Reply #162: #3. Radioequilibrium places few limits on the accumulation of I-129.

[NNadir]

Assuming 30% thermal efficiency, at constant power the current nuclear energy capacity would allow for the accumulation of over 43 million metric tons of Iodine-131 before radioequilibrium was reached and the I-129 fission product was decaying as fast as it was formed.

Fortunately it would take millions of years of continuous operation of nuclear plants to accumulate such an amount: Currently the total worldwide annual production of I-129 amounts to less than 2 MT per year. Because of the extremely long half life of I-129, over 15 million years, the effect of nuclear decay on the accumulation of this isotope is currently close to negligible.

It is interesting to speculate how much I-129 could theoretically accumulate if 100% of the world's energy capacity were provided by nuclear energy. If we assume, as some people do, that world energy demand will rise to 1000 exajoules by 2050, and if we also assume that all of this energy were produced by nuclear fission, the theoretical maximum would be about 1 billion tons. The rate of accumulation would be initially about 50 tons per year at the outset, the rate of accumulation slowing over the hundreds of millions of years that the approach to equilibrium would require. Of course the world's supply of uranium and thorium will likely have been depleted by that time.