- Occupies an odd and conflicted position
in our modern debate over energy
- It is free of air pollution produced by
- Yet is has been clouded by
- waste disposal problems
- Public safety concerns have led to
- The US generates the most electricity
from nuclear power
- but only 20% of US electricity comes
- France gets 76% of its electricity
from nuclear power
Fission releases nuclear energy
Nuclear reactors use uranium-235 (143
- Over 99% of uranium occurs as 238U
- 235U is enriched to 3% and
formed into pellets (UO2)
- After several years in the reactor,
uranium is depleted
Breeder reactors make better use of fuel
- Breeder reactors use 238U
(normally a waste product)
- A neutron is added to 238U to
form 239Pu (plutonium)
- Are expensive, complex and dangerous
- work at very high temperature
- require liquid sodium for cooling
- a very reactive material if exposed
to air or water
Nuclear power delivers energy cleanly
- Nuclear power helps us avoid emitting
600 million tons of carbon each year
- Power plants pose fewer health risks
Nuclear power poses small risks,
- It poses the possibility of catastrophic
- The most serious accident in the US =
Three Mile Island in Pennsylvania in March 1979
- Partial Meltdown = coolant water drained
from the reactor
- The incident was rated a five on the seven-point International
Nuclear Event Scale: Accident With Wider Consequences
- Cleanup started in August 1979, and
officially ended in December 1993, with a total cleanup cost of about $1
Chernobyl was the worst accident yet
- 1986 explosion at the Chernobyl plant in
- More than 100,000 residents evacuated
- The battle to contain the contamination
and avert a greater catastrophe ultimately involved over 500,000 workers
- The landscape for a radius of 20 miles
is still contaminated
- 31 people killed directly
- Thousands more became sick
A man looks at the New Safe Confinement (NSC)
structure at the Chernobyl Nuclear Power
Plant April 23, 2013.
Waste disposal of nuclear material
remains a problem
- Spent fuel rods and all other waste must
be put in a safe location
- For many years wastes were dumped into
- Waste is held in temporary storage
- Spent rods are stored in water
- US plants are running out of room
US storage of high-level radioactive
Waste storage at Yucca Mountain, Nevada
- It is safer to store all waste in a
- It can be heavily guarded
Benefits of storing wastes at Yucca
- It is remote and unpopulated
- It has minimal risks of earthquakes that
could damage tunnels and release radioactivity
- Its dry climate reduces chances of
- It is on federal land that can be
protected from sabotage
Concerns with Yucca mountain site
- Some argue that earthquakes and
volcanoes could destabilize the site's geology
- Fissures in the rock could allow
rainwater to seep into the caverns
- Nuclear waste will be transported there
from around the country
- Shipments by rail and truck over
thousands could cause a high risk of accident or sabotage
Fukushima Daiichi nuclear disaster
primarily by the tsunami following a 9.0 magnitude
earthquake on March 11, 2011.
- Immediately after the earthquake, the
active reactors automatically shut down their sustained fission reactions.
- The earthquake triggered a 43 to 49
ft-high tsunami that arrived approximately 50 minutes later. The waves
overtopped the plant's 19 ft seawall, flooding the basements of the power
plant's turbine buildings and disabling the emergency diesel generators
- The tsunami also destroyed the
emergency generators cooling the reactors, causing reactor 4 to overheat
from the decay heat from the fuel rods.
- The insufficient cooling led to three
nuclear meltdowns and the release of radioactive material beginning on March
12. Several hydrogen-air chemical explosions occurred between March 12 and
Image on 16 March 2011 of the
four damaged reactor buildings. From left to right:
Unit 4, 3, 2 and 1. Hydrogen-air explosions occurred in Unit 1, 3 and 4, causing
structural damage. A vent in Unit 2's wall, with water vapor/"steam" clearly
prevented a similar large explosion.
- The government initially set in place a four-stage
- a prohibited access area out to 3 km, an on-alert
area 3–20 km and
- an evacuation prepared area 20–30 km.
- On day one, an estimated 170,000 people were evacuated
from the prohibited access and on-alert areas.
- Prime Minister Kan instructed people within the on-alert
area to leave and urged those in the prepared area to stay indoors.
- The latter groups were urged to evacuate on 25 March.
- The 20 kilometer exclusion zone was guarded by roadblocks
to ensure that fewer people would be affected by the radiation.
- The earthquake and tsunami damaged or destroyed more than
one million buildings leading to a total of 470,000 people needing
- Of the 470,000, the nuclear accident was responsible for
154,000 being evacuated.
- As of March 2016, of the original 470,000 evacuees,
174,000 evacuees remain .
Radiation hotspot in Kashiwa, February 2012.
- Comparison of radiation levels for different nuclear
- The incident was rated 7 on the International Nuclear
Event Scale (INES).
- This scale runs from 0, indicating an abnormal situation
with no safety consequences, to 7, indicating an accident causing widespread
contamination with serious health and environmental effects.
- Prior to Fukushima, the Chernobyl disaster was the
only level 7 event on record, while the Three Mile Island accident was rated
as level 5.
Risks from radiation:
- Very few cancers would be expected as a result of
accumulated radiation exposures even though people
in the area worst affected by Japan's Fukushima nuclear accident have a
slightly higher risk of developing certain cancers such as leukemia, solid
cancers, thyroid cancer and breast cancer.
- Estimated effective doses from the accident outside Japan
are considered to be below (or far below) the dose levels regarded as very
small by the international radiological protection community.
THE QUESTION TO ASK IS NOT
"IS THERE ANY RADIOACTIVITY PRESENT?" BUT RATHER,
"HOW MUCH, AND IS IT ENOUGH TO BE HARMFUL?"
detected airborne iodine and cesium throughout the Northern Hemisphere in
the aftermath of Fukushima.
- Radioactivity from the airborne plume over the nuclear
plant settled onto the ground.
- Ground sampling showed the highest
radiation dose rates measured were clearly elevated, but were also too low
to cause short-term or long-term health risks.
- In the words of oceanographer Miriam Goldstein,
radioactivity from this accident in seawater is "detectable but not
hazardous." I had no qualms about eating sushi when I was in Japan the month
after the accident, as well as in later trips to the West Coast.
- It took decades to clean up the
reactor at Three Mile Island, and a quarter-century after Chernobyl there's
still a lot of work to be done. It might be decades before Units 1, 2, and 3
are cleaned up, and it might be even longer before people return to the
evacuated zone around the reactor site.
Dilemmas slow nuclear power's growth
The future of nuclear energy
- 75% of nuclear plants in Western Europe
will be retired by 2030
- But some nations are rethinking this
because of concerns over climate change
- Asian nations are increasing nuclear
- 56 plants are under construction
- US industry has stopped building plants