23.04.2013 Views

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

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

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

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

6.38<br />

the necessary leaktightness <strong>of</strong> the mined out cavity. All <strong>of</strong> these areas would require tech-<br />

nical resolution before construction could begin.<br />

Cavity Charging. Cavity charging methods would depend on many variables including: the<br />

radioactivity <strong>of</strong> the charge; whether the charge were liquid or slurry; whether charging were<br />

batch or continuous; and whether charging were a long-term or short-term operation. The<br />

methodology for charging has not been defined or optimized. Considering the heat <strong>of</strong> the<br />

waste, the depth <strong>of</strong> the cavity, and possible corrosion and material plate-out, considerable<br />

technical effort would be required in this area.<br />

In addition, the effect <strong>of</strong> a 2,000-m-long steam line on cavity charging would have to be<br />

determined. A vertical pipe <strong>of</strong> this length would act as a distillation column. Also, the en-<br />

gineering required to construct such a pipe (i.e., the number and type <strong>of</strong> expansion joints,<br />

effect <strong>of</strong> bends, etc.) has not been performed.<br />

Shaft Sealing. There would be two phases <strong>of</strong> shaft sealing: sealing after construction<br />

but before waste charging starts and sealing after the waste is emplaced but before rock<br />

melting begins.<br />

Sealing after construction would be the easier <strong>of</strong> the two operations because there would<br />

be sufficient time to check the work. However, sealing before rock melting begins would have<br />

to be done fairly quickly and in a potentially contaminated environment. <strong>Radioactive</strong> contam-<br />

ination and possible residual steam venting would present substantial problems in trying to<br />

seal the shaft after charging. Because <strong>of</strong> the number <strong>of</strong> pipes connecting the cavity to the<br />

surface, this operation would require considerable expertise. Both the materials and methods<br />

required would need further study and experimentation.<br />

Volatile Fission Products. The quantities and behavior <strong>of</strong> the potentially volatile fis-<br />

sion products would have to be determined. Nuclides in this category include 10 3 Ru and<br />

10 6 Ru. Equipment would have to be designed to trap and remove these products from the waste<br />

stream or to return them in the coolant back to the cavity. Alternatively, they might be re-<br />

turned to the processing facility. There might also be a liquid and solid carryover from the<br />

steam, which would contaminate the condenser as well as increase the hazard from any poten-<br />

tial leak. Practical technical considerations in this area would have to be examined before<br />

this concept could ever be considered viable. There is also a potential problem with tritium<br />

being carried with the steam.<br />

Criticality Potential. Because 99.5 percent <strong>of</strong> the uranium and plutonium would have been<br />

separated from the spent fuel during reprocessing, the potential for criticality in the HLW<br />

is small. If experimental and modeling results indicated that criticality might be attained<br />

at some point in one <strong>of</strong> the rock melt concept scenarios, and if the results <strong>of</strong> such an excur-<br />

sion were undesirable from either an engineering or a safety standpoint, additional work<br />

would have to be carried out to develop methods <strong>of</strong> mitigation, possibly involving the addi-<br />

tion <strong>of</strong> a high neutron cross section "poison" to the HLW as it is emplaced in the repository.<br />

It would be necessary for the "poison" to remain dispersed in the proper place upon cooling.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!