Given strontium 90's specific activity of 142 curies/gram (https://ntrs.nasa.gov/citations/19680020487), in mass terms that's 14 micrograms/kg for the LD50. Gram for gram, strontium 90 is about 1000 times as acutely deadly as arsenic, or 3 times as deadly as the chemical warfare agent sarin. A commercial power reactor of 1000 MWe output can have an inventory of tens of kilograms of strontium 90 in the core [1] along with even more acutely dangerous shorter-lived fission products.
Nuclear reactors are safe because of careful defense-in-depth in their engineering and operation. They need deeper, more stringent safety systems than steel plants or ammonia plants because they contain substances much more toxic than those found in steel plants or ammonia plants. You also see extreme safety practices in facilities that handle non-radioactive poisons, if the poisons are potent enough:
The LD50 for strontium 90 in hamsters (90 day survival) is 2 millicuries per kilogram: http://www.rrjournal.org/doi/abs/10.2307/3573895
Given strontium 90's specific activity of 142 curies/gram (https://ntrs.nasa.gov/citations/19680020487), in mass terms that's 14 micrograms/kg for the LD50. Gram for gram, strontium 90 is about 1000 times as acutely deadly as arsenic, or 3 times as deadly as the chemical warfare agent sarin. A commercial power reactor of 1000 MWe output can have an inventory of tens of kilograms of strontium 90 in the core [1] along with even more acutely dangerous shorter-lived fission products.
Nuclear reactors are safe because of careful defense-in-depth in their engineering and operation. They need deeper, more stringent safety systems than steel plants or ammonia plants because they contain substances much more toxic than those found in steel plants or ammonia plants. You also see extreme safety practices in facilities that handle non-radioactive poisons, if the poisons are potent enough:
"Inside Fort Botox"
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[1] https://www.osti.gov/servlets/purl/6822946 See table 2.2 "Fission product inventories"