1.The nuclear fuel contains almost all of the radioactivity (>99%). 2.The nuclear fuel continues to generate heat after the reactor is shut down. a.19 MW after 1 day b.12 MW after 1 week c.7 MW after 3 months 3.The fuel must be cooled, or there is a risk of fuel damage and release of radioactivity.
Fuel Temperature ( o F) Activity Available for Release (Curies) Stainless Steel Melts
From Areva Presentation The Fukushima Daiichi Incident – Dr. Matthias Braun Reactor Service Floor (Steel Construction) Concrete Reactor Building (secondary Containment) Reactor Core Reactor Pressure Vessel Containment (Dry well) Containment (Wet Well) / Condensation Chamber Spent Fuel Pool Fresh Steam line Main Feedwater
Earthquake causes loss of offsite power. Emergency Diesel Generators supply power Tsunami disables EDGs Steam dumps to wet well Water level in reactor decreases Fuel heats up Cladding is damaged and releases noble gases and volatile isotopes (cesium and iodine) From Areva Presentation The Fukushima Daiichi Incident – Dr. Matthias Braun > 99.9% of radioactivity is in the fuel
Large volume in wet well eventually heats to boiling and no more pressure suppression Pressure increases Hydrogen created by high temperature reaction of cladding & steam Operators decide to vent primary containment gas to secondary containment Gas has fission products and hydrogen From Areva Presentation The Fukushima Daiichi Incident – Dr. Matthias Braun
Background is – 0.01 mR/hr Fukushima Daiichi Main Gate dose rates dependent on wind direction & events: 3/14: 50 mR/hr 3/15: 300 mR/hr due to venting from Unit 2 3/15: 1200 mR/hr due to explosion & fire on Unit 4 3/16: 850 mR/hr explosion on Unit 2 3/17: 1100 mR/hr – releases from Units 2 and 3 of plant U.S. 7 th Fleet ship contaminated helicopter crew. US news crews returning after 2 wks have contaminated equipment.
Date, TimeEvacuateShelter March 11, 15:42 - Loss of power in Nuclear Power Plants March 11, 21:233 km10 km March 12, 05:4410 km March 12, 18:2520 km March 15, 11:0620 km30 km March 21 – First food restrictions: spinach, kakina, & milk April 22 – Selected areas km termed Planned Evacuation Zones if estimated dose > 20 mSv (2 rem)
Note –no significant deposition events noted after 3/19
I-131, Cs-134, Cs-137 Milk Produce (leafy vegetables, spinach, etc.) Drinking water (peak at 3x 30 km, now below limits). Seawater, fish products Initially prevented sale of food & seafood within 30 km radius Recent identification of beef with Cesium contamination.
Type of Sample Percent above Action Level for I- 131 Percent above Action Level for Cs-134 and Cs-137 Meat and Eggs0% Milk4%0.2% Produce2%5% Seafood0.4%7% Tea Products0%14% Total2%5% Data from April - July After this synopsis of data on the WHO website, some samples of beef were found above the 500 Bq/kg limit for meat.
*Infant water and milk limit is 100 Bq/kg IAEA Limits based on 1 rem per year to most restrictive individual (generally infant) if consuming food for 1 year at the limit
Resin Spraying for Soil Control Rx 2 – Leak to the Sea
As a nuclear or industrial accident, it was major – resulted in evacuation, loss of a major electricity source, and uncertainty in the public for months. It was not a major health catastrophe, and it is not likely that there will be significant health effects. Why? – The emergency plan actually worked. Despite the initial confusion, people were evacuated, controls were placed on food, etc.