The Accident and Health Effects

On April 26th, 1986, at 1:23 am, Alexander Akimov did what he and thousands of other nuclear plant operators have been trained to do. When confronted with confusing reactor indications, he initiated an emergency shutdown of Unit 4 of the large electricity generating station near Pripyat in the Ukraine.

By doing so, he unwittingly initiated an explosion whose effects continue to be felt throughout the world. On the occasion of the tenth anniversary of the Chernobyl accident, it is appropriate to understand what went wrong and what has been done to prevent it from happening again.

Before pressing the AZ button - used to initiate an emergency shutdown - Akimov and his fellow operators were immersed in the conduct of a special test. The procedure was designed to prove that the reactor would be provided with sufficient cooling water even if a complete loss of power to the large electric generating complex occured while the emergency cooling system was inoperable.

According to engineering calculations, the inertia of the plant's big 500 MW electric turbines would allow them to generate enough electricity to keep cooling water pumps operating during the 30 to 50 second delay required to start the emergency diesel generators.

The engineers who designed the test were specialists in electric generators, not in nuclear reactors. The historical record indicates that there was little consultation with nuclear reactor specialists during the procedure preparation.

The test was planned for a time when the plant was to be shut down for routine maintenance and its power output was not needed for the national electrical grid.

Establishing the initial conditions for the test proved difficult and more time consuming than initially planned. The first problem was that the grid needed the power longer than expected. It was after midnight when the plant was finally allowed to begin the test, and a new shift of operating personnel had just taken over. The new shift was not very familiar with the test and did not get a complete briefing by the off-going shift operators.

The actions of the off-going shift operators had put the plant into an unusual situation because the power history and the resulting concentration of fission product poisons was different than any situation considered during the design of the control system.

The man in charge of the test, Anatoli Dyatlov, the deputy chief engineer of the plant, had been involved in the test preparations and in setting the initial conditions. The new operators deferred to him for decisions, because of his experience, his official position and his familiarity with the specific test protocol.

There were several times during the period immediately prior to the test when the plant technicians considered action that could have averted the catastrophe. They did not like the way that the plant was responding to their control inputs.

If they had taken appropriate action, however, there is no guarantee that they would have been rewarded for their decision. In fact, there is every likelihood that they would have been punished for delaying the test and the subsequent maintenance period. Dyatlov had a reputation as an irritable taskmaster; apparently he was especially impatient on the night of the accident.

Though Soviet reactor plant operators were not under pressure from their bosses to maximize financial profit, the Communist political system provided considerable incentive to maximize production for the benefit of the the state and the party. Failures or perceived weakness were often severely criticized or punished by demotion or reassignment. During the night of April 26th, all the Chernobyl operators had to offer as a reason to discontinue the test was a sense of confusion over the plant indications.

Apparently, Akimov must have comforted himself with the knowledge that he knew exactly where the AZ button was and readied himself to push it if it became necessary. There is no way he could have known that pushing the button could lead to a dangerous insertion of positive reactivity.

Much has been made of the fact that RBMK reactors can develop what is known as a positive void coefficient of reactivity. What that long phrase means is that increasing boiling caused by increasing core temperature can lead to an increase in core reactivity, an increase in core power and even more boiling. This positive feedback mechanism is assiduously avoided in most reactor plant designs.

What has not been so well understood is that the shutdown button of an RBMK could, under very special initial conditions, initiate a positive insertion of reactivity that could increase core temperature rapidly enough to cause a steam explosion. No nuclear reactor plant can explode in a manner even remotely similar to an atomic bomb, but, as boiler operators have known for well over a hundred years, a steam explosion can pack quite a punch.

Though much has been made of the lack of a "safety culture," lack of containment, and violations of procedures by operators, the specific cause of the Chernobyl explosion and subsequent release of radioactive material from the Chernobyl reactor was a shutdown system that initiated a positive reactivity accident. For those readers who have never operated a nuclear reactor, it might be helpful to think of the cause as a brake pedal that - without the driver's knowledge - transformed itself into an accelerator.

It took far longer than it should have to find the technical cause of the accident, largely because efforts were made to protect the designers and their powerful bosses and to fix the blame on the less politically connected operators.

The design fault that caused the explosion required several straightforward technical modifications that have now been completed on all operating RBMK reactors. There is essentially no chance that the accident could happen again.

However, the fix has not satisfied the calls for action from those that do not understand the production of electricity. The fix has - rationally enough - not satisfied the desires of those that want to use the accident as an excuse to get rid of nuclear power for political or competitive reasons.

Health Effects

The health effects of the accident at Chernobyl have been the subject of numerous intensive studies. Here are the results.

Two people died during the accident itself; one was killed by the explosion and one suffered a heart attack. A third person died early the next morning from thermal burns (he was scalded by steam.) 237 people were initially diagnosed as suffering from acute radiation exposure and were hospitalized for treatment. Of those, 21 were estimated to have received doses ranging from 6 to 16 Gy (600 to 1600 RAD) over a short period of exposure. 20 of the 21 died in spite of intensive medical attention including some highly publicized bone marrow transplants.

Many of these highly exposed people were fire fighters who had severe thermal and radiation induced burns covering much of their body. These burns greatly complicated their treatment.

Twenty-one patients received acute doses of between 4 and 6 Gy (400 to 600 RAD). Of those 7 died. 55 people received acute doses between 2 and 4 Gy with one death. No deaths occurred among the 140 hospitalized people with exposures below 2 Gy.

Therefore, the immediate death toll from the accident was 31. Since the accident, 11 more deaths - possibly caused by radiation - have occurred among the population of highly exposed people, bringing the death toll to 42.

Some of the patients continue to require periodic treatment for radiation related illnesses. None of the highly exposed people were members of the general public; all received their exposure because of occupational responsibilities related to the nuclear plant or casualty control.

That answer rarely satisfies people who are curious about the effects of the accident. There have been far too many widely published stories about cancers, birth defects, thyroid disorders or other symptoms.

The best estimate of radiation related illness is that there have been approximately 500-600 excess cases of thyroid cancer, mostly in children, in the areas most affected by the radioactive fallout. As of early 1996, three deaths have been associated with this disease. There is some speculation among scientists that the potassium iodide pills given to prevent I-131 uptake by the thyroid may have contributed to the cancers. In areas where iodide was not administered, only two cancers have appeared.

There have been no excess leukemias, congenital abnormalities, adverse pregnancy outcomes or any other radiation induced disease in the general population.

There have been other health effects from the accident that are far more disturbing, mainly because they could have been prevented.

One effect has been an increase in stress related illnesses. The stress can be attributed to both fear of radiation and to the severe dislocation of people caused by government ordered evacuations.

Many of the peasants in the area near the Chernobyl power plant lived in the same village where their ancestors had lived for centuries. In some cases, they were evacuated without any belongings or other resources, even when there was little chance of being exposed to additional doses of radiation.

The fear of radiation is a natural result of years worth of intensive propaganda campaigns and a general lack of knowledge of recorded health effects. People generally fear things they do not understand, especially when they have been repeatedly told by authority figures that their fear is justified.

The level of reported stress or psychological impact also seems to have been affected by the government program designed to compensate the victims. People who claim to have been negatively affected are eligible for regular cash payments, medical care and for special assistance in housing and job placements. These incentives provide ample reason to blame poor health on radiation exposure from Chernobyl.

Poor diets have also contributed to poor health in the region near the accident site. Because of stringent safeguards against potentially contaminated food, locally grown food is often discarded despite the minimal potential health impact. This action ignores the fact that vitamin deficiencies are far more dangerous than slight contamination and the fact that "clean" food is often unavailable. In some ways, the overall effect is similar to that of concerned mothers who switched their children from apples to processed snack foods in the wake of the 60 Minutes episode on Alar.

Another disturbing fact is that as many as 200,000 women decided to abort healthy fetuses because of concern that they might have been damaged in the womb by minor radiation exposures. There is no evidence of any birth defects caused by the radiation levels experienced by expectant mothers after the accident.

There has been an increase in alcoholism following the accident. Here are some explanatory quotes from Piers Paul Read's book, Ablaze: The Story of the Heros and Victims of Chernobyl. "The extra allowance paid for the purchase of clean food was spent entirely on drink - vodka when they could get it, on wine when they could not." And, "The idea that vodka was an antidote to radiation was widely accepted even by educated people. . ."

The lesson that should be learned from the study of Chernobyl's health effects is that many of the worst potential effects of a nuclear accident can be prevented. Decision makers, including those who make decisions for their families, need to make the effort to educate themselves about radiation health effects.

In the aftermath of the Chernobyl accident, scientists, national authorities and local officials all proved themselves woefully ignorant of the potential effects of radiation exposure and unable to make decisions that minimized the overall health effects on the population.

In defense of the people who made poor decisions following Chernobyl, their ignorance can be attributed to the fact that nuclear information has been considered a high level secret in many nations. There was little readily available information or guidance.

In cases where scientists or physicians were consulted for their recommendations, their perceived credibility had more to do with rank or official position than with their knowledge of radiation health effects. Deferring to rank rather than knowledge or experience can be dangerous, especially if the information sources are defensive about their ignorance.