Environmental Engineering Reference
In-Depth Information
Table 5.2 Maximum BUs achieved vs Regulatory limits (excludes LUAs),
A. Strasser in Adamson et al . (2010, ZIRAT 15 Annual Report)
Country
BU (GWD/MT)
Batch
Assembly
Rod
Pellet
Regulatory limit
USA
54
58
62
73
62.5 peak rod
Belgium
50 - 55
55 UO 2 assy, 50
MOX assy
Czech Republic
51
56
61
60 peak rod
Finland
45.6
46.5
53
45 assy
France
47
51 UO 2 42
MOX
52 assy
Germany
58
62
68
65 assy
Hungary
50
62
Japan
50
55
62
55 UO 2 assy, 45
MOX assy
Korean
Republic
46
60 rod
Netherlands
51.5
58
64.5
60 rod
Russia
45
56
60
68
Spain
50.4
57.4
61.7
69
Sweden
47
57.2
63.6
60 assy, 64 rod
Switzerland
58
60
65
71
75 pellet
Taiwan
60 rod (P), 54
assy (B)
UK
44.3
46.5
50
55 pellet
Ukraine
50
Source: A.N.T. International, 2011
￿
He gas pre-pressurization during fabrication
￿
fi ssion gases
￿
He from transmutation of B in burnable absorbers
￿ ￿ ￿ ￿ ￿ ￿
￿
alpha decay of the Pu isotopes in the fuel during storage
and their pressure is further raised by the fuel decay heat. All of these pres-
sure sources, except the pre-pressurization level, are burnup dependent.
The pressure outside the cladding in the cask is only slightly above atmo-
spheric. Creep deformation of the cladding will occur at a relatively constant
rate early in life, when the internal gas pressure, the cladding stresses and
the cladding temperature are at their highest. As the decay heat decreases
with time, the gas pressure and the cladding temperature both decrease. In
addition, the internal free volume of the fuel rod increases as the cladding
creeps outward, decreasing the gas pressure and cladding stresses further.
All three of these factors eventually reduce the creep rate to a negligible
value (Adamson et al ., 2010 ).
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