A Review of Criticality Accidents A Review of Criticality Accidents

Pu Spherical Critical Mass (kg)
Figure 39. Critcial masses of homogeneous water moderated plutonium spheres. The points suggesting an
intermediate curve apply to water reflected Pu(No 3 ) 4 solution with 1 N HNO 3 and 3.1% 240 Pu content. The accidents
are shown by numbered circles.
(Accidents 4, 6, and 8) that fall significantly below
10 15 fissions per liter. This indicates either a slow
excursion, in which there is not a spike in the classic
sense, or simply a yield estimation that was incorrect.
There being no compelling evidence for either case,
these table entries have been left as they were reported
in the prior editions.
About half of the accidents listed in Table 10
indicate that there was no spike yield. This should be
interpreted as indicating a slow excursion, i.e., one
62
12
10
1
11
5
1
10
17
7 18
Unreflected
Limiting Critical Density a ñPhase Pu Metal
0.4
0.005 0.01 0.1 1 10 20
Density of Pu (kg/ )
Water
Reflected
Data from Water Reflected Spheres
Data Derived from Water Reflected Cylinders
239Pu Metal–Water Mixtures
from Polystyrene Compact Data
Unreflected Sphere Data
239Pu Metal–Water Mixtures
from Solution Data
with a time duration of minutes or longer between
power peaks. This definition of slow is consistent with
an inverse period of 10 ms –1 or less. Note that
accident 20 was a metal system. While there are no
plutonium metal experiments to provide a basis for
comparison, the two Los Alamos critical experiment
accidents with plutonium metal (1945 and 1946)
exhibit similar specific spike yields.
20