Frederik Pohl - Chernobyl

"It is still too high," Varazin announced. "Add another pump!"

It was seven minutes after one. And all of a sudden, without transition, Kalychenko's bright mood vanished. He began to worry.

The first indications of trouble were the pressure readings in the water system. "Pressure is dropping in the drying drum," reported one of the engineers.

The shift chief glanced at Varazin, who said impatiently, "Yes, of course. Carry on." But he looked nervous too. With two extra pumps forcing water into the system, the steam generation had slowed; there was more water coming in than the core could boil into vapor at once, and so in the great drum, where the steam was extracted to feed into the turbines and the remaining water pumped back into the circulation system, pressure had begun to fall. Paradoxically, that meant more steam there, as the water that had been squeezed liquid found room to expand. Kalychenko listened and thought he could hear, in the distant throb of the pumps, a laboring sound as they tried to pump vapor instead of liquid water.

Then the state printout computer flashed a warning: Reactor should be shut down at once.

"Chief Engineer Varazin!" Kalychenko cried. The old man was looking strained now, but he said:

"Yes, of course. We are operating under unusual conditions, which the program is not designed for."

"Then shall I-"

"Certainly not!" said Varazin, biting his lip. "Comrade Khrenov and our guests will be back at two, and I don't want to have a dead reactor for them." He glanced at the clock. It was twenty minutes after one. "Close the stop control valve," he ordered.

Kalychenko looked at the shift chief for confirmation before he obeyed, but the man only nodded. His face was pale. Reluctantly Kalychenko switched the stop control valve off; it was the last of the automatic safety features.…

Then it all went sour.

"Temperature's rising!" screamed the shift chief. And everyone stared at the thermal readings-from seven percent of normal power, already at fifteen… twenty… in ten seconds it went to a full fifty percent of normal power. And in Kalychenko's mind, as he gazed awestruck at what was happening, there flashed a picture of the interior of the reactor core, with each of the 1,661 tubes filled with water… only the pressure was dropping… and the water turned prematurely into steam, steam that was not dense enough to soak up neutrons, that let the reaction pick up speed…

There was a distant thud.

"What was that?" Varazin cried, and then in the same breath: "Insert rods! Fifty percent rods, immediately!"

But the rod operator was reporting that the control rod motors were not responding; the rods would not penetrate the core. "Emergency shutdown then! At once!" Varazin shouted, and held his breath.

But the rods would not go in. "Something is blocking them!" the rod controller shouted, his voice shaking. Kalychenko heard the words incredulously, for that was impossible! There was nothing to block the rods in their sockets-why, it would mean that the interior of the reactor itself had suddenly become warped, or shrunken, or broken-

The next explosion was much louder. The walls shook. Dust sprang out from the walls, hanging like a sudden shimmer of ice fog in the air. The lights went out-all of them, even the lighted meters and dials on the full-wall instrument board.

"Oh," moaned Varazin, "my God."

"Emergency circuits!" cried the shift chief, and the man next to Kalychenko, muttering oaths, reached for the switch.

At least then the instrument lights went on again, but what they said was insane. Temperature readings simply off the scale, radiation levels that could not be believed. And the noise did not stop with the explosion. There was a rumbling thunder of walls going down, a patter of something hard falling on the roof, a crackle that could only be flame.

"Go and see what has happened to the reactor," ordered Varazin.

It was at least an instruction to follow. Most of the men in the main control room jumped up to comply. Even Kalychenko rose from his useless board, but as he started through the door he caromed off one of the other hurrying men, who swore and thrust him out of the way. Kalychenko fell heavily. By the time he got up, most of the men had rushed out to peer down at the reactor chamber.

Kalychenko's arm hurt where he had fallen on it. He hesitated, rubbing the arm, then turned and went the other way. It was unquestionably a cowardly act. It also saved his life.

Saturday, April 26

There is a difference between the nuclear reactions in a power plant-even a plant with a "positive void coefficient"-and an atomic bomb. The difference lies mainly in the fuel. Power-plant uranium is slightly enriched with the touchy isotope, U-235. Bomb uranium is very much so. This governs the speed of the reaction in which one fissioning atom releases a neutron, which strikes another atom and causes it to fission, and so on in the familiar "chain reaction." The links of this chain happen very fast in either case. In a bomb, there can be a hundred million successive links in a single second. In a power plant, only about ten thousand. For a human operator the difference doesn't really matter much, because he can't react quickly enough to intervene in either case. But within the core it is the difference between a nuclear accident and a bomb blast. If the core of Reactor No. 4 had been of weapons-grade uranium, the nuclear reaction would have gone on to involve far more of the fissionable material before the force of the explosion had time to blow it away. Since it was not, the nuclear explosion "blew itself out." Its kinetic force scattered its own fuel elements, and in the process destroyed only part of one building instead of an entire city. The later consequences, however, were of course another story.

In that first moment the shift engineer, Bohdan Kalychenko, had saved his life by running away from the reactor. On the perimeter of the plant, the hydrologist-engineer, Leonid Sheranchuk, saved his by running toward it. When he saw the great fireworks display blossom terribly overhead, he stood transfixed. Flaming debris rained down on everything, on the ground, on the buildings, on the man with the bicycle, on the man on foot twenty meters away, even on the roof of the ambulance that was slowly turning around to return to the scene of the explosion. A huge chunk of something the size of a football fell only meters away; it blazed blue, and he could feel the heat of it. Graphite? Could it be graphite ? From the core of the reactor itself? He couldn't tell; really, if that were the case, he didn't want to know. But none of the debris fell on Sheranchuk.

At first he was shielded by the guard's cabin. Then he ran for the nearest entry to the plant-not because he reasoned out that that was the right thing to do, but because the plant was in mortal peril and he could not do anything else-and it happened to be the door to the section of the building that contained the main control room for Reactor No. 4, on the far side from the blazing, spitting inferno that had been the reactor itself, with the whole turbine hall between.

Even as he entered he heard the clanging alarm that ordered evacuation. But that was wrong! Sheranchuk knew instantly that it was wrong; you didn't run away from a nuclear plant because there was an accident; you had to do whatever you could, whatever that might be, to keep the accident from becoming terribly worse.

"Stop!" he yelled, trying to bar the door with his body, but someone roughly pushed him aside and someone else stumbled past to the red-lit outside. "No, wait!" he cried. "What are you doing? Go back to your stations! You can't leave the plant untended!"

Some swore at him, some did not hear. Some he seized by the shoulders and turned around by brute force. There were too many for him-shift operators, maintenance workers, radiation monitors, two older men he thought were observers from another plant-he even caught a glimpse of two men, wrangling as they trotted away along another corridor, that looked like Khrenov and Chief Engineer Varazin.