Transcript Nuclear Energy - University of Massachusetts Boston

Nuclear Energy
Nuclear Energy
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How does a nuclear reactor work?
Is it a major energy source worldwide?
Is it Green?
Problems
– Waste Disposal
– Accidents
• Future
– Research
– Generation IV
Nuclear Energy Plant
• Nuclear Fission
• 235U + n → 236U → 92Kr + 141Ba + g + 3n
• Chain Reaction
• Controlled by control (graphite) rods and water
coolant
• Heat from reactor is cooled by circulating pressurized
water
• Heat exchange with secondary water loop produces
steam
• Steam turns turbine generator to produce electricity
Present Nuclear Energy
• 100 plant produce about 20 % of the
electricity in US
• 431 plants worldwide in 31 countries produce
about 17 % of the world’s electricity
• Environmental Impact
– No Greenhouse gases
– Completely contained in normal operation
– Spent fuel issue
Waste Disposal
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Waste kept at plant, but running out of room.
Site chosen in Nevada for nuclear waste.
Research on safe transportation
Nuclear proliferation; fuel is very dilute and
not easily converted to weapons grade
• Stored in very heavy casings (difficult to steal)
Accidents
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Nuclear Meltdown
Fukushima Daiichi
Chernobyl
Three Mile Island
Environmentalist watch dogs note other near
misses in recent years
Fukushima - 2011
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6 Power plants on site
9.0 earthquake , followed by a 45 ft tsunami
Flooded power plant
1/10 radiation that was released in Chernobyl
accident
More info
• Reactor 4 had been defueled at time of
shutdown and Reactors 5 and 6 were in
shutdown mode for routine maintenance
• The tsunami destroyed the connection to the
grid
• The tsunami flooded the pumps, shorting
them out
• Reactors 1-3 experience complete meltdown
more
• Tokyo in 2008, an IAEA expert warned that a strong earthquake
with a magnitude above 7.0 could pose a "serious problem" for
Japan's nuclear power stations.
• In the late 1990s to comply with new regulatory requirements,
three additional backup generators for reactors Nos. 2 and 4 were
placed in new buildings located higher on the hillside. All six
reactors were given access to these generators, however the
switching stations that sent power from these backup generators to
the reactors' cooling systems for Units 1 through 5 were still in the
poorly protected turbine buildings. All three of the generators
added in the late 1990s were operational after the tsunami. If the
switching stations had been moved to inside the reactor buildings
or to other flood-proof locations, power would have been provided
by these generators to the reactors' cooling systems.[
• Hydrogen Explosions: Zr + 2 H2O → ZrO2 + 2 H2
• Sea water
Chernobyl (1986)
• A planned test gone horribly wrong
• The test
– See if turbine generator could power the water pumps that cool the
reactor in the event of a loss of power
– Crew shut off power too rapidly, producing a Xe isotopes that poisons
the reactor
– In response the rods were lifted to stimulate reaction
– The lower cooling rate of the pumps during the experiment led to
steam buildup that increase reactor power
– Temperature increased so rapidly, that rod insertion could not be
performed in time to stop meltdown
– Roof blew off, oxygen rushed in a caused fire that spread radioactive
material over a large area
Blame
Management communication
A bizarre series of operator mistakes
Plant design, poor or no containment vessels
Large positive void coefficient (steam bubbles in
coolant)
Poor graphite control rod design
Poorly trained operators
Shut off safety systems
Helicopter drops
Coverup
Consequences
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Deaths of plant and workers
Medical problems (short and large term)
Thyroid cancer
Contaminated soil as far as Great Britain
Billions of $
Comparison
• A key difference between the Fukushima
accident and the Chernobyl accident was that
the Chernobyl explosion shattered the fuel
and flung it out of the reactor building, while
at Fukushima there was no steam explosion
driven by the release of fission energy.
Three Mile Island
• Partial meltdown
• No radiation escaped
• Caused fear of nuclear power and cost $ in
terms of clean up
• Operator error and lack of safety backups in
design
• In some ways the accident showed how the
kind of catastrophic disaster at Chernobyl is
avoidable
types
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Generation I – retired; one of a kinds
In operation Gen II and Gen III
Gen II was a large design changes
Gen III and Gen II, upgraded with many safety
features along the way
• Gen III plus (passive safety systems)
• Gen IV, 30 yrs away
Gen IV
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Very High Temperature Reactor
Advance Nuclear Safety;
Address Nuclear Nonproliferation and
Physical Protection Issues;
Are Competitively Priced
Minimize Waste and Optimize Natural
Resource Utilization
Compatible with Hydrogen Generation
Gen IV Roadmap - 2002
• Solicited design models
• Chose six design models to base future
research
• Out of these six, the DOE has relatively
recently selected two for further investment
– Very-High Temperature Reactor (VHTR)
– Sodium-Cooled Fast Reactors (SFR)
Very-High Temperature Reactor
• Reach temperatures > 1000 C
• Drive water splitting for hydrogen production
– 2 M m3
• 50% efficiency for producing electricity
• Heat and power generation
• Fuel recycling/reprocessing
• Fuel coating requirements, absorbers, ceramic
rods, vessel materials, passive heat removal
systems
Show pic
Actinide management
• To support effective actinide management a
fast reactor must have a compact core with a
minimum of materials which absorb or
moderate fast neutrons. This places a
significant heat transfer requirement on the
coolant.
Sodium-Cooled Fast Reactors
• Old technology
• Management of waste
• Low system pressure, high thermal conductivity, large safety
margins.
• Burns almost all of the energy in uranium, as opposed to 1%
in today’s plants
• Smaller core with higher power density, lower enrichment,
and lower heavy metal inventory.
• Primary system operates at just above atmospheric pressure
• Secondary sodium circulation that heats the water (if it leaks,
no radiation release)
• Demonstrated capability for passive shutdown and decay heat
removal.