Chernobyl Trip Part Two - Chernobyl Nuclear Power Station
It was about 2pm when we left the nursery, and the temperature was beginning to hit the mid twenties. As we climbed back into the car, even at just under 5 Km away, we could see the Chernobyl Nuclear Power Plant (CNPP) through gaps in the forest to our side. What is left of the Chimney for reactor 4 was reaching high into the sky, matched only by the new New Safe Confinement Shelter (The massive arch that will slide over the current aging sarcophagus). Photograph locations around the CNPP were quite restricted, so we stopped around 2 Km away, next to the cooling channel to take some photos.
Nuclear Reactors 5 and 6
At the time of the accident, reactors 5 and 6 were still under construction and nearing completion. In fact, a total of 14 reactors were planned and reactors 1, 2 and 3 were still in operation after the event, even up until 2000. Reactors 5 and 6 were just over the cooling channel from where we stopped. The forest was quite dense between us and the buildings, but we could clearly see the construction site; The cranes frozen in time since 1986. The exterior was rusting badly, with visible signs of deterioration - be it from the natural elements, radiation or looting, which was widespread throughout the 90s and 00s.
The two reactors were also going to be much more powerful than 1-4. So much so that all the turbine halls and cooling channels would not have been enough to cool either reactor. The solution was to build two cooling towers - one of which was almost complete, the second of which was in early construction. Unfortunately we couldn't see the second tower as it was below the tree line, but the first stood way above, ringed with construction scaffolding at the top.
The radiation levels were around 1.00 microsieverts/hour here, even at 2 Km away. You would be about 4 times over the annual "safe" limit if you were to live here all year. We were warned not to go near the verge leading to the cooling channel, as radiation levels there were much, much higher.
Reactors 1,2,3 and 4
Getting back in the car again, we continued around the cooling channel towards the entrance gates. As we went through, we were told not to take photos while traveling around the plant. We drove around the eastern edge, around the back of the station. We weren't really sure why we were not allowed to take photos, as there really wasn't much to see; a high wall and administration buildings separated us and the reactors.
Eventually, we turned a corner on the north-west side - and there it was. The CNPP Reactor 4 - the site of the worlds worst nuclear disaster.
At 01:23 on the 26th April 1986, Reactor 4 suffered a catastrophic power surge resulting in a steam explosion in the core during the testing of an emergency cooling feature. The test was planned to bridge a 45 second gap of power to the cooling system in the event of a power grid failure during a reactor shutdown. Diesel generators had been used before, but took 45 seconds to reach full power. It was thought that the power from the steam turbine slowing down could generate enough power to provide energy to the cooling system for 40 of the 45 seconds, which would be enough time to make it safe. The test was originally planned to be run on the 25th April, but due to another power station going offline, they had to delay it. When they were ready to proceed, the day-shift and evening-shift works had left and night-shift were only just starting.
Briefly, a series of errors left the reactor in a unstable state. The minimum power required for the test was 200 MW, where 700 MW was needed. Most of the control rods were manually removed and safety systems disabled to keep the core at a stable power output. When the test began, however, the power started to rise. Thirty-six seconds into the test, a manual emergency shutdown was triggered, causing the control rods to be inserted. Due to a design floor of the reactor, graphite in the rods temporarily displaced cooling agent, causing a significant temperature and power rise. Normally it would have been replaced with boron once the tip of the rods were in, but the sudden rise in temperature fractured the rods, causing them to become stuck. The power output then shot up to 33,000 MW (ten times the normal power output) causing a rapid steam build up, which triggered the first explosion. The explosion was powerful enough to send the 2000-ton upper plate through the roof of the reactor housing.
Seconds after the first explosion, a more powerful second explosion happened, dispersing the damaged core and the graphite moderator throughout the area. The graphite then caught fire from the oxygen in the air, believing to have considerably increased the radiation levels. Radiation levels in the core were around 300 Sieverts (that's 300,000,000 microsieverts, or 750,000 times the lethal dose - enough to last you about 0.0048 seconds). The dispersed fuel and graphite was around 150 Sieverts.
After the event, it took until December for the debris to be cleared and the sarcophagus to be constructed. 500,000 workers called "Liquidators" or "Bio-robots" were used, the majority of which reached their lifetime limits of radiation in their 40 second working time slots. A few days ago I watched a documentary on the cleanup which I would highly recommend seeing. It contains a lot of footage and shows you the sheer scale and challenge of the task.
Fast-forward to today, and the reading is between 2 and 3 microsieverts/hour out in the open where we were standing - about the same as you would get flying. Looking like a structure from the future, the "New Safe Confinement Shelter" is due to be finished by the end of 2014 and will slide over the existing reactor house. There, it will be sealed for up to 100 years, and one of the reasons that I wanted to make the trip this year.
We spent about twenty minutes at the reactor, and it was uncomfortably hot. In order to reduce radiation on the ground, the entire area's top soil up to 2 meters down was removed. Concrete slabs were then placed and new, fresh, top soil was brought in from outside the zone and placed on top. As such, there were no trees for relief from the sun.
Finally, we got back into the car and headed for Pripyat...