Boiling Water Reactor

Kevin BurgeeJaniqua Melton

Alexander Basterash

What it isA type of light water nuclear reactor used for the

generation of electrical powerIt is the second most common type of electricity-

generating nuclear reactor after the PWR (Pressurized Water Reactor)

BWR vs PWRBWR

The reactor core heats water, which turns to steam and then drives a steam turbine

PWR The reactor core heats

water (does not boil) then exchanges heat with a lower pressure water system which then turns to steam to drive a steam turbine

-Uses mineralized water as a cooler and neutron moderator-Heat is produced by nuclear

fission in the reactor core, causing the water to boil and

produce steam-Steam is used directly to drive a turbine after which it is cooled in a condenser and turned back to

liquid water-It is then returned to the reactor

to complete the loop

Control SystemChanged by two ways

Inserting or withdrawing control rodsChanging the water flow through the reactor core

Positioning control rods is the standard way of controlling power when starting up a BWRAs control rods are withdrawn, neutron absorption

decreases in the control material and increases in the fuel, so reactor power increases

As control rods are inserted, neutron absorption increases in the control material and decreases in the fuel, so reactor power decreases

Control by Flow of Water As flow of water through

the core is increased, steam bubbles are more quickly removed, amount of water in the core increases, neutron moderation increases

More neutrons are slowed down to be absorbed by the fuel, and reactor power increases

As flow of water through the core is decreased, steam voids remain longer in the core, the amount of liquid water in the core decreases, neutron moderation decreases

Fewer neutrons are slowed down to be absorbed by the fuel, and the power decreases

AdvantagesThe reactor vessel works at substantially lower

pressure levels (75 atm) compared to a PWR (158 atm)

Pressure vessel is subject to less irradiation compared to a PWR, so it does not become as brittle with age

Operates at lower nuclear fuel temperatureFewer components due to no steam generator or

pressure vessel

SizeA BWR fuel assembly comprises 74-100 fuel rodsThere are approximately 800 assemblies in a

reactor coreThis holds up to about 140 tons of uranium

The number of fuel assemblies is based on the desired power output, reactor core size, and reactor power density

Steam Turbine Steam produced in the

reactor core passes through steam separators and dryer plates above the core, then goes directly to the turbine

The water contains traces of radionuclides so the turbine must be shielded during operation and radiological protection must be provided during maintenance

Different VariationsEarly series

BWR/1-BWR/6Advanced Boiling Water Reactor (ABWR)Simplified Boiling Water Reactor (SBWR)Economic Simplified Boiling Water Reactor

(ESBWR)

BWR/1-BWR/6The first, General Electric, series of BWRs

evolved though 6 design phasesBWR/4s, BWR/5s, and BWR/6 are the most

common types in service today

BWR/4

Advanced Boiling Water Reactor

Developed in the late 1980sUses advanced technologies such as: computer

control, plant automation, in-core pumping, and nuclear safety

Power output of 1350 MWe (megawatt electrical) per reactor

Lowered probability of core damage

ABWR

Simplified Boiling Water Reactor

Produces 600 Mwe per reactorUsed “passive safety” design principles

Rather than requiring active systems, such as emergency injection pumps, to keep the reactor in safety margins, was instead designed to return to a safe state solely through operation of natural forces

Ex. If the reactor got too hot, a system would release soluble neutron absorbers or materials that greatly hamper a chain reaction of absorbing neutrons. This would then bring the reaction to a near stop

Economic Simplified Boiling Water Reactor

Output of 1,600 Mwe per reactorHas the features of an ABWR with the distinctive

safety features of the SBWRHas been advertised as having a core damage

probability of only 3×10−8 core damage events per reactor-yearThis means there would need to be 3 million

ESBWRs operating before one would expect a single core-damaging event during their 100-year lifetimes

ESBWR

DisadvantagesContamination of turbine by short-lived

activation products (Nitrogen-16)An unmodified Mark-1 containment can allow

some degree of radioactive release to occur