The FuTure oF nuclear Fuel cycle - MIT Energy Initiative

Chapter 5 Appendix — Waste Management
prinCipleS oF WaSte manaGement
Radioactive waste, like any other forms of waste, is the residual product from the operation
of a facility. Its potential impact on the public and the environment depends on its physical,
chemical and radionuclide characteristics. These characteristics determine risk and establish
a recommended disposition path for the material.
For any hazardous waste, there are only three waste management options: destruction
(transformation to a less hazardous substance), dilution to acceptably low concentrations
in the environment, or isolation from mankind and the biosphere for a period commensurate
with the longevity of the hazard. The primary method for management of radioactive
wastes is isolation. The isolation should be long enough such that if and when the radioactive
residues eventually re-appear in the biosphere, they will be present at concentrations
low enough to satisfy some health-based dose acceptance criteria.
This waste management strategy is a consequence of the defining characteristic of radioactive
materials—they decay to non-radioactive elements over time. For example, radioactive
cobalt-60 has a half-life of ~5 years. With a half-life of 5 years, half the cobalt-60 decays
away to stable nickel-60 in 5 years. In another 5 years, half of the remaining cobalt-60 decays
away. The process continues until all the cobalt-60 is gone. Most radioactive wastes
contain mixtures of different radioactive isotopes where the characteristics of the longerlived
radionuclides usually determine the preferred disposal option. Figure 5A.1 shows the
SNF radioactivity versus time after discharge from the reactor.
For any radioactive waste, the waste isolation technology chosen depends upon the half-life
of the radionuclide, geochemical mobility, and radiotoxicity. For radionuclides with halflives
of a few days or less, such as some medical wastes, the waste may be stored in a cabinet
or closet at the facility until the radionuclides have decayed to very low concentrations. For
longer-lived wastes, the disposal (storage) facility must isolate the waste for longer periods
of time.
WaSte Generation
Different fuel cycles generate different waste streams. Table 5A.1 lists wastes from the open
and closed fuel cycles. The United States has an open fuel cycle. Several countries (France,
Japan, etc.) recycle fissile materials back to reactors.
appendix to chapter 5: Waste Management 155