One of the most successful ways to conserve valuable raw materials is to pay careful attention to manufacturing and use processes so that less of the material is wasted. There is ample opportunity for process type improvements in the nuclear power industry, even though many improvements have already been made.
There are also institutional hurdles that must be overcome in order to make full use of available technology. These barriers are similar to those faced in many other industries where efforts to reduce environmental damage are being advocated.
Before discussing this issue, there are a few bits of terminology that need to be understood. The term “burn-up” refers to the amount of energy produced by a given quantity of nuclear fuel. The normal units for burn-up are MegaWatt-days/tonne of heavy metal.
A tonne (1000 kg) of uranium, thorium or plutonium, the heavy metals useful in reactor fuels, could release almost one million megawatt days of heat energy if completely fissioned. Unfortunately, our current state of the art is far from complete fission.
Then and Now
Nuclear scientists and engineers have made some progress over the years. The earliest reactors normally achieved burn-ups of about 5,000 to 7,000 MWdays/tonne (about .5 to .7 percent of the ultimate potential.) Standard light water reactors using low enriched uranium now achieve routine burn-ups of 35,000 to 45,000 MWdays/tonne (3.5 to 4.5 percent of the potential).
Some well tested advanced reactors have achieved levels of 150,000 to 160,000 MWdays/tonne (15 to 16% of the potential). Commercial reactors using the designs from these programs would produce about a quarter of the waste of current reactors even without any recycling program.
United States naval reactors, optimized for high endurance operation, achieve routine burn-ups of 500,000 to 600,000 MWdays/tonne (50 to 60 percent of the potential). Since these reactors use valuable highly enriched uranium, the remaining material was routinely recycled for many years. The downsizing of the nuclear navy and the reduction in demand for highly enriched uranium led to the 1992 decision to close down the reprocessing facility in Idaho. The waste is now simply stored.
Efficiency Equals Design
The amount of burn-up that can be achieved is a function of the material properties of the fuel, the nuclear properties of other materials in the reactor including the coolant, the reactor control system, the fuel loading scheme and the enrichment of the fuel.
It might be useful to think of a fire analogy in trying to understand why there is such a large variation in the percentage of material that can be effectively “burned” in various kinds of reactors. Depending on how the fire is built and operated, there will be varying amounts of wood left over.
In the early days, reactors were really designed like charcoal production fires, the goal was to convert uranium into a product (plutonium), not to produce the maximum amount of energy. Modern light water reactors are like large bonfires trying to burn very wet wood with a small amount of kindling. The kindling burns and then the fire goes out leaving most of the wood intact. Naval reactors are like small fires that are carefully tended to produce the maximum heat from a limited quantity of high quality material.
The basic methods available to improve fuel use efficiency focus on improving the percentage of neutrons that are absorbed in fuel over other materials in the core, improving the resistance of the fuel structural materials to irradiation damage and increasing the amount of potential fuel in a given volume.
As might be expected from an optimization problem with so many variables, achieving maximum energy release from nuclear fuels is a complex endeavor. It involves weighing the cost of changes versus the benefits obtained.
The effort has the potential for nuclear utility cost reductions, however, because it not only reduces waste and associated storage difficulties, but it reduces the time that the reactor is shut down for refueling. It also reduces the cost of fabricating, transporting and handling the fuel for a given reactor. Several of the advanced reactor programs have projected major savings from increases in nuclear fuel usage.
Nuclear fuel suppliers, however, have been slow to develop advanced fuel cycles that can reduce fuel use and waste production. We must always remember that one person’s cost is another person’s revenue. The most economical choices for energy consumers are not always the most economical choices for nuclear fuel suppliers.
Nuclear fuel companies have resisted improvements in fuel life in a manner reminiscent of the resistance offered by the biased ply tire industry to the introduction of long life radial tires. If fuel suppliers provide fuel that can last two to four times as long as their current product, they will sell less fuel to their existing customers.
The Nuclear Regulatory Commission helps keep the established fuel suppliers in business through its licensing process. It takes years to gain approval to alter the licensed fuel cycle for a given reactor plant. The Commission calls it a “conservative” approach, but the result is to allow companies that produce existing products to maintain their markets for many years after competitive improvements have been demonstrated in laboratories.
John W. Simpson, a former high level executive with Westinghouse, the world’s largest supplier of light water reactor fuel, has recently written a book titled Nuclear Power from Underseas to Outer Space that gives some insight into his former company’s nuclear fuel business strategy. Simpson stated, “As film is to the camera manufacturer, nuclear fuel is to the reactor builder. It’s a business that has the potential of continuing sales for the life of the plant.”
Unlike tire consumers, utilities are somewhat constrained in their ability to shop for better fuel. As Simpson wrote, “The customer utility was free, of course, to buy future fuel from our competitors, but the utilities thought they might experience difficulties buying future fuel from anyone but the plant vendor for technical reasons . . . We also wanted to sell as many fuel reloads with the initial plant order as possible . . . This fuel business has continued to be a mainstay of our nuclear business, along with reactor service, long after plant orders were a distant memory.”
One of the services that Westinghouse and other fuel supply companies have traditionally provided to nuclear utilities is support during refueling outages. This is a large business involving thousands of people and millions of dollars worth of sales to the company. Short-lived fuel has been a profitable product for many years.
The strategy of maintaining fuel sales high by restricting performance, however, is doomed to failure in a competitive market. Have you purchased any biased ply tires recently?