The Cornucopia of Nuclear Power

You will remember from chapter 21 that we have two neutrons, on average, emitted whenever a U235 atom undergoes fission - or "splitting." One of these is necessary to fission another atom to keep the chain reaction going. But what happens to all of those second neutrons? Some of them, as mentioned, are absorbed by the structure of the reactor or by the control rods, which slide in and out of the reactor to keep the reaction at - or just very slightly above - the critical point. But others smash into, and are captured by, the plentiful U238 atoms that make up from 95% to 96.5% of the fuel rod contents. When this happens, a truly miraculous thing takes place: This practically worthless material is transformed into one of the most concentrated sources of energy on Earth - or in the universe for that matter - plutonium 239, and element so evil that it was named for the god of the underworld. (Not really, but that's what some would have you believe.) [Plutonium was named in honor of the discovery of the planet Pluto, just as neptunium and uranium were named for Neptune and Uranus.]

This happens in every one of the world's 500 power reactors, plus thousands of research reactors, every day they are in operation. In fact, a sizable fraction (up to about 30%) of electrical energy generated by a power plant comes from this plutonium, which arises as a natural consequence of the uranium fission reaction - without any effort on our part - and supplements the scarce U235 fuel.

Some reactors, however, are designed to intentionally make plutonium. If it is to be used in bombs, it is normally made in a reactor with another modulator - such as the carbon-modulated reactor at Chernobyl. A reactor designed specifically to make only fuel-grade plutonium is called a breeder reactor, since new fuel is "bred" from an almost worthless byproduct of the refining cycle. [Breeder technology seems to be on hold for a couple of reasons: (1) in the prevailing anti-nuclear climate, few entrepreneurs or speculators are willing to make investments in nuclear power for fear of laws that can make their investment instantly worthless; and (2) at the present time there is a glut of plutonium available from the dismantlement of nuclear weapons.]

Are we speculating here on new technology like "fusion" power? Hardly.

The first reactor ever to produce electric power from nuclear energy was a "liquid metal fast breeder reactor" known as the EBR-I. (By the way, liquid metal means that the coolant was not our old friend water, but liquid sodium; fast means that it used "fast neutrons," not the slowed-down, moderated variety.) Designed by physicist Walter Zinn in 1944, his brainchild went critical at 11 am, December 20, 1951 - producing the first steam in history produced by man-made nuclear heat. Like the Manhattan reactor in Chicago and the SLOWPOKE reactor in Canada, EBR-I was not designed to produce electrical power but to prove the concept of fuel breeding (which it did along with its successor, EBR-II). [Declared a national landmark in 1966, the EBR-I is open to the public from mid June to mid September. Located eighteen miles southeast of Arco, Idaho, on Highway 26, visitors must be at least sixteen years old (too much neutron violence?) and U.S. citizens (fear of spies who might steal this technology?).]

The EBR-II had "on the spot reprocessing," which reprocessed 35,000 fuel elements between 1965 and 1969. But the facility was not without problems: the fence around it kept out the coyotes, causing the rabbit population to outbreed the reactor.

Does the ERB-II sound a little familiar? It should since it has another name we used in chapter 21 - the Integral Fast Reactor (IFR).

While many U.S. politicians have never heard of breeder technology, Europeans have. Sadly, "Green" activists there have been successful in shutting them down or keeping them from ever starting up.

CANDU and SLOWPOKE

While the United States - with its post-World War II enrichment technology and capacity - built power reactors using enriched uranium, the Canadians took a different approach. You may recall that deuterium (2H) reacts with oxygen to form "heavy water" - an unusually good moderator that bounces back and slows down neutrons that might ordinarily escape the reactor. The most interesting thing about the Canadian CANDU heavy water reactor - from the standpoint of community or home power plants - is that it uses natural (unenriched) uranium. This doesn't get them off the hook from an initial energy expenditure, however, since heavy water is expensive to separate - about $100 per pound and costing $100 million dollars for a full-scale 1,000 megawatt reactor. It does, however, eliminate the problem of enrichment. The CANDU design has many parallel fuel assemblies with the heavy water coolant/moderator flowing through each. To refuel the reactor, it doesn't need to be shut down; you just cut off the water to stop the nuclear reaction in a section isolated for refueling, and then change out the "spent" fuel assemblies.

["Spent" fuel assemblies aren't really spent at all - they have more than 95% of the initial fuel remaining with only a few percent of "daughters" that contaminate the rest and absorb the needed neutrons.]

Even more interesting from the standpoint of decentralization is the Canadian SLOWPOKE reactor, which is as safe and secure as a Sierra Club official working for the Environmental Protection Agency. [Safe LOW POwer Kritical Experiment - but it's not experimental anymore, having been in operation for more than twenty-five years. (Canadians may be great reactor designers, but they seem to have a little problem with their spelling.)]

Figure 34 shows a cutaway sketch of this "pool" type reactor - so named because it operates submerged in a pool of water. Unlike PWRs and BWRs, it does not have "defense in depth" - because it doesn't need it. The laws of physics provide it with more than enough protection.

The original design has a maximum operating temperature of 80 degrees Celsius with a cylindrical core about nine inches in diameter by nine inches in height. Surrounding the enriched-uranium fuel assembly are beryllium reflectors, which keep the reactor critical... as long as the water density remains high. If the reactor "heats up," the lower water density slows the reaction bringing the temperature back to the design point. [SLOWPOKE I and II have been operational for some time; the series is now up to V or VI, but I haven't been able to get much information on the later models.]

Suppose all the water evaporates or is sloshed out by an earthquake? Naturally, the reaction stops, as the moderator is gone. But also the power density is so low that nothing happens to the fuel. The reactor just goes dormant until someone takes an action to bring it back to life. [Typically the operators do not have access to the reactor.]

As Canadian scientist Dr. John Hilborn, who conducted experiments leading to the SLOWPOKE, said, "It is safer without operators than with them." [From an interview with Petr Beckmann, Access to Energy, Vol. 8, No. 9, May 1981, pp. 1-2.]

The original SLOWPOKEs were not designed as power reactors. Their heat output (which is considerably higher than any possible electrical output) is a mere twenty kilowatts, equivalent to about thirteen hair dryers. Their function, as mentioned, was not to produce electricity but to transmute certain materials into radionuclides, primarily for medical purposes. But the concept of a low-temperature, inherently safe, non-polluting, inexpensive-to-fuel, produce-power-where-you-need-it reactor is intriguing for those who would like to have energy independence. [Some electric utilities might oppose such a competitive concept, but they would, as mentioned, be in the best position to provide service for local power reactors.]