 The road to reactor design development has led to many dead ends or defunct designs, and one such installation would leave a cave contaminated and a country's nuclear ambitions almost in tatters. If you like what we do here at Plain Difficult, consider helping the channel grow by liking, commenting and subscribing. Let's get started. After a few industrial accidents we are back to looking at a nuclear industry disaster, and this one has been on my to-do list for quite some time. This is mainly due to it being a nuclear reactor inside an underground cavern, James Bond Villain style. Today we're looking at the ill-fated and short-lived Lucien Reactor in Switzerland. I'm going to rate it here on my disaster scale. Lucien sits in the west of Switzerland and is a small town with a population today of around 4,000. However, we will be going back to 1968, when the town was the home to a new experimental reactor. In the late 60s, Lucien had a population of roughly 2,000. Switzerland's power supplies in the late 1950s and early 1960s used hydroelectric, imported coal and oil. As the atomic age became a thing of not just the early nuclear innovators, Switzerland took interest in this new potential of power. In 1955, a private company, Reactor AG, was set up with shares owned by Swiss industry and the federal government. In 1958, a federal atomic energy commission was set up with an advisory panel for the country's atomic aspirations. Reactor AG was eventually wholly owned by the government. Part of this new burgeoning nuclear industry was the desire to have a completely designed, constructed and owned nuclear reactor. By designing and building its own reactors, the Swiss government hoped to monopolise on the country's atomic industry. For this to happen, a reactor needed to be built, and this leads us back to that little town in West Switzerland. In July 1962, construction began with the reactor built into a hillside on the southern outskirts of the town. The reactor complex was housed inside three rock caverns, with a horizontal connecting tunnel. The control room was above ground at the end of this passageway. In theory, building a reactor underground makes sense as you already have a natural containment structure. However, this would cause problems in an accident, as limited space meant any remediation works would cost a lot, but we will have a look into that a bit later on. The designer reactor made use of low enrichment uranium. This was picked due to the small size of the reactor and was cheaper and easier to source compared to fuel of high enrichment. Because of the low enrichment fuel, heavy water was used as the reactor's moderator, and this slowed down neutrons to ensure a more even chain reaction. This lab moderator was one of the two that could be used for low enrichment uranium, the other being graphite. The reactor used a different form of coolant than its moderator, and this was pressurized CO2. The reactor had 73 fuel elements consisting of slightly enriched metallic uranium rods clad with magnesium zircoi alloy and was situated in seven vertical channels bored into a graphite block that was centered in a zircoi pressure tube with pressurized CO2 for cooling the fuel rods. These fuel cans had fins around the outside to help with cooling, similar to what you find on an air-cooled engine or the ill-fated wind scale. The core was split into two halves, each with a CO2 blower and a steam generator. The coolant gas was pumped into the top channels at 6.28 MPa and 223 degrees Celsius. And exited the channels at a pressure of 5.79 MPa and at a temperature of 378 centigrade. The vertical pressurized tubes were located in an aluminium calanderer that contained the reactor's moderator. The heat in the primary cooling loop used a steam generator interacting with a secondary loop containing water, which after the steam was created was used to turn a turbine in turn generating electricity. Surrounding the core was a steel and concrete structure used as shielding. The unit had six safety rods and four control rods, used for complete shutdown and output power management respectively. As always with the reactor, the unit had a scram facility to shut it down in the case of an emergency. The reactor produced 30 MW of heat, which was used to create 6 MW of electrical energy and it first went critical in 1966. Two years later, throughout 1968, the reactor had run for around 70 days at varying power levels all the way up to 100%. However, between October 68 and January 69, the reactor was shut down to investigate a number of odd occurrences, most notably moisture in the CO2 coolant loop. Tests using two different blowers showed some serious water ingress. In December 1968, during a blower test run, water was swept into reactor core, although the moisture only reached the outer fuel elements. In total, an estimated 50 litres of water was thought to have entered the primary loop. Water settled inside the pressure tubes of the coolant within the core and began to corrode the magnesium alloy components. Eventually this weakened the vital coolant channels. In January 1969, in preparation for restarting the reactor, both blowers were powered up and around 15 litres of water was dislodged. However, not just the water was moved, corrosion products produced over four weeks of the moisture ingress also were spread around. These products settled and blocked some of the coolant channels. On January 21st 1969, the reactor was made critical, shortly after four o'clock in the morning. And in the course of the day, the power was increased in steps, with checks and corrective work being performed during the intervals. As the reactor was started up, it reached a 9 megawatt power level. Temperature sensors were installed throughout the core, however, not every fuel channel had the ability to check how hot it was getting. What the operators didn't know was that the channels where the corrosion products had settled in started to see a rise in fuel temperature. At around 5.15pm, the power was increased to 12 megawatts. At this time core position 59 was at a temperature of around 640 degrees centigrade. 30 seconds later, the fuel element in position 59 began to melt, starting with the fins of the fuel can. Shortly after the can temperature reached over 1100 degrees centigrade, some of the fuel rod's graphite column blew apart, further rupturing the pressure tubes. The melting and rupturing of the fuel elements led to a release of fission products into the coolant, initiating a reactor scram. This was the first point that the operators had realised that something was going wrong. The heavy water entered the ruptured fuel elements and began to heat up. Fission products made their way into the Kalandra, increasing its pressure. The Kalandra was equipped with several rupture discs for the event of an over-pressurisation. One of these gave way, leading to the moderator now contaminated being released into the reactor structure. A bubble of CO2 then forced a total around 1100 kilograms of moderator into the spaces between the various radiation shields around the core. The pressure in the tank was temporarily reduced. The fuel element continued to burn, increasing the core temperature to near 1800 degrees centigrade. The heat caused more of the fuel elements to buckle and the pressure increased burst the final Kalandra rupture discs. The scram initiated the isolation of the reactor cavern by automatic closure of ventilation ducts. In total around 7400 kilograms of moderator was expelled from the Kalandra and eventually the spillage made its way into the cavern. Initially, a gamma dose rate of around 120 rads an hour was measured in the upper chamber of the reactor cavern. However, this quickly reduced in the following hours. The reactor destroyed one fuel element and seriously damaged the moderator tank of the reactor, meaning serious amounts of contamination had escaped. Some had escaped the apparently isolated main cavern into the other two parts of the complex and eventually made its way to the control room 40 minutes after the initial fuel damage. The control room experienced 10 times the maximum admissible concentration for occupation exposure. The operators donned gas masks to continue managing the disaster. After analysis of the gaseous contamination in the control room, it consisted of rubidium 88, which has a short half-life of around 18 minutes. The contaminated air had made its way out of the main containment via holes cut into the cavern for cables. It was thought that during the active phase of the event, doses in all cases were less than 150 millirems. Now the damage to the fuel and Kalandra, the Swiss operators deemed the reactor to be a write-off and thus went with it the dreams of a wholly indigenous nuclear program. On top of that, the country had a massive radioactive hole in the ground. Initially, an analysis was taken of the gasses inside the main reactor cavern. It was decided that it could be vented to atmosphere via the plant's iodine-filtered vent stack. Between January 1969 and March 1970, the initial phase of decontamination was undertaken and consisted of recovery of as much heavy water as possible, drying the cavern atmosphere and removing tritium vapours. Next came the dismantling of the unit, starting with defuelling, except for the damaged fuel element. Then the pressure and Kalandra tubes were cut and removed. The Kalandra had to be sectioned for packing for disposal. After the upper portion of the Kalandra's vessel had been removed, the damaged fuel element and its pressure tube were finally recovered. The final steps included disassembly of the highly contaminated systems and the decontamination of the station for treatment of radioactive material. Dismantling and decontamination was completed by 1973. The inside of the caverns were painted to keep in the contamination of an estimated 40 gigabit quills. All the works ended up being far more difficult than the usual decommissioning of a reactor. This was because of the inferior idle location for an NPP being underground. In 1988 the decision for two of the caverns to be filled with concrete, entombing the dangerous remains, was made by the Swiss owners of the site. After final completion of the decontamination in the mid 1990s, regular monitoring has taken place on the former site. Nuclear power did not end however in Switzerland, as up to around 40% of the country's energy is provided by nuclear power. However, the plants' reactor designs were supplied by foreign nations. The Swiss government has said that it will not build any new plants and will not replace any of their current operations once they have reached operational life expectancy. And hydroelectricity is safer, unless you're at Sejano Szczyszenska. I hope you enjoyed the video. If you'd like to support the channel financially, you can on Patreon from $1 per creation. And that gets you access to votes and early access to future videos. I have YouTube membership as well from 99 pence per month, and that gets you early access to videos. Check me out on Twitter and also if you want to wear my merch you can purchase it at my Teespring store. And all that's left to say is thank you for watching.