Under The Hood With Duncan Williams - South Korean APR 1400 Reactor Plant Surprises UAE Officials

South Korean APR 1400 Reactor Plant Surprises UAE Officials

 - By Duncan Williams -

Officials in the United Arab Emirates (UAE) are currently analyzing bids for a $40 billion contract to build and operate the country’s first nuclear reactor.  Although the bidders include well-established leaders in the nuclear industry, a Wall Street Journal article published on November 16, 2009, titled “Korea Gains as Nuclear-Plant Bidder,” indicates that a bid submitted by a South Korean consortium is much more competitive than anyone first thought.  The UAE also accepted bids from a French consortium, including Areva, Gaz de France (GdF), Suez SA, Electricité de France and Total SA, as well as a US-Japanese consortium, including General Electric Co. and Hitachi Ltd.

The South Korean consortium is led by Korea Electric Power Corp., which includes the construction units of Samsung and Hitachi, and Westinghouse, a unit of Japan’s Toshiba Corp.  Korea Electric Power Co. works in conjunction with several other Korean entities, including Korea Nuclear Fuel Co., Ltd., Korea Hydro & Nuclear Power Co., Ltd., Korea Plant Service & Engineering Co., Ltd., and Korea Power Engineering Co., Ltd.

According to the Wall Street Journal article, the Korean team submitted a bid for a reactor known as the Advanced Power Reactor (APR) 1400, which is a pressurized water reactor having a capacity of 1400 MW.  There are currently no APR1400 plants in operation, but four of these plants are currently being built in the Republic of Korea and are scheduled to become operational in 2013-14.  

The UAE officials were surprised that the APR1400 design rivals the submissions from the other consortiums.  The French consortium submitted designs for the European Pressurized Reactor (EPR), and the US-Japanese consortium submitted designs for the Advanced Boiling Water Reactor (ABWR).  All three plants are designed to operate for 60 years – twice as long as most conventional nuclear reactors in use today.  Additionally, all three plant designs require refueling after approximately 18 months of operation.  While the EPR will take 57 months to build, both ABWR and the APR1400 will only take 48 months to construct.

Surprisingly, the APR1400 includes safety features not found in conventional reactors.  For example, the design includes a missile shield to defend against both an internal and external missile attack.  The design even includes seismic restraints and improved materials that would prevent damage to the reactor in the event of an earthquake.

The basic design of the reactor vessel of the APR1400 is shown on Korea Hydro & Nuclear Power’s (KHNP’s) website. The reactor vessel contains the nuclear fuel which drives the fission process in the reactor.  In order to remove heat produced by the fission process, water is pumped into the reactor vessel through 4 inlet nozzles, and exits through 2 outlet nozzles.  The outlet nozzles are placed vertically higher than the inlet nozzles in order to promote natural circulation in the event of a loss of pumps.

The nuclear fuel for the APR1400 was designed by Korea Nuclear Fuel.  The APR1400 uses uranium dioxide, processed from enriched uranium-235.  To manufacture the nuclear fuel, the uranium dioxide must first be processed into a powder form.  It is then pressed into cylindrical pellets of approximately 10mm in length, 8mm in width, and weighing 5.2 grams.  Approximately 365 pellets are then stacked end-to-end inside a hollow fuel rod made of a zirconium-niobium alloy.  

A spring is placed on one end of the tube to keep the pellets tightly packed and held in place.  The tube is then pressurized with helium gas as both ends of the fuel rod are welded shut.  The helium gas improves the transfer of heat from the fuel pellets to fuel rod.  Helium is an inert gas, so it won’t react with the pellets as the reactor is operating.

PLUS7 fuel assembly - click for full sizeThe sealed fuel rods are then arranged into what is known as a PLUS7 fuel assembly.  In order to produce one PLUS7 fuel assembly, hundreds of fuel rods are formed into a rectangular box arrangement and held in place by a series of spacer grids.  These novel spacer grids are partly made of inconel, and include mixing vanes which - unlike conventional nuclear reactors - intentionally create a turbulent flow of water over the fuel rods.  Turbulent flow is necessary in the APR1400 to prevent the water from boiling in the reactor vessel where the high-energy nuclear fuel is located.

Unlike the ABWR design submitted by the US-Japanese consortium, boiling in the reactor vessel of the APR1400 can cause severe safety concerns.  Without a turbulent flow, the water would form a smooth stream across the exterior of the fuel rod and would absorb an excessive amount of heat.  If the water begins to boil, bubbles would coalesce on the surface of the fuel rod, forming a thin film of air that prevents heat removal.  As the heat builds up in the fuel rod, the metal would begin to melt resulting in the release of uranium, along with its fission products, into the water.

To prevent this, spacer grids are formed with mixing vanes which create a turbulent flow of water throughout the reactor vessel.  [Mixing vane mid grid]  Turbulent water flow reduces the amount of time a particle of water is adjacent to the fuel rod, thus preventing boiling and the subsequent formation of thin layers of film.  As can be seen in the diagram, the spacer grids are square-shaped and can hold 16 x 16 fuel rods.  Sensors are placed in the large central hole in the spacer grid, and support guides containing non-nuclear material are placed in the four remaining large cavities to provide structural support.  Fuel rods are positioned in the smaller holes in the grid and are held in place by a combination of springs and dimples.  This unique design allegedly reduces the wearing and scratching of the fuel rods.  The spacer grids near the bottom and top of the PLUS7 fuel assembly also include filters which prevent particulates from entering or exiting the reactor vessel.

spring - click for full sizeTo get an idea of the power output by the APR1400, one uranium dioxide pellet produces about 1,600 KWh of electricity, which is the average amount of electricity that one household uses over an 8 month period.  Each fuel rod contains 365 pellets, and one PLUS7 fuel assembly is made up of 236 fuel rods.  This means that each fuel assembly contains about 86,140 uranium dioxide pellets.  Since there are 241 fuel assemblies in each APR1400 reactor vessel, one APR1400 reactor can generate enough electricity to power roughly 13.3 million homes for one year.

control room - click for full sizeThe APR1400 also comes with a sleek control room, which places many of the reactor plant operators in one central location in order to improve communication.  Many of the redundant operational backup systems found in conventional reactor plants have been eliminated.  The computer consoles in the control room not only display overviews and instructions for upcoming procedures, but they also display links to any other cross-referenced procedures.

IRWSTAnother interesting feature of the APR1400 design is the in-containment refueling water storage tank (IRWST), which is kept in the same area as the reactor vessel.  The purpose of the IRWST is to quickly fill the reactor in the event of a pipe rupture or any other casualty causing a loss of coolant.  Instead of placing the IRWST in a separate area connected to the reactor vessel via piping and valves as in a conventional reactor, the IRWST in the APR1400 design surrounds the reactor like a moat in a doughnut shaped tank.  The close proximity of the IRWST ensures that water will be continuously supplied to the reactor vessel to remove heat in the event of a loss of coolant casualty.

Of course, one of the biggest factors influencing the UAE officials is the cost of the reactor plants.  Even though the price tag attached to each bid remains confidential, it is apparent that the Korean consortiums bid is extremely competitive.  If the APR1400 is chosen, it would be the first time that Korea would export its nuclear technology to another country, solidifying its place as a key player in the global nuclear industry.

Last Week's Column:

Under The Hood With Duncan Williams - Everything You Always Wanted To Know About MOX Fuels

Everything You Always Wanted To Know About MOX Fuels  - By Duncan Williams - Last week a nuclear reactor in Genkai, Japan, became the first Japanese nuclear reactor to use a type of nuclear fuel known as mixed-oxide (MOX) fuel.  Although uncommon in Japan and America, MOX fuel is currently used in at least 30 reactors throughout ...

About Duncan Williams
Duncan Williams graduated from the University of Florida in 1994 with a B.S. in Physics, and a minor in mathematics.  Upon graduation, he was commissioned  in the U.S. Navy where he completed training in the Navy’s Nuclear Propulsion program.  He then served onboard an aircraft carrier, the USS Theodore Roosevelt, as a reactor control division officer.  Onboard, he was responsible for the operation and maintenance of the electrical and mechanical components that make up the reactor control systems.  This includes the control rod drive mechanisms, the reactor safety and emergency systems, the reactor coolant pump systems, and the ion exchangers.  He also developed and implemented ship-wide reactor safety drills in order to educate sailors in reactor safety.

Duncan then transferred to the U.S. Naval Academy, where he served as a senior instructor teaching Thermodynamics to senior cadets.  While serving as an instructor at the Naval Academy, Duncan attended night law school at the George Washington University Law School.  After receiving his J.D. in 2004, he resigned his commission and began working as an intellectual property associate with Kenyon & Kenyon LLP.  While at Kenyon & Kenyon, he drafted numerous patents relating to medical devices, electronic devices, telecommunications, as well as other technologies.  He also has experience in all stages of patent litigation, and has represented numerous Fortune 500 companies in protecting their intellectual property rights.  Duncan is currently an intellectual property associate at Blank Rome LLP.

If you have questions, comments, or know of a patent that you think Duncan should review E-mail Duncan Williams>> duncan@nuclearstreet.com 

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  • Although I enjoy your "under the hood" posts I'm not sure you got far enough under this time.  You have ignored the evolutionary origins of the design which start with Combustion Engineering's System 80 as operating at Palo Verde and proceed through the scaled down 1000 MWe versions built in Korea with technology transfer from then ABB-CE. The Advanced Light Water Reactor (ALWR) features like the IRWST that were introduced for the USNRC  Design Certification of Sytem 80+ and then applied to development of the Korean Next Generation Reactor (KNGR) with  additional features developed in Korea

  • Thanks for your comment.  You are correct in that the APR1400 has roots in Combustion Engineering designed nuclear plants.  Let's trace thiese roots starting back in the 80s.  I'll provide links to support my assertions, but you may have to copy this links to the URLs in your browser instead of simply clicking on it.

    The nuclear plants in Palo Verde are based on the Combustion Engineering 80 design, and were placed online in Arizona in 1986: www.eia.doe.gov/.../palo_verde.html

    In 1990, Combustion Engineering became a subsidiary of a Swiss-Swedish conglomerate called Asea Brown Boveri (ABB): en.wikipedia.org/.../Combustion_Engineering

    The Combustion Engieering 80+ design was certified by the NRC in 1997: www.nrc.gov/.../s97-12.html.  I belive this design was capable of running on 100% MOX fuels.  There were no licensees in the US for this design.

    In 2000, Westinghouse bought ABB: www.westinghousenuclear.com/.../1980_2003.shtm

    As I mentioned in the article, Westinghouse is part of the Korean consortium which made the bid for the APR1400.  In fact, Westinghouse and Korea Nuclear Fuel have recently formed a new company, called KW Nuclear Components Comapny, Ltd., to develop and manufacture reactor plant parts for plants in South Korea, including the APR1400.  This new company will be located in South Korea: nuclearstreet.com/.../westinghouse-knf-team-to-manufacture-control-element-assemblies.aspx

    As for the IRWST, you are correct that the donought design was taken from the CE 80+.  Unlike the APR1400, the containment building design for the CE 80+ was a reinforced sphere.  Here is a link to a National Academies Press website showing a cross-sectional view of the CE 80+ containment building and IRWST: www.nap.edu/openbook.php

    I am always willing to go further under the hood, so keep the comments coming.

  • Anonymous


    you're quite right mentioning the hazard of departure from nucleate boiling on th fuel rods. However, the bubbles forming in boiling water are steam, not air.

  • Anonymous

    Hi Duncan,

    Great article.  The technical information is accurate, but the economics may be off a bit.   The three Palo Verde units combined claim to serve 4 million people.


    Your example appears to take credit for the potential energy in the fuel, not the typical energy generated by each unit.

  • Unfortunately, a lot of the technical information in the article is not accurate, and Mr. Williams does not know how to do basic math.  He also does not know how much electricity "a household" uses on a monthly or yearly basis.  Let's look at the following paragraph:

    "To get an idea of the power output by the APR1400, one uranium dioxide pellet produces about 1,600 KWh of electricity, which is the average amount of electricity that one household uses over an 8 month period.  Each fuel rod contains 365 pellets, and one PLUS7 fuel assembly is made up of 236 fuel rods.  This means that each fuel assembly contains about 86,140 uranium dioxide pellets.  Since there are 241 fuel assemblies in each APR1400 reactor vessel, one APR1400 reactor can generate enough electricity to power roughly 13.3 million homes for one year."

    First, a UO2 pellet produces no electricity.  It produces heat, which is used to make steam to turn a turbine to make electricity.  However, if Mr. Williams' data are about the uranium content (5.2 g) of a fuel pellet is correct, each pellet contains about a 1/4 of a gram of U-235, assuming about 5% enrichment.  (Note:  It's actually a little less than that, because of the mass of oxygen in UO2; the mass of U is only about 88% of the total.)  If all of the U-235 in a pellet were fissioned (which is not the case, but we'll ignore that here), some relatively simple math (along with knowledge of the energy released in a fission event and the number of atoms in a gram of U) indicates that the pellet would generate about 20 billion joules of heat.  One killowatt-hour (kWh, not KWh) is one thousand joules per second times 3600 seconds per hour, or 3.6 million joules, which means that the pellet--over its lifetime in the reactor (which can be 3-5 years) generates about 6000 kWh of heat (rounding off for the sake of simplicity).  If the thermodynamic efficiency of the plant is about 35%, which is about what KEPCO claims, each pellet would generate the equivalent of about 2000 kWh of electricity over its lifetime.  Assuming an average lifetime of 4 years, this works out to about 500 kWh of electricity per pellet per year.  

    Now, I don't know about Mr. Williams' "household," but where I live, an "average" family uses somewhere between 1000 and 2000 kWh per month of electricity (not 1600 kWh in 8 months).  Let's call it 1000, to make the math easier, since 500 x 2= 1000.  Thus, 24 pellets would be needed for one year's electricity.  With about 21 million fuel pellets in the reactor, one finds that  the output is enough for around 900,000 households per year.  Of course, it might be easier to say that with an electric output of about 1400 MW, if the plant operates for about 8000 hours per year (roughly a 90% capacity factor), it would generate about 11.2 million MWh, or 11.2 billion kWh.  If one household uses about 12000 kWh per year (rounding off 12 x 1000), this also works out to around 900,000 households.  Call it a million, in round numbers.  In any event, 13.3  million  (Mr. Wllliams' result) is a rather preposterous number.

    This comment is already too long, or I would elaborate on other errors, such as Mr. Williams' incorrect implication that mixing vanes are not used in other reactor fuel assemblies and his explanation of the effect of turbulence on convective heat transfer.  Mr. Williams may be a fine attorney--but his engineering and math skills leave much to be desired.

  • Incidentally, my above comment also serves to illustrate the amazingly concentrated energy content of uranium.  Using my numbers, one household's annual electric energy needs can be satisfied by roughly 1.5 g of U-235 (24 pellets times 1/16-gram of U, assuming the 1/4-gram in the pellet has a 4-year reactor lifetime).  Anthracite coal, on the other hand, puts out about 27 MJ/kg, which means that for the equivalent energy output--even assuming a 40% thermodynamic efficiency for a coal-fired power plant--a single household would require about 4000 kg (4 metric tons) of coal!