Nuclear Steam Power Plants
1. Pressurized Water Reactor (PWR)
Pressurized water reactors (PWRs) are nuclear power reactors that use ordinary
water under high pressure as coolant and neutron moderator. The primary coolant loop is kept
under high pressure to prevent the water from boiling. This puts strong requirements on the
piping and pressure vessel and hence increases construction costs.
PWRs are one of the most common types of reactors and are widely used all over the world.
More than 230 of them are in use to generate electric power.
PWR has two coolant loops, so the water in the secondary loop is not contaminated by
Ordinary water is used as primary coolant in a PWR and flows through the reactor at
a temperature of roughly 315°C (600°F). The water remains liquid despite the high
temperature due to the high pressure in the primary coolant loop (usually around 152 bar
[2200 psig]). The primary coolant loop is used to heat water in a secondary circuit that
becomes saturated steam (in most designs 62 bar [900 psi], 276°C [530°F]) for use in
the steam turbine.
In a Secondary Cooling System (which include the Main Steam System and the
Condensate-Feedwater Systems), cooler water is pumped from the Feedwater System and passes
on the outside of those steam generator tubes, is heated and converted to steam. The steam
then passes through the a Main Steam Line to the Turbine, which is connected to and turns
the Generator. The steam from the Turbine condenses in a Condenser. The condensed water is
then pumped by Condensate Pumps through Low Pressure Feedwater Heaters, then to the Feedwater
Pumps, then to High Pressure Feedwater Heaters, then to the Steam Generators. The diagram above
simplifies the process by showing the steam turbine, condenser, pumps, feedwater heaters, the
steam generator, moisture separator and Reheater.
Nuclear power plants generally cannot reheat process steam due to safety requirements for
isolation from the reactor core. This limits their thermodynamic efficiency to the order
2. Boiling Water Reactor (BWR)
The BWR typically allows bulk boiling of the water and is characterized by two-phase fluid
flow (water and steam) in the upper part of the reactor core.
The operating temperature of the reactor is approximately 300°C (570°F) producing steam at
a pressure of about 70 bar (1000 psi). Current BWR reactors have electrical outputs of 570
to 1300 MWe.
The circulated water eventually is heated enough to convert to steam. Steam separators in the
upper part of the reactor remove water from the steam. The steam then passes through the Main
Steam Lines to the Turbine. The steam typically goes first to a smaller High Pressure (HP)
Turbine, then passes to Moisture Separators, then to the 2 or 3 larger Low Pressure (LP) Turbines.
There are 3 low pressure turbines, as is common for 1000 MWe plant. The turbines are
connected to each other and to the Generator by a long shaft.
The steam, after passing through the turbines, then condenses in the Condenser, which is
at a vacuum and is cooled by ocean, sea, lake, or river water. The condensed steam then is
pumped to Low Pressure Feedwater Heaters. The water then passes to the Feedwater Pumps which in
turn, pump the water to the reactor and start the cycle all over again.
3. Gas-Cooled Reactor (GCR)
A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and
carbon dioxide as coolant. Although there are many other types of reactor cooled by gas, the
terms GCR and to a lesser extent gas cooled reactor are particularly used to refer to this type
The GCR was able to use natural uranium as fuel, enabling the countries that developed them to
fabricate their own fuel without relying on other countries for supplies of enriched uranium,
which was at the time of their development in the 1950s only available from the United States
or the Soviet Union.
Magnox is a type of nuclear power/production reactor that was designed to run on natural uranium
with graphite as the moderator and carbon dioxide gas as the heat exchange coolant. It belongs
to the wider class of gas cooled reactors. The name comes from the magnesium-aluminium alloy
used to clad the fuel rods inside the reactor. Like most other "Generation I nuclear reactors",
the Magnox was designed with the dual purpose of producing electrical power and plutonium-239
for the nascent nuclear weapons program in Britain. The name refers specifically to the United
Kingdom design but is sometimes used generically to refer to any similar reactor.
The Gas Turbine Modular Helium Reactor (GT-MHR) resulted after the work in the area of
Brayton-cycle-coupled nuclear reactor systems. It has many advantages in the areas of economics
and safety. With the modular helium reactor design, the GT-MHR provides additional flexibility
to be used in industrial processes requiring high process heat. The unique design of the
Brayton-cycle PCU offers additional advantages over conventional LWR steam turbines. Coupled
with the MHR, efficiencies of ~47%-51% are attainable; much higher than the ~32% of conventional
LWRs. In addition, the PCU and MHR require a smaller housing structure and no containment
building like that in LWRs. Gas turbine MHR's modular nature facilitates preconstruction and
remote assembly at the site, significantly reducing construction costs and time.
The current design has many advantages, which currently make it the most desirable option.
The vertical design eliminated bowing caused by gravity, facilitating that the turbocompressor
blades don't fail by coming in contact with the walls and allowing a higher rotational
asynchronous speed. A smaller footprint is required to house the equipment, lowering construction
TPT can help you in following questions:
- Optimization of thermodynamic design of FW Heaters and Deaerator
- Optimization of thermodynamic cycles improves of the efficiency of power plants
- Failure analysis & reliability/availability for improvement of existing heat exchangers