Nuclear Power Plants
Sunny Mistry
Fall 2014
Introduction:
As the world population continues to increases each year, the requirement to provide sufficient
electricity to supply the population continues to rise. With an increase in electricity requirements,
electricity generation also increases which causes an increase in pollution due to CO2 emissions. This
increase in pollution can change the global climate. This study will evaluate the heat generated by
nuclear fuel and evaluate parametric studies using different variables using the COMSOL software suite.
Additionally, this study will compare the carbon footprint of nuclear power plant and a fossil fuel power
plant such as coal.
Background:
Nuclear power has been around for quite some time. The first commercial pressurized water reactor
was developed in the 1960s by Westinghouse. This reactor had a capacity of 250 MW and was located
in Rowe, MA. (Error! Reference source not found.) Meanwhile, General Electric designed first boiling
water reactor the Dresden 1. This reactor was designed for a capacity of 250 MW and was first started
in 1960. (0)
Figure 1: Pressurized Water Reactor (Error! Reference source not found.)
Pressurized water reactors have three major fluid systems. System 1 is the primary system which is
water that passes through the nuclear fuel with in the reactor. This fluid system pumps fluid into the
reactor. The reactor control rods are raised to expose the fuel pin, which causes a fission reaction and
increases in temperature of the coolant media. As the primary fluid system passes through the reactor,
it increases in temperature and since the primary fluid system is pressurized the boiling point of the
water in increased to allow for more heat carrying capacity. The primary fluid system water is routed
into the steam generator, which is where the water is run through a heat exchanger, and used to create
steam using a secondary fluid system. The “cooler” water coming out of the steam generator is cycled
back into the pump and cycles through the primary fluid system again and is never mixed in with the
secondary system. On the secondary system the fluid in the steam generator flashes to steam and is
sent into the turbine which uses steam to spin the blades on the turbine. The turbine is attached to a
shaft which is tied into the generator which generators electricity and provides it to the grid. As the
steam condenses back into water after exiting the turbine generator the water is still relatively hot
therefore it is cooled by a third system. The third system further cools the water coming out of the
steam generator by tubes that tie into a cooling tower. The cooling tower further lowers the water
temperature of the secondary system creating a bigger temperature differential between the primary
fluid system and the secondary fluid system to increase the heat carrying capacity of the steam. (Error!
Reference source not found.)
As the next decade progressed, the design of the nuclear reactors became more and more advanced to
where higher capacity reactors became available. Capacities of 1000 MW became available which
required major construction. The advancement in nuclear technology was applicable to both the
pressurized water reactor and the boiling water reactor configurations. (0)
In the 1950, the first nuclear powered submarine, the USS Nautilus, was put to sea. This advancement
in submarine design allowed the USS Nautilus to stay submerged traveling up to 25 knots for weeks on
end. This technology was then implemented on multiple naval ships such as the USS Enterprise, an
aircraft carrier powered by eight nuclear reactors, and a cruiser the USS Long Beach, which was powered
by two nuclear reactors. Naval ships continue to utilize the nuclear technology as a propulsion system.
(Error! Reference source not found.)
Discussion:
This paper goes into parametric studies of the effects of changing variables for the basic nuclear fuel pin
problem found in homework 7 problem 2. The nuclear fuel pin in the problem had the dimensions
shown below in Figure 1.
Figure 2: Fuel Pin - Elevation View
As stated above, multiple variables were modified to see the effects of the variable on the nuclear fuel
pin. This report goes into the details of modifying each variable and looks at the resultant from the side
study. Each parametric study is broken down into a sub section within the report to show the effect of
each variable. These studies were based on using the COMSOL MultiPhysics software suite. The
following modifications were made to the fuel pin:
1.
2.
3.
4.
5.
6.
Baseline Study:
Decreased Inflow Water Temperature
Decreasing Inflow Water Thickness
Decreased Inflow Water Velocity
Increasing Height of Fuel Pin
Increased Inflow Water Velocity
Increasing Surrounding Water Thickness
This study evaluated the fuel cell from Homework 7 Problem 2. In this problem, the temperature
gradient was evaluated in a fuel pin. This first case was assuming a uranium fuel pin to have a 15 mm
radius, a protective steel layer that is 3 mm and surround in 30 mm of water. The height of the fuel pin
is 300 mm. The thermal conductivities of the nuclear fuel and the clad are 30 W/(m K) and 21.5 W/(m K).
The internal heat generation from the nuclear fuel is 4E6 W/m3. It was assumed that the water
temperature around the clad was 573 K and has a velocity of 0.001 m/s.
Figure 3: Fuel Pin - Elevation View
Figure 4: Baseline Fuel Pin Results
From this study it can be concluded that the temperature at the top of the fuel pin will be about 964 K.
This shows that the cooler water which is flowing up from the bottom is cooling the fuel pin initially, but
as the water travels up the fuel pin the uranium continues to heat up and the water is able to remove
some of the heat from the uranium.
Parametric Study 1:
This first side study evaluated the effects of keeping the inflow water temperature lower. The
temperature was modified from 573 K to 473 K to see the effects of the inflow temperature has on the
overall system. All other variables were left unchanged as stated above in the baseline section.
Figure 5: Parametric Study 1 - Fuel Pin Configuration
Figure 6: Parametric Study 1 - Fuel Pin Results
As it can be seen in Figure 6, lowering the inflow temperature lowers the overall temperature at the top
of the fuel pin. This is expected as the inflow water temperature is what removed heat from the fuel pin
and moves it into the steam generators. Therefore, providing a lower inflow temperature for a longer
length of the fuel pin should be able to provide increase heat carrying capabilities from the water. This
would allow for hotter water to reach the steam generators thus creating more steam required to spin
the turbines.
Parametric Study 2:
In this study, the water volume around the fuel pin was reduced from 30mm to 7.5mm. The purpose of
this side study is to evaluate the effects of the thickness of the water around the fuel pin and the impact
to the fuel pin temperature. The remainder of the variables were left unchanged.
Figure 7: Parametric Study 2 – Fuel Pin Configuration
Figure 8: Parametric Study 2 - Fuel Pin Results
The results from this study shows that the thickness of the surrounding water plays a key part in
reducing the overall temperature of the uranium fuel pin. This creates a significantly higher
temperature at the top of the fuel pin of 4838E3 K. This is caused by there not being enough water
capacity to transfer the heat out of the fuel pin.
Parametric Study 3:
In this study the water velocity surrounding the fuel pin was reduced from 0.001 m/s to 0.0001 m/s to
see the effects of inflow water velocity has on the fuel cell temperatures. All the other variables were
left unchanged.
Figure 9: Parametric Study 3 Fuel Pin Configuration
Figure 10: Parametric Study 3 Fuel Pin Results
As a result, seen in Figure 10: Parametric Study 3 Fuel Pin Results, reducing the inflow water velocity
increases the overall temperature of the fuel pin to 1043 K. This concludes that decreasing velocity of
the water passing the fuel cell has a negative effect on the fuel pin. This is because the water is not able
to draw the heat out of the fuel cell.
Parametric Study 4:
In this side study, the height of the fuel pin has been increased from 300mm to 500mm. This was to
understand the effects of increasing the height of the fuel pin and to see the impacts to the temperature
of the fuel pin.
Figure 11: Parametric Study 4 Fuel Pin Configuration
Figure 12: Parametric Study 4 Fuel Pin Results
Based on this evaluation it can be seen that increasing the height of the fuel pin increases the overall
surface temperature of both the fuel pin assembly and the water surrounding the fuel pin. This is
because there is more uranium producing heat and that heat has to be driven into the water.
Parametric Study 5:
In this parametric study, the overall velocity of the inflow water was increased from 0.001 m/s to 0.01
m/s. This increase would require more pump power to increase the flow of water into the reactor in
order to simulate this. Increasing the water speed does require more power because the pumps have to
work at a higher speed to pump more water into the system.
Figure 13: Parametric Study 5 Fuel Pin Configuration
Figure 14: Parametric Study 5 Fuel Pin Results
Based on the results seen in Figure 14, the temperature is lower than in the baseline study. This is
because the water is able to move faster pass the fuel pin assembly and therefore above to pull more
heat from the uranium fuel out and away faster, and thus lowering the overall temperature of the fuel
pin.
Parametric Study 6:
In this parametric study the water thickness around the fuel pin was increased from 30mm to 300mm.
This is to understand the arrangement requirements for how close each uranium fuel assembly can be
to another assembly. Similarly the other parameters of this study were not modified.
Figure 15: Parametric Study 6 Fuel Pin Configuration
Figure 16: Parametric Study 6 Fuel Pin Results
Based on this evaluation it can been seen that the water surrounding the fuel pin has a very little impact
on the overall temperature of the fuel pin. It does seem that the water thickness that was set in the
given problem may have already been set to the optimal thickness and therefore increasing the water
thickness does not impact the overall temperature of the water.
Comparison to coal power plant:
A nuclear power plant compared to a coal-fired power plant has its own pros and cons. In this section
this study will evaluate nuclear power from a cost, environment and lifecycle aspect and compare it to a
coal-fired power plant.
Cost Comparison:
In general, site preparation, construction, manufacturing, commissioning and financing a large nuclear
reactor power plant is very costly. Thousands of workers and large amounts of steel and concrete are
required for construction of the facility and design of the nuclear components. Also included in the cost
would be the cost of fuel, operation and maintenance, and provisions for funding the cost of
decommissioning the plant and the end of life. This decommissioning cost will include discarding the
fuel and waste management appropriately. It is estimated that the average nuclear power plant costs
about $5,339 kW. (Error! Reference source not found.) About half of this cost is associated to the cost
of manufacturing the reactor fuel. The cost of 1 kg of uranium as reactor fuel is $2360. The uranium
fuel is highly concentrated which makes this energy source easily and cheaply transportable. One
kilogram of uranium is equivalent to about 20,000 times as much energy as the one kilogram of coal.
(Error! Reference source not found.) Based on a similar evaluation done for a coal-fired power plant
the estimated cost for a coal-fired power plant was $3,500 per kW. (Error! Reference source not found.)
Environmental Comparison:
Nuclear power plant emit no carbon dioxide, sulfur dioxide, nitrogen oxides, mercury or other toxic
gases. A properly functioning nuclear power plant should not attribute to any climate change. The
cooling towers seen at nuclear power plant are simply provided for cooling of water therefore only emit
water vapors. If a nuclear plant is located near a water source such as a river, lake or ocean the hot
water from the cooling towers are usually discharged into the water therefore increasing the local
temperate in the area. This has a slight impact on the local fish and algae population. (6)
Coal-fired power plants emit a great amount of greenhouse gases and other harmful pollutants to the
atmosphere on a daily basis. This contribution to the atmosphere increases the formation of acid rain,
nitrogen oxides, which when combined with VOCs can create smog and toxic compounds of mercury.
Burning coal can release over two pounds of carbon dioxide into the atmosphere for every kW-h of
electricity it creates. (6)
Life Cycle:
Based on a life cycle analysis that was completed on different electricity generation sources in 2011, the
results show that on average Coal-fired power plants produce the most amount of CO2/GW-h. This study
those that among the technologies listed in the analysis nuclear is a clean energy source and produces
on average 29 CO2/GW-h, which is small compared to output from other sources.
Figure 17: Summary of Lifecycle Green House Gases Emission Intensity
Conclusion:
In conclusion, it can be seen that the performance of the nuclear fuel pin as shown above has many
variables to attribute to the overall performance of the system. This study did not evaluate multiple
variables and the overall effect to the temperature of the system as it was outside of the scope of this
report. The overall cost of a nuclear reactor is less than the overall cost of a coal-fired power plant. A
nuclear reactor provides less CO2 emissions than a coal-fired plant, and when evaluated from a life cycle
aspect a nuclear power plant provides lower overall emissions when compared to coal-fired plant.
1.
2.
3.
4.
5.
6.
7.
8.
Works Cited
Capstick, Bob. "Yankee Nuclear Power Plant." Yankee Nuclear Power Plant. N.p., n.d. Web. Dec.
2014. <http://www.yankeerowe.com/>.
"Nuclear Power in the USA." Nuclear Power in the USA. World Nuclear Association, Nov. 2014.
Web. Dec. 2014. <http://www.world-nuclear.org/info/Country-Profiles/Countries-T-Z/USA-Nuclear-Power/>.
"Pressurized Water Reactor (PWR)." Pressurized Water Reactor (PWR). Nuclear Tourist, 19 Dec.
2005. Web. Dec. 2014. <http://www.nucleartourist.com/type/pwr.htm>.
"Nuclear-Powered Ships." World Nuclear Association. N.p., 24 Nov. 2014. Web. Dec. 2014.
<http://www.world-nuclear.org/info/non-power-nuclear-applications/transport/nuclearpowered-ships/>.
"The Economics of Nuclear Power." Nuclear Power Economics. World Nuclear Association, Sept.
2014. Web. Dec. 2014. <http://www.world-nuclear.org/info/Economic-Aspects/Economics-ofNuclear-power/>.
Schlissel, David, Allison Smith, and Rachel Wilson. "Coal-Fired Power Plant Construction Costs."
Synapse Energy. N.p., July 2008. Web. Dec. 2014. <http://www.synapseenergy.com/project/coal-fired-power-plant-construction-costs>.
Matthews, Mike. "Which One Is Better for the Environment: Coal or Nuclear?" Home Guides.
Demand Media, n.d. Web. Dec. 2014. <http://homeguides.sfgate.com/one-better-environmentcoal-nuclear-78760.html>.
Report, Wna. "Comparison of Lifecycle Greenhouse Gas Emissions of Various Electricity
Generation Sources." Comparison of Lifecycle Greenhouse Gas Emissions of Various Electricity
Generation SourcesContents (n.d.): n. pag. World Nuclear Association. June 2011. Web.
<http://www.worldnuclear.org/uploadedFiles/org/WNA/Publications/Working_Group_Reports/comparison_of_life
cycle.pdf>.