Fukushima: What Really Happened

What broke Fukushima Daiichi?

Let’s start off by saying that what happened was bad, I’m not going to say that it wasn’t. We all know better and we aren’t in the business of lying to people. However, I am going to put some things in perspective for you.

Fukushima Daiichi nuclear disaster began when a record tsunami made landfall, caused by a cat 9 earthquake, which was the strongest to ever hit Japan and 4th strongest in recorded history. It caused waves over 130ft (40.5m) to travel 6 miles (10km) inland and destroyed over 1 million structures. That’s quite a punch. The nuclear facilities took no serious damage from the quake or Tsunami outright. This is thanks to the industry safety factors, which create a large buffer of security. It’s why buildings are able to resist storms without taking damage.

The Fukushima Daiichi Nuclear disaster  was the contained meltdown of 3 reactor cores-often called units-located at the city of Fukushima, Japan. So lets jump in and understand what really happened. What happened is that the diesel backup generators (1st backup) used to pump coolant water through the reactors were knocked out from the earthquake, 6 of the 7 to be exact. I’d like to mention that these are only used when the plant is shut-down in emergencies. So, the alternate backup generators (2nd backup) kicked in and managed things until the tsunami hit and also knocked out the battery backups (3rd backup). That was 3 different backup sources taken down, that’s like getting a flat tire, using a patch kit, trying to merge but getting another flat, putting on the spare, that goes flat, patching it, and it going flat again as you’re out of patches.

So the units (1, 2 & 3) couldn’t cool properly and things started to get dicey. Due to the surrounding area being blocked off by the tsunami damage, it took a while to assess what was going wrong at the plant and address it. The water used to cool the unit core’s turned to steam. Some safety measures vented this steam into a different chamber to prevent a Chernobyl style explosion (we learned from that and all applicable reactors were modified to prevent a repeat). But with less water to cool, the cores got hotter and hotter. Eventually core 1 melted into the bottom of the containment structure, and then cooled and solidified. It melted into the cement, that’s a lot of heat, but again the safety factor was there to plan for it, so it could only get through less than a quarter of the cement.

But before unit 1 melted, some chemical reactions took place and caused a hydrogen buildup, and subsequent explosion. (read: Not the same as a bomb) This was because some of the safety venting needed power and caused it to flow backwards through the piping and eventually met air, which caused the explosion. For unit 3, the core damage from the melting core caused some hydrogen to leak into the main containment structure and cause another explosion. Then a final explosion was due to shared venting between unit 3 & 4, and the pressure forcing the hydrogen to flow to unit 4 and then explode.

During the build up to these explosions, water was being directly pumped into the units to prevent overheating and pressure buildup. They had no eyes on instrumentation, due to no power, and had to do their best with reacting to what they believed was going on. Two weeks after the tsunami, power was established alongside consistent cooling. This allowed them to verify no further issues and begin containment of radiation.

The radiation was from a rupture in unit 2 and the hydrogen gas explosions from units 1 & 3. While this is definitely not desired, it is not the threat that it has been made out to be. Overall leakage is about 15% of what Chernobyl was for perspective. The on-site radiation was handled with suits and monitors, all within allowable levels that are strenuously followed. If you’d like an outline of how much radiation was released, the effect it had in the surrounding areas, and the world please go to this article.

But what about around the plants? The contamination to the surrounding area was blown out of proportion. It was still below all safety thresholds (one spot was an exception to this, Iitate). Please check out the article on allowable dosage for more information. But due to misinformation, people are still not allowed in certain areas.

What we learned from this event was that the backup (2nd) generators need to be housed above basement level, even though there are benefits to them being there. Additionally, the ability to have cooling that requires no energy source is a must for new reactor designs. This has been implemented, and in many cases, there are multiple levels of backup that don’t need an energy source.

What I’d like to re-iterate is that what happened at Fukushima was a disaster. Everything humans build have a tolerance rating, which is evaluated at a maximum reasonable level, and the Japan reactor is no different, all forseable and even unlikely disasters were planned for and designed around, but what hit them exceeded even the excess safety factors that were projected. The global industry learned and adapted right away to keep everyone safe. But due to misinformation and media drive for stories, there was misguided fear and apprehension as to the nature of the disaster. Many initiatives and policy changes were the direct result of this disaster, which can be found here at 5MN (Here)

Here are the previously mentioned articles: safety factor, Fukushima radiation. Additionally, the source has a much more in depth analysis of what happened along with the with official reports. We at 5MN would be happy to answer questions that you may have to the best of our ability, just leave a question below.

Remember, check sources and ask questions. 

Source:

http://www.world-nuclear.org/information-library/safety-and-security/safety-of-plants/fukushima-accident.aspx

Leave a Reply