HP019: Nuclear Disasters

HP019: Nuclear Disasters

Nuclear Disasters. Thanks for all your feedback on the show thus far please keep it coming. Some great information in the links below.


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On Saturday April 26, 1986 one of the worst nuclear disasters in history occurred in the old Soviet Union at Chernobyl. The official death toll was 31. Scientists would later estimate that thousands more would die in the next 10 to 20 years. At it’s height the Chernobyl nuclear power plant generated 4,000 watts of electricity. It’s 4 RBMK 1,000 reactors were built on either side of a giant smokestack, which released gas and steam into the atmosphere.

A 12-foot thick concrete disc, the upper biological shield, separated the core of the reactor from the refueling machine above. The main part of the core is a large graphite block this so called moderator controls the nuclear reaction.

The nuclear reaction is caused by the uranium fuel rods lowered into the graphite. The reaction heats them up and they heat water in pipes along the side of the reactor. This water turns to steam, which turns turbines, and the turbines create electricity.

The Chernobyl disaster was devastating but it wasn’t with out warning. Twice before the world had been on the brink. The first of these incidents had occurred in a far more sinister context than Chernobyl. The windscale plant in Cubmbrea provided the fuel for Britain’s nuclear bomb. On October 10, 1957, it fueled near disaster. It was built to manufacture nuclear weapons. The reactor design was primitive. At the end of World War 2 American’s denied Britain access to their most sophisticated nuclear techniques. Windscale did have a graphite moderator, but the design did not take into account the dangerous build up of latent energy in the graphite. They also had not allowed for the fallibility of human operators. The core overheated, the fuel caught fire, and the instrumentation that would have showed something wrong jammed.

The core eventually caught fire. Everything was then on fire. The operator in charge on the morning of the accident did not have an operating manual. So he had no way to cross check his work to make sure everything he was doing was correct. He was also assuming that the instrumentation he was looking at was correct. In fact there was no instrumentation sensors in the area where things started to go wrong that morning. There were two more problems for the managers of the Windscale plant. They didn’t reveal how bad the fire was and it was an air-cooled reactor, but pumping air into the reactor only fed the fire. Eventually, they figured out that the only way to put out the fire was with water. They sent the entire staff home and on Friday morning, the 11th of October at 8am they turned on the hoses and held their breath, in case the reactor blew up, but it didn’t and the fire gradually began to subside and eventually went out. Fortunately, the release of radioactivity took place from a 394 foot tall chimney.

This did not reduce the concentrations that people would breathe on the ground. The whole cloud from the windscale accident was blowing down over Britain from the North to the South. Low-level radiation fell over the majority of the British population. The people feared that radiation would get into their food chain. There was a milk ban over 200 sq. miles. What the authorities didn’t dump, housewives did. Milk was identified as the main radiation hazard. A 3-month restriction on milk was enough to allow the risk to die away. At Windscale, the main damage was to milk farmer businesses.

21 years later at 3 mile island in Pennsylvania. The clean up bill topped a billion dollars. Initially presented as a minor mishap it was the worst nuclear accident in American history.

3 mile island was a US built pressurized water reactor operated by the Metropolitan Edison Company. The plant was evacuated when a pump driving water around the system failed during maintenance. An emergency pump then also failed. The ensuing chaos was compounded when a valve got stuck open. This meant that much of the emergency cooling water being pumped in burst out again. Which no water entering the reactor there was nothing to maintain the temperature and the water that was inside began to steam off. The fuel became uncovered and got very hot and melted down. Fear of the consequences was again matched with a fear of revealing the truth. Chaos bread more chaos. The red light notifying the managers of the pumps malfunction was hidden behind a cardboard tag on the control panel. The authorities with no information tried to assure a frightened population and at the same time tried to make evacuation plans for more than 6,000 people.

What worried the managers and staff at the plant was the possibility of a massive build up of a gas bubble that could blow up and blast the top of the reactor off, releasing a huge amount of radioactive material. What worried plant owners was being responsible for the evacuation of all Pennsylvania. A 5-mile evacuation was suggested for pregnant women and small children. Schools in the area also closed. The estimate of the plant was that 12,000 people would need to evacuate. In actuallity, over 400,000 people decided to evacuate. After 3 mile the public did not trust nuclear power. The general idea that you get from reading the reports of the incident was that of complete chaos. The staff was either contradicting each other or did not know what to do. After the accident American scientist were much more open. More wide spread knowledge meant more safety.

Windscale had about 2-3 days before it was too late. 3 Mile Island had 120 seconds. And on April 26, 1986 there was another accident at a soviet power plant 80 miles from Kiev in the Ukraine. Chernobyl had less than 40 seconds before there was no going back. 8 seconds after that the entire nuclear system was destroyed. It happened in the Unit 4 reactor. It was the result of an experiment that went very wrong. It was planned for a Friday afternoon, but postponed at the orders of the electricity boards controller. They were trying to find a way to get a little bit more electricity out of the turbine generator after the reactor had shut down before the emergency diesels came on. Because diesel engines in the old Soviet Union tended to be both unreliable and sluggish they might not start up fast enough when the reactor stopped. They thought that they would be able to take advantage of the fact that these big turbines were still spinning turning the generator even after the steam supply into the turbine had been cut off. They wanted to use those last moments of turbine spinning to get any extra electricity out of that they could.

Safety standards in the old Soviet Union were appalling. There just wasn’t a safety culture at all. Six different safely mechanisms were closed down. They did an extraordinary number of dangerous things. They shut off the emergency cooling system, they closed the valves so the water could not get into the reactor through the emergency system. They effectively shut off the system that would have normally shut down the reactor safely. By the time of the test 1 am on Saturday the control room shifts had changed no one knew who had shut what off. The reactor design didn’t help. RBMK reactors could develop a “positive voyca effect.” Which is a when the water in the tubes surrounding the reactor begin to boil. This can make the reactor generate more power, which in turn generates more steam, which equals more electricity.

They may not have been a safety culture, but there was certainly a secrecy culture. Despite wide spread reports from the west, especially Sweden, of sharply increased radiation levels. The first pictures of Chernobyl only appeared on television on May 4th. For the experiment, operators reduced the power, but below a certain power level the reactor gets unstable, so they tried to compensate by increasing the steam pressure. Steam and heat both increased. There are control rods, which deal with this, but the operators couldn’t get them in quick enough. So at 1:23 in the morning Chernobyl exploded like a pressure cooker. The radiation spread varied with wind direction and force. On the day of the explosion the radiation was obviously localized. By the 28th (day 3) it had blown over large parts of the northern Soviet Union and was spreading into Scandinavia. By the following day more of Scandinavia plus much of Eastern Europe and Germany were affected.

By May 5th, 10 days after the accident, the radiation cloud had affected much of Europe. The evacuation of Parpete the nearest town was agreed at 9 in the evening on Saturday. Buses were commandeered from all over the Ukraine and the population was moved out on Sunday afternoon and evening. Prapete, home for 45,000 people became a ghost town. Now the empty town was cut off by roadblocks and even those trucks allowed in on official business were forbidden form being used anywhere else in the Soviet Union. Amid all the despair the story of Chernobyl is also one of tremendous courage by the fireman and troops brought in to control the deadly blaze. The emergency measures they took were heroic by any standards and involved personal bravery of quite an incredible degree on the part of the thousands of people, firefighters, plant personnel, and helicopter pilots.

The top of the reactor was a gaping hole which in subsequent television images allowed you to see the glowing graphite fire inside the center of the reactor. They had to try to stop the radioactivity being spread into the air from the chimney. So they decided to start dumping materials into the top of the reactor, first to put out the fire, then to stop the escape of radioactivity. They brought in a lot of military helicopters with volunteer pilots and tied slings carrying sand and lead to the bottom of the helicopters. They hovered over the reactor and dropped their loads for about 10 days. The pilots received high amounts of gamma radiation and contamination from the radionuclides they were flying through. Miners from the Ukraine region of Dondas teamed up with under ground or metro train builders from Kiev. Their task was to put a 900 ft. sq. base under the reactor in case the molten core burned right through the bottom. Firemen and workers from other power stations were drafted to try to clear what was left of Unit 4 as well as the adjoining Unit 3 reactors. Soviet television showed pictures of them with a clock timing them; they had just one minute and ten seconds to work before they would become overwhelmed with radiation. All this was bravery of the highest order but from what we now know it was almost certainly a tragic and unnecessary waste of life. In particular the attempts to stop or cover up the molten core were useless. The tunneling was also appears to be useless given latest American research which paints an entirely different picture of what happened. When Chernobyl exploded the roof was blown right out. The huge circular concrete lid of the upper biological shield was blown up and pivoted and came crashing down in the reactor core where it was wedged. By now the reactor core was just a molten mash of deeply dangerous radioactive debris.

This burned through the concrete of the lower biological shield before settling on the concrete below. Here, it stabilized itself and nature itself averted the ultimate nightmare of the China syndrome. Towards the 7th, 8th, and 9th day of the disaster the fuel fused and burned its way through the concrete rooms under the reactor like lava. It finally, dissipated its heating power, came to rest and solidified and that was the end of the accident. But it wasn’t the end for those brave power station workers and firemen. Official figures say that only six firemen died but it is difficult to believe there weren’t many more as radiation related illness took their toll. The trial of those declared responsible appeared the following year. The defendant included the former station director who was sentenced to 10 years. What is left behind is almost a desert. They are monitoring and still there is a safety zone, which is about 19 miles around the plant and still a lot of contamination on the lands around the nuclear power plant.

These areas which are the size of about 100,000 sq. miles. It is empty and you can’t do any agriculture what so ever. A museum at Chernobyl tells the story for generations to come. Where the heroism of those who helped is remembered. The doomed Unit 4 reactor is buried inside a giant concrete tomb which has to be renewed every 40 years. Chernobyl will be unsafe for hundreds of years. The most radioactive elements such as Season 137 have half-life of 30 years. After several hundred years then one might be able to send in machines to encapsulate the debris and make it safe but it will be a very long-term project.