England's Windscale Reactor Releases Radiation

Date October 10, 1957

A fire at the Windscale nuclear reactor released radioactive iodine, cesium, and strontium into the atmosphere, requiring the confiscation and disposal of milk from 200 square miles of countryside. The accident marked the first time a significant amount of radioactive material was released outside a nuclear plant’s boundaries.

Locale Seascale, England

Key Figures

• William Penney (1909-1991), director of the Atomic Weapons Research Establishment of Great Britain, who headed the official inquiry into the Windscale accident
• Harold Macmillan (1894-1986), prime minister of Great Britain, 1957-1963, who kept the official report of the Windscale accident secret for decades

Summary of Event

The Windscale number one and number two nuclear reactors, built near the village of Seascale on the west coast of England, were designed to convert uranium into plutonium for use in the British nuclear weapons program. The Windscale reactor cores consisted of steel tubes containing uranium fuel interspersed in a 50-foot cube of graphite. The graphite served as a moderator, slowing the neutrons emitted in uranium fission so that they could more easily induce the fission of other uranium atoms.

The Windscale reactors were cooled by huge blowers, which forced air over the core and then up tall smokestacks. An array of filters in the smokestacks was designed to remove any radioactive particles picked up by the air as it flowed over the core.

Reactors that are moderated by graphite are susceptible to sudden, unpredictable releases of Wigner energy, energy stored in the graphite from the interaction with neutrons emitted during the fission process. The release of Wigner energy can result in rapid heating of the reactor core. A spontaneous release of this Wigner energy had occurred at the Windscale pile number one in 1952. Following that incident, procedures to control the release of Wigner energy were developed. The reactor was shut down at regular intervals, and the core was allowed to heat up by shutting down the airflow over the core. As the core heated, the stored-up Wigner energy was gradually released in a slow, controlled fashion.

At 1:03 a.m. on October 7, 1957, Windscale pile number one was shut down for a planned Wigner energy release. During the day, the core cooled and the thermocouples, electronic thermometers that monitor the temperature at various locations throughout the core, were checked. By 7:25 p.m., the operators were ready to begin the Wigner release process. They shut off all blowers and then restarted the core at a low level of power production to cause the graphite to heat up. On the morning of October 8, the operators became concerned that the core had not been heated sufficiently to induce the desired release of Wigner energy, and some thermocouples indicated the core was already beginning to cool.

A second core heating was begun at 11:05 a.m. This time, the operator allowed the level of power generated in the core to exceed that called for in the operating procedure, and a rapid increase in temperature was observed. Control rods, which absorb neutrons and slow the reaction rate, were reinserted into the core to reduce the power-generation rate. The operator was unaware that one or more of the uranium fuel elements had overheated and that their steel tubes had ruptured.

The Wigner energy release was triggered by the second heating, and the core temperature rose as expected throughout the day of October 9. Although instruments within the reactor gave no indication of a problem, the uranium in the fuel elements with ruptured tubes was exposed to air, and it began to burn. This led to the failure of nearby fuel rods, and the fire began to spread. Late on the evening of October 9, the blowers were turned on again to cool the core after the release of Wigner energy.

Early on the morning of October 10, radiation detectors inside the smokestacks indicated a rise in radioactivity. The operator interpreted this as a normal consequence of the cooling air flowing around the core again. At noon, the smokestack detectors again indicated a rise in radioactivity, a weather station on the roof of the reactor detected radioactivity, and the reactor core temperature continued to rise. At this point, the operator realized that the tubes of some fuel elements had failed. The fire, however, had not yet been recognized. No public announcement of the radiation release was made.

During the afternoon, plant workers, dressed in radiation-protective clothes, entered the reactor enclosure. They removed an access plug in the pile wall to view the fuel elements at the hottest spot in the reactor, and they observed the fuel tubes glowing red. The severe heat had distorted the fuel tubes so severely that they could not be removed. The fire was recognized, but the heat release in the damaged region of the pile could not be stopped.

By this time, the wind had shifted from its daytime direction, carrying the radioactive releases out over the Irish Sea, to a nighttime pattern that blew toward the shore. This wind deposited radioactive fission products on the town of Seascale, slightly more than 1 mile from the reactor site, and further along the sparsely populated section of the English coastline. The town of Barrow-in-Furness, with a population of more than sixty thousand, was less than 100 miles away. Health physicists, monitoring the radioactivity outside the plant boundaries, recognized three possible hazards posed by the escaping radioactive material: whole-body gamma irradiation, respiration of fission fragments, and ingestion of fission fragments deposited on crops or concentrated in milk and meat. At the levels detected, only ingestion was believed to pose a serious health hazard.

A plant spokesperson made the first announcement of the accident, indicating that the amount of radiation released was not hazardous and that there was no danger of a reactor explosion. At midnight, the decision was made to cool the reactor with water. Officials recognized that the use of water would ruin the multimillion-dollar reactor and that the water could result in the production of hydrogen gas, with the possibility of a hydrogen explosion.

At 9:00 a.m. on October 11, two plant technicians and the local fire chief carried a hose to the top of the containment structure and aimed a spray of water at the core. This produced radioactive steam, which escaped through the smokestacks. The fire was quickly extinguished, and the core began to cool down. Within twenty-four hours, the danger of further radiation release had ceased.

Significance

The Windscale accident was the first nuclear reactor accident that resulted in a significant release of radioactive material outside plant boundaries. The most serious radioactive release at Windscale was that of iodine 131. The total release of iodine 131 at Windscale was estimated at 20,000 curies, a measure of the number of radioactive decays per second. (The Three Mile Island incident in Pennsylvania, in comparison, released only twelve to sixteen curies of iodine 131; iodine 131 release for bomb testing at the Nevada nuclear test site was estimated to be about five thousand times that of the Windscale release.) The human body is very efficient at absorbing ingested iodine and concentrating it in the thyroid gland.

Iodine 131 has a short half-life; one-half of the initial iodine 131 decays in eight days. Iodine 131 is, therefore, only a short-term problem. During that short period, however, iodine deposited on the ground can be ingested by animals and can become concentrated in milk and meat.

The radiation exposure of workers at the Windscale pile and the nearby Calder Hall nuclear reactor facility was regularly monitored by film badges. None of the workers received serious exposures to the radiation. The release of radioactive materials outside the plant boundaries was monitored by health physicists.

The countryside near the reactor was sparsely populated, consisting mostly of farmland and pasture. Samples of the milk given by the cows in pastures near the Windscale plant showed radiation levels on October 11 at about six times higher than permitted. The decision was made to confiscate milk from twelve dairy farms located within 2 miles of the plant. Later surveys, however, indicated that an area of about 200 square miles had experienced significant iodine 131 contamination. By October 14, milk was being confiscated from 150 farms covering a 200-square-mile area. Local residents reportedly expressed concern about the safety of the milk they had been drinking after the accident.

Thousands of gallons of contaminated milk were shipped to the Milk Marketing Board depot in Egremont, where the milk was dumped into sewers that carried it into the Irish Sea. The milk ban continued for several weeks, and farmers were compensated for their financial losses. Ten thousand gallons of milk from outside the contaminated area had to be shipped in for human consumption. Some cows, sheep, and goats from the contaminated area were confiscated, killed, and buried. The thyroid glands of animals slaughtered for meat were collected and tested by the government.

Workers in a nearby coal mine were exposed to radiation drawn into the shafts through the mine’s ventilation system. Some had to be replaced temporarily by workers from outside the region to minimize the cumulative radiation exposure of any individual worker.

Reporters sent to the area received confusing and sometimes contradictory answers to their questions. The Manchester Guardian carried its first report of the Windscale accident on October 12, two days after the release of radioactive materials. It reported that plant workers had been warned of a possible radiation hazard but that there was no danger to the general public. It was not until October 16 that the Manchester Guardian reported on the collection and confiscation of milk supplies from the contaminated area.

The lack of information from government sources and Windscale officials proved unsettling for some local residents, who were concerned about contamination of the water supply and their outdoor safety. The British Atomic Energy Authority responded by assuring residents that the water supply was safe. Lower levels of radioactivity were carried by the winds in a southeasterly direction. Three hundred miles away, in London, an unusually large level of fission products was detected in the air on October 12, although this information was not released until 1958. Large areas of England and northern Europe received detectable radioactive fallout from the accident. The governments of Denmark, the Netherlands, Belgium, and France all reported detectable increases in radioactivity from the Windscale accident.

An official inquiry into the Windscale accident was headed by William Penney, the director of the Atomic Weapons Research Establishment of Great Britain. The cause of the accident was a combination of sensor failures, human errors that compounded the initial problem, and gaps in the scientific knowledge about how the reactor worked. Official statements summarizing the report indicated that it was unlikely that anyone was harmed by the radioactive fallout deposited on the countryside from the Windscale accident.

Follow-up studies on children in the contaminated area are consistent with these official statements. Iodine concentrates in the thyroid after ingestion, and measurements of thyroid gland contamination showed the greatest amount of iodine in any child’s thyroid to be 0.28 microcurie. Since a continuous amount of 0.1 microcurie is regarded as safe, this temporary elevation was not regarded as hazardous. These levels would likely have been much higher if milk from the contaminated region had been consumed.

British prime ministerHarold Macmillan, who was interested in improving relations with the United States, decided not to release the full text of the official report because he was concerned that its release might jeopardize cooperation on nuclear weapons between the United States and Great Britain. Not until thirty years later, when the full text of the official report was released, was it announced that other radioactive isotopes, including polonium 210, had also been released in the accident. The National Radiological Protection Board of Great Britain had estimated that as many as thirty-three cancer deaths could have occurred as a result of the release of radioactive material from Windscale.

The Windscale accident demonstrated that the monitoring and control of milk is one of the first safety precautions required after the release of fission products into the environment. The accident also demonstrated that quick and authoritative information on the extent of a radioactive release is required to minimize public apprehension over the extent of the danger.

Bibliography

Baverstock, K. F., and J. Vennart. “Emergency Reference Levels for Reactor Accidents: A Re-Examination of the Windscale Reactor Accident.” Health Physics 30 (April, 1976): 339-344. An in-depth discussion of the radiological hazards resulting from the Windscale accident, including the results of follow-up studies and a reinterpretation of the original data in the light of further understanding of the hazards of low-level radiation.

Blair, Ian. Taming the Atom: Facing the Future with Nuclear Power. Bristol, England: Adam Hilger, 1983. A pronuclear overview of atomic power from the British perspective.

Fuller, John G. We Almost Lost Detroit. New York: Reader’s Digest Press, 1975. Chapter 5 provides an extensive account of the Windscale accident, focusing on the radiation release and its impact on the local population. The chapter includes quotations from local residents and plant officials.

Novik, Sheldon. The Careless Atom. Boston: Houghton Mifflin, 1968. An account of the accident at Windscale, including details on how the reactor was operated, the sequence of events leading up to the accident, and the effects of the radioactive material deposited on the countryside.

Takada, Jun. Nuclear Hazards in the World: Field Studies on Affected Populations and Environments. New York: Springer, 2005. A general, and brief, work that examines the consequences of nuclear disasters and near-disasters on local populations and environments. Discusses radioactive dosages, monitoring of radiation, the effects of radiation on the human and nonhuman body, and environmental protection.

Thompson, T. J., and J. G. Beckerly. Reactor Physics and Control: The Technology of Reactor Safety. Vol. 1. Cambridge, Mass.: MIT Press, 1964. This account of the Windscale accident provides extensive excerpts from the official British government report on the accident.