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

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104<br />

CONSEQUENCE ANALYSIS<br />

Three sources <strong>of</strong> error are identified in the discussion <strong>of</strong> the release fractions. The<br />

first is that releases <strong>of</strong> mixed fission products and actinides have been omitted. WASH-1238<br />

(AEC 1972) states that actinides available for release in the pellet-clad gap would be neg-<br />

ligible compared to other nuclides. Mixed fission products were conservatively assumed<br />

available for release due to leaching <strong>of</strong> fuel pellet surfaces. The leaching mechanism could<br />

only occur if clad failure occurs before the loss <strong>of</strong> cask coolant. This is not the case in<br />

Accident 6.2.8 (DOE/ET-0028). Actinide and fission product releases from the fuel may be<br />

possible following an impact that disrupts the fuel pellets and cladding. Accident 6.2.7 in<br />

DOE/ET-0028 discusses this possibility.<br />

Second, this comment states that the amount <strong>of</strong> 85 Kr released is understated by<br />

Table 4.1.1-12 <strong>of</strong> DOE/ET-0029. The stated value in the table is low by 400 Ci <strong>of</strong> 85 Kr.<br />

The effect <strong>of</strong> this error is less than 1% <strong>of</strong> the doses reported in DOE/ET-0029.<br />

The last part <strong>of</strong> this comment relates to the release fraction for Cs. The release<br />

fraction, 6 x 10- 4 <strong>of</strong> all cesium was obtained from NUREG-0069 (NRC 1976b). Half <strong>of</strong> the<br />

fuel elements are assumed to rupture in the accident. This results in a release fraction<br />

for all cesium isotopes <strong>of</strong> 3 x 10 - 4 . Multiplying this value by the various isotope inven-<br />

tories yields the releases reported in Table 4.1.1-12 <strong>of</strong> DOE/ET-0029.<br />

Draft p. N.4<br />

Issue<br />

The consequences presented in p. N.4 for severe accidents are based on the dose<br />

received by persons from radionuclides released to the atmosphere. Since severe accidents<br />

may cause a reduction in shielding efficiency, doses resulting from radiation emanating<br />

directly from the cask should also be evaluated. The description <strong>of</strong> severe accidents in<br />

Table 6.2.6 <strong>of</strong> DOE/ET-0028 indicates a small opening will exist in the cask.<br />

Accident number 6.2.8 is based on number 6.2.7. Number 6.2.8 assumes that no emergency<br />

action is taken to cool the cask involved in the 6.2.7 accident. This results in 50% <strong>of</strong> the<br />

fuel rods being perforated in number 6.2.8 instead <strong>of</strong> only 1% being perforated in number 6.2.7,<br />

in addition to 100% <strong>of</strong> the coolant being released in both accidents. Thus, release fractions<br />

in number 6.2.8 should be 50 times higher than in number 6.2.7. Indeed, for 85 Kr, 1291, and<br />

3 H the release fractions given are 50 times higher for number 6.2.8 than for 6.2.7. However,<br />

although mixed fission products and actinides are reportedly released in number 6.2.7, only<br />

134Cs and 1 3 7 Cs are reported as being released in number 6.2.8. This can also be seen in<br />

Tables 4.1.1-10 and 4.1.1-12 <strong>of</strong> DOE/ET-0029 which gives the actual number <strong>of</strong> curies released.<br />

Note that Table 4.1.1-10 gives the curies released for accident number 6.2.6, a moderate acci-<br />

dent in which only 5% <strong>of</strong> the cavity coolant is released and only 0.25% <strong>of</strong> the fuel rods<br />

exhibit cladding failure. The table shows fission products such as 90Sr and 95 Nb and the<br />

actinides such as 239 Pu and 242 Cm being released. Table 4.1.1-12, which lists the radio-<br />

nuclides released for accident number 6.2.8, the severe accident does not contain any <strong>of</strong> the

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