A criticality assessment of five representative transportation packages was performed to determine
whether existing package designs can be used to transport unirradiated increased enrichment (within the
HALEU range) LWR fuel materials of different forms. The following representative packages were
evaluated:
1. Traveller (PWR fuel assemblies, PWR and BWR fuel pins),
2. CHT-OP-TU (UO2 powder and pellets),
3. VersaPac (U-metal/TRISO),
4. TN-B1 (BWR fuel assemblies), and
5. DN-30 (UF6)
The results provided for each package evaluation include enrichment and packaging limits
(e.g., maximum HAC package array size as a function of enrichment) and the identification of benchmark
critical experiments that are appropriate candidates for use in computer code validation (determination of
keff bias and bias uncertainty for the application).
Table 31 summarizes the range of enrichment and transportation array size combinations that each design
could support based on criticality calculations. In some cases, additional trade-off options to permit
increased enrichment are indicated (i.e., increased Gd rod credit in BWR assemblies). These criticality
analysis results indicate that there are viable means for increasing enrichments into the HALEU range
across the spectrum of fuel forms with differing increase amounts available for different packages.
The Traveller package can support transportation of PWR and BWR UO2 fuel rods up to 10 wt% in the
rod pipe container. Determining an upper fuel assembly enrichment limit for the Traveller is difficult due
to the complexity of the safety analysis, which covers numerous fuel designs and three versions of the
package. Subcritical margin is relatively insensitive to package array size due to the use of Boral plates
and polyethylene moderator blocks, which limit neutronic interaction between packages. The Traveller
standard version could support transportation of 5.5 to 6.5 wt% 235U (assembly average) PWR fuel
assemblies for some fuel designs through a combination of transportation array size limits and safety
analysis margin harvesting. In addition, maximum enrichment can be increased by crediting minimum
integral poisons in the fuel assembly, similar to the TN-B1 BWR assembly package. Numerous critical
experiment candidates are available for validation of 5 to 8 wt% 235U Traveller models.
The CHT-OP-TU package can be configured to transport up to 18 wt% UO2 powder and up to 16.5 wt%
UO2 pellets through a combination of oxide vessel diameter and package array size. Numerous critical
experiment candidates are available for validation of 5 to 16.5 wt% 235U CHT-OP-TU models.
The Versa-Pac package is currently licensed to transport U materials enriched up to 100% 235U with a
235U content maximum allowed mass determined by enrichment bin and packaging type. Because the
Versa-Pac is already licensed to transport HALEU and has mass limits that are a function of enrichment,
no additional evaluation was performed.
The TN-B1 package can support transportation of BWR fuel assemblies up to 10 wt% (assembly average)
using a combination of package array size and gadolinia rod credit. Subcritical margin is highly sensitive
to package array size in the un-poisoned TN-B1. Numerous critical experiment candidates were
identified for validation of 5 to 8 wt% 235U TN-B1 models.
The DN-30 package can support transportation of UF6 up to 9.5 wt% by reducing transportation array size
from unlimited (5 wt% 235U) to 2 packages (9.5 wt% 235U). These results are based on retaining the 10 CFR 71.55(b) exemption from the assumption of water leakage into the containment system. Because the
limiting accident conditions do not include water in-leakage, the neutron energy spectrum of the DN-30 is
harder than other evaluated packages and only a few critical experiments were identified with a similarity
index (ck) of 0.8 or higher. Discussion of methods for validation penalty assessment is provided in the
|Traveller|PWR FA1|~6|Small| Enrichment increases ~0.5% with array size halved. Additional margin is available for some fuel designs and package versions. |
|Traveller|PWR FA1|~7|1| Approximate limit for a single package without additional margin credit. |
|Traveller|PWR FA1|8|Large| Same array size as for the current limit with credit for 52 IFBA per fuel assembly. |
|Traveller|PWR/BWR fuel pins|>10|Infinite| Additional margin is available to support higher enrichment. |
|CHT-OP-TU|UO2 powder|5|50| Current limit, 8 in. pipe. |
|CHT-OP-TU|UO2 powder|8|18| 7.5 in. pipe. |
|CHT-OP-TU|UO2 powder|18|48| 6 in. pipe. |
|CHT-OP-TU|UO2 pellets|5|50| Current limit, 7.5 in. pipe. |
|CHT-OP-TU|UO2 pellets|6.9|18| 7.5 in. pipe |
|CHT-OP-TU|UO2 pellets|16.5|48| 6 in. pipe. |
|Versa-Pac|Multiple|10|100| 55 gal drum, 5 in. pipe, 1,605 g 235U. |
|Versa-Pac|Multiple|20|100| 55 gal drum, 5 in. pipe, 1,215 g 235U. |
|TN-B1|BWR FA2|5|100| Current limit, 13 Gd rods/assembly. |
|TN-B1|BWR FA2|6|49| 13 Gd rods/assembly. |
|TN-B1|BWR FA2|7.8|25| 13 Gd rods/assembly. |
|TN-B1|BWR FA2|9.8|16| 13 Gd rods/assembly. |
|TN-B1|BWR FA2|8|100| 24 Gd rods/assembly. |
|DN-30|UF6|5|Infinite| Current limit. Few benchmark candidates. |
|DN-30|UF6|6.7|6| HUR sphere governs. |
|DN-30 |UF6|12.5|1| HUR sphere governs. Few benchmark candidates. |
1PWR FA = PWR fuel assembly, one per package, assembly average enrichment
2BWR FA = BWR fuel assemblies, two per package, assembly average enrichment
