The environment, nuclear crises and human survival

Gerald Lalor and Charles Grant, Guest Columnists

The situation in Japan with the reactors is ongoing and far from clear. The nature of the observed radioisotopes indicates some core damage and Japan's Nuclear and Industrial Safety Agency and others have reported higher-than-normal levels with occasional spikes, but are not considered dangerous. The wind has been blowing northwest to southeast, towards the Pacific Ocean, which helps reduce risks from local contamination without threatening other nations. A variety of measurements is under way.

The results, of course, vary with location and time, but typically have been in the microsievert range (e.g. 338 microsieverts per hour at the west gate of the site complex at 2000 GMT: measured on March 16). Tens of thousands of people living in a 20km-30km zone around the plant have been evacuated, although it seems unlikely that they would receive high enough radiation doses to produce health effects. The World Health Organisation said recently that the risk to public health from radiation leaks seems to be "very low". ABC has reported that three workers have received radiation treatment, but there seem to be no serious radiation casualties though higher-than-normal doses were being accumulated by several hundred workers on site.

Radiation levels

Elevated radiation levels have been reported in some samples of food and water. Shipments of milk and vegetables from near the affected plant have been stopped, though Chief Cabinet Secretary Yukio Edano explained, "At the moment, these vegetables are not harmful to people's health. However, the current situation could continue for a time, and that was the reasoning behind a warning not to distribute or consume some goods from Fukushima prefecture." Residents as far away as Tokyo were told not to give tap water to babies because of iodine radiation levels at twice the safety level. These levels fell next day and the city's governor showed his confidence by drinking tap water in front of cameras.

The situation is fluid. The levels of iodine are expected to decrease within a few weeks once releases to the atmosphere at Fukushima Daiichi have ceased. In any case, the doses are too low to present an immediate health concern and would be meaningful only for a large population for a much longer period than a few weeks. Edano said that if someone were to eat the vegetables for 10 days then they would be exposed to about half of one year's background radiation. This is hardly much of a risk; a view which the US Department of Energy (DOE) agrees as radiation levels outside the Fukushima Daiichi nuclear plant are well below those that would pose an immediate risk. This view does not seem to have been taken into account however, as the United States became the first country to block the import of milk and fresh produce from the areas around the plant. Once 'man-made' radionuclides at almost any level are reported in soil, water and food products, there are concerns among consumers and importers.

Nearer the Fukushima Daiichi power plant, public broadcaster NHK has reported higher levels, including 965 becquerels from iodine-131 per kilogram at Iitate. In Tamura, levels were 365 becquerels per kilogram from iodine-131 on March 17, but these fell to 161 becquerels per kilogram two days later.

Secretary Edano stressed that the radioactivity measured from the samples poses no immediate threat to health. In the case of the milk samples, even if consumed for one year, the radiation dose would be equivalent to that a person would receive in a single CT scan. The levels found in the spinach were much lower, equivalent to one-fifth of a single CT scan.

To date, disaster at the plant has been averted but the situation is still considered serious and the final solution will be expensive. Nuclear radiation, invisible and insidious, gives us the creeps. It also has to be taken into account that the country is greatly stressed by the other consequences of the earthquake and tsunami. In the North, more than a quarter of a million people are in shelters. Exhausted rescuers are still sifting through the wreckage of towns and villages, retrieving bodies and some 27,000 persons have been confirmed dead or missing. Amid the suffering, though, one detects a sense that the corner is being turned. Aid is flowing and phone, electricity, postal and bank services have resumed, though they can still be patchy.

Comparisons with Three Mile Island and Chernobyl

Unlike these two previous accidents, the Japan event was caused by an external factor of extraordinary power. The tsunami, at 14 metres, was well beyond the overall design value of 6.5 metres of the essential external plant. Japan's Nuclear and Industrial Safety Agency declared the accident as Level 5 on INES scale - an accident with wider consequences -the same level as Three Mile Island in 1979 and 2 below that of Chernobyl. Few radiation casualties and no deaths have been reported, though higher-than-normal doses are still being accumulated among the several hundred workers on site. In all probability, some reactor cores will have to be written off. In all cases, the proximate causes were loss of coolant, but the reasons for this were very different.

The Three Mile Island accident in 1979 has been the most serious commercial reactor accident in the US and the reactor core, though it was destroyed, was controlled with no resulting injuries and very small offsite releases of radioactivity. Nevertheless, it had a great impact on reactor operations and emergency response in the country and elsewhere.

Summary of Events at Three Mile Island

Here, too, there was a failure in the secondary non-nuclear section of the plant. The main feedwater pumps stopped running and the turbine and the reactor shut down automatically. Without cooling, the pressure in the nuclear system began to increase and was successfully vented, but the valve did not close when an acceptable pressure was achieved and the signals available to the operator failed to show that it was still open and that the cooling water was pouring out. The instruments provided confusing information and the operators, thinking that the core water level was sufficient, reduced the flow. This led to partial meltdown, but there was no breach of containment building and no massive radiation release. The health effects of the accident were negligible. While that reactor was destroyed, all the radioactivity was contained - as designed - and there were no deaths or injuries. The accident had a significant effect on Western reactor design, operating procedures and operator training.

Chernobyl

There is enormous and sometimes contentious literature on the Chernobyl disaster some of which is summarised here. The accident that destroyed the Chernobyl 4 reactor was the worst ever. It killed 30 operators and firemen within three months and there were many further deaths later. There were 134 confirmed cases of acute radiation syndrome (ARS). A large proportion of childhood thyroid cancers since the accident was likely caused by intake of radioactive iodine from fallout.

The 1986 Summary Report on the Post-Accident Review Meeting on the Chernobyl Accident (INSAG-1) accepted the view of the Soviet experts that "the accident was caused by a remarkable range of human errors and violations of operating rules in combination with specific reactor features which compounded and amplified the effects of the errors and led to the reactivity excursion". In particular, according to an IAEA report: "The operators deliberately, and in violation of rules, withdrew most control and safety rods from the core and switched off some important safety systems." The human factor was a major element in causing the accident."

Another factor was the design of the RBMK-1000 graphite moderated pressure tube-type reactor. It, too, is a boiling light water reactor with an output of 1,000MWe and one its important characteristics that contributed to the accident was the positive void coefficient, where an increase in steam bubbles ('voids') is accompanied by an increase in core temperature. In the particular case, this overwhelmed all other influences on the power coefficient.

Early on April 26, 1986, a test was being carried out to determine how long turbines would spin and supply power to the main circulating pumps after a loss of the main electrical power supply. This involved a series of operator actions, including the disabling of automatic shutdown mechanisms, and the reactor became extremely unstable. The operator tried an emergency shutdown, but it was too late. A peculiarity of the design of the control rods caused a dramatic power surge as they were inserted into the reactor. The core heated rapidly, leading to rapid steam production. The overpressure partially detached the cover plate of the reactor, rupturing the fuel channels and jamming all the control rods halfway down.

A large area of Europe was contaminated: West Germany, Italy and Greece suffered most, as the radioactive substances, mostly iodine and caesium, wind-borne deposits on soils far from the point of origin were absorbed by plants and animals. Since Europe is a major exporter of food, the indirect effects of Chernobyl were global. Jamaica refused a shipment of powdered milk because its radioactivity was just below the international limits.

About 200,000 people ('liquidators') from all over the Soviet Union were involved in the recovery and clean-up during 1986 and 1987. Many of these received high doses of radiation, averaging around 100 millisieverts. Some 20,000 of them received about 250 mSv and a few received 500 mSv. Later, the number of liquidators swelled to more than 600,000, but most of these received only low radiation doses. The highest doses were received by about 1,000 emergency workers and on-site personnel during the first day of the accident.

A few hundred thousand persons were resettled into less contaminated areas, and the initial 30km radius exclusion zone of 2,800 square kilometres was extended to cover 4,300 square kilometres. With the exception of thyroid cancer, direct radiation-epidemiological studies performed in Belarus, Russia and Ukraine since 1986 have not revealed any statistically significant increase in either cancer morbidity or mortality induced by radiation. But the report does a large proportion of child thyroid cancer fatalities were attributed to thyroid cancer caused by radiation exposure.

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