Nuclear CrisisFukushima Power Plant – Japan

Post March 11, 2011

– Earthquakes, Tsunamis, and Meltdowns: Putting the Japanese Nuclear Accident in Perspective –

Nedjla Ougouag Harold Washington College

04/27/11

The Fukushima power plant 6 reactors

12

3

4

56

How does nuclear power work?• The way nuclear power plants work is by using a fissile atom like uranium-

235 or plutonium 239. • When this atom absorbs a neutron, fission occurs in which

the nucleus splits into two lighter nuclei and releases energy, radiation, and more neutrons.

Energy output: 1 gram of Uranium is equivalent to 2.37 tons of coal!

• Uranium-235 is kept in the reactor vessel in the form of fuel rods. • Heat from nuclear fission causes water to vaporize in the steam generator inside the

reactor vessel • Water also functions as the coolant• The vaporized water in the steam generator passes through the turbine to generate

electricity. It then condenses back into liquid phase and the cycle repeats. • The control rods are used to control the rate of fission in the reactor by absorbing

neutrons, and are typically made of Boron.

• A fair amount of radioactive waste is created by this cycle and is usually stored in cooling pools on site before final disposal.

Design of the Fukushima reactors• Fuel: Low Enriched Uranium• Cooling: BWR light water• Combined output of 6 reactors

in the plant: 4.7 Gwe. • Dai-ichi (number one) was built

by GE in1967 – Commissioned in 1971.

Overview of the Fukushima plant

Reactor safety ratings for earthquakes and tsunamis vs

March 11 events

1. Unit 1 was built to sustain a 0.18 g-force (1.76m/s2) peak ground acceleration. …(but was rated at 0.49 g-force!)

2. The reactors were tested for a duration of 30 sec.

3. The design basis for tsunamis was 5.7 meters.

1. The ground shook for as long as 5 minutescompare to 30 sec rating!

2. Actual peak ground acceleration was 2.7g (26.4m/s2) compare to 0.18 g-force (1.76m/s2)!

3. The Tsunami experienced was 14 m compare to 5.7 m rating!

On March 11, 2011:

What went wrong1) Unit 1: Explosion, roof blown off (12 March)

2)

3)4)

1)

5)

5)5)

5)

2) Unit 2: Explosion (15 March), Contaminated water in underground trench, possible leak from suppression chamber

3) Unit 3: Explosion, most of concrete building destroyed (14 March), Possible plutonium leak

4) Unit 4: Fire (15 March), Water level in spent fuel pools partly restored

5) Multiple trenches: probable source of contaminated water, partly underground, leak stopped (6 April)

Further events• Units 4, 5 and 6 had been shut down prior to the earthquake for planned

maintenance.

• Reactors 1, 2 and 3 shut down automatically after the earthquake, and the remaining decay heat of the fuel was being cooled with power from emergency generators.

• HOWEVER the subsequent tsunami disabled the emergency generators required to cool the reactors.

• Over the following three weeks there was evidence of – a partial nuclear meltdown in units 1, 2 and 3 (fuel rods); – visible explosions, suspected to be caused by hydrogen gas in units 1 and 3; a

suspected explosion in unit 2, that may have damaged the primary containment vessel;

– a possible uncovering of the units 1, 3 and 4 spent fuel pools.

Consequences• Radiation releases caused large evacuations, concern over food and water

supplies, and treatment of nuclear workers.

• Example: As of March 29th

– Concentration of Iodine 131 in seawater, 330 m south of the discharge canal of units 1 to 4 was 130,000 Bq/l (that’s 3,355 times the regulatory limit!).

– Concentration of Cesium 134 was 520 times the regulatory limit, and Cesium 137 was 350 times the limit.

• Why the concern?

Nuclide Half-LifeQuotient (Conc/Limit)

99mTc

6 hours 0.0

131I 8 days 3355.0

134Cs 2 years 520.2

136Cs 13 days 9.5

137Cs 30 years 352.4

140Ba 13 days 16.7

140La 2 days 6.3

What has been going on since…• Saturday, 9 April

– Continuing struggle to keep water on the reactors to cool them and prevent further meltdown risk.

– Remote controlled 95-ton pump from two miles away shooting water into the damaged reactors.

– A survey of radiation in seawater outside unit 2 shows radioactive isotope concentrations (iodine-131, cesium-134 and cesium-137) falling for the third straight day since the leak was plugged. However, the levels are still much higher than legal levels.

• Monday, 11 AprilCoolant injection into reactors 1 and 3 was interrupted for 50 minutes due to a loss of power after a strong earthquake.

• Monday, 18 AprilThe Associated Press is reporting that two PackBot ground robots from iRobot have entered Unit 1 and Unit 3 of the crippled Fukushima nuclear power plant and performed temperature, pressure, and radioactivity measurements.

• Friday, April 22The Japanese government extended the evacuation zone of Fukushima prefecture to 50 kilometers from the stricken plant.

The remaining residents within 20 to 50 kilometers were ordered to leave the area within a month because of continued excessive high levels of radiation exceeding recommended annual levels

The government plans to build 30,000 temporary homes by the end of May, and an additional 70,000 will follow.

• Hydrogen explosion Fukushima Unit 1

A few pics…

What is a meltdown? Is Japan experiencing a meltdown?

• A meltdown is what happens when the fuel rods in a nuclear reactor overheat and melt, releasing energy and radiation outside of the nuclear reactor.

• What is happening in Japan at Fukushima might best be described as a partial meltdown as the fuel rods are melting themselves but not the protective dome in which they reside.