I was looking at this answer that talks about how a good alternative to Radioisotope Thermoelectric Generators would be fission reactors. It makes a number of good points, but in the comment thread there was a discussion of the particular issue that in both cases if there is a worst-case-scenario accident and the launcher burns up in the atmosphere, radioactive material is widely dispersed. From Final Environmental Impact Statement for the Mars Science Laboratory Mission:
The predicted mean radiological dose to the maximally exposed individual from an unlikely launch area accident would be about 0.1 rem. No short-term radiological effects would be expected from such an exposure. Each exposure would, however, yield an increase in the statistical likelihood of a latent cancer fatality over the long term... Less likely launch area accidents include explosion on the pad, situations where the spacecraft is detached from the launch vehicle, and accidents where the vehicle safety systems are assumed to fail. The probabilities of these types of accidents range from approximately 1 in 8,000 to 1 in 800,000, and could result in higher mean releases of plutonium dioxide (up to 2 percent of the MMRTG inventory) with the corresponding potential for higher consequences. The maximally exposed individual could receive a dose ranging from a fraction of one rem up to about 30 rem following the more severe types of very unlikely accidents, such as ground impact of the entire launch vehicle.It should be noted that there are large variations and uncertainties in the prediction of close-in dose modeling for such complicated accident situations. Assuming no mitigation actions, such as sheltering and exclusion of people from contaminated land areas, radiation doses to the potentially exposed members of the population from a very unlikely launch accident could result in up to 60 mean additional cancer fatalities over the long term. Results of the risk assessment also indicate that for the very unlikely accident that involves ground impact of the entire launch vehicle, roughly 90 square kilometers (about 35 square miles) of land area could be contaminated above the 0.2 μCi/m 2 screening level.
I asked about this as it wasn't clear to me how the two systems compare, RTGs releasing plutonium and micro fission reactors releasing uranium. The response was that the fresh U-235 fuel in a launched fission reactor is 'a trivial biological risk compared to either RTGs or reactors that have been operating and producing fission products'.
How exactly does it compare quantitatively? I accept the statement but it would be nice to know the details, as plutonium production for RTGs has started up again, while fission reactor development languishes.
