The secrecy covering the Windscale site and its mission did not help the publicity crisis that arose when it hit the newspapers in London and Manchester. Simply cautioning people about drinking milk or leaving windows open was enough to cause some concern. At one leak point a scientist at Windscale, Dr. Frank Leslie, wrote a letter to the Manchester Guardian on October 15, expressing disappointment that the government had given no warning to the public until the matter was resolved. Harold Macmillan, the excitable Prime Minister, had to be restrained from seeking out Dr. Leslie and strangling him manually. The Penney report was finally declassified and released to the public in January 1988.
On November 8, 1957, about a month after the Windscale fire, the British bomb program achieved what it had so dearly sought. Above the southern end of Christmas Island in the Pacific Ocean, the two-stage thermonuclear device Grapple X went off with a bang, yielding 1.8 megatons. Penney’s development crew had done it almost correctly, and a bomb that was built to give one megaton unexpectedly wiped out the military installations on the other end of the island with 80 % over yield. A triumphant British delegation of scientists was invited to Washington to talk about thermonuclear topics with some fellows from the Lawrence Livermore Lab, and the shutout was broken. From that point on, the United Kingdom was granted technical parity with the United States in matters of nuclear weapons and use of the Nevada Test Site.
The replacement plutonium production reactors for the Windscale units were already up and running, as of August 27, 1956, at the Windscale site. Four large graphite reactors using closed-loop cooling by carbon dioxide, named Calder Hall Piles 1 through 4, produced 60 megawatts of electricity each, and were considered to be the world’s first nuclear reactors making significant commercial power. In reality, the purpose of these reactors was to convert uranium-238 into plutonium-239 and to manufacture tritium. Calder Hall Pile No. 1 ran for nearly 47 years before it was finally shut down in 2003.
A sister plant named Chapelcross was built on an abandoned airfield in southwest Scotland near the town of Annan. The plant, comprising four 180-megawatt Calder Hall reactors, was completed in 1959. Its purpose was to produce plutonium and tritium, with 184 megawatts of electricity on the grid being a secondary byproduct. The Calder Hall and Chapelcross reactors were safer and more complex than the antique Windscale units. The carbon dioxide cooling gas worked just like air being blown through, but it was contained in a closed loop, pumped back into the bottom of the core after the heated gas had been used to make steam in heat exchangers. The steam, which was used to turn the turbo-generators, was also in a closed loop, and the ultimate heat sink for disposing of the waste energy was one large cooling tower per reactor, dumping heat into the atmosphere. There was not much worry of fire in a graphite pile cooled with fire-suppressing carbon dioxide. Even an unlikely steam explosion would not release fission products into Scotland.
For efficient plutonium production, the fuel was still metallic uranium, this time enclosed in cans made of magnesium oxide. It was code-named MAGNOX, and this became the type designation for a series of 26 power reactors built in the UK. Magnesium oxide is perfectly fine as a canning material, as long as it does not get too hot or too wet. If left too long in a cooling pond, the magnesium oxide corrodes and leaks, and the fuel inside can melt easily if deprived of coolant while fissioning.
Given the Cold War pressures of producing Poseidon and Trident missile warheads and the risky fuel design, these improved graphite reactors were remarkably safe. There were no meltdowns or fires of the Windscale severity, but there were some interesting incidents.
The Chapelcross piles were just like the Calder Hall piles, only different. They were built in series, starting with Pile No. 1, and improvements were added as the construction progressed. Pile No. 1 required annealing, similar to the Windscale piles, but, starting with Pile No. 2, the graphite fuel channels were lined with graphite sleeves. The sleeves were fragile and were something else that could break, but they were designed to let the graphite run so hot it would never require annealing. In Chapelcross Pile No. 2 on May 19, 1967, after seven years of running at full power, the graphite sleeve inside one of 1,696 fuel channels crumbled and blocked the flow of carbon dioxide coolant over the fuel canisters. At least one fuel canister overheated, the uranium melted and caught fire, breaking open the can and sending radiation alarms into a tizzy.[132] Considering that a MAGNOX reactor is loaded with more than 9,000 fuel canisters at one time, this would seem a small statistical problem, but full-blown disasters can start small and memories of the Windscale fire were still fresh. The reactor was scrammed immediately, and the accident investigation began.
Unlike the Windscale piles, the more advanced gas-cooled reactors were built with the fuel channels cut vertically, and fuel handling was semi-automated to prevent workers from having to get anywhere near the reactor cores. The entire core was encased both in a steel pseudo-sphere as protection from fission product leakage and a pressure vessel, containing the cooling gas and keeping broken fuel cartridges off the landscape. This was an excellent plan, but peeking into a fuel channel was not as easy as it was in the old days. A special television camera was built, mounted on the end of a pole that could be positioned over the burned fuel channel to look in and see what had happened. This device confirmed that the fuel channel was blocked with graphite debris and that it would have to be cleaned of this and the remains of the burned fuel, but unfortunately the camera broke off and fell into the reactor. It did everything but scream as it tumbled off into the abyss, with the monitor screen image spinning and then going black. This would complicate the repair.
It took two years, but the men at Pile No. 2 were able to design a workable plan for restoring the plant to full operation. Three men were outfitted in fully sealed radiation suits with closed respirators. Each man was given only three minutes to work, during which he would receive his entire year’s allowed radiation dose working at the top end of the core in a concentrated radiation field. One at a time, they moved quickly through the forest of control rods to the clogged fuel passage and ran a scrubber on a long pole down the hole, cleaning the passage and restoring its roundness.
The cleanout was successful, and Chapelcross Pile No. 2 resumed operation. All was good until 2001, when the Chapelcross power plants seemed to trip over a streak of bad luck.
Fuel has to be changed-out at the MAGNOX reactors at least twice a year. First, the burned fuel, blisteringly radioactive with fission products, must be pulled out of the fuel channels and lowered down a chute and into a lead coffin. This is accomplished using the discharge machine, which runs on rails on the floor of the crane room, addressing holes that are opened one at a time, giving access to the reactor below. An operator rides in a seat on the back of the machine, which weighs a hefty 60 tons. Half of that weight is lead shielding to protect the operator from what he is pulling out of the reactor, and if the machine is operating properly, the workers never see or touch the fuel cartridge.
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Quoting the OSHA