Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, January 30, 1994 TAG: 9401300094
SECTION: NATIONAL/INTERNATIONAL PAGE: A1 EDITION: METRO
SOURCE: Boston Globe
DATELINE: LENGTH: Long
Contrary to previously available accounts of the world's worst nuclear accident, his work has shown that the initial explosion did lead to a complete core meltdown, and that the 5,000 tons of material dumped from helicopters to douse the blazing core actually missed its target.
As a result, the radioactivity released during the disaster was up to four to five times greater than previously published estimates, confirming suspicions that had been voiced by many researchers but were strenuously denied by international and Soviet authorities.
In addition, the effort to entomb the reactor in an airtight sarcophagus of concrete, and to prevent it from contaminating nearby river water with a 1 1/2-mile-long concrete dike, has been equally unsuccessful, says Alexander Sich, a nuclear engineer who turned his research into a 500-page doctoral dissertation he presented to MIT's nuclear engineering department this month.
Those efforts may actually be increasing the risk of further contamination, Sich and Russian officials say. Today, according to scientists at the site, there are more than 11,000 square feet of holes in the concrete building allowing water, air and other materials to pass in and out.
"I believe the sarcophagus was and still is the most dangerous structure in the nuclear industry," said Alexander Borovoi, the Russian scientist in charge of monitoring and studying the site. "One hundred eighty tons of partially burned nuclear fuel remains in this building," and rainwater is constantly pouring in and further weakening the shaky structure.
On the positive side, however, what Sich found appears to alleviate fears that such a disaster would lead to the "China Syndrome," in which a molten reactor core would burn through the bottom of a nuclear plant, contaminating vast amounts of ground water and setting off a potentially enormous steam explosion. Although the Chernobyl core melted into a lava-like mass that burned through the reactor vessel and flowed into the lowest recesses of the massive plant, it never broke through the concrete floor of the plant basement, and the nuclear reaction simply burned itself out after 10 days, Sich concluded.
Morris Rosen, deputy director of the International Atomic Energy Agency's division on nuclear safety and the man responsible for that agency's analysis of the Chernobyl accident, was surprised by most of Sich's conclusions, he said in a telephone interview.
Told of Sich's calculation that more than 185 million curies of radioactive material, and possibly as much as 250 million curies, was ejected in the ten days after the accident, Rosen said, "I don't think I've heard numbers like that before. . . . It would be very surprising." Soviet officials have claimed that 50 million curies were released.
(A curie is the amount of radioactivity contained in one gram of radium. While health effects of different types of radiation are hard to compare, the U.S. Department of Energy estimates that as little as 10 millionths of a curie of plutonium, if inhaled, could cause cancer.)
Rosen was surprised and skeptical of Sich's conclusion that virtually all the material dumped on the reactor building by helicopters missed the core entirely, and that the radiation releases continued until they stopped of their own accord, rather than being suppressed.
"It's a new theory that I haven't heard of, but I can't say it's crazy," Rosen said.
Rosen conceded that the staff of the international agency "have never made a study with the level of detail" of Sich's work.
No one from the West has ever spent the time or had access to the amount of information that Sich has, several specialists agree. Many doctors, ecologists, biologists and nuclear physicists have visited the site since the explosion April 26, 1986, but none has stayed long.
"Being there one day at a time is no comparison to being there for 18 months and really getting a clear sense of things," said Richard Wilson, a Harvard professor of nuclear physics who has made many visits to Chernobyl. Sich, he said, is the only person he knows who has made an extended study of the site, which is about 10 miles from Kiev, in what is now the independent nation Ukraine.
Norman Rasmussen, professor of nuclear engineering at MIT and author of a 1975 U.S. report on the risks from nuclear power plants and Sich's thesis adviser, said Sich's work is "probably the best analysis of what took place during the 10 days after the accident, of what they did and what they tried to do."
"Although most people who've looked at it suspected that more" radioactivity was released than the Soviets acknowledged, Sich has "given enough new data to show that it is plausible. . . . I think the evidence is very strong," Rasmussen said.
Sich said there are major inaccuracies and omissions in the official version of the events after the 1,000-megawatt Chernobyl 4 nuclear reactor exploded. The official version, based on 1986 reports from Soviet officials and scientists, has generally been accepted, if not entirely believed, by international agencies that studied the accident, including the International Atomic Energy Agency. Although many questions have been raised from the start, until now there has been insufficient solid evidence to back up the contrary scenarios.
Some of Sich's conclusions are based on his own analysis, and some are simply information that has been known to scientists at the site, and in part by some Western scientists, but never previously assembled into a comprehensive picture of the events. Among his findings:
Of the more than 5,000 tons of sand, lead, boron (a neutron-absorbing element), clay and other materials dumped from helicopters to try to put out the burning nuclear core, shield its radioactive material from the atmosphere and stifle any further releases of radioactive material, virtually none reached its target. This major countermeasure to limit contamination was undertaken by helicopter pilots who repeatedly flew into a lethal cloud of radioactivity - all, apparently, for nothing.
Because the quenching material missed its target, the core material burned and melted unimpeded and uncovered for almost 10 days, going through a total meltdown and burning right through a 6-foot-thick steel and gravel barrier beneath it. While the possibility of a core meltdown has always been part of "worst-case" analyses of nuclear reactor accidents, it had never happened before to this extent. Until the first indications began to surface during Soviet surveys of the reactor in 1988, there had been no evidence that it happened at Chernobyl.
Because the core remained exposed to the air for 10 days, it released four to five times more radioactivity into the environment than has ever been officially acknowledged. While doubts were raised about the official estimates as early as 1986, and some Russian officials had since conceded privately that those figures were low, there had never been a detailed accounting, based on precise data from inside the reactor building, of exactly how much radioactive material escaped.
The fact that the 1,800 helicopter missions flown in an attempt to smother the core may have accomplished nothing, Wilson emphasized, "doesn't detract from the heroism of the people who were doing it." At least one of them paid with his life, and his body is buried beneath a monument in Moscow - inside a lead coffin.
In addition to providing a better understanding of what happened at Chernobyl during those fateful days in 1986, information gleaned from the site by Sich and other researchers could hold some important cautions for future management of the poisoned site and of other similar reactors in former Soviet territory.
The dike built to prevent radioactive materials from washing into the nearby Pripyat River has actually increased the risk, Sich said, because it is acting like a dam, holding back ground water and raising the water table. The water table is now less than 15 feet below radioactivity-contaminated material, he said.
Furthermore, the 24-story concrete "sarcophagus" built to prevent any further release of radioactive materials from the shattered reactor is structurally unstable, in danger of collapsing and is full of holes, said Borovoi, the Russian nuclear physicist.
Sich's study underscores concerns over the fact that 15 reactors of the same type as Chernobyl, called the RBMK type, considered an inherently unsafe design that could easily produce another accident, are still operating in Russia, Ukraine and Lithuania. Of all the reactors in the world, "they're the least safe," said Wilson.
After studying what went on during the Chernobyl accident, Soviet engineers designed a series of modification to the RBMK reactor that should increase safety and reduce the danger of another accident. But it is not clear whether all the recommended improvements have been made at all the RBMK reactors, nor whether the changes are adequate to ensure safety, some Western nuclear engineers say.
by CNB