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Management of Commercially Generated Radioactive Waste - U.S. ...

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105<br />

CONSEQUENCE ANALYSIS<br />

additional fission products or actinides listed for the less severe accident. Is this<br />

simply an oversight or is the contribution to the dose from these nuclides negligible<br />

compared to the dose resulting from the nuclides that are listed?<br />

A study conducted by Battelle's Pacific Northwest Laboratory, "An Assessment <strong>of</strong> the Risk<br />

<strong>of</strong> Transporting Spent Nuclear Fuel by Truck," PNL-2588, uses release fractions for actinides<br />

and fission products other than gases that are significantly higher than those derived from<br />

the accidents described in DOE/ET-0028. As previously shown, the release fractions for<br />

actinides and mixed fission products in accident number 6.2.8 should be 50-times higher than<br />

those used in accident number 6.2.7. Table 6.2.6. <strong>of</strong> DOE/ET-0028 shows a release fraction<br />

<strong>of</strong> 1 x 10 -8 for actinides and mixed fission products for accident number 6.2.7. The release<br />

fraction for accident scenarios that involve creep rupture <strong>of</strong> fuel rod cladding. Since in<br />

accident number 6.2.8 it is assumed that 50% <strong>of</strong> the rods fail, the release fraction for acti-<br />

nides and other fission products should be 1 x 10 -5 if the results <strong>of</strong> PNL-2588 are used.<br />

Recommend the basis for the release fraction for actinides and other fission products should<br />

be 1 x 10 -5 if the results <strong>of</strong> PNL-2588 are used. The basis for the release fractions used<br />

in the PNL study should be resolved.<br />

The following discussion shows that the amount <strong>of</strong> 85 Kr released for accident number<br />

6.2.8, the most severe accident, has been underestimated. Table 6.2.7 <strong>of</strong> DOE/ET-0028 indi-<br />

cates that 30% <strong>of</strong> the 8 Kr will exist in fuel rod void spaces. Accident number 6.2.8<br />

assumes that 50% <strong>of</strong> the fuel rods are perforated so that the release fraction reported in<br />

Table 6.2.6 <strong>of</strong> DOE/ET-0028 is 0.15. This table also indicates that the cask inventory given<br />

in Table 3.3.8 <strong>of</strong> DOE/ET-0028 should be used for determing the actual number <strong>of</strong> curies<br />

released. Table 3.3.8 indicates 9.5 x 103 curies per MTHM. Since Table 6.2.6 indicates<br />

that a cask will contain a 4 MTHM, this means a total inventory <strong>of</strong> 38 x 103 curies <strong>of</strong> 8 5 Kr.<br />

With a release fraction <strong>of</strong> 0.15, this results in 5.7 x 10 3 curies <strong>of</strong> 85 Kr being released.<br />

Table 4.1.1-12 <strong>of</strong> DOE/ET-0029 shows only 5.3 x 103 curies <strong>of</strong> 85Kr being released. (208-NRC)<br />

Response<br />

This comment discusses potential reductions in shielding efficiency for .a cask involved<br />

in a severe accident, compares releases from Accident 6.2.7 to those from 6.2.8, compares<br />

release fractions used in DOE/ET-0028 to those in currently available literature and points<br />

out an error in the calculation <strong>of</strong> 85 Kr releases for Accident 6.2.8. The first three areas<br />

are discussed below. Please see the response immediately above for a discussion <strong>of</strong> 85Kr<br />

releases.<br />

Accident 6.2.8 in DOE/ET-0028 is a cask loss <strong>of</strong> cooling accident postulated to occur<br />

following a moderate impact or derailment that disables the mechanical cooling system. An<br />

impact <strong>of</strong> this type would not be severe enough to significantly reduce the cask shielding<br />

and therefore was not considered in Appendix N <strong>of</strong> the draft Statement. Some reduction in<br />

shielding may be possible in a severe impact like that postulated in Accident 6.2.7 but

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