Ithink the design may have been a contributory factor, but not because it was primitive or faulty from an operational point of view. The design is very sophisticated, but it entails a large number of individual controls, many more than are needed in the pressurized water reactors which are also produced in the Soviet Union as well as in nuclear industries in the West. The Chernobyl reactor came into operation in 1983 and it uses graphite rods as well as water. Similar systems also operate in Britain and in the us, but they are most useful in the military field because they produce the high-grade plutonium needed to make nuclear bombs. When the Americans started their civil nuclear power programme they designed an entirely new type of pressurized water reactor (pwr) for the purpose, but the Soviet government decided to adapt the military design to civilian purposes.
The key design difference is that the pwr system has all the fuel elements attached to a single block which is raised and lowered by a single control mechanism. The block is comparatively small, with a high concentration of uranium attached. When the fuel is spent, the whole block is put in a concrete coffin and disposed of. The graphite-moderated reactor, on the other hand, has individual fuel rods, each of which is individually controlled, entering a separate pressurized tube, surrounded by rods of graphite. This is very convenient if you want to reprocess the spent fuel rods to extract plutonium: you can remove one rod at a time and introduce it individually into the chemical reprocessing system.
Military reactors of this type are small, but their adoptation for civilian use requires a great increase in the number of rods, so that the Chernobyl reactor had 1,600 individual tubes with their own separate controls for temperature, pressure and so on. This involves much more detailed human control over the process but it also brings a greater margin for human error. Moreover, in the event of a serious accident in the fuel process, pwrs present, in principle, a greater danger of melt-down than graphite-moderated reactors. The pwrs are much smaller—about two to three metres long compared with the eleven to seventeen metres of a Chernobyl-type reactor. But the heat from the fuel element is much more concentrated in pwrs—which is crucial in relation to the danger of melt-down and a so-called China syndrome. But in the case of Chernobyl, the advantage of diffuseness and the presence of more than a thousand tons of graphite were cancelled out by the graphite fire.
Part of the explanation was a kind of scientific patriotism. The pwr reactors which the ussr produces and exports to Eastern Europe as well as the fast-breeders are developed from American models, while the graphite reactors were basically invented by Soviet scientists. There is also scientific and institutional conservatism: many of the scientists who developed the design remain in powerful positions to this day,
The decision to site reactors near large cities like Leningrad, Sverdlovsk and Kiev was mainly governed by economics. The difference in price between nuclear and non-nuclear electricity generation in the Soviet Union is very small—Russian economists reckon nuclear power is marginally cheaper by a few kopeks a kilowatt. But that marginal advantage depends on closeness to big population centres, so that electricity power lines are short and the heat from the reactor can be used as well. Chernobyl is actually quite far from a large city. Leningrad’s reactors are much nearer, as is the Voronezh plant. There is a reactor of this type only forty kilometres from Sverdlovsk, which has over a million people, and the Kursk and Kostroma reactors now under construction are only two kilometres from the city limits. The other factor behind the siting decision is the view expressed by such leading scientists as the President of the Academy of Sciences, Alexandrov, that unlike Western reactors, Soviet nuclear-power plants are 100 per cent safe. This claim may have had some basis in the sense that there had not yet been a major accident involving the reactor fuel cycle in a Soviet power station, while there had been a number of major accidents of this kind in the West. But of course there must have been many minor accidents which were not reported, and perhaps also serious accidents known only to top designers, scientists and administrators. And of course there was the nuclear waste disaster in the Urals. Arbatov, writing in Izvestiya the other day, sought to stress that this was the first serious reactor accident in the Soviet Union out of a total of 153 reported throughout the world. But the inescapable fact is that this was not just one more to add to the list: it was the worst so far.
At this stage we can still only guess what happened. We don’t know if the crisis began with a technical fault or as a consequence of human error, or both. There could have been a technical fault in one of the tubes. These are produced by the thousand in Leningrad and it is possible that despite the quality checks one was faulty. A fault in the sensor system, apparently imported from the West, could also have been responsible. But the accident reminds me of one that occurred in a similar type of reactor in Idaho, usa in 1961. There the reactor was being shut down for maintenance and the problem occurred when the worker did not put the moderating rod in soon enough and the reactor became too hot. Three people were killed and the plant was highly contaminated.
The Chernobyl accident began in the early hours of Saturday morning when the number of people on the shift was probably minimal. The reactor was apparently already shut down for a maintenance check when the malfunction occurred. The low staff presence, though fortunate in limiting the initial casualties, may have contributed to the disaster that was to follow. For with such a complex system, involving individual control of all 1,600 pressurized sub-systems, the minimal numbers of