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.]

Home Is Where the Radiation Is

Table 11 – Chernobyl Cs 137 Burden in Various Areas vs. Natural Background
Location	Range (Bq/m^2)
European Cs 137 contamination outside former USSR	20,000 to 23,000
Cs 137 contamination inside former USSR	40,000 to 5,000,000
Natural radionuclides in soil of above areas	177,000 to 6,500,000
Source: Table 2 in 1997 statement by U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) member Zbigniew Jaworowski

From Table 11, radon is apparently the dominant source of background radiation. As pointed out earlier, it has not always been considered to be such, as residential radon seems not to have existed until December 1984, when a nuclear worker set off radiation alarms on his way into the Pennsylvania Limerick power plant. A subsequent investigation showed that the residential radon level in the Reading Prong area of Pennsylvania and New Jersey exceeded the level found in many mines. Always quick with a horror story, the EPA "found" this new "danger" to millions of citizens and gleefully reported that as many as 20,000 lung cancer deaths in the United States are caused by residential radon. Perhaps someone at the EPA should have been reading a certain $36 per year newsletter.

Petr Beckmann was well aware of this noble gas situation, as evidenced by 106 different mentions of radon in his newsletter Access to Energy from September 1979 through June 1992. [Now edited by Dr. Arthur Robinson, President and Research Professor, Oregon Institute of Science and Medicine, Box 1250, Cave Junction, OR 97523. Back issues, twenty-one-year CD-ROM, and index available.]

Professor Beckmann was wise enough not to condemn the radon levels out of hand, but he took the bureaucrats to task for their double standard: One hand of government was tightening industrial radioactive emission standards to ridiculously low levels, while the other hand was encouraging/demanding that homeowners modify their homes to the point where radon doses to the average citizen were hundreds - if not thousands - of times greater than the levels dictated to nuclear workers. Here is an example from the November 1983 edition of his newsletter - prior to the EPA's "discovery" of residential radon:

"Although radon exposures of the public are regularly hundreds and even thousands of times higher than from nuclear power operations, that alone may not be cause for alarm. Our purpose here is not to scare readers with the dangers of radon, but to point out the inconsistency of the media and of the politicians bent on pleasing them."

When it came to radon, one might ask about the government's myopia for so many years. Well, one might also remember that during this period we were having one of our regularly scheduled energy crises and were being urged to seal up our residences and commercial buildings. (Anyone born before 1960 should surely remember Carter's "thermostat cops.") Without ventilation, the heavy gas, almost eight times heavier than air, seeps into basements or lower floors with additional amounts coming from unvented or poorly vented natural-gas heaters. There appears to have been a contest between which "crisis" was more important - energy or radiation. Energy shortage was first out of the gate, but it's radiation coming down the homestretch.