USA

U.S.A. and Nuclear Waste ...

Storage of Spent Fuel (January, 2010)

Yucca Mountain Nuclear Disposal Site Is Dead, Says Longtime Advocate (December, 2009)

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Nuclear Power Industry News is a blog about utilities, companies, suppliers in the nuclear energy market.
As posted at http://nuclearstreet.com/blogs/nuclear_power_news/archive/2010/01/06/Under-The-Hood-With-Duncan-Williams-_2D00_-Mitsubishi_1920_s-US_2D00_APWR-01062.aspx

Storage of Spent Nuclear Fuel

- By Duncan Williams -

One of the most controversial issues regarding nuclear power is the storage of used nuclear fuel once it has been removed from a nuclear reactor.

Currently, most spent nuclear fuel in America are being temporarily stored in pools of water at the reactor plant where it was used. Submerging the spent nuclear fuel in at least 20 feet of water has been proven to successfully safeguard the environment from any harmful radioactivity.

Back when reactor plants were first being designed and built, it was assumed that research would someday lead to a means of reprocessing the spent fuel or that some central permanent repository would be developed. Thus, there was no reason to develop an alternative means of storage other than these temporary storage pools.

However, America has yet to develop a reprocessing facility or a central repository for permanently storing the spent nuclear fuel. As a result, the pools at the nuclear facilities all across America are filling up with spent nuclear fuel with many reaching their maximum capacity.

The Nuclear Regulatory Commission (NRC) regulates the storage of spent nuclear fuel by issuing regulations as well as licenses for such storage. Since the storage pools have been reaching their maximum capacity, the NRC has been allowing some of the nuclear fuel that was previously stored in the pools to be transferred to above ground dry storage casks.

According to the NRC regulations, the spent nuclear fuel can be transferred after it has been in a pool after one to five years, depending on the type of nuclear fuel.

Typically, the storage casks are cylindrical and are made of steel and concrete. These casks are extremely heavy, weighing over 150 tons, and often have a height of over 16 feet. The spent fuel is placed inside a canister, which is itself placed inside the inner cavity of the cask.

Since the spent nuclear fuel still produces a considerable amount of heat, there must be some means to allow this heat energy to escape the cask while it is stored. Often, ventilation ducts are used to remove this residual decay heat.

As shown in the diagram of a typical storage cask, top ventilation ducts (15) and bottom ventilation ducts (16) are located around the circumference of the cylindrical body of the cask, allowing gas to flow through and remove the decay heat emitted from the spent nuclear fuel.

In order to sufficiently shield the environment from radiation, these casks are made of very thick steel and concrete which makes them extraordinarily heavy. The weight of these enormous casks often complicates simple procedures such as moving the casks from one place to another. To this end, the Department of Energy has approved certain methods of light-weight shielding that provides adequate protection to the surrounding environment while reducing the weight of each cask. U.S. Patent No. 6,372,157, issued on April 16, 2002, describes the various radiation shielding used in casks that can significantly reduce the weight of these casks.

This technology was originally developed by Science Applications International Corporation (SAIC), but was later assigned to the Department of Energy. The patent discusses that the spent fuel pellets themselves (depleted uranium dioxide pellets) can be mixed with a cement binder to form a material known as DUCRETE, which can be used as a shielding in the cask. Since the depleted uranium dioxide pellets have a greater density than the gravel aggregate normally used in concrete, the thickness of the shielding can be greatly reduced.

As a result, the cask’s diameter can be reduced by two-thirds, and the weight can be reduced from 150 tons to approximately 90 tons. However, DUCRETE does not transfer heat well and thus requires complicated ventilation ducts in order to properly cool the cask. Furthermore, the cement matrix has been shown to degrade after a period of time due to water-cement-uranium dioxide reactions at warm temperatures.

However, the patent describes a process of turning the used uranium dioxide pellets into much smaller particles, such as a powder or microspheres, which can be further processed into a shielding material. In order to form the shielding, several materials are added to the depleted uranium dioxide microspheres, such as resin, pitch, aluminum powder, alumina, hydrogen, boron, gadolinium, hafnium, erbium, and/or indium. The resulting mixtures is a liquid which can then be poured into the outer walls of the cask.

As shown in the diagram from the patent, the inner wall (22a) and the outer wall (24a) are made from thick forged steel. The liquid shielding material (28a) is then poured into the cavity between the inner wall (22a) and the outer wall (24a). After applying high temperatures to the outer wall, the liquid material forms a solid pyrolitic uranium compound (PYRUC). The PYRUC shielding is also layered into the cask lid (28b) as well as the cask bottom (28c).

The PYRUC shielding conducts heat much better than other available shieldings, which means minimum ventilation is required to cool the cask. In addition, the PYRUC shielding retains its physical properties up to 1000 C, which is much higher than is required by NRC regulations. Due to its high temperature resistance, an inner canister containing the spent nuclear fuel is not required, further reducing the overall size and weight of the cask. The patent explains that the overall cost of constructing the cask will be $600,000-$700,000, which is significantly less expensive than casks made of all concrete and steel.

The cost of the storage cask, as well as licensing fees, are one of the biggest factors faced by owners of reactor plants when determining which storage cask on the market to utilize. For example, a reactor plant owner would be required to pay the DOE a license fee for using the PRYUC shielded cask mentioned above. However, reactor plant owners can also use other cask designs which have been approved by the NRC.

One of the more predominant makers of these NRC-approved casks is Holtec International, Inc., who holds various patents relating to this technology. For example, U.S. Patent No. 7,590,213, issued on September 15, 2009, describes an improved cask which can be placed partially below ground. As can be seen by the diagram from the patent, only the top portion of the cask sits above ground level (23).

Above grade inlets (27) are located about 10 inches above ground level (23), which allow air to enter the cask while reducing the probability that rain or flood water will enter the cavity. The canister containing the spent radioactive fuel is placed inside the inner cavity (26) of the cask. The cavity is surrounded by a thick low carbon steel shell (34) and bottom plate (38) which are hermetically sealed to one another. A layer of insulation (37) surrounds the steel in order to prevent excessive transmission of heat decay from the spent fuel canister to the concrete (21). This insulation is made from blankets of alumina-silica fire clay (Kaowool Blanket), oxides of alumina and silica (Kaowool S Blanket), alumina-silica-zirconia fiber (Cerablanket), and alumina-silica-chromia (Cerachrome Blanket).

The bottom of the cask (22) made of a reinforced concrete slab. The lid (41) is also made of concrete and has four outlet ventilation ducts (42) which allows air to escape from the cavity (26). Filters or attenuators are placed in all ventilation ducts in order to prevent the escape of any harmful radioactive debris.

In conclusion, it is clear that demand for these storage casks will continue to grow rapidly as the number of spent nuclear fuel assemblies from reactor plants continue to rise. So far, America has been using the dry cask storage technology for 20 years with no incident. There is no doubt that this technology will continue to develop to meet the climbing demand.

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.

Yucca Mountain Nuclear Disposal Site Is Dead, Says Longtime Advocate

By PETER BEHR of ClimateWire
Published: December 2, 2009

Former Sen. Pete Domenici, a longtime advocate of nuclear power, said yesterday that it is time to give up attempts to create a permanent disposal site for the nation's nuclear waste fuel at Yucca Mountain in Nevada. He urged the Obama administration to move ahead with a planned blue-ribbon commission to find an alternative.

"We need to be realistic here," the former New Mexico Republican legislator said in a speech in Washington. "Yucca Mountain, once chosen as the site for permanent disposal of nuclear waste, is dead."

President Obama has cut off Energy Department funding for the Yucca Mountain project, following through on a campaign commitment to Senate Majority Leader Harry Reid (D-Nev.), the project's powerful and implacable opponent.

DOE declined to comment last week on reports that the department would withdraw the project's permit application at the Nuclear Regulatory Commission. But DOE spokeswoman Stephanie Mueller said that "the president and Secretary [Steven] Chu have made it clear that nuclear waste storage at Yucca Mountain is not an option, period."

"Yucca Mountain is political. Everybody knows that," Domenici said in an interview after the speech. "The truth of the matter is, the world has passed by the idea of putting spent fuel rods -- as hot as they come out of the reactor -- underground in perpetuity."

Chu has proposed creating a new panel to study options for permanent disposal or reprocessing of spent fuel. Sources familiar with the administration's plans say that former Indiana Rep. Lee Hamilton (D), president of the Woodrow Wilson International Center for Scholars, and former National Security Adviser Brent Scowcroft have been approached to lead the commission.

But as Domenici noted yesterday, the administration has not yet acted. "The blue-ribbon commission has been discussed but has no legitimate momentum. We must quickly make this commission a reality," he said.

A $23 billion question

The Energy Department agreed in 1982 to store spent civilian reactor fuel and high-level radioactive wastes beginning in 1998, and in 1983, utilities began paying into a fund to cover storage costs. The fund has a balance of $23 billion currently, based on annual payments by utilities of $750 million, plus interest earnings, minus design work on the Yucca Mountain facility and other costs.

But to date, DOE has not taken on any civilian nuclear wastes "and currently has no identifiable plan for handling that responsibility," said Kim Cawley of the Congressional Budget Office, in testimony to the House Budget Committee in July.

The spent fuel is stored instead at reactor sites, and the Nuclear Regulatory Commission has concluded there is space to continue on-site storage safely for at least the balance of this century.

Many nuclear power plant operators have sued the Energy Department for breach of contract over the waste storage issue, however. In response to the suits, the federal government has paid utilities more than $565 million to cover the utilities' on-site fuel storage costs, and that number could rise to $12 billion by 2020, according to DOE -- assuming the government has created a storage option by then, Cawley said.

"A legislative solution would be preferable to the current drain on the resources of the courts and the Department of Justice caused by the seemingly endless litigation," Deputy Assistant Attorney General Michael Hertz told the committee at the same hearing.

Recycling pushed as a waste-reducing option

Domenici said the $23 billion in the waste fund should be used to fund a pilot project on recycling spent fuel, which could substantially reduce the amount of storage space required. Opponents of reprocessing say it would increase the risk that radioactive materials could fall into terrorists' hands.

Other countries are proceeding with new nuclear reactors, he continued, urging that the United States take leadership in developing strategies for waste treatment that effectively manage the threat of proliferation of nuclear materials for weapons. "The United States can acknowledge reality, or we can continue to bury our head in the sand while nuclear waste, and nuclear proliferation dangers, build up throughout the world."

He praised the recent commitment by the United Arab Emirates to rely on international nuclear fuel suppliers as it develops nuclear power, pledging to return spent fuel to the United Kingdom and France and to refrain from recycling its own fuel. "This is a model that, with modifications, may work in future agreements with other nations," he noted.

He added that this model requires adequate international infrastructure to responsibly manage used fuel through arrangements for take-back, treatment, recycling and storage of spent fuel. "America's present domestic policy is out of step with our demonstrated technology and scientific abilities," he said.

Another potential approach could be based on the Waste Isolation Pilot Project in New Mexico, Domenici said. It stores less toxic nuclear wastes in salt deposits 3,500 feet underground.

Domenici also criticized the Energy Department for continued delay in carrying out an $18.5 billion loan guarantee program for new nuclear reactors that was authorized by Congress in 2005.

Administration officials are still debating the amount of up-front payments that reactor developers would have to pay to obtain the guarantees, based on how the government assesses the risk of loan defaults if projects cannot be completed.

"I find it especially perplexing that the Department of Energy and the Office of Management and Budget are still negotiating the level of the credit risk fee," he said. "If the fee is set too high, we will never build the next generation of nuclear plants," he added.

Domenici said a fee of 1 percent of the guaranteed loan would be adequate. The Union of Concerned Scientists and other nuclear power critics and skeptics say that the costs of building new reactors are rising, threatening successful project completion, and the risk fee should be set substantially higher.

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