208. URANIUM FROM SEAWATER (PART 2)
Continuing from the previous article (#207)...
Quantoken brought up some issues about U238 and U235, so first let's get clear on that point. These are the facts:
- Natural uranium (yellow cake) is made up of 99.3% U238, and 0.7% U235, and only the latter is directly fissionable. So quantoken is right that a kilogram of uranium harvested from the sea contains only about 7 grams of U235, which is the actual fuel in a conventional reactor.
- Reactor fuel is comprised of 3-5% U235.
- The following illustration shows what 25 tons of reactor fuel (3-5% U235) can do (click to enlarge):
- "One ton of natural uranium can produce more than 40 million kilowatt-hours of electricity. This is equivalent to burning 16,000 tons of coal or 80,000 barrels of oil." Source
More detail on the economics is provided by a Russian website, which has an English translation of a technical report by the JAERI group. This report gives a detailed cost analysis for a system capable of meeting one-tenth of Japan's electrical power needs, and concludes:
The recovery cost was estimated to be 5-10 times of that from mining uranium. More than 80% of the total cost was occupied by the cost for marine equipment for mooring the adsorbents in seawater, which is owning to a weight of metal cage for adsorbents. Thus, the cost can be reduced to half by the reduction of the equipment weight to 1/4.So high costs come from an unexpected direction: construction of mooring. The paper describes the issues:
Each of the recovery systems investigated here is based upon using a layered adsorbent in the form of polymeric nonwoven and mooring in seawater after insertion of such adsorbent into a stainless steel cage. As a result, about 80% of cost is for mooring even though costs very according to the mooring method. This is due to construction spending for mooring the large mass of adsorption beds. This adsorbent has a specific gravity equivalent to that of seawater and has no net weight within seawater itself. However, weight of the metal cage occupies the majority of the weight of the adsorption bead of Figure 4, so weight is particularly imparted in seawater only by the metal. For example, in the case of the chain-binding method after pulling up, it is estimated that mooring cost declines to 62% if weight of this adsorption bed can be lowered by 50%, and mooring cost declines to 42% when weight can be lowered to 25%. Therefore uranium recovery cost may possibly be greatly lowered if a light cage material is used in place of the metal mesh of stainless steel. Also since this adsorbent was obtained in a length-wise continuous cloth-like form, if a method of mounting other than the assumed insertion into a cage as shown in Figure 4 is used (e.g., if a method is adopted of supporting the multiple adsorbent sheets streaming in the current), then an entirely different method would be is used for mooring than that utilized here.Clearly this technology, while totally practical and proven, is at a very early stage of development, and costs could be slashed in a number of obvious ways (i.e. piggybacking the equipment on other moorings like offshore windmills, switching the cages to a plastic with a specific gravity closer to water, or anchoring the sheets with light, high-strength fibers rather than cages and ropes).
Also, even assuming that we use the JAERI system as is, with a worst case uranium price 10 times that of land mining, uranium oxide comprises only a small fraction of the retail price of electricity. It accounts for 32% of the cost of nuclear fuel (Source), and nuclear fuel only comprises 20% of the total cost of nuclear power plant operation (Source). Thus uranium accounts for at most 6% of the final electrical bill. So if your current electric rate in the U.S. is $0.08/kwh, a switch to sea uranium would raise your electric rate to about $0.12/kwh. That's hardly an "end of civilization" price rise, and indeed is still just half the current retail price of electricity in Japan: $0.25/kwh (Source).
The above shows that cost will not be a significant barrier in harvesting uranium from seawater. So how much is out there? A lot:
Thus the amount of uranium in seawater was calculated and the results showed that the Black Current off Japan carries approximately 5.2 million tons a year. This amount is equivalent to the earth's remaining inventory of this ore. At present, Japan consumes about 6,000 tons of uranium per year. So even if only 0.1 percent of what flows along Japan can be recovered, the domestic demand for uranium can be supplied, and that is why I have continued to propose taking advantage of the uranium in seawater as an energy resource. Source
-- by JD