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Nuclear Accident in Japan:A Summary
Dennis Quinn, CHPDAQ, Inc.
Fukushima Nuclear Reactors
Fukushima Nuclear Reactors
Fukushima Daiichi Nuclear Reactors
Boiling Water Reactor Basic Flow
Boiling Water Reactor Design
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Nuclear Reactor Fuel Design
~96 rods per assembly~400-800 assemblies per Rx
Key Points1. 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 dayb. 12 MW after 1 weekc. 7 MW after 3 months
3. The fuel must be cooled, or there is a risk of fuel damage and release of radioactivity.
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Stainless Steel Melts
Prior to Accident
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 lineMain 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
Earthquake and Loss of Electric Power
• 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
Accident Progression
From Areva Presentation The Fukushima Daiichi Incident – Dr. Matthias Braun
From Areva Presentation The Fukushima Daiichi Incident – Dr. Matthias Braun
Hydrogen Explosion
Early Releases and Dose RatesBackground is 0.005 – 0.01 mR/hrFukushima Daiichi Main Gate dose rates dependent on wind direction & events:
3/14: 50 mR/hr3/15: 300 mR/hr due to venting from Unit 23/15: 1200 mR/hr due to explosion & fire on Unit 43/16: 850 mR/hr explosion on Unit 23/17: 1100 mR/hr – releases from Units 2 and 3 of plant
U.S. 7th Fleet ship contaminated helicopter crew.US news crews returning after 2 wks have contaminated equipment.
Emergency Planning ActionsDate, Time Evacuate Shelter
March 11, 15:42 - Loss of power in Nuclear Power Plants
March 11, 21:23 3 km 10 km
March 12, 05:44 10 km
March 12, 18:25 20 km
March 15, 11:06 20 km 30 km
March 21 – First food restrictions: spinach, kakina, & milk
April 22 – Selected areas 20-30 km termed Planned Evacuation Zones if estimated dose > 20 mSv (2 rem)
Water and Food Products
I-131, Cs-134, Cs-137MilkProduce (leafy vegetables, spinach, etc.)Drinking water (peak at 3x limit @ 30 km, now below limits).Seawater, fish products
Initially prevented sale of food & seafood within 30 km radiusRecent 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 Eggs 0% 0%
Milk 4% 0.2%
Produce 2% 5%
Seafood 0.4% 7%
Tea Products 0% 14%
Total 2% 5%Data from April - July 2011. After this synopsis of data on the WHO website, some samples of beef were found above the 500 Bq/kg limit for meat.
Food and Drinking Water Japan Limits (Bq/L or Bq/kg)
Nuclide
Water, Milk
Vege-tables
Meat, Fish
IAEA for all food
I-131 300* 2,000 2,000 3,000
Cs-134 200 500 500 1,000
Cs-137 200 500 500 2,000*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
Workers Meeting for Recovery 4/1
Bags of Radwaste (PPE, Plastic, etc.)
Contaminated Water and Soil Control Issues
Resin Spraying for Soil Control
Rx 2 – Leak to the Sea
Contamination Control Silt Fence
Mega Float Arriving Yokohama
Remote Operated Vehicle
Remote Monitoring & Protection
International Nuclear and Radiological Event Scale (INES)
Chernobyl Level 7
Fukushima DaiichiLevel 7
TMI Level 5
Status according to World Health Org
As of July 2011
So How Bad Was It?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.