Basic Elements of Static RTG's
Load
Energy
Conditioning
Control
Energy Conversion
Radioisotope
Fuel
Energy Transfer
Heat Rejection
Shielding
Power Generated by Radioisotopic Heat Sources
Power (t) =
Initial # of Radioisotopes
No
ln 2
Decay Rate, s-1
l= t
1/2
Energy Released Per Decay
MeV
E
Number of Radioisotopes
Left After t Years
Power (t) =
No • E • ln 2
t1/2
exp -(
exp -(
t•ln 2 )
t1/2
t•ln 2
t1/2
)
Important Characteristics of
Radioisotopic Heat Sources
Physical Properties
• Isotope
• Type of Radiation
• Energy of Decay
• Half Life
• Curies/gram
• Curies/Watt
• Watts/gram
• Total kWh
Realizable
Commercial Properties
• Form of Compound
• Melting Point
• Isotopic Purity
• % Isotope in
Compound
• Watts/g (compound)
• Watts/cm3 (comp.)
Production Properties
• Recovery From Power
Reactor Fuel
• Production Rate in
Power Plants
• Availibility
• Price
Most Commonly Used Isotopes for
Radioisotope Heat Sources
Co-60
Sr-90
Ru-106
Cs-137
Cm-242
Ce-144
Cm-244
Pm-147
Tm-170
Po-210
Pu-238
Main Decay Mode Of Most Favored
Radioisotopes
MAINLY
GAMMA
Co-60
MAINLY
BETA
Sr-90
Ru-106
Pm-144
Tm-170
GAMMA
& BETA
Cs-137
Ce-144
MAINLY
ALPHA
Po-210
Pu-238
Cm-242
Cm-244
Half Life of RTG Fuels
87.4
Pu-238
30
Cs-137
28
Sr-90
18.1
Cm-244
5.24
Co-60
2.6
Pm-147
1
Ru-106
0.78
Ce-144
0.45
Cm-242
0.38
Po-210
0.35
Tm-170
.1
1
10
Half Life-Yr
100
1000
Decay Energy of Radioisotopes
Cm-244
Cm-242
Pu-238
Isotope
Po-210
Tm-170
Pm-147
Ce-144
Cs-137
Ru-106
Gamma Ray
Beta
Alpha
Sr90
Co-60
0
1
2
3
4
5
6
Particle Energy-MeV
7
8
Specific Activity of RTG Fuels
Pu-238 17
Cm-244
81
Cs-137
87
Isotope
Sr-90
Pm-147
Co-60
142
928
1130
3180
Ce-144
Cm-242
3320
Ru-106
3394
4500
Po-210
6048
Tm-170
0
2000
4000
Curies/gram
6000
8000
Power Density in RTG Isotopes
141
Po-210
120
Cm-242
33.1
Ru-106
25.6
Isotope
Ce-144
Co-60
Tm-170
Cm-244
17.4
13.6
2.65
Sr-90 0.96
Pu-238 0.56
Cs-137 0.42
Pm-147 0.33
0
2 0 4 0 6 0 8 0 100120140160180200
Watts/gram
Isotope
Comparison of Specific Activity and Activity Required to Produce a Watt
Pu-238
30
17
Cm-244
29
81
Cs-137
207
87
Sr-90
148
142
2788
Pm-147
928
65
Co-60
Curies/Watt
Curies/gram
1130
124
Ce-144
3180
28
Cm-242
3320
102
Ru-106
3394
32
Po-210
4500
445
Tm-170
6048
0
2000
4000
6000
Curies/gram or Curies/Watt
8000
Total Energy Content in RTG Fuels For Reasonable Mission Times
575
Co-60
350 (0.4)
Po-210
310
Cm-242
210
Ru-106
Isotope
(5)
(1)
(10)
190
Cm-244
(0.4)
150 (1)
Ce-144
74 (10)
Sr-90
(10)
47
Pu-238
Tm-170
33
Cs-137
33
Pm-147
0
6
(0.4)
(10)
(3)
100
200
300
400
500
600
Total kWh/g for Stated Time (Y) Period
700
Commercial Fuel Form
(% Isotope in the Metallic Element)
Co-60
(10 %)
Metal
Sr-90
(55 %)
SrTiO 3
Ru-106
(3.3 %)
Metal
Cs-137
(35 %)
Ce-144
(4. 5%)
Pm-147
(95 %)
Tm-170
(10 %)
Po-210
(95 %)
Metal
Pu-238
( 80 %)
Pu O
Cm-242
( 0.45 %)
Cm-244
( 18.1 %)
CsCl
Ce 2O
3
Pm 2O
3
Tm 2O
3
2
Cm 2O
3
Melting Point of Commercial RTG Fuel Compound
2375
Tm-170
2310
Ru-106
2250
Pu-238
2190
Isotope
Ce-144
2130
Pm-147
Cm-242
1950
Cm-244
1950
1910
Sr-90
1480
Co-60
646
Cs-137
Po-210
0
255
500
1000
1500
2000
Melting Point °C
2500
3000
Concentration of Active Radioisotopes
95
Po-210
86
Isotope
Cm-244
Cm-242
82
Pm-147
82
70
Pu-238
28
Cs-137
23
Sr-90
Co-60
10
Tm-170
8.8
Ce-144
3.8
Ru-106
3.3
0
10
20
30
40
50
60
70
% Active Isotope
80
90
100
Commercial Specific Power Level of RTG Iostopes
134
Po-210
98
Cm-242
2.27
Cm-244
1.74
Isotope
Co-60
Tm-170
1.2
Ru-106
1.1
Ce-144
1
0.39
Pu-238
Pm-147
Sr-90
Cs-137
.1
0.27
0.22
0.12
1
10
100
Watts/g compound
1000
Specific Power Density of Leading Radioisotopes
1210
Po-210
882
Cm-242
20.4
Cm-244
15.8
Isotope
Co-60
13.7
Ru-106
9.6
Tm-170
6.2
Ce-144
3.9
Pu-238
1.8
Pm-147
1.01
Sr-90
Cs-137
.1
0.38
1
10
100
Watts/cm3
1000
10000
Production of Radioisotopes in Commercial Power Plants
36
Cs-137
16
Sr-90
15
Isotope
Pu-238
Ce-144
3.8
Pm-147
3.6
2.3
Ru-106
Cm-244
0.4
Po-210 0
Cm-242 0
Co-60 0
Tm-170 0
0
10
20
30
40
Production Rate in Power Reactor- kg/1000 MWeY
Future Cost of RTG Fuels
2800
Po-210
2000
Isotope
Cm-242
Pu-238
300
Co-60
280
Cm-244
170
Tm-170
136
Ru-106
120
Pm-147
75
Ce-144
50
Sr-90
20
6.5
Cs-137
0
500 1000 1500 2000 2500 3000 3500
Cost $ per Gram (pure)
Energy Cost For Fuel Only For Reasonable Missions
350
Pm-147
235
Po-210
138
Isotope
Pu-238
125
Tm-170
Ru-106
23
(1)
Cm-244
22
(10)
Co-60
15
(5)
Ce-144
11
(1)
Sr-90
6
(10)
Cs-137
4
(10)
0
100
200
(0.4)
(0.4)
180
Cm-242
(3)
(10)
(0.4)
300
400
Cost/kWh for Stated Mission (Y)
500