‘No Clear-Cut’ Link : Chernobyl Seen as Reminder to U.S. on Safety

One year after the Chernobyl nuclear disaster, the U.S. Nuclear Regulatory Commission has concluded that the causes of the Soviet accident have little direct bearing on the safety of American nuclear power plants, but they serve as yet another reminder that complacency is dangerous with a technology as unforgiving as nuclear power.

Based on detailed reports that the Soviet Union has supplied to the International Atomic Energy Agency in Vienna, government and industry analysts have concluded that the accident April 26, 1986, was the unique product of egregious blunders by Soviet operators and a novel reactor design with inherently dangerous features that would have been unacceptable in the West.

“People think there is no clear-cut nexus between the specific occurrence of this accident and our plants,” Harold Denton, a senior official of the Nuclear Regulatory Commission, said.

‘Hazardous Technology’

Yet, Denton noted, while “that particular accident can’t happen (in the United States), it does not say that we can’t have severe accidents. . . . This is basically a hazardous technology if not properly operated. This means you have to have discipline in the control room, detailed procedures and a knowledgeable staff that doesn’t go bypassing safety systems in the dark of the night to run a test.

“If you turn off all the safety systems in a U.S. plant and pull all the control rods out, you’re going to cause problems,” he said, noting that technicians at Chernobyl had turned off key safety systems to conduct an unauthorized and ill-planned test.

In recent years, the safety systems of U.S. reactors have been equipped with interlocking devices designed to shut down a reactor automatically if an operator tries to bypass a critical safety feature. In the wake of Chernobyl, Denton said, these interlocks are “worth another look” to ensure their adequacy.

The 1000-megawatt Chernobyl reactor, 60 miles north of Kiev, exploded at 1:23 a.m. last April 26, lofting a plume of radioactive debris that forced governments across Europe to take special measures to protect food supplies.

31 Dead, 200 Hospitalized

According to Soviet accounts, 31 workers died from the immediate effects of burns and radiation, 200 were hospitalized and 135,000 people were evacuated from 71 nearby towns and villages. In neighboring Poland, government doctors distributed 16 million doses of protective iodine to children and adults who stood in long lines beneath scattered showers of mildly radioactive rain.

Despite Chernobyl’s limited technical relevance to Western systems, the emotional impact of the accident and the radioactivity it spread around the world have revived an anti-nuclear movement in the United States that had grown quiescent in recent years.

“The ultimate lesson of Chernobyl,” Sen. Edward M. Kennedy (D-Mass.) said in February in a phrase that has become an epigram of the accident among nuclear opponents, “is that human and technological error can cause disaster anytime, anywhere.”

Chernobyl has emerged, for example, as an emotional new element in long-running battles over the licensing of the Shoreham nuclear plant on Long Island and the Seabrook plant in New Hampshire. At issue in both cases are questions about emergency planning to cope with a major accident.

In Maine, opponents will test their strength this fall with a ballot measure aimed at closing the state’s only nuclear power plant. In California, Massachusetts and Texas, opponents are seeking state legislation to ban nuclear power plants.

U.S. Operations Modified

In addition, spurred by Congress and environmental groups, the Department of Energy has modified operations at the only U.S. reactors with basic design features similar to the water-cooled graphite reactor that exploded and burned at Chernobyl: The department has temporarily idled its military production reactor at Hanford, Wash., to install new safety features and has reduced power at another military reactor near Savannah, Ga.

“The tragic meltdown at Chernobyl has raised an unparalleled challenge for the anti-nuclear movement,” Richard Rudolph and Scott Ridley wrote in the current issue of the journal Radical America. “For U.S. activists, the radioactive wind out of the Ural Mountains arrived at a time of relative calm. . . . The question is: what changes will it bring? And more importantly, will the changes last?”

Some recent public opinion samplings suggest that Chernobyl’s impact on American perceptions of nuclear power were smaller and more evanescent than the nuclear industry had feared or its opponents had hoped.

Although U.S. utilities have ordered no new reactors since 1978, a major nuclear building program they set in motion in the 1970s is now coming to fruition. Thus, in the year of Chernobyl, seven new power reactors went into operation in the United States, more than at any time since 1973-74. According to the Atomic Industrial Forum, an industry trade group, 105 nuclear plants now produce 17% of the nation’s electric power. When all current construction is completed in about 1990, the proportion of nuclear electric power will reach 20%.

Grudging Acceptance

That such licensing could proceed at a near-record pace last year, despite the worst accident in the 45-year history of the technology, suggests to some analysts that it has achieved broad, if grudging acceptance.

“A massive shift in public opinion is just not there” as a result of Chernobyl, said Gene Pokorny, of Cambridge Reports, a Massachusetts opinion research firm that has tracked public attitudes toward nuclear electric power since 1974. “By and large, American public opinion is where it was before the accident.”

Predictably, Pokorny said, the Three Mile Island accident in Pennsylvania in 1979--which destroyed a reactor but released essentially no radioactivity--had much larger and more lasting effects on public perceptions of nuclear energy. Chief among these was the growth of committed, “hard-core” opponents to about 18-20% of the adult population from about 10%. There the level remains, even after Chernobyl.

Although polls show that relatively few Americans actively favor building more nuclear plants--or coal-fired power plants, for that matter--a large majority seem to accept those already running as an unavoidable necessity, Pokorny said. In a nationwide sampling of 1,500 adults in February, 10 months after Chernobyl, 79% said nuclear energy will be “important” in meeting future energy needs, a marginal increase from 73% in 1984-85.

‘Realistic’ Energy Source

Similarly, when asked to pick the leading source of electric power in 10 years from among oil, coal, natural gas, nuclear, solar, wind and hydroelectric power, 37% chose nuclear. In addition, Pokorny said, 79% of those polled in February said they expected the U.S. need for nuclear power to increase, while 67% agreed that it was a “very good” or “realistic” large-scale source of electricity.

Paradoxically, he suggests, the Chernobyl accident “may have forced the public to confront the realities of nuclear energy, as a here-and-now source of power, even if one not fully liked or fully understood.”

In the intervening year, U.S. and other Western experts have learned a great deal about the Soviet approach to reactor safety and the design of the Chernobyl reactor, a novel “national” technology that was a source of pride among Soviet engineers. In retrospect, the design appears to be flawed in a variety of ways not previously understood by Soviet safety analysts.

Also, discipline at Chernobyl--the plant that boasted the most trouble-free performance of the country’s 14 similar units--was far more lax than the Soviet reputation for regimentation and control would suggest.

Massive Block of Graphite

To achieve a rapid buildup of nuclear power in the western third of the country, where oil and coal resources are diminishing, the Soviets set out in the mid-1960s to build two radically different varieties of reactor. One was a series of conventional, pressurized water-cooled reactors intended partly for export to Moscow’s trading partners.

The other was the Chernobyl model, essentially a massive block of graphite, a form of carbon that facilitates the nuclear fission reaction, pierced by hundreds of uranium fuel assemblies that did not require the difficult and exacting fabrication of steel pressure vessels that hold the fuel in conventional reactors.

Soviet designers also convinced themselves that their graphite reactors were, on balance, safer than those pioneered by the Americans and adopted by most of the rest of the world. In 1979, shortly after the Three Mile Island accident, Pennsylvania Gov. Richard Thornburgh toured nuclear power plants in the Soviet Union and was told confidently that the issue of safety there had been “solved.”

According to an analysis released in February by the NRC, Soviet engineers knew their graphite reactors had a tendency to race out of control if large steam bubbles were allowed to develop in the 1,600 cooling channels--a characteristic known as a “positive void coefficient,” and one long since designed out of conventional Western power reactors.

The Soviets, however, felt that strict adherence to operating procedures would compensate for this drawback. So certain were Soviet designers that these reactors were invulnerable to a catastrophic accident that they built them without the huge all-enveloping steel-and-concrete containment shells that are the most visible feature of Western reactors.

Turning Down the Power

The operating procedures on which safety depended collapsed at Chernobyl on the night of April 25-26, as technicians began powering down the reactor for routine maintenance. As low power levels were reached, a safety experiment was to be carried out on one generator.

However, the test had not been authorized by senior safety authorities, and the technicians who conducted it--and apparently were in charge in the control room that night--were turbine and generator technicians, not qualified reactor operators. Nor was the line of authority clear among the technicians who assembled for the test.

Without elaborating, the Soviets have told Western experts that the test had to be performed that night or delayed for a year, giving it added urgency. Despite a series of difficulties over many hours in reducing the reactor’s power level, compounded by operator mistakes and the reactor’s inherent instability at low power levels, the technicians decided shortly after 1 a.m. on April 26 to proceed with the experiment in the face of clear signs of a developing emergency.

To simplify the test and make it easier to repeat, they had turned off emergency control systems.

Fraction of a Second

As control rods were withdrawn beyond allowable limits, cooling water in the reactor flashed to steam. In a fraction of a second, the nuclear reaction raced out of control, and for a brief moment, according to Soviet calculations, Chernobyl reactor No. 4 generated 100 billion watts of thermal energy, 100 times its rated maximum power.

The “maximum credible accident” that the reactor had been designed to withstand was the rupture of one pressure tube carrying cooling water past the fuel in the core. Within two to three seconds, all 1,600 tubes ruptured as a steam explosion tossed aside the reactor’s 1,000-ton steel and concrete cover, obliterated the roof, spewed out burning chunks of graphite and began the expulsion of 100 million curies of radioactive wastes into the atmosphere over the next 10 days.

According to an analysis prepared by the Electric Power Research Institute, and published by the NRC in its February report on Chernobyl, the operator errors that triggered the disaster formed only one of several potential pathways to a major accident that Soviet designers appear never to have considered, or taken seriously.

U.S. authorities have concluded that Soviet safety researchers in general have paid far less attention than their Western counterparts to plotting out “what-if” scenarios of potential accidents, estimating their probability and taking corrective measures. Almost certainly, a major reason has been the absence of public--and for the most part, internal--debate over nuclear safety issues in the Soviet Union.

‘It Was a Best Seller’

Mechanical failures ranging from a break of the main steam line to a blockage of cooling water in one coolant channel, the Electric Power Research Institute study suggests, could result in severe damage through sequences of events not contemplated in the design. NRC officials took copies of the report on a recent visit to Moscow and Chernobyl, and one who took part in the trip said “it was a best seller. Everyone wanted one.”

With so few common bonds between technologies, U.S. regulators, in their search for lessons from Chernobyl, have focused on the human factors that contributed to the accident, such as boredom and complacency. Curiously, the NRC’s Denton suggests, both Chernobyl and Three Mile Island occurred at night, perhaps because trained operating crews everywhere are less alert and more likely to be undermanned at these hours.

One lesson, he said, may be that “if you have abnormal circumstances” on a night shift, “then shut down till the morning crew comes in and analyzes it.”

Since Three Mile Island, he noted, most U.S. utilities have increased the number of control room shifts from four to six, with one shift always engaged in training, testing their skills on computer-simulated accidents. Even so, boredom in the control room still appears to be a problem.

Sleeping on Duty Charged

Earlier this month, the NRC took the unprecedented step of shutting down the Philadelphia Electric Co.’s Peach Bottom plant while it investigates charges by a utility employee that control room operators often slept on duty.

In one post-Chernobyl proposal, the NRC staff has suggested that senior safety managers be appointed at every nuclear plant, whose only responsibility would be to watch over the shoulders of control room staff for safety deviations. Utilities have resisted the idea on the ground that senior control room operators already fill this requirement.

The agency is also exploring the development of watch-dog computers that would serve much the same purpose, not to run a reactor but to monitor the actions of those who do.

Ultimately, the NRC’s Denton said, Western nations are unlikely to tolerate severe reactor accidents--even those like Three Mile Island that stop short of releasing dangerous radioactivity--more than once in a generation.

“We need to focus on these operating details, the training of operators, and make sure we don’t have anything that comes close,” he said. “You can’t have very many of these events before the public says, ‘This technology isn’t mature enough. Let’s go back to coal.’ ”