POWER August 2012 - 66

NUCLEAR
The Fukushima Effect
Critics of multiple-reactor sites are quick to
reference the events at Fukushima, where the
plant operator was forced to shift resources
from one unit to another, thus making these
sites less attractive from a safety perspective.
However, the events at Fukushima were, more
than anything else, the result of plant and site
configuration. This viewpoint also ignores
the inherent differences between SMRs and
the Fukushima plant, Mowry said. Table 2
summarizes the multi-layer design features
that mitigate extreme beyond-design-basis
challenges and " Fukushima-type " events.
The Babcock & Wilcox Co. manufactures
naval nuclear reactors for submarines and
aircraft carriers. For security purposes, U.S.
military technology will not be transferred to
the mPower reactor project; however, the factories
already exist and the additional investments
for the initial stages of market adoption
are minimal. Another advantage is that the
reactor is small enough for the reactor vessel
head and bottom to be forged in North America.
The B&W Nuclear Operations Group's
Barberton, Ohio, and Mount Vernon, Ind., locations
specialize in the design and manufacture
of large, heavy components. These two
Table 2. Multi-layer design features mitigate extreme beyond-designbasis
and " Fukushima-type " events. Source: Babcock & Wilcox mPower Inc.
Events and
threats
Earthquakes
and floods
Loss of offsite
power
Station
blackout
Emergency
core cooling
B&W mPower reactor design features
Seismic attenuation: Deeply embedded reactor building dissipates energy, limits motion.
" Water tight " : Separated, waterproof reactor compartments address unexpected events.
Passively safe: AC power not required for design basis safety functions.
Defense-in-depth: Two backup diesel generators for grid-independent AC power.
Three-day safety-related batteries: Safety-grade batteries support fully automated
mitigation of all design basis accidents for 72 hours.
Defense-in-depth non-safety-related batteries: Provide additional redundant power to
important systems and plant control functions for beyond-design basis accidents.
Gravity, not pumps: Natural circulation decay heat removal; water source in containment.
Robust margins: Low core power density and small core limit energy release.
No operator action required: For 72 hours to mitigate consequences of all design basis
accidents.
Containment
integrity and
ultimate heat
sink
Spent fuel
pool integrity
and cooling
Passive hydrogen recombiners: Prevention of explosions without need for power supply.
Internal cooling source: Ultimate heat sink inside underground shielded nuclear island.
Extended performance window: At least 14 days without need for external intervention.
Protected structure: Underground, located within nuclear island.
Large heat sink: 30+ days before boiling and uncovering of fuel, and 20-year
storage capacity.
2. The B&W mPower reactor electric power generation cycle. Source: Babcock & Wilcox mPower Inc.
Primary containment
barrier
MSIV
RSB barrier
Moisture
separator reheater
MS stop valve
Extraction to deaerator
& LP FWH
TEWAC generator (3,600 rpm)
HP turbine
LP turbine
Extraction to HP
FW heater
Main steam
turbine bypass
LP extraction
Main condenser
Deaerator
Main condenser hotwell
MFWIV MFW
control
valve
HP extraction
HP FWH
LP
extraction
LP FWH
Condensate
polisher
Reactor
Main feedpumps
August 2012 | POWER
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67
Condensate
pumps
Gland seal
steam
Gland steam
condenser
LP FWH
LP FWH

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POWER August 2012

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