The Nuclear Flask Train Crash Test

Nuclear reactors in power stations use fissile radioactive isotopes to produce heat, which powers turbines to generate electricity. When the nuclear fuel is depleted and can no longer sustain significant fission, it becomes waste, though it remains highly radioactive. The disposal of spent nuclear fuel is a critical concern for all nations utilizing nuclear power. The standard method involves sealing the waste in large, airtight casks and burying them underground. Notable disposal sites include one in New Mexico, USA, and another in the Bartensleben rock salt mine in Morsleben, Germany. There have also been attempts to bury nuclear waste on the seabed.

The nuclear flask train collision test at Old Dalby Station in 1984. Photo credit: Wikimedia Commons

Both spent and active nuclear fuel are transported between power stations and storage or reprocessing facilities in large containers known as nuclear flasks. These flasks must be exceptionally robust to prevent leaks, as any breach could pose a significant environmental hazard and lead to disastrous consequences.

A typical nuclear flask consists of an internal container encased in a steel shell, with walls 15 inches thick, and cooling fins to dissipate the heat generated by the contents within. Spent fuel is still radioactive and produce significant amount of heat by radioactive decay. Usually, spent fuel that has been removed from a reactor is stored in water-filled pool for a year or more in order to cool them. Once they have cooled sufficiently, they are shipped off to processing plants in nuclear flasks. Each flask weighs more than 50 tons, but the actual weight of the spent nuclear fuel it carries is usually just a fraction of its gross weight—just 2.5 tons.

In the United Kingdom, nuclear flasks are primarily transported by rail. For over forty years, British Nuclear Fuels Ltd. has safely transported these flasks across the country without any significant incidents. However, persistent concern from anti-nuclear groups led the British government to conduct a series of public demonstrations to reassure the public of the flasks' safety. These demonstrations were intended to demonstrate that the flasks are designed to withstand extreme conditions and to reinforce public confidence in the safety measures surrounding the transport of nuclear materials.

Nuclear flasks (white colored) sits on specially built wagons ready to ship. Photo credit: TrainBoard

On July 17, 1984, a dramatic safety demonstration was conducted in which a 140-ton Class 46 locomotive was deliberately crashed at 100 mph into a derailed wagon loaded with a nuclear flask. For the test, the flask was loaded with three tons of steel bars to simulate nuclear fuel rods and filled with water pressurized to 100 pounds per square inch. Despite the tremendous force of the impact, the flask sustained only minor cosmetic damage and lost a mere 0.2 pounds per square inch of pressure, effectively demonstrating its resilience.

The crash took place on the Edwalton to Melton Mowbray test track used experimentally by British Railways Research Department, near the site of Old Dalby Station. The event was attended by representatives from British Railways, the Central Electricity Generating Board, members of the press, and other invited guests. Two viewing stands with tiered seating were set up on either side of the track, and a live commentary was provided over loudspeakers. The atmosphere was almost festive, with music playing over the public address system and marquees set up for exhibitions and refreshments. The last time such a pomp and show was made over a deliberate train crash was in 1896 at the Great Texas Train Crash.

The “Flatrol” wagon carrying the flask was laid on its side diagonally across the tracks, with its bogies separated from it, as if they had come off in its “derailment”. The nuclear fuel flask was thus on its side, still in the well of the wagon, with its lid facing towards the oncoming train, and angled so that it would be struck by the locomotive at its weakest point, the joint between the lid and the body of the flask.

The class “46” locomotive used in the collision had entered into service in 1961 and was retired just the previous year. In the two decades it had accumulated more than a million miles on its odometer. For the test, it was pulling three carriages behind.

The test train started from Edwalton, approximately eight miles from the crash site, gradually building up to the required speed. Originally, the locomotive’s maximum speed was capped at 90 mph, but for the test it was specially tuned to achieve 100 mph. The locomotive was started remotely using a switch. Additionally, magnets were placed in the track which could be energized if needed, to apply the train brakes, if the test needed to be aborted.

On impact, the train derailed while the nuclear fuel flask was dragged for some distance along the tracks before it rolled away from the wreckage. The “Flatrol” wagon body flew into the air and came down across the roof of the leading coach.

The Central Electricity Generating Board declared the test a success, expressing confidence that these results would help alleviate public concerns about the safety of transporting irradiated nuclear fuel. The flask used in the test is now on display at the training center at Heysham 1 Power Station.