Frederik Pohl - Chernobyl

"Because," said the Chief Engineer severely, "we must be quite sure. We will do this test a number of times, keeping careful record of the results each time. It is a matter of safety, after all-and we can't be too careful in a matter of the safety of the Chernobyl Power Plant!"

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 are, after all, more interested in the turbines and the steam generation than in the nuclear aspects of the operation, perhaps we should take a look at some of the other systems?"

"Can we take a look at something to drink?" one of the visitors grinned.

"We can do our best. Let me see, it's one o'clock. If we come back, say, at two, I think things will be in order. Don't you think so, Comrade Varazin?"

"I hope so," said Varazin.

At least with Khrenov gone everyone breathed a little more freely, but the job didn't get easier. It got worse. With great difficulty they managed to stabilize the power output of Reactor No. 4 at 200 megawatts electric, a fifth of its normal capacity. Kalychenko called out the reading and reached for the switch that would maintain that level. "Shall I engage the automatic systems?" he asked, finger poised.

"Certainly not," snapped Varazin, looking frayed. "It is far too high. Cool the reactor a bit."

"There are six pumps already going," the shift chief reported.

"Engage a seventh!"

Kalychenko marked the time when the seventh pump was cut in, three minutes after one. And indeed the temperature of the core began to respond; it was not the cooling of the water that made it happen, but the added liquid water in the system absorbing a few more neutrons.

The atmosphere in the control room was excited now, with the engineers and operators calling the numbers back and forth to each other, like spectators at a football game. Even old Varazin was shifting from one foot to another as he watched the readouts with them, and Kalychenko began to think about what all this meant. If this experiment succeeded, it could well be a model for every nuclear power plant in the Soviet Union. There would be commendations, perhaps cash awards-perhaps they would be written up in Literaturna Ukraina, even in Pravdal Well, no, he cautioned himself, that was not likely; this sort of thing one did not advertise in the open press, since the West had no business knowing what went on in critical Soviet industries. But it would be in the records! Even Khrenov would not fail to list all the people who had contributed to such a success somewhere in his file folders…