the fuel during holdtime, and providing a vent capability. The next major 

 problem or difficulty would involve the transfer of gas from cryogenically 

 stored containers. The gas must be delivered at controlled flow rates and 

 pressures. A suitable control system must, therefore, be developed. 



Many fuel cell concepts exist for a wide variety of cell types and fuels. 

 At present, fuel cell systems are either in development or prototype stages, 

 with the major effort being applied to the hydrogen-oxygen cell, which is the 

 most advanced type. Hydrazine-air or oxygen cells have also had considerable 

 development effort for land applications because of their relatively low cost 

 and the availability of their fuel supply. 



Hydrogen-oxygen cells are of primary interest for underwater power 

 systems because of their high efficiency, high energy content, and easily 

 handled waste product (water), as well as the availability of their reactants 

 (hydrogen and oxygen) from numerous chemical compounds. The hydrogen- 

 oxygen fuel cell power source is lighter than the hydrazine-air type, but 

 requires a pressure hull enclosure. The hydrazine-air cell has potential as an 

 off-hull, pressure-compensated system which would then provide the lightest 

 power source. 



The application of hydrogen-oxygen fuel cells as submerged power 

 plants will require a major design and engineering effort. The technical 

 feasibility of fuel cells and the handling of cryogenic reactants has been 

 established for surface and space applications, but the ocean environment 

 presents many problems to be resolved for safe, reliable, and maintenance- 

 free deep ocean fuel cell power sources. Therefore, the feasibility of 

 utilizing suitable fuel cells for deep ocean applications is not apparent at this 

 time, and fuel cells were excluded from the study program. 



Lead-acid and silver-zinc battery systems are suitable for submerged 

 use. Both types are in production and have been successfully tested down to 

 the required depth of 20,000 feet. Nickel-cadmium and silver-cadmium 

 batteries are more expensive and offer no advantages. Batteries may be 

 enclosed in pressure hulls or in oil-filled pressure-compensated systems. The 

 selection of enclosure depends on the depth of power plant submergence, on 

 the cost of obtaining buoyancy and on safety. For the unattended system 

 where explosions due to hydrogen gassing are possible, the pressure- 

 compensated system was selected since it is safer, lighter, and less costly. 



Batteries alone have a limited energy capacity as the main power 

 source. However, they can function effectively as emergency or auxiliary 

 power sources. The disadvantages of battery systems are the need for 

 inverters for converting DC to AC, the varying output voltage, and the losses 

 involved in multiple energy conversions. 



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