CELL VOLTAGE E, VOLTS

Figure 5. Idealized performance curve for a fuel cell. The value E=1.229 volts at 25°C is the maximum permitted by thermodynamics for a H2/O2 cell at standard conditions. In Region I, loss of voltage occurs principally at the electrodes. In Region II, this loss is increased by the internal resistence of the cell. in Region III, the perpendicular decrease in voltage results from a limitation in mass transport.

The equation for the curve is explained in Liebhafsky and Cairns “Fuel Cells and Fuel Batteries," soon to be published by John Wiley and Sons.

Figure 6. Consequence of One Kind of Lack of Uniformity in a Fuel Battery. Interrupting the supply of oxygen and of hydrogen to one cell in a series-connected battery causes the other cells to "drive" the afflicted cell. Undesired electrode reactions in the afflicted cell result.

POWER watts/cm2

Figure 7. Idealized curve based on Figure 5 showing how the power generated by a fuel cell varies with curent density. Comparison with Figure 5 will show that the cell voltage at the current density for maximum power has fallen to about 0.6, which means reduced efficiency.

Figure 8. The Fuel Battery for Project Gemini. A pictorial history of its development by the General Electric Company.

Question 2: What are your views on the problem of ultimate disposal of nuclear fuel wastes (after reprocessing) when nuclear-electric power becomes a dominant factor?

Answer: In a broad sense, this question has been the subject of considerable study, concern, and-in many cases-debate by nuclear industry professionals, State and Federal agencies, and other interested groups or individuals both domestically and worldwide for over two decades. During this time, high-level waste handling practices have evolved and sufficient operating experience has been accumulated to prove the applicability and, in general, the acceptability of these methods for radioactive waste storage on an interim basis, as contrasted to permanent or ultimate disposal.

Fission product wastes derived from solvent extraction separations plants (the current standard reprocessing method) are generally classified into four categories: high-, intermediate-, and low-level aqueous wastes, and gaseous wastes. The principal characteristics of these waste streams are as follows:

High-level wastes.-High-level waste is generally the waste raffinate from the first cycle of solvent extraction. This raffinate stream is acidic and contains 99.9-plus percent of all the fission products originally present in the spent nuclear fuel. The raffinate stream is normally concentrated by evaporation to yield a final waste solution of a few hundred gallons per ton of uranium processed. This final high-level waste solution is stored in either an acidic or alkaline form in underground tanks (either stainless steel or mild steel) with ancillary operating facilities and instrumentation to detect maloperation of the specific containment systems employed.

The water rejected from the waste concentration step above is contaminated with far lesser quantities of fission products than the original high-level wastes and is subsequently handled as an intermediatelevel waste.

Intermediate-level wastes.-These wastes are generally composed of : 1. Second-cycle wastes derived from the solvent extraction process.

2. First cycle waste condensates.

3. Coating wastes derived from the chemical decladding of nuclear fuel elements.

4. Aqueous wastes accumulated from washing and purifying the organic extractant.

These wastes, either singly or pooled, are concentrated by evaporation. The distillate is routed to the low-level waste treatment system. The concentrated waste (still bottoms) is stored in underground tanks. The volume of intermediate-level waste generated per ton of uranium processed is several fold larger than that for the high-level waste.

Low-level wastes.--Low-level wastes are made up of water rejected from the distillation of intermediate-level wastes, process cooling water which has the potential of becoming contaminated, and other related process streams. This very large volume waste stream is treated by various methods to reduce the fission product content to acceptable levels and is then discharged to the environment. The fission products which were removed or "scavenged" from this solution are retained by tank storage on the plant site.

Gaseous wastes.-Gaseous wastes contain volatile fission products. (for example, krypton and xenon) and other fission products that escape the chemical separations operations with process and ventilation air (for example, radio-iodine, tritium, and so forth). The gaseous wastes are treated chemically and filtered extensively to meet discharge limits for the disposal of gaseous wastes to the atmosphere.

CHARACTERISTICS OF WASTE STORAGE PRACTICE

From the foregoing, it is immediately evident that:

1. The fission product wastes are retained at the separation plant in a liquid and mobile form. Thus, these wastes are stored, not disposed of.

2. The only material disposed of, in the strictest sense and excluding the gaseous wastes, is water.

3. The integrity of the storage vessel is all important. Successive generations of storage tanks must be available as the original vessels fail from corrosion or other causes.

4. The storage system must be monitored continually to detect failure of the containment system resulting in the unwanted dispersal of fission products in a mobile form to the environs.

ACTIVITIES IN THE WASTE MANAGEMENT FIELD

The U.S. Atomic Energy Commission is currently supporting a multimillion-dollar program within the AEC complex to develop and demonstrate practical and economic means of converting high-level aqueous wastes, typical of those assumed to be produced by the commercial fuel reprocessing industry, to immobile solids. These fission product-containing solids, either as calcines or after conversion to "glasses," are to be packaged in high integrity metal containers suitable for permanent storage in special geological formations, that is, salt mines, and so forth. It is to be noted that the conversion of the liquid