Since radioisotopes are the product of reactor 
operations or separation of spent fuel, careful con- 
sideration must be given to selection and avail- 
ability of isotopes when considering them for 
electric power production. Some isotopes are 
completely unavailable. With others, price is 
changeable and reflects many factors, some un- 
related to actual isotope demand. A careful survey 
of information supplied by the Atomic Energy 
Commission regarding cost and availability is 
mandatory before planning to utilize such systems. 
Isotopes are expensive. With a somewhat opti- 
mistic 25 per cent engine cycle efficiency, power 
output of 15 kilowatts would require 60 thermal 
kilowatts with an expected cobalt-60 isotope cost 
of $390,000. 
As with reactor systems, radiation and waste 
heat must be considered. The advantages and 
disadvantages of deep ocean reactors are similar to 
isotope systems. The transportation of a radio- 
isotope system is difficult due to the necessity of 
continuous shielding and heat rejection. 
Assuming acceptable weight characteristics and 
cost considerations, radioisotope systems can pro- 
vide small-power supplies having low maintenance 
and high reliability for a number of relatively 
constant power consumers (such as fixed environ- 
mental monitoring systems, transponders, buoys, 
wellhead controls, and communications and navi- 
gation systems). 
6. Conclusions 
Reliable, cost effective, high energy per unit 
weight and volume power sources are a primary 
requisite for a wide variety of undersea applica- 
tions. Existing power sources in various develop- 
ment stages for other applications are potential 
candidates for underwater service, but each re- 
quires considerable adaptation to the ocean envi- 
ronment and to specific underwater applications. 
Clearly, no single candidate is preferable over the 
entire energy spectrum in which submersibles, 
habitats, and other undersea systems may operate. 
The current need for suitable power sources for 
submersibles is urgent. Excluding combatant sub- 
marines, only rechargable batteries have been 
employed for main power in manned, selfpro- 
pelled submersibles. The NR-1 will be the first 
submersible with nuclear power. Batteries impose 
severe weight, payload, and endurance penalties on 
VI-36 
small vehicles. Until fuel cells, small nuclear plants, 
and other power sources can be developed for 
deep ocean service, submersible capabilities will be 
seriously limited. Figure 3 is a general presentation 
of approximate ranges of useful outputs for 
various power sources for submersible systems 
illustrating the point that no one type would 
satisfy all missions. Figure 4 summarizes the 
comparative usefulness potential for various power 
sources. The diversity of advantages and disadvan- 
tages of each also enforces the need for pursuing 
diverse approaches in power source development. 
Heth 
rte CRYOGENI 
seseesccem, STORAGE 
sngensesssa. 
euesacesaess ° 
: kilowatts 
FUEL CELLS 
PHOTOVOLTAIC 
OR RADIOISOTOPE 
ELECTRICAL OUTPUT 
DURATION 
FROM HERE ON 
LIFETIME & 
RELIABILITY 
LIMIT CONTROL 
Figure 3. The range of useful outputs for 
various power sources. 
Figure 4 
COMPARATIVE USEFULNESS OF 
VARIOUS POWER SOURCES! 
cart Ambient 
Criteria 
Low High Endur- Pressure 
Power | Power ance Capa- 
sie bility 
eT te ed ae Lan oe 
Battery. . 3 5 5 1 
Silver Zinc 
Battery. . <4 4 4 1 
FuelCell . . 2 3 3 3 
Chemical 
Dynamic. 4 2 3 4 
Isotope ... 1 5 1 3 
Nuclear 
Reactor 
: 1 is best; 5 is poorest. 
