2nd Kobe Univ. Brussels European Centre Symposium
September 19, 2011

Present Status of Japanese Nuclear
Power Plants and Radiation Disaster

Keiji ODA
Graduate School of Maritime Sciences
Kobe University

1Contents
1. Nuclear accident in Fukushima
2. Discharge of radioactive materials
3. Exposure risk & radiation protection
4. Future problems

Structure of BWR
Fuel Assembly

PelletContainment
Pressure
Vessel

Steam

Fuel

Fuel RodControlRodWater

2

Fukushima Daiichi NPS

3

Higashi Doori

Onagawa

Epicenter
Tokai

NPS’s in Japan

6 units in Fukushima-1 NPSHeight of Tsunami

4ExpectedGroundTsunamiHigashi- Onagawa
Doori

Fukushima-1 Fukushima-2 Tokai-2
No.1-4
No.5,6

Tsunami Attack56Plant Status as of August
Unit

#1

#2

#3

#4

#5

#6

OK

1971.3

1974.7

1976.3

1978.101978.4

1979.10

Power output [MW]

460

784

784

784

784

1100

Shutdown

ReactorCooling
PoolContainment

Automatic Shutdown
just after earthquake
Circulating water cooling
Injection N2 gas

Shutdown for OutageOK
FuelremovedOK
Circulating cooling system
Decontamination byprocessing facility

OKCold Shutdown

OKOKOKExplosion
1. Nuclear explosion- Chain reactions take place in a moment like A-bomb- Never occurs in nuclear fuels (enrichment: 3-5 %) forpower plants
2. Vapor explosion- Melt fuel contacts with water (cooling or ground water)- All fission products released like Chernobyl accident
3. Hydrogen explosion- Zircalloy clad with high temperature interact chemicallywith water- Release of gaseous and volatile materials (Iodine, Cesium)

7

Nuclear Fuel & Atomic Bomb

8U-235
U-235
neutronU-238

Nuclear Fuel(3-5%)

Atomic Bomb(>90%)

Natural Uranium(0.7%)

U-235Hydrogen Explosion

HydrogenContainmentPressure
VesselControl
Rod910Contamination
Deliberate
Evacuation
Area

Restricted
Area
Evacuation
Prepared Area
in case ofEmergency

Monthly Change of Fallout
Cesium fallout [MBq/km2] observed in Osaka
10,000

Nuclear Tests
by USA & USSR
May, 1963

1,000
Nuclear Tests Chernobyl Accident
by China
May, 1986
100
Fukushima Accident
April, 2011
10

10.1

0.01
1960

'70

'80

'90

2000

'10

11

Estimation of Radiation Risk
For better understanding …
1. Existing of natural radiation
cosmic rays, soils, food, etc
2. Investigation of A-bomb survivors- No effect on embryo and fetus under 100-150 mSv- Significant increase in relative cancer risk over 300 mSv- No hereditary effect observed on human
3. Ability of repairing DNA damage
4. Comparison with other cancer risks- 50 % for cancer risk, 30 % for cancer death by other causes

12Natural Radiation

13

Image of radiation emitted fromvegetables
-rays from K-40

About 7,000 Bq in human body(0.2 mSv/year)

Data from A-Bomb Survivors- Investigation for 120,000 persons- Relative risk
= Cancer risk for exposed group to that for control group
3.0

1.4

2.5

1.3

2.0

1.2

1.5

1.1

1.0

1.0

0.5

0.90

0.80100200300

4000100200300

Dose [mSv]

Dose [mSv]

Leukemia

Solid TumorResponse under 300 mSv is unclear for statistical reason

400

14

Future Problems

15

1. Technical Problem- Natural circulating cooling system- Securement power source (multiplicity)
2. Security- Energy security- Counter-terrorism
3. Contamination and harmful rumor- Decontamination technique and handling of radioactive wastes- Control of discrimination and over-response against exposure
4. Tradition of nuclear engineering to next generation- Technology of nuclear safety- Sustainable education system