Critical mass
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Smallest fissile material mass which under fixed conditions
(type of fissile material, geometry, moderated/immoderate system, etc.)
initiates a self-perpetuating chain reaction. The table contains the
minimum critical mass for some nuclides under certain conditions.
Isotope |
Smallest critical mass in spherical
shape for aqueous solution at optimum moderation
|
Smallest critical
mass in spherical shape for metal (fast systems) |
| |
Unreflected
(kg) |
Water-reflected
(kg) |
Unreflected
(kg) |
Steel-
reflected
(kg) |
U-233 |
1.080 |
0.568 |
15.8 |
6.1 |
U-235 |
1.420 |
0.784 |
46.7 |
16.8 |
Np-237 |
-
|
- |
63.6 |
38.6 |
Pu-238 |
- |
- |
9.5 |
4.7 |
Pu-239 |
0.877 |
0.494 |
10.0 |
4.5 |
Pu-240 |
- |
- |
35.7 |
19.8 |
Pu-241 |
0.511 |
0.246 |
12.3 |
5.1 |
Am-241 |
- |
- |
57.6 |
33.8 |
Am-242 |
0.042 |
0.020 |
8.8 |
3.0 |
Cm-243 |
0.280 |
|
|
|
Cm-244 |
- |
- |
26.6 |
|
Cm-245 |
0.116 |
0.054 |
9.1 |
3.5 |
Cm-247 |
|
|
|
|
Cf-249 |
|
|
|
|
Cf-251 |
|
|
|
|
Smallest critical masses for some fissile material under certain boundary conditions
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11 - 15 March 2018
Munich, Germany
30 September - 04 October 2018
Prague, Czech Republic |
