whoever they were, they were not welcome to Kalychenko. Nor was Khrenov, who certainly had no business being present at this purely technical matter. As for Chief Plant Engineer Varazin, well, certainly the man had every right to be anywhere in the plant he chose, at any time. Still, Kalychenko had never before seen him in the control room after midnight before. With all these people present there would be no good chance to disappear for half an hour or so for a little rest from his duties.
Both Khrenov and the Chief Engineer looked freshly washed and shaved, and humorously apologetic to their guests for getting them out of bed at this uncultured hour. 'Still, now you can see how hard we work here at Chernobyl,' Varazin said affably. 'In any case, you're just in time. We've already begun to reduce power on Reactor Number Four.'
'Excellent,' said one of the visitors politely, glancing around. 'And the Director and Deputy Director?'
'The Director has left the entire matter in the hands of Chief Plant Engineer Varazin.' Khrenov smiled. 'As to Smin, I tried to call him, but he is off on some private errand. So when they come in to work on Monday, we will be able to give them both a pleasant surprise.'
'Exactly,' Varazin agreed, rubbing his hands together. 'Now, as designated test leader, I must give a briefing.' He stepped toward the board and raised his voice. 'May I have your attention, please? As provided by the regulations, it is my duty to brief you all on the experiment we are conducting. But don't stop what you are doing. Continue to reduce the power; we don't want to be here all night!'
Kalychenko listened with half an ear. Most of his attention was on the tricky business of lowering, the temperature of Reactor No. 4, though what the Chief Engineer was saying was certainly interesting. Kalychenko almost forgot to be sleepy as he heard the plan.
The basic intention of this experiment, Varazin announced, was to see if useful power could be generated from the heat usually wasted while a nuclear reactor was down for maintenance. The reactor never stopped being hot, of course; it never would until at last the plant was finally decommissioned, somewhere in the next century, and probably not for some time even then. But it was not the practice to try to use that heat while the reactor was being serviced. Now, perhaps Chernobyl could lead the way to new practices.
By the time he got to the new practices, more of the observers were drifting in, looking sleepy. Varazin nodded affably to them, and added, 'This is how we will lead the way for our colleagues all over the Soviet Union. Also,' he went on, looking serious, 'these measures could be of great importance under catastrophic conditions. They could insure a steady supply of power to keep our operations stable until, for example, the auxiliary diesels could be started. Are there any questions?'
The shift chief raised his hand. 'I do not quite understand what 'catastrophic conditions' we are preparing for, Vitaly Aleksandrovitch,' he called.
'Who can say?' smiled the Chief Engineer. 'A very bad storm? An earthquake? Or' — he frowned meaningfully at them—'a sudden nuclear attack from our enemies, perhaps.'
'Ah,' said the shift chief, enlightened. 'Of course. But there is still a question in my mind. Why don't we simply shut down the reactor instead of trying to lower the output?'
'Because,' said the Chief Engineer severely, 'we must be quite
Kalychenko groaned silently. A number of times! They would be at this all night! — and, likely enough, well into the Saturday morning shift, too, the way things were going. With resignation he bent to his work.
The normal night shift in the control room was only half a dozen men, just a skeleton crew to keep things going. There was not much need for electrical power in the late night hours in the Soviet Union. Good Soviet citizens went to bed at night so they could rise, bright-eyed and refreshed, for the next morning's work.
Tonight was different. Besides Kalychenko's own crew, there were four men left over from the late evening shift, looking oppressed at being kept on overtime for which they were not likely to be paid, plus the observers, the Chief Engineer, and the Personnel man, Khrenov.
To lower the power on a reactor like the RBMK is not like turning down the gain on a radio set. To shut it off entirely is much easier. You simply thrust home all the boron rods, two hundred and eleven of them, piercing the graphite core from top and bottom and in all its parts. The element boron is poisonous to nuclear reactions. Boron soaks up neutrons; they cannot go on to make another atom fission, and so the reaction stops; that is the easy way.
To slow the nuclear reactor down is another matter entirely. There are three separate ways to do it. First, for a rough approximation, you shove a few additional rods into the core. Not too many; you don't want the reaction to die. (Once the reactor stops waste products begin to accumulate — the element xenon is the worst of them, since it is a worse poison to nuclear reactions even than boron. Then it is impossible to start again until weeks have passed and the xenon has decayed away.)
Then there is a certain measure of fine control that can be attained by varying the mixture of gases in the sealed space surrounding the core. Some of the gases soak up neutrons in the same way that boron does, though not as strongly; to slow the reaction a bit, you simply add more of those gases to the mix.
Finally, there is water. The water that flows up through the core to turn to the steam that drives the turbines also has the neutron-absorbing characteristic — as long as it is water. Once it has turned into steam, which is less dense, it soaks up fewer neutrons, and thus the nuclear reaction picks up speed. This condition is called a 'positive void coefficient,' a technical term which means only that the more steam there is in the tubes the faster the reaction will go. This also means that the faster the reaction goes, the more steam will be generated— consequently adding to the 'voids' — consequently adding to the speed of the reaction — consequently adding to the steam…. It is a delicate balance to keep a reactor, any reactor, poised between dying and running away, and so controlling a power reactor is a constant dance of rods and pumps.
When things were going well, Kalychenko enjoyed his part in the dance. Most of it was automatic, anyway. There were heat sensors all through the reactor core. The optimum running temperature of the one hundred eighty tons of uranium fuel was hundreds of degrees hotter than the ignition temperature of the graphite slabs. Graphite is carbon. Carbon burns. But it couldn't burn without oxygen, and oxygen was carefully excluded from the mix of gases in the surrounding jacket. If the temperature of the reactor climbed too high or fell too low, there would be a signal from the expensive imported Western instruments that monitored it. Then the operator would engage the motors that thrust a few rods farther in or took them a bit less deep. If it climbed drastically high, the operator would not be involved at all; automatic pumps would rush floods of new cold water into the core to cool it down.
That could not happen this night, because the automatic system had been turned off hours before, but then, no one ever wanted to let things get so far that the automatics were tripped anyway.
Another thing no operator wanted — at least, Kalychenko certainly didn't want it! — was to try to lower the temperature slowly. That was a sweaty business, because at low power levels the RBMK was notoriously hard to control. The trouble was that it was so big. The temperature sensors could not be everywhere. One part of the core could be at exactly the temperature desired, while another, an arm's length away, could be soaring to dangerous levels without warning. So Kalychenko did sweat, and swore under his breath, because the bitch was obstinately rising and falling, down to ten percent power, then up to thirty, slowly down again as they inched a few rods back in — then almost dying on them, down to the range where xenon began to form, until they had withdrawn all but six of the rods entirely and were coaxing it back to life.
When Kalychenko took his eyes off the board long enough to glance at a clock it was only one a.m.! He wasn't sleepy any more. He was simply exhausted. Only one, and he had worked harder than he usually did in a full shift. And everyone else was on edge too.
Even the GehBeh, Khrenov, had lost his warm, hooded look. Just behind where Kalychenko sat at his board, Khrenov was quarreling softly with the Chief Engineer. 'What is the matter, Varazin?' he demanded. 'Can't you control this thing? Must I find Smin and bring him here?'
Varazin flushed, glancing at the observers. 'I am Chief Engineer, not Smin,' he whispered fiercely.
'And I am responsible for Personnel. Perhaps I have been deficient in my duties. It may be that I have not screened this plant's personnel with sufficient care.'
Varazin flinched, but said sturdily enough, 'If you have complaints in that respect, Comrade Khrenov, there will certainly be time to discuss the matter. This is not the time. May I remind you that I am in charge here?'
Khrenov looked at him thoughtfully for a moment, then gave a long sigh. He turned to the observers with the smile back on his face. 'What a pity,' he said genially, 'that this operation should take so long. Since most of you
