The 50 year integrated doses from ground deposition were taken from IAEA-TECDOC-1162

1.4. RESULTS
The multiplying factors applicable to both facility contamination and atmospheric releases are obtained by dividing the value for each radionuclide by that for 131I. These are given in Table 14 and 15. Table 16. lists the results as they should be used in INES (i.e. rounded to one significant figure).

As Appendix 1 also includes Table 14, Table 15, and Table 16; please refer to the Manual for these.

Isotope

Multiplication factor

a Lung absorption types: S - slow; M - medium; F - fast. If unsure, use the most conservative value

Am-241

8,000

Co-60

50

Cs-134

17

Cs-137

40

H-3

0.02

I-131

1

Ir-192

2

Mn-54

4

Mo-99

0.08

P-32

0.2

Pu-239

10,000

Ru-106

6

Sr-90

20

Te-132

0.3

U-235(S)a

1,000

U-235(M)a

600

U-235(F)a

500

U-238(S)a

900

U-238(M)a

600

U-238(F)a

400

U nat

1000

Noble gases

Negligible (effectively 0)