The best source of discussion I've seen so far (largely free of pro/anti-nuclear discussion and politics is here. It's up to 16 pages as I write this but it's worth reading through because there are some nuclear engineers or at least people with nuclear experience in the mix.
Radiation Dosage Nomenclature:
- Gy - Gray = an absorbed dosage amount
- Sv - Sievert = an "effective" dosage amount
- Rem - Rontgen = Same as Sv but different measurement system
Sv = Q x Gy
where Q is a function of the type of tissue that absorbs the radiation, the type of radiation, and other factors. Sometimes it is written as two variables Q & N. It can vary quite a lot depending on the type or radiation (photons = 1, alpha particles = 20), the organism and the organ/tissue of the organism.
Keep in mind that absorbed dosage (e.g., Grays) is a specific and real measurable quantity. Effective dosage (e.g., Seiverts or Rontgens/Rems) is more wishy-washy but is more relevant when considering biological effects.
1 Sv = 100 Rem
Sv and Gy have the same units (Joule/kg)
Dose Impact:
- < 0.5 Sv or < 50 Rem - Nothing serious
- 0.5 - 2 Sv or 50-200 Rem - Illness (nausea) but rarely fatal
- 2 -6 Sv or 200-600 Rem - Serious illness (hair loss, hemorrhage) and fatality possible
- 6+ Sv or 600+ Rem - Generally fatal
Think of it this way. Most reports have been in microSv or milliRem:
- 1,000,000 (1 million) microSv would cause mild illnesses but not be fatal.
- 100 Rem (100,000 milliRem) would cause mild illnesses but not be fatal.
Examples of Dose Sizes:
- 1 year of exposure of natural radiation = 300-350 milliRem (1,000 milliRem in 1 Rem)
- X-rays = 10-130 milliRem (depends on what is x-rayed)
- 1 year of working at a nuclear plant = 300 milliRem (so they get 600 millirem total)
- 1 hour airplane ride = 0.5 milliRem
- Radiation levels briefly hit at Fukushima plant on 3/14 via Twitter = 0.8 Rem per hour (still very small doses but don't hang around for long)
- 3/15 - I don't have a first hand source but this seems reliable. "According to TEPCO and other sources, high levels of radiation were detected at multiple locations near the plant--30 millisieverts (30,000 microsieverts) per hour between the No. 2 and No. 3 reactors, 400 millisieverts (400,000 microsieverts) around the No. 3 reactor, and 100 millisieverts (100,000 microsieverts) near the No. 4 reactor. These unfortunately are big big numbers. These are spot readings so it's unclear how long they lasted or how far spatially they extended.
- Dose the USS Ronald Reagan reportedly ran into off the coast of Japan = 30 milliRem in 1 hour
Plants in Question ("????" denotes I don't really trust the data sources yet or information is presented as a possibility)
Fukushima I (Dai-ichi)- 6 BWR (2 more were planned) varying in size from 460MW to 1,100MW
- Units 4, 5, 6 were already shut down for routine inspection
- Unit 1
- Cooling system compromised
- Radioactive Cesium and Iodine detected (byproducts of fission) (????)
- Radiation levels hit 0.07 Rem/hr
- Nuclear rods exposed (????)
- Reactor building exploded
- Seawater used as coolant
- Primary containment - Intact
- Spent fuel cooling pool - OK
- Unit 2
- Cooling system compromised
- Reactor runs with plutonium mixture (MOX)
- Radiation levels peaked at 0.3 Rem/hr but had dropped to 0.03 Rem/hr
- Nuclear rods exposed and melted (????)
- Reactor building intact
- Cooling system may have been damaged by Unit 3 explosion (????)
- Primary containment - Compromised (????)
- Spent fuel cooling pool - OK
- Unit 3 -
- Cooling system compromised
- Boric acid/water used as coolant
- Radiational levels peake
- Nuclear rods exposed (????)
- Reactor building exploded
- Primary containment - Intact
- Spent fuel cooling pool - OK
- Unit 4
- Spent fuel cooling pool - Not OK? Fire?
- Reactor building exploded
Fukushima II (Dai-ni) - 4 BWR all 1,100 MW
- All 4 reactors successfully shut down automatically
- Units 1, 2, 4 cooling water pumps damaged
- Units 1, 2, 3 have reached "cold shutdown"
- Unit 4 still being cooled
- No pressure releases have taken place
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