Radionuclide Decay Radionuclide Decay and Exposure to Gases and and Exposure to Gases and
Gas Decay ProductsGas Decay Products
Radionuclide exposure is a Radionuclide exposure is a function of both released function of both released
amounts and radioactive decay amounts and radioactive decay until the time of exposure. until the time of exposure.
Major Fission Product Gases
Xenon
Iodine
Iodine isotopes with significant yields and half-lives and their xenon gas daughters
Cesium
Barium
Major Long Lived Fission Product Gas
Krypton
Krypton gas isotope with significant yield and half-life
Activity Relationship to Half-Life
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1 2 3 4 5 6 7 8 9 10
Number of Half-Lives
Frac
tion
of O
rigin
al A
ctiv
ity
1/ 2 1/ 2 1/ 20 0 0 0/ 2 / 4 /8t t tN N N N⎯⎯→ ⎯⎯→ ⎯⎯→
Exponential decay results in >99% decay after 7 half-lives and >99.9% decay after 10 half-lives
Ingrowth of daughter (D) Ingrowth of daughter (D) radionuclides from parent (P) radionuclides from parent (P)
when Twhen T½½PP < T< T½½DD and Aand AD0D0 = 0= 0
Gases estimated to have been released after the SRE accident werGases estimated to have been released after the SRE accident were primarily the e primarily the isotopes of nonisotopes of non--reactive noble gases Xenon, Krypton, and Argon identified below.reactive noble gases Xenon, Krypton, and Argon identified below.
The rate of decay of a The rate of decay of a radionuclide is a function of its radionuclide is a function of its
halfhalf--life (Tlife (T½½).).
Potential Activation Product Gas
Potential activation gas from argon in helium purge gas
Source for Table Data : National Nuclear Data Center, Brookhaven National Laboratory, http://www.nndc.bnl.gov/nudat2/
Argon
Potassium
Some radionuclides decay to Some radionuclides decay to other radionuclides but other radionuclides but
eventually the decay chain ends eventually the decay chain ends in a stable (nonin a stable (non--radioactive) radioactive)
isotope. isotope.
Radioactive Production and Decay of SRE Reactor GasesRadioactive Production and Decay of SRE Reactor Gases
Radioactive Decay of SRE Reactor Inventory and Estimated ReleaseRadioactive Decay of SRE Reactor Inventory and Estimated Releasess
I-131/Xe-131m Ingrowth and DecayActivity Units
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 10 20 30 40 50 60 70
Days
Frac
tion
of O
rigin
al A
ctiv
ity
I-131: T1/2 = 8.04 days
Xe-131m: T1/2 = 11.9 days
Combined Activity
Kr-85 DecayT1/2 = 10.7 years
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 10 20 30 40 50 60 70 80 90 100
Years
Frac
tion
of O
rigin
al A
ctiv
ity (l
inea
r sca
le)
Acitivities of Other Significant Fission Products After Shut Down of the SRE Reactor
(Total Reactor Core Inventory )
1.0
10.0
100.0
1000.0
10000.0
100000.0
1000000.0
0 5 10 15 20 25 30 35 40 45 50
Years
Act
ivity
(Cur
ies)
Sr-89
Ba-140
Ce-141
Ru-103
I-131
I-133
I-135
Cs-137
Ce-144
Zr-95
Sr-90
Cs-134
Acitivities of Gases After Shut Down of the SRE Reactor(Estimated Inventory Released to the Environment)
0.10
1.00
10.00
100.00
0 10 20 30 40 50 60 70 80 90 100Days
Act
ivity
(Cur
ies)
Xe-133
Kr-85
Xe-135
Xe-131m
Kr-85 DecayT1/2 = 10.7 years
0.001
0.010
0.100
1.000
0 10 20 30 40 50 60 70 80 90 100
Years
Frac
tion
of O
rigin
al A
ctiv
ity (l
og s
cale
)
Log scale provides a straight line for the exponential decay
WhenWhen the exponential decay is plotted on a log scale the plot is linethe exponential decay is plotted on a log scale the plot is linear. ar.
The plots below show the amounts of noble gases estimated to havThe plots below show the amounts of noble gases estimated to have been e been released after the SRE accident, the total reactor inventory of released after the SRE accident, the total reactor inventory of other fission other fission
products at the time of the accident, and their decay over time.products at the time of the accident, and their decay over time.
I-133/Xe-133 Ingrowth and Decay (Activity)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 5 10 15 20 25 30 35
Days
Frac
tion
of O
rigin
al A
ctiv
ity
I-133: T1/2 = 20.8 hours
Xe-133: T1/2 = 5.24 days
Combined
I-135/Xe-135 Ingrowth and Decay (Activity)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 10 20 30 40 50 60 70
Hours
Frac
tion
of O
rigin
al A
ctiv
ity
I-135: T1/2 = 6.57 hours
Xe-135: T1/2 = 9.1 hours
Combined
Radioactive DecayRadioactive Decay
Due to nuclear instabilityDue to nuclear instabilityMode depends on direction to Mode depends on direction to belt of stability. Possible belt of stability. Possible Modes:Modes:
Alpha decay (Alpha decay (αα))Beta decay (Beta decay (ββ--))Positron Decay (Positron Decay (ββ+)+)Electron capture (EC)Electron capture (EC)Spontaneous FissionSpontaneous Fission
HalfHalf--lives are longer as decay lives are longer as decay moves closer to belt of stabilitymoves closer to belt of stability
Decay Chains Associated with SRE Reactor Fuel Elements Decay Chains Associated with SRE Reactor Fuel Elements (Thorium(Thorium--232 only used in SRE Core II)232 only used in SRE Core II)
Decay mode depends on Decay mode depends on direction to belt of stabilitydirection to belt of stability
Radioactive Decay and Equilibrium of SRE Reactor FuelsRadioactive Decay and Equilibrium of SRE Reactor Fuels
< 10-15
10+00
10-15 10+01
10-07 10+02
10-06 10+03
10-05 10+04
10-04 10+05
10-03 10+07
10-02 10+10
10-01 > 10+15
Seconds
Number of Neutrons
Num
ber o
f Pro
tons
Radionuclide Decay Half-Life Patterns
238U4.5E9 y
234Th24 d
234mPa1.2 m
234U4E5 y
230Th7.7E4 y
226Ra1600 y
222Rn3.82 d
218Po3.05 m
214Pb26.8 m
214Bi19.9 m
214Po1.6E-4 s
210Pb22.3 y
210Bi5.01 d
210Po138 d
208PbStable
Beta
Alpha
Uranium-238 Decay Chain
232Th1.4E10 y
228Ra5.8 y
228Ac6.13 h
228Th1.91 y
224Ra3.66 d
220Rn55 s
216Po0.15 s
212Pb10.6 h
212Bi60.6 m
212Po3E-7 s
208Tl3.1 m
208PbStable
Beta
Alpha
Thorium-232 Decay Chain
1/3
2/3
Number of NeutronsN
umbe
r of P
roto
ns
Radionuclide Decay Mode Patterns
Decay mode depends on Decay mode depends on direction to belt of stabilitydirection to belt of stability
Radioactive Decay and Equilibrium of SRE Reactor FuelsRadioactive Decay and Equilibrium of SRE Reactor Fuels
The time it takes for the The time it takes for the daughter to reach equilibrium daughter to reach equilibrium
with the parent depends on the with the parent depends on the halfhalf--life of the daughter. life of the daughter.
Because of the long halfBecause of the long half--life of life of intermediate members in the intermediate members in the
UU--238 and U238 and U--235 decay chains, 235 decay chains, equilibrium is only established equilibrium is only established
for early short halffor early short half--life life daughters. All members of the daughters. All members of the ThTh--232 decay chain approach 232 decay chain approach
early equilibrium.early equilibrium.
Ingrowth of daughter (D) Ingrowth of daughter (D) radionuclides from parent (P) radionuclides from parent (P) when Twhen T½½PP >> T>> T½½DD and Aand AD0D0 = 0= 0
Th-234 and Pa-234m Ingrowth from U-238
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 20 40 60 80 100 120 140
Days
Frac
tion
of U
-238
Orig
inal
Act
ivity
U-238Th-234 and Pa-234m
U-238: T1/2 = 4.5E9 years
Th-234: T1/2 = 24 daysPa-234m: T1/2 = 1.2 min
Only these two short half-life daughters grow significantly toward equilibrium in 50 years.
Ingrowth of early decay chain Ingrowth of early decay chain short halfshort half--life daughters from life daughters from
UU--238238
Ingrowth of early decay chain Ingrowth of early decay chain short halfshort half--life daughters from life daughters from
UU--235235
Ingrowth of long halfIngrowth of long half--life life daughters from Udaughters from U--234234
Ingrowth of decay chain short Ingrowth of decay chain short halfhalf--life daughters from Thlife daughters from Th--232232
Th-231 Ingrowth from U-235
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
0 1 2 3 4 5 6 7 8 9 10
Days
Frac
tion
of U
-235
Orig
inal
Act
ivity
U-235Th-231
U-235: T1/2 = 7.04E8 years
Th-231: T1/2 = 1.06 days
Only this one short half-life daughter grows significantly toward equilibrium in 50 years.
Th-230 through Po-210 Ingrowth from U-234
0.0000001
0.0000010
0.0000100
0.0001000
0.0010000
0.0100000
0.1000000
1.0000000
0 20 40 60 80 100 120 140
Years
Frac
tion
of U
-234
Orig
inal
Act
ivity
U-234Th-230 > Po-210
U-234: T1/2 = 4E5 years
Th-230: T1/2 = 7.7E4 years
None of the U-234 decay chain daughters grow significantly toward equilibrium in 50 years.
Ra-228 and Th-228 through Tl-208 Ingrowth from Th-232
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40 50 60 70 80 90 100
Years
Frac
tion
of T
h-23
2 O
rigin
al A
ctiv
ity
Th-232
Ra-228
Th-228 > Tl-208
Th-232: T1/2 = 1.4E10 years
Ra-228: T1/2 = 5.8 yearsTh-228: T1/2 = 1.9 yearsRa-224 > Tl-208 < 3.66 days
All of the Th-232 decay chain daughters grow significantly toward equilibrium in 50 years.
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