Reply #165: #6. I-129 is always produced in the presence of I-127.

[NNadir]

In nuclear fission of actinides both I-127, the stable isotope of iodine, and I-129 are produced. After the short lived isotopes such as I-128 and I-131 have decayed, all of the iodine that remains is a mixture of a stable isotope and a radioactive one.

For U-235 fissioned under thermal conditions, the I-129/I-127 ratio is about 85%. For Pu-239 fissioned thermally, the I-129/I-127 ratio is about 74%.

This raises two difficulties. The first is that in a circumstance where geological disposal is contemplated, bulk is unnecessarily raised by 15-25%. The second is that in the case of transmutation being chosen, between 15-25% of the transmuting neutrons or protons will be wasted transmuting a non-radioactive species.

On the plus side, as I will cover in the next series on mitigating factors, this property of there always being an isotopic mix, somewhat serves to dilute the effect that I-129 can have with respect to health.