FUEL ELEMENTS

Without deprecating the care needed in constructing facilities in other parts of the cycle, it can be said that the fabrication of fuel elements is an extremely important operation. Fuel elements are exposed to high temperatures, corrosion and radiation damage during their use. Yet they must be constructed with a minimum of nonnuclear materials to reduce wasteful neutron consumption.

In addition, they are precision products because they must be carefully spaced so as to maintain the design fuel moderator ratio and lattice spacing.

Further, their exact spacing is necessary to maintain coolant flow patterns and to avoid hot spots which would cause burnout.

Likewise, to avoid hot spots they must be uniform in quality and fuel content. Finally, they must be capable of maintaining all of these characteristics during power reactor cycles that last on the order of a

I have here a fuel element to indicate what these things look like.. This element has been split in two to permit a view to the interior of the element.

This is a model of the elements used in our materials testing reactorand incidentally is also representative of the elements that will go into our engineering test reactor, but it is also typical of the style and size of elements used in power reactors.

It may seem ironical that this element is so large and bulky but it is because nuclear fuel is so concentrated a form of energy that it has to be spread out to permit the heat to be removed and keep the element from melting.

The energy content is frequently dramatized by saying that a small lump is sufficient to drive a ship around the world several times. However, in practice, that small lump has to be fabricated into fuel elements like these. This element is about 4 feet long and weighs about 10 pounds. Yet it contains only about one-fifth of a kilogram of uranium.

I described the great care that must be used in fabricating these elements. This is one of those factors that facilitates the safeguard job. Fuel elements can be serially numbered and can be kept track of as discrete units. The numbering is usually done anyway for process control, so that the effect of a change in manufacturing method can be correlated with its performance in the reactor. Thus, the same technique is used both for safeguards and for ordinary business pur

poses.

Because of the rigorous service requirements, these elements are not handled like logs or iron bars nor are they cut in two like this, but are treated very carefully. Kid-glove treatment is not an exaggeration, because perspiration from bare hands would lead to chloride corrosion. This care is a serious matter for the reactor operator who examines these elements minutely when they arrive at the reactor site. His

interest represents a sort of built-in safeguard measure since the checking of the element numbers and condition will detect theft or tampering. A variation in and between fuel elements is important in the operation of the reactor. Variations would cause hot spots and they would be reflected in abnormal operation conditions. Here again, the same techniques are used both as a safeguard measure and for operational or process control. Through the point of fuel fabrication these elements can be handled by hand. Once they move into the reactor and begin producing power, any further handling must be done with the equivalent of 11-foot poles because of the radiation they emit.

The radiation depends upon the burn-up but an element coming out of the MTR, for example, radiates about 3 million R/hour. If you wore to carry 1 of these elements for 20 seconds, even after it had cooled 90 days, the radiation dosage would probably be lethal.

These elements are transported in 10-inch-thick lead casks that weigh about 10 tons. The casks cost about $15,000, which is more than the Value of the fuel material in them.

REACTORS DESCRIBED

Because of this radiation, fuel elements in a reactor are in the quivalent of a vault. A reactor can be described very crudely as a heavy casing containing fuel elements and surrounded with many feet of shielding materials. The casings will run to 8-10-inch thicknesses of steel. Surrounding this may be a 3-foot-thick tank of water as a neutron shield and then 5 feet of concrete biological shield.

Most reactors are designed for shutdown fuel reloading, so that elements cannot be removed without shutting the reactor down. And, for reasons of economy, power reactors don't shut down very often. Operating cycles of a year or more are typical. Now, this is pretty significant from the safeguard standpoint, because it means that, for the major fraction of the time it is in use, the fuel material is locked up in the reactor in this highly radioactive field.

Nuclear reactors differ from conventional powerplants with respect to the fuel inventory required. Coal inventories usually amount to about 3 months' consumption. Nuclear-reactor inventories are equivalent to 2-3 years' consumption. This is due, of course, to the basic physics of a chain reaction, which requires an inventory of fuel before the reactor can operate. Therefore, it is necessary to have a substantial amount of material in order to get the reactor going. Conversely, it is not possible to secretly divert several months' worth of consumption because the reactor probably would have to shut down. This inability to operate without the inventory is relevant to the possibility that a nation might close its borders and confiscate Agency material. There is no question that this is a possibility, but it certainly seems to be an unlikely possibility for several reasons. Considering, first, the plain economics of the matter, the reactor inventory for a 50-megawatt electricity plant would represent on the order of $3 million to $4 million. In order to obtain such inventory, the country would have had to spend $20 million to $30 million for the reactor, since fuel materal will be provided only as required for specific projects.

The confiscation would terminate the supply of fuel and, therefore, the reactor would shut down, so that the $20 million to $30 million investment would be useless.

Further, because the project would have been approved only if the power were needed, the disruption in power supply would be quite serious. In addition, the enrichment level of fuel in power reactors is something like 2 to 3 percent U-235, which is not suitable for weapons.

Moving on this chart (see appendix) from the reactor station to the next one, when the reactor is shut down to change fuel, elements are removed by remote handling devices and put into cooling storage. This is usually a concrete tank or canal that is filled with water. Water dissipates the fission-product heat and is a cheap shielding material, and the elements can be inspected and handled under water. Cooling is provided for economic reasons. Elements could be processed immediately after discharge from the reactor, but the incremental radiation would necessitate more expensive facilities.

It is cheaper to let the radiation decay in cooling basins than to build the more costly processing plants. The radiation decreases rapidly at first, while the short-lived fission products decay, and then diminishes in its rate of decay.

This cooling is, of course, a relative matter. These elements, even after 2 or 3 months in the cooling basins, are still very radioactive and must be handled with remote devices and have to be transported in massive, shielded casks to the chemical-processing plant, which is the next step in this cycle chart.

THE CHEMICAL PROCESSING PLANT

The purpose of the chemical-processing plant is to recover the unused fuel and separate it from the fission products and plutonium. The usual method is to dissolve the fuel elements in acid and then use solvent extraction for the purification and recovery steps. These operations are carried out within shielded canyons by remotely controlled equipment, because of the radiation present. It is not until the end of the process that it is safe to use more conventional means of processing. Even then, the plutonium must be handled with special care because of its toxicity.

A chemical-processing plant is a complex and substantial facility. It is massive because of the shielding required. It is an engineering nightmare because piping, valving, and equipment must be incorporated in this massive structure and must be constructed to permit process modifications. Once the piping is in, imbedded in concrete, it is there until the plant is torn down. All operations are performed by remote control, and equipment must be designed to be as trouble free as possible since, once the plant has operated, it is highly radioactive and any maintenance work becomes a major operation. The radiation decomposition of the solvent requires it to be purified regularly, so that the degradation products do not interfere with the preferential extraction process. Uranium is extracted from the solution, while plutonium and fission products are held back by adjustment of oxidation state and acidity. Several similar cycles are required to achieve decontamination. The building is zoned and pressure dif

ferentials maintained on the air supply, so that any leakage which might carry radioactivity is inward and discharges through tall stacks equipped with elaborate filters.

In spite of the complexity of the process and plant, recovery efficiencies are measured in the 99.9-percent range, with the balance going along with the fission products as unrecoverable material. I mentioned earlier that such a facility is a substantial one. A plant capable of handling the throughput for 1 million kilowatts will cost on the order of $20 million. Therefore, plants of this kind are not likely to be constructed except in countries with sufficient industrial capability to construct and utilize substantial blocks of nuclear power.

The chemical processing completes the power-reactor cycle. The recovered uranium is returned to the fuel-fabrication plant for reuse. Eventually, the plutonium will do likewise, but meanwhile it will go into Agency storage. The fission products either go into storage or are separated and packaged for use as radiation sources.

THE POWER CYCLE PROVIDES SAFEGUARDS

I have described these operations as steps in a cycle. The fact that it is a cycle is significant from the safeguard standpoint, because it means that we are concerned with an integrated operation which has a number of check points from which data can be correlated. What happens in one part will show up somewhere else, and this constitutes a sort of built-in safeguard.

The quantitative relationships of a power cycle will vary, of course, with particular designs, but a typical system will include a 3-month fabrication cycle, a reactor cycle of a year or year and a half, a 3month cooling period, and a 3-month chemical-processing cycle. Since these periods are indicators of the location of inventories of material, it is evident that most of the inventory is in the reactor most of the time. Also, the material is in a highly radioactive condition about 85 percent of the time.

Because the operation is a cycle with a number of check points on the flow of material, it is possible to maintain a material balance. Diversions would make such a balance impossible and so removals tend to anounce themselves. The fact that most of the inventory is in the reactor and has to stay there and be used for its intended purposes makes diversions self-signalling. The Agency is not limited, however, to awaiting such signals since the safeguard provisions of the statute provide for complete and continuing coverage of the entire cycle from the beginning of a project. It provides for on-the-spot inspection, for access to any place or person involved in the project, and for confirmatory measurements.

MATERIAL ALLOCATION FOR SPECIFIC PROJECTS

The Agency will allocate material only for specific projects and only in amounts required for those projects. This is a matter of selfinterest because each Member will be concerned that fuel is used efficiently. This concern will apply not only to attempts at diversions but also to sloppy operations, which, therefore, cannot be used to cover up attempted diversions. Accordingly, the accounting for material