Japanese nuclear accident FAQ 7

[trottiey]

Since my other thread is getting a little unwieldy, I thought I would start this one to summarize frequently asked questions:

1) What type of reactors are these?
Fukushima Dai-ichi
Unit 1: BWR-3, 460 MW, activated 1970
Unit 2: BWR-4, 784 MW, activated 1974
Unit 3: BWR-4, 784 MW, activated 1976
BWR = Boiling Water Reactor

2) What happened to the backup power?
The plant survived the earthquake well, and the backup diesel generators came on-line as planned. But an hour later, the tsunami came through and damaged some of the generators. Replacement generators were flown in, but could not be hooked up in time. The cooling pumps need megawatts of power, and hooking up this amount of power is not trivial.

3) Why not use the battery power?
The pumps are too big and battery power would have been insufficient. Battery back-ups are only used to run the valves, lights, computers, etc.

4) Where did the hydrogen for that explosion come from?
Hydrogen is normally produced in a nuclear reactor by radiolysis of the cooling water. Reactors have recombiners, igniters, and other means to dispose of this hydrogen before it becomes an explosion hazard. But when the core gets too hot, the zirconium cladding around the fuel will react with the water to produce much more hydrogen. (This reaction is rapid and exothermic, so in laymen's terms this is sometimes described as "burning" the core.) The amount of hydrogen overwhelmed the capacity of the recombiners, accumulated in secondary containment, and exploded.

5) So what is the latest status?
Something will have changed by the time I finish writing this FAQ. I've generally found the most accurate information from World Nuclear News, and they're also quite fast in posting updates:

http://www.world-nuclear-news.org/

6) Am I at risk?
For those who are in the immediate area and subject to evacuation orders, you are at low risk of radioactive contamination. Those who do get contaminated may have a slightly increased lifetime risk of cancer, but the most likely outcome will be that you will never suffer health effects from this for as long as you live. For the rest of you, please trust that nuclear professionals have trained all their lives for this event, and they are managing the situation. Much greater damage is being caused by ongoing fires, flooding, water shortages, etc. If you have a comfortable life, please consider helping out with financial donations to disaster relief organizations.

 

[vpl]

Trottiey

Why not make this into an official FAQ? Then you can update it as needed.

Patricia Lougheed

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[guizmy]

I see something unethical and untransparent in the way this crisis is managed by local and international Nuclear autorities respective to the critical nature of the risk that hold on public safety as far as concerned with Nuclear Accident.

Normally when the loss of coolant has been reported the situation should have been immediately categorized as highly critical and dangers clearly identified despite the fact that some panic can occur on people as side effect. However what we noticed in the media during the last three days is the opposite and the message delivered by different autorities has been always a "conforting message" in distorsion with a situation that was getting worst hours after hours.

There is definitely a lack of transparence and perhaps a "monopole of information". I mean People can be exposed to harmful radiation in Japan but also worldwide and whatever is the amount of radiations it is definitely the right of people to be fully and fairly informed.

The meltdown of the rods was definitely probable after report of loss of coolant but autorities did not rise any critical trigger in the very beginning on media communications.

Can someone inform us about the Regulations actually in place that apply to Local and Nuclear Autorities and ensure public is informed in such a way no information is hidden or dismissed?

I understand "Act of Gods" are not under human control, but Nuclear technology deployment remains a human initiative and with regard to this I beleive any potential dismiss of information to the public is unethical.

Please tell me if I am having some paranoia here or do you also perceive things in similar way in US and worldwide?

 

[trottiey]

There have been a number of communication problems through this event for a number of reasons:
-the high technical complexity of the event
-misinterpretations by non-technical reporters
-language barriers
-failings on the part of the electric utility
But I don't think that the nuclear authorities and companies have intentionally misled the public.

A loss of coolant accident (LOCA) does not necessarily mean the rods will meltdown. For example, LOCA's also occured at Fukushima Daini (seperate from Dai-ichi) and Tokai reactors at the same time, but recovery was successful. Meltdown is now unlikely at those plants.

You should never classify an emergency conservatively, for the same reason you should not pull a fire alarm unless there's a fire. Emergencies need to be classified accurately, and response needs to be proportional to the risks. A disorderly evacuation of tens of thousands of people could wind up killing more people than it saves; at a minimum it diverts resources from an already overburdened emergency response network. With hindsight, the Daini evacuation appears unnecessary, while the Dai-ichi evacuation was timely. So no, they should not jump to the highest state of alarm at the first sign of trouble.

If you want to rate the integrity of nuclear professionals, I think you should include in your evaluation the workers at Fukushima Dai-ichi. They have stayed at their posts through a record-breaking earthquake, a tsunami that submerged plant buildings, and two massive explosions that left one dead, ten injured, and two missing. In all likelihood, they had advance warning of those explosions, but they stood their ground. The radiation levels they are now facing are well beyond occupational limits, and their training would have shown them calculations of how much their life expectancy drops for each hour they remain on site. And still, they report for duty daily, do overtime, and provide terse professional status updates to the outside world.

 

[rmw]

THere is way too little information at this point and what information that there is is unreliable. I will hold any judgements I might make until I have real facts, not ignorant journalists sensationalism or anti-nuclear proponents prognostications.

What I have seen so far makes me want to puke.

All in all, it is not a good day for nuclear.

I regret that.

rmw

 

[trottiey]

Thank you vpl, I was not aware of that feature.

 

[vpl]

Trottiey

Thanks for issuing the FAQs!

Patricia Lougheed

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[Gillespie]

I have a question about the seawater they are using as a coolant.
How is it being brought in?

How does it cool the reactor? Does it just flood the whole reactor?

Does it just turn to steam?

 

[guizmy]

I remember one of my EPC project for Refinery extension located in Europe. Refinery are critical Plants but for sure not to that level of Nuclear one. The Owner of refinery was an US Major. When doing the ENG, I was surprised that one of the Primary focus of the US Client ENG was the scenario of Emergency trip in the event of complete Electric Power Failure in the Plant. During our meetings with this Client, Honestly I thought they were exagerating by insisting so much on that aspect. Shortly, that considerations led to particular design of equipments (e.g Pressurized run down tank for oil). Now I understand better that it was a deep culture of risk.

I simply dont understand how can be possible to not envisage the failure of Diesel Generators when doing kind of Hazops study in such Nuclear Plant.

As already pointed out, UPS cannot feed coolant pumps given the MW power required, so clearly in case of Electric power failure in the Plant the only Back up was the Diesel Generators.

Do you know if in other Nuclear Plant worldwide, there are other back up solutions than D/Gs to drive coolant pumps? Is the coolant system Loop redundant? any reduandant power cables to power grid?

Were the D/Gs redundants in Fukushima? if so were the D/Gs located at different location in the Plant ?

 

[trottiey]

Given the recent news of fire in the unit #4 spent fuel bays and damage to the unit #2 containment, my earlier statement about risk may be obsolete. Not enough information has come out yet to accurately re-assess the risks, but they have probably risen higher in probability and greater in geographic scope than I earlier indicated. I will try to provide better updates in the FAQ section when I have more information myself.

 

[itsmoked]

It's my understanding that the batteries do indeed support the pumps but for only 8hrs.

I'm inclined to believe this as I suspect bigger submarines where running in this realm of 1,000hp and they didn't have the luxury of space a fixed installation would.


Why are they "struggling" to dump water on these things? Filling a below-ground tank with water doesn't strike me as being really hard. Is it the fact that they have to overcome pressure that's inside the vessel?

What kind of pressure exists in these distressed reactors? Are we talking 1000+ PSI?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[trottiey]

It's not a tank, it's a pressure vessel. The operational pressure of the main vessel would be around 1000 psi; the accident pressure somewhat higher. The primary containment pressure would be around 60-120 psi. Injecting water means using higher pressure, keeping it below the design limits of the vessels, and maintaining enough flow to compensate for boiling. In order to do all of the above, the operators must vent excess steam to make room for new water. But you want to avoid venting because that causes hydrogen explosions and environmental releases. It's a balancing act that's made harder by damaged generators, broken power lines, drained batteries, and diesel shortages.

 

[owg]

I can't help wondering if it might have been better to keep the plants "running" or restart them after the big shake, but turned right down. The idea is to not have to call upon the diesel generators. The operators must have known that water can follow a quake and that the diesels are vulnerable. Can they make enough power to run the regular cooling/generation circuit with the control rods fully or partially inserted? This is not a serious suggestion, just a thought.

HAZOP at

http://www.curryhydrocarbons.ca

 

[vpl]

It's kind of hard to keep the plants running with no electricity.

Patricia Lougheed

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[printing724]

I was an operator in the US Navy. Left the nuclear field at discharge many years ago, but have learned some things about civilian reactor design in the past few days that I don't understand.

In an S5W submarine plant, operation of the main system isolation valves, initiation of decay heat removal, and injection of makeup water can be accomplished without any electricity being available. The decay heat removal system was driven by a thermal siphon, and valve movement and makeup water injection were accomplished by the potential energy stored in a high pressure water and air system.

In an installation like Fukushima, it seems that the emergency systems all rely on having a supply of electricity available to move water around. In this case, the "potential energy" that is delivered to the emergency systems to move the water is stored in a diesel fuel tank. With 20/20 hindsight, it now appears that some failure scenarios of this fairly complex energy conversion system (diesel generators and associated electrical distribution)were left off the table.

I understand that the scale of a civilian plant as opposed to a submarine plant might make the scaling up of similar non-electrical systems expensive. But, expensive compared to what?




Kevin Snyder
SW2010 x64 SP3
Win 7 Pro
Core2 Quad Q6600 2.4Ghz 8Gb
NVIDIA Quadro FX570
3D Connexion SpacePilot Pro

 

[owg]

vpl - Thanks for the comment. I thought perhaps if a plant continued to generate electricity it would be able to keep its own internal electrical users supplied. These might include MOVs, electric drivers, cooling fans, battery chargers, etc.

HAZOP at

http://www.curryhydrocarbons.ca

 

[trottiey]

Sure, bringing one reactor back up to cool the other two might work, with some clever makeshift work. But now you're playing double-or-nothing. You've just turned a nuclear reactor back on right after it went through a record-breaking earthquake, and you haven't had time to give it a full inspection for damage. So do you want a risk of loss of coolant on three shutdown cores, or a risk of one full power core out of control?

 

[printing724]

Returning one reactor to service may not be possible in a relevant time frame due to xenon poisoning following a shutdown from power. Commercial cores use 3-5% enriched fuel. Xenon buildup following a shutdown inserts a substantial amount of negative reactivity.

I'm not sure of the timeframe involved in a commercial plant, but do know that one of the (several) reasons why naval reactors use highly enriched uranium fuel (90% plus enrichment) is to provide enough positive reactivity to enable a startup immediately following a reactor scram.

Fast scram recovery is a scripted procedure used to return a combat vessel to an operating status as quickly as possible after a reactor shutdown.

Kevin Snyder
SW2010 x64 SP3
Win 7 Pro
Core2 Quad Q6600 2.4Ghz 8Gb
NVIDIA Quadro FX570
3D Connexion SpacePilot Pro

 

[owg]

Thanks for taking my suggestion seriously. I was not suggesting restarting in the current situation. I think you folks are quite correct that after a big shake it would not be wise. I was thinking for the future it may be best if the units don't shut down completely after a small shake. However I think better protection for the diesel back up units is justified. That is all from me on this subject.

HAZOP at

http://www.curryhydrocarbons.ca

 

[rmw]

I made the point in another thread on this topic in this forum - they are legion - that IF the problem with the plant failure was flooding of major electrical equipment, bringing the plant right back up is probably out of the question.

And Printing... that may be the difference. Military vessels and subs in particular have to be designed to operate after flooding. There might be some ideas that would carry over.

But I also made the point somewhere in some thread close by that after tripping a power plant and putting a whole islanded city in the black, even with a lot of bottled up potential energy, it was useless without certain auxiliaries (condenser cooling water pumps) that a naval vessel wouldn't lack (seawater and lots of it outside).

rmw