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.