Fukushima: The Accident Waiting To Happen

This week, TEPCO released its final report of its internal investigation into the Fukushima nuclear disaster, and admits it failed to adequately prepare for the disaster, but cast blame on the government for adding “unnecessary confusion” to the accident.

The report is based on 600 interviews, inspections, and other data, and concludes that the tsunami was much larger than TEPCO had expected.

The company denied that it was taking too long to disclose data, “We did not mean to hide information, but there was a lack of enough explanation.”

The report notes that after the Unit 1 explosion, conditions on the site prevented workers from continuing to conduct emergency operations at Units 2 and 3, leading to the subsequent meltdowns at all three reactors.  Prior to the Fukushima Daiichi nuclear disaster, the risk of a severe accident at one unit affecting emergency operations at another unit had not been considered.

Largely the report from the utility appeared content to attempt to justify its actions, still clinging to the defense that the utility “could not predict an occurrence of the event which was far beyond our expectation,” despite the fact that the utility and regulators knew the tsunami threat was serious, yet purposefully delayed any meaningful investigation or action.

TEPCO says there is still a need for studying what actions should be taken in the event that a nuclear reactor has lost all of its functions, and I would agree, it is not uncommon to find ourselves in situations where we not adequately prepared for the unexpected.

European regulators group Ensreg also says that operators must plan for the possibility that their chosen design may be flawed.

“The important lesson from Fukushima is that you might be wrong on your design basis,” Philippe Jamet, chairman of the peer review board for the EU’s nuclear safety stress tests said in a Platts article.  “So you need an extra layer [of safety precautions] for when you are wrong on how your design basis copes with unpredictable external events,” he said.

The Fukushima disaster was not ‘unexpected’ as much as it was ignored, tsunamis of that magnitude had occurred in the past, TEPCO knew that a tsunami of only 10 meters would cause a potential loss of power, and they should have reasonably foreseen it to happen again.

The location of the plant was on a bluff which was originally 35-meters above sea level. During construction, however, TEPCO lowered the height of the bluff by 25-meters. The lowered height would keep the running costs of the seawater pumps low.

TEPCO’s analysis of the tsunami risk when planning the site’s construction determined that the lower elevation was safe because the sea wall would provide adequate protection for the maximum tsunami assumed by the design basis. However, the lower site elevation did increase the vulnerability for a tsunami larger than anticipated in design.

“Why are the pumps at water level?” one might ask.  Because it is much easier and cheaper to push water from the base of the building then to suck it up from the top, thus pumps at water level.

An in-house study in 2008 pointed out that there was an immediate need to improve the protection of the power station from flooding, as a 10.2 meter wave could inflict damage to the generators. Officials of the department at the company’s headquarters insisted that such a risk was unrealistic and did not take the prediction seriously.

Three years later the report was sent to NISA, where it arrived on the 7 March 2011, just 4 days before the plant was hit by the tsunami.

I don’t know if I personally would be able to claim that I was unprepared if I knowingly designed a plant to withstand a magnitude 7 earthquake in a part of the world known for generating up to a magnitude 9, or if I had then continued to operate with a 6 meter tsunami protection wall, despite knowing that a 10 meter tsunami could cause a loss of power event, and also knowing there had been three 10 meter tsunamis in the last 100 years.

The requirements for shutting down a nuclear reactor after a earthquake or tsunami are well-known, the fact that equipment was not in place, provisions for alternate back up power, and pumping equipment in case of emergencies was not in place is attributable to politics and profit-based decisions.

Still, it never ceases to amaze me how inadequate the backup systems are for nuclear power plants. Look at the hydrogen explosions as an example, they demonstrate either fundamental lack of understanding for the capabilities for the generation of hydrogen, or a severe lack of hydrogen control, the devil is in the details.

In general, the scientific community is fairly knowledgeable when it comes to hydrogen and its potential for combustion.  There has been a lot of research done not only within the nuclear industry, but within the scientific community as a whole, so it is hard to believe that it was due to a lack of understanding that if hydrogen levels accumulated there would be a potential for an explosion.

An inherent potential problem of the BWR is the fact that if the cooling system fails for whatever reason, the water in the fuel rod tank starts to over-heat, it gets even worse when the zirc-reaction moves from creating steam to reaching a critical state of separation of hydrogen and oxygen gases from the super-heated water once the temperature reaches 2000 degrees Celsius or 3632 degrees Fahrenheit.

This then creates an extremely hazardous condition when the hydrogen gas accumulates at the top, and the oxygen gathers at the bottom of the reactor. This can easily lead to gases being forced from inside the reactor, one scenario involves the reactor head lifting due to a release from the upper drywell head, others only require migration through any of the penetrations or equipment hatches.

Unless the hydrogen can be released into the atmosphere immediately there will be an explosion; ie Fukushima. The Three Mile Island workers were extremely lucky in that they were able to release the radioactive hydrogen gas into the atmosphere before it ignited thus avoiding the unthinkable.

So we have a good understanding of when the hydrogen is generated, where it may proliferate to (everywhere), how much is generated, and what happens next.

 

Reactor 1 Explosion

 

Reactor 3 Explosion

 

Around the world, industry workers and officials are haunted by the visuals of the Fukushima reactor buildings exploding like they did, for most, this was the first time that many of them had even considered the possibility.  Prior to Fukushima, regulators and licensees had relied on hardened vents to prevent an explosive mixture from building up in the reactor building.

New data from Fukushima is confirming what some in the industry had already long feared, that venting might not be the best option.  Some experts have long claimed that if workers wait to vent after the containment is full of hydrogen, due to the tendency of hydrogen to leak through various connections in the reactor building itself, and mix with air, it is likely that venting might not be able to eliminate the risk the hydrogen poses.

Hydrogen easily moves through places where we think it won’t, it is almost impossible to create a valid recreation through research alone without experimentation.  With hydrogen you don’t even need an ignition source, even static electricity could set off an explosion.

This is a situation that regulators around the world didn’t really evaluate fully, and at this point, the information from Fukushima is not yielding any easy answers.  There is a lot of information that has been brought up, leaking seals, core-concrete interactions, and yet no one in the regulatory or industry camps has any idea how to completely mitigate the hydrogen problem away.

With the money they make, all nuclear plants around the world should be forced to put in back-up systems for back-up systems in case of complete failure to prevent the release of radioactive materials.

The industry claims to rely on defense-in-depth, but even that falls woefully short if every possibility is not explored, if every ramification not identified.  Ideally, every safety precaution should be taken and enforced to prevent the loss of life.

The Ensreg report likewise, recommended an EU-level assessment of national hazard margins, safety reviews at least every 10 years, containment integrity and “prevention of accidents while limiting all possible consequences.”

But simply put, there is no foolproof way of preventing nuclear disaster, there is no such thing as “leak-tight”.  The industry spin-masters will always find a way to blame such things on “human error,” but the truth is, nuclear power is by its nature an unstable compound that is just waiting for the inevitable sequence of events that will reopen ‘Pandora’s Box’ time and again.

The one thing that we can all agree on is, it is going to be a very long time before we have any real comprehension of the Fukushima disaster, it will be immensely difficult to arrange the collection of critical information and consensus on mitigative actions, yet the industry does not see that in conflict in any way with current expansion projects.

A lot of this will be affected upon which opinions are voiced, which organizations are involved, who is paying who to do what, and ultimately where the interests lie and the incentives are.

Source: NHK

Source: JiJi Press

Source: CNN

Source: Platts

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