Sellafield status update: Pile 1 decommissioning plans moving slowly but steadily forward

Publish date: March 17, 2005

Written by: Charles Digges

SELLAFIELD, England—Early in World War II, British Prime Minister Winston Churchill understood the effect nuclear deterrence could have against future wars. But after a short period of nuclear collaboration with the United States—during which many of England’s most vaunted nuclear scientists took part in the Manhattan project— Washington dried up with the passage of the MacMahon atomic energy act in 1946, effectively leaving England to develop its own atomic bomb.

Churchill was nonetheless insistent, and in a furious push between 1947 and 1950, as a war ravaged England began to rebuild, a plutonium production reactor called Pile 1 went online under the guidance of John Cockcroft, head engineer at the Windscale facility—later renamed Sellafield—in Northwest England on the Irish sea near the town of Seascale. A year later, Pile 2 went into commission.

Both reactors were roughly based on the design of the United States Hanford facility—the design of which Britain’s scientists had a passing acquaintance with—which produced the material for the US atomic bombs dropped on Hiroshima and Nagasaki in 1945.


The 1957 fire and possible reasons behind it
Because of the graphite composition of Pile 1’s charge face—the insertion point for fuel elements—it was susceptible to something called the Wigner Effect, wherein the constant bombardment by neutrons builds up potential energy in the form of heat before being released, thus posing a fire hazard within the graphite.

To reduce deleterious effects of this, which included distortion of the graphite face that made fuel charging and discharging more difficult, Pile 1 underwent regular processes during which thermal energy was released by gradually heating the graphite above normal operating temperature, a process called annealing.

Annealing had been performed 8 times on Pile 1 between 1952 and 1957, but was becoming increasingly more difficult and often had to be augmented by additional heat bursts. On October 8th 1957, Pile 1 was shut down, as per routine for its ninth annealing procedure. Unusually high temperatures were recorded in the process, and when technicians examined the phenomenon by removing the access hole to the core, it was discovered the Pile was completely ablaze before a single alarm sounded.

A bulk injection of carbon dioxide failed to extinguish the fire. Technicians scrambled to withdraw the fuel elements, but removing 72,000 fuel elements from 3880 channels was taking more time than they had. It remained burning within the bio-shield of the reactor for two days until an infusion of water and a shutting off the air ducts on October 10th finally starved the fire of oxygen.

In the aftermath, it was determined that over 20 percent of the reactor core was damaged in the fire. But with the building of the Calder Hall plutonium production facility, nuclear authorities saw little benefit in trying to repair the damage done to pile one.

The precise cause of the fire has never been determined, but it has been voiced by several experts that human error lay at its base. UKAEA officials told Bellona Web that the annealing process was carried out too rapidly, thus setting the blaze. In addition, according to Bellona investigations, safety regulations that governed the annealing process were ad-hoc and incomplete, which only made matters worse.

Pile 1 building manager Carl Nyerscough told Bellona Web during a visit to the facility last week that “a large degree of the human factor was involved.”

“There were likely some basic misunderstandings of the technology involved which might not have occurred if they had known more about how the Americans were doing it at Hanford,” he said. This was made impossible after the passage of the MacMahon act in 1946.

Standing atop the bio-shield of Pile 1, Nyerscough pointed to several man-hole type shaft covers down which fire fighting equipment can be lowered into the reactor should a fire begin in the affected area of the reactor from which damaged uranium fuel elements have not entirely been removed. He also pointed out fire fighting equipment located atop the pile.

“This is basically pro forma stuff that you will in any nuclear installation,” he said, and estimated that chances of a new fire within Pile 1 at “zero.”

Radioactive releases resulting from the fire
The fire led to two major releases of radioactivity to the air. The first large release occurred when the natural uranium inside the reactor core caught fire. The second occurred when the reactor was finally showered with water and the air ducts closed.

A huge cloud of steam transported radioactive particles and gases up into the air. The radioactive cloud drifted southward with the prevailing winds over most of England and continued into Europe, a Bellona investigation published in its 2003 Sellafield report says.

Fifty-four Workers at the Sellafield facility itself were exposed to radiation doses 150 times higher than the prescribed dose limit, while many who lived nearby were exposed to radiation doses 10 times higher than the maximum lifetime doses.

Though UKAEA knew about the high radiation levels, it was nevertheless decided not to evacuate the population, the Bellona report says.

The fire also had devastating consequences on local milk production in Cumbria area. The day after the fire, the authorities halted the distribution of milk from 17 farms in the district, and on October 12, 1957 the Medical Research Council ruled that milk containing more than 3,700 Bq of radioactive iodine-137 per litre should not be consumed. It was assumed that this limit would affect all milk production in an area of approximately 500 square kilometres; consequently, all milk from this entire area was recalled, the Bellona report says.

The measure was hardly taken in vain: The activity measured in one of the milk samples was as high as 50 000 Bq per litre, coming from a farm located 15 kilometres away from Pile 1, according to Bellona’s findings.

Three days after the initial recall of milk produced in the most exposed area went into effect it was discovered that some milk produced further away was contaminated with iodine-137. Milk samples taken from a farm in Grasmere in the Lake District showed concentrations of between 4 400 Bq per litre and 6 600 Bq per litre.

Despite these discoveries, the milk was nevertheless distributed to the market.The papers documenting these figures were classified by the government so as to avoid "unnecessarily alarming" the population, the Bellona investigation revealed.

The majority of the restrictions on milk distribution were lifted on November 4th 1957, while the remaining restrictions were cancelled on November 23rd, only about a month after the accident. In all, about two million litres of milk containing iodine-131 were dumped into the ocean or nearby rivers, Bellona’s report says.

Efforts have been made to estimate the extent of the radioactive releases. It is believed that the accident led to a release of between 600 and 1,000 TBq of iodine-131, between 444 and 596 TBq of tellurium-132, between 2.2 and 45.5 TBq of caesium-137 and about 0.2 TBq of strontium-90.

The British Prime Minister at the time, Harold MacMillan, suppressed all technical information concerning the accident. He feared that the conclusions of the accident report—that the accident occurred as a consequence of operator negligence and poor instrumentation, as well as the accident report’s reference to an earlier accident in 1952—would adversely affect the population’s confidence in the nuclear energy programme, postponing the development of British nuclear weapons.

Macmillan declared that complete openness about the accident would jeopardise national security, Bellona’s report revealed.

It was 25 years before official estimates of the accident’s effects on the health of local inhabitants were made public. In 1982, the British National Radiological Protection
Board issued a report describing the full truth about the Windscale accident. It was estimated that 32 deaths and at least 260 cases of cancer could be attributed to the fire. However, independent experts maintain that the fire actually led to over a thousand deaths.

Safety culture today
Sellafield is standing down from its Cold War footing, and is rapidly tranforming into a series of decommissioning projects.

British Nuclear Group, which was established in response to the creation of the the Department of Trade and Industry’s Nuclear Decommissioning Authority (NDA) following the Energy Act of 2004, will be the management and operations contractor on the Sellafeild licenced site. NDA will take ownership of the Sellafield site on Arpil 1st of this year. As such it is hard to imagine such MacMillan-scale cover-ups occurring again.

The NDA will hold tenders among global heavyweights like Bechtel, Cogema and British Nuclear Group to continue decommissioning work at Sellafield.

British Nuclear Group’s information officer Stagg speculated that by 2008, companies like these will be included in the bidding process, but that whether they will work onsite at Sellafield will be left to the discretion of the NDA.

This could imply management changes at the top, but on the ground, employees view the coming of the NDA as something more cosmetic than ground shifting.

“We expect some lay-offs, sure,” said on worker who asked that his name not be used.

“But Sellafield is our local business and people around here just call it ‘the factory.’ It’s hard to imagine a total overhaul of the workforce especially when so many of us have this place as the family trade.”

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