Danger of nuclear reactors as explained by Alvin Weinberg

Alvin M. Weinberg, nuclear physicist (Director of Oak Ridge National Lab and pioneered the pressurized water reactors and boiling water reactors used in nuclear power plants, worked on the Manhattan Project, appointed to President’s Science Advisory Committee during the Eisenhower and Kennedy administrations), 1973:

• [A]re there concerns regarding the possibility that these systems may malfunction and cause hazard to people and to the environment? This is a perfectly legitimate question that deserves serious and thoughtful consideration; and it is this aspect of the matter that I shall address… The potential hazard of a nuclear system arises from the toxicity both of the materials that keep the system burning and from the fission product ashes. Plutonium-239… is lethal to man in doses of about 16 thousandths of a gram if ingested in the lungs; Strontium-90, with a half-life of 30 years, will be lethal if about 70 millionths of a gram is ingested; Iodine-131, with a half-life of eight days, will be lethal after ingestion of only about 30 billionths of a gram.

• As I have said, even during the Manhattan Project, we realized that a nuclear reactor could undergo what is known as an excursion [see Chernobyl] – that is, if too many control rods were removed, the reactor power could surge to dangerous levels. This, however, is not the main worry, for such excursions are inherently self-limiting both in time and magnitude.
• Rather, the worry is that in a very high-powered reactor, immediately after the chain reaction has stopped, the fission products at least momentarily continue to generate 7% as much energy… Thus a high-powered chain reactor must continue to be cooled for a considerable time after shutdown if fuel meltdowns are to be avoided. It was Edward Teller who some 25 years ago insisted with great prescience that in these respects nuclear reactors were potentially dangerous, and therefore they should be subjected to the most searching kind of technical scrutiny… The response of the engineer… was to build a… containment vessel around every reactor; the second [was] various back-up safety systems… to prevent the reactor core from melting. Why bother with the back-up cooling systems if the containment vessel in final analysis will catch whatever radioactive debris might be created in an accident and thus prevent harm befalling the public? And indeed this was the attitude in the earliest days… As long as reactors were relatively small we could prove by calculation that even if the coolant system and its back-up failed, the molten fuel could not generate enough heat to melt itself through the containment However, when reactors exceeded a certain size, then it was no longer possible to prove by calculation that an uncooled reactor fuel charge would not melt through its containment vessel. This hypothetical meltthrough is referred to as the China Syndrome for obvious reasons. Since we could not prove that a molten fuel puddle wouldn’t reach the basement of a power reactor, we also couldn’t prove whether it would continue to bore itself deeper into the ground. Whether or not the China Syndrome is a real possibility is moot. The point is, however, that it is not possible to disprove its existence. Thus, for these very large reactors, it is no longer possible to claim that the containment shell, which for smaller reactors could be relied upon to prevent radioactivity from reaching the public, was sufficient by itself. In consequence, the secondary back-up cooling systems… must now be viewed as the ultimate emergency protection against the China Syndrome… if one is trying to be practically 100 percent sure of always being able to cope with a reactor meltdown, then one must… be absolutely certain that the engineered safety features, particularly the emergency core cooling system, will work as planned.

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