The FuTure oF nuclear Fuel cycle - MIT Energy Initiative

Chapter 4 — Interim Storage of Spent
Nuclear Fuel
introduCtion
Spent nuclear fuel storage is a required step in all open and closed fuel cycles. This is a
consequence of the nuclear characteristics of SNF. The radioactivity decreases rapidly with
time resulting in radioactive decay heat and gamma radiation decreasing rapidly with time.
There are large safety and economic incentives to allow the radioactivity of SNF to decrease
before transport, processing, or disposal.
Upon reactor shutdown, SNF is intensely radioactive and generates large quantities of decay
heat—equal to about 6% of the power output of the reactor. However, the radioactive decay
heat decreases very rapidly reaching 0.5% in one week. The refueling strategy in LWRs is
to transfer the SNF from the reactor core to the SNF storage pool (Fig. 1) where the water
provides cooling and radiation shielding. In the following decade, the radioactivity after
the first rapid decrease in radioactivity will decrease by another factor of 100. Reactor SNF
storage is a safety function to provide time for the SNF decay heat to decrease sufficiently
that a serious accident can no longer happen.
Figure 4.1 Wet Storage System — Spent Fuel pool
chapter 4: Interim Storage of Spent nuclear Fuel 43