The FuTure oF nuclear Fuel cycle - MIT Energy Initiative

Repository Regulation and Performance Assessments
In the United States, the Environmental Protection Agency (EPA) defines the safety standard
that the repository must meet 12 . For the proposed YM repository, the EPA maximum
allowable radiation dose at the boundary of the repository for the most exposed person 13
must not exceed 15 mrem/year anytime during the first 10,000 years or 100 mrem from
10,000 to one million years. As a basis of comparison, the total average annual radiation
dose to an American is estimated to be 360 mrem/year. While the regulatory standards vary
from country to country, the allowable releases in other countries is some fraction of the
natural background radiation levels.
It is difficult to predict what will happen far into the future. This has led to examination of
different types of safety indicators 14 to obtain some perspective of future risks independent
of any specific site or facility. These indicators are generally based on observations of the
performance of natural analogues including uranium ore deposits, other metal ore deposits,
and the evolution of natural nuclear reactors over time. 15 For example, the U.S. Nuclear
Regulatory Commission 16 has also compared the relative toxicity of a radioactive waste
repository to a uranium ore body to help establish a reasonable time frame of concern when
evaluating a repository. Their analysis indicates that within about 10,000 years the repository
toxicity is within a factor of ten of the ore body.
The results of many different types of assessments have created the broad consensus within
the geological and scientific community that a properly sited and designed repository presents
very low risks to the public.
There are proposals to burn radionuclides in wastes in nuclear reactors to improve repository
performance by destroying (1) the more toxic long-lived radionuclides in waste or (2)
the major heat-generating radionuclides. Our analysis and analysis by others 17 have found
only limited benefits in the context of waste management.
p Chemical behavior, physical form, and half-life determine the potential for release of a
radionuclide from a repository—not toxicity. Destroying the most toxic radionuclides
may or may not improve repository performance.
p The radionuclides that limit repository performance are different for different geologies.
If the goal is to destroy the radionuclides that limit repository behavior, the repository
site must be known before undertaking a program to burn specific actinides.
p There are risks associated with actinide burning. Our analysis (Chapter 6) shows that it
would take a century or longer to destroy a significant fraction of the long-lived radionuclides.
The risks of processing and handling such wastes appear significantly greater than
the risks of disposal.
Some closed fuel cycles destroy selected long-lived radionuclides as a byproduct of fissile
fuel recycle. It is a benefit that should be considered when considering alternative fuel cycles.
appendix to chapter 5: Waste Management 161