Basic Research Needs for Geosciences - Energetics Meetings and ...

APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTcontain. Recycling spent nuclear fuel can prove beneficial in terms of managing nuclear waste byreducing the quantity of waste needing to be isolated. A given repository size can therebyaccommodate waste that has produced more energy per ton of original nuclear material.The total waste capacity of any geologic repository will be constrained by many factors such asavailable physical space, waste volume, waste thermal density, and most importantly, postclosurerepository performance requirements (effective dose to the public). In particular,significant thermal benefits could potentially be achieved through separation/recovery ofactinides and key fission products from spent nuclear fuel. Reduced thermal densities mayprovide flexibility in the ability to optimize the design of subsurface facilities while meetingthermal criteria and goals.Removing the actinides and key fission products from the waste may also potentially reducelong-term environmental risks. The benefits of an advanced nuclear fuel cycle that includesreprocessing of spent nuclear fuel depend on the density with which waste can be loaded intonew waste forms, and on the repository design and its ability to accept all waste forms.There is scientific consensus that the disposal of spent nuclear fuel and high-level radioactivewaste in deep geologic formations is potentially safe and feasible (National Research Council2001; International Atomic Energy Agency 2003), provided that sites are chosen andcharacterized well, and that the combination of engineered and natural barriers is designedappropriately. However, as illustrated by the history of decisions on radioactive waste disposal inthe U.S., many issues still need to be resolved.Although the U.S. has decided that it will sequester waste in volcanic formations in an aridregion with a thick unsaturated zone, other possibilities were previously entertained. Saltformations were originally considered to be the most promising hosts for a repository. Suchformations would theoretically prevent transport of liquid and would become self-sealing in theevent of fracturing. Another possibility considered was the thick basalt lava sequence in theColumbia Plateau region. Each geologic environment generates specific technical and scientificchallenges, but there are many issues common to all.The primary goal of waste management is to ensure that the health risks of exposure to radiationfrom spent nuclear fuel discharged from nuclear reactors and other high-level wastes over timeremain below an acceptable level (Table 6). To meet this goal, most disposal strategies rely on asuccession of multiple, robust safety barriers. This barrier system can be subdivided intoengineered and natural components.Table 6. EPA regulatory limits associated with geologic disposal of radioactive waste.Radionuclide or type of radiation emittedCombined Ra-226 and Ra-228Gross activity (including Ra-226, but excluding Ra and U)Combined - and photon-emitting radionuclides to the whole bodyor any organ, based on drinking 2 L/d from the representativevolumeTable modified from DOE 2002a (Table 5-9).EPA limit5 pCi/L15 pCi/L4 mrem/yBasic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems Appendix 1 • 25