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trottiey (Nuclear)
14 Mar 11 13:24
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.
Helpful Member!  vpl (Nuclear)
14 Mar 11 17:15
Trottiey

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

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

guizmy (Mechanical)
14 Mar 11 17:36
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?
 
Helpful Member!(6)  trottiey (Nuclear)
14 Mar 11 18:33
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 (Mechanical)
14 Mar 11 19:27
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 (Nuclear)
14 Mar 11 20:56
Thank you vpl, I was not aware of that feature.
vpl (Nuclear)
14 Mar 11 21:44
Trottiey

Thanks for issuing the FAQs!

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

Gillespie (Structural)
15 Mar 11 1:09
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 (Mechanical)
15 Mar 11 2:28
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 (Nuclear)
15 Mar 11 6:51
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 (Electrical)
15 Mar 11 7:29
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 (Nuclear)
15 Mar 11 7:43
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 (Chemical)
15 Mar 11 7:58
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 www.curryhydrocarbons.ca

vpl (Nuclear)
15 Mar 11 8:46
It's kind of hard to keep the plants running with no electricity.

Patricia Lougheed

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Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

printing724 (Electrical)
15 Mar 11 9:45
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
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owg (Chemical)
15 Mar 11 9:57
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 www.curryhydrocarbons.ca

trottiey (Nuclear)
15 Mar 11 13:33
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 (Electrical)
15 Mar 11 14:06
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 (Chemical)
15 Mar 11 15:52
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 www.curryhydrocarbons.ca

rmw (Mechanical)
18 Mar 11 21:34
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
MintJulep (Mechanical)
18 Mar 11 21:56
I'm sure no one is thinking of bringing anything back online in anything close to its design capacity.

Most likely the goal is to get some pump of some sort running, and pump water onto things that are hot.

If memory serves, the spent fuel pool water circ pumps are one or two decks below the top of the pool.  It's very possible that they are undamaged by flooding, explosions or fire.
rcchap (Mechanical)
22 Mar 11 12:19
trottiey:  Nice job on the Q&A.  It makes be sick to watch the mainstream media interview a UCS physicist or a politician as a nuclear industry "expert".  It is important to get the facts out there.  

Printing724:  Keep in mind that sub plants are PWRs, so you have the capability to remove heat with natural circulation using the steam generators.  Some PWRs in the US also have this capability. One that I worked at could be cooled as long as you had a few feet of water in the steam generator.  BWRs (like Fukushima) are different.  They have recirculation pumps and supression pools.  They may not be able to be cooled as easily using natural circulation.  (Rickover knew what he was doing, eh?)
trottiey (Nuclear)
22 Mar 11 20:56
Thanks rcchap! I find that most nuclear types tend to avoid interviews about safety issues, or at least avoid speaking openly about them. So it's not wonder the journalists resort to the second-rate guys for answers. This doesn't help anyone.
rmw (Mechanical)
22 Mar 11 21:30
I'd appreciate it if they would scrounge up some second rate guys.  I don't think we've had that quality yet.

rmw
msquared48 (Structural)
22 Mar 11 23:00
Trottiey:

You might add saving face to your 18:44 list posting of communication problems.  Unfortunately this is a reality that is frequently ignored and factored into the communication equation.

And could you please address the role that the presence or lack of oxygen played in the explosions and fires?  I have heard rumors that seem ridiculous.  Thanks.  

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

msquared48 (Structural)
22 Mar 11 23:51
Sorry, but I meant NOT factored.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

trottiey (Nuclear)
23 Mar 11 23:01
Wow, I hadn't heard anything about the oxygen controversy until you pointed it out. I can confirm that ridiculous rumours are rampant out there, and I can't afford the time to disprove them all. But here's some basic reality checks that should help:

1) Radiolysis routinely produces both hydrogen and oxygen in normal reactor operation. Recombiners dispose of the radiolysis products by turning them back into water. Radiolysis will continue at a reduced rate when the reactor is shut down, but recombiners may not work (or lose efficiency) if they don't have electrical power.

2) If the core overheats, the zirconium-water reaction may produce hydrogen and zirconium oxide, (and maybe some form of hydroxide?) but no oxygen. The recombiners are no help if they don't have enough oxygen to react with the hydrogen.

3) In a meltdown scenario, you could have hydrogen production from both of the above sources. The flammability and explosive bands for hydrogen and oxygen are impressively wide, buy the energy output tends to be weaker at the edges of the bands than for a perfect stochiometric mix.

4) You can't rule out an explosion inside the reactor pressure vessel. It didn't happen in Three Mile Island, but I know of two other reactors where it did. Those cases were relatively innocuous pops relative to the vessel strength. They bent some attached piping and cracked supports, but the vessel itself didn't seem to notice.

The next three points are educated guesswork, not be trusted.

5) The venting procedures are unclear to me, but it appears that some RPV coolant was vented to primary containment. I'm told that there are some pneumatic actuators inside their primary containment, and I'm guessing they run on air. So the pneumatic exhaust becomes an additional source of oxygen, raising the risk and potential power of the explosion, inside a significantly weaker vessel.

6) I can't make much sense of the secondary containment design, i.e. the reactor building, except as a collector of fugitive emissions and holding tank for the filters and exhaust stack. Therefore I presume that any vent to atmosphere, either from the RPV or from primary containment, is supposed to go through secondary containment. That would reduce the flow rate through the filters and increase their effectiveness, but it means mixing the hydrogen with a lot of air. Going out on a limb, I would guess that the refuelling deck was meant to be frangible in the event of overpressure.

7) Someone eventually got the idea to cut vent holes in secondary containment of unit 2, 5, and 6 to improve hydrogen venting. You can see these square holes in the walls on some pictures. Those three units now look much better from the outside than 1, 2, and 4, so somebody deserves a raise.

The last three points are not necessarily true, but they at least give a plausible alternative to some of zany conspiracies you can Google.

Having said all that, the hydrogen explosion are still puzzling to the best nuclear chemists I work with. As best as we can figure out, any plant should normally have enough recombiner and igniter capacity within containment to handle this accident scenario. So why didn't they work? Were they broken or blocked? Was the hydrogen production or venting far higher than our estimates? Did someone plug them into a regular outlet instead of one that was protected by the back-up battery system? Was this just another effect of the extended station blackout? We'll have to wait for the lessons learned report years hence to get complete answers.
printing724 (Electrical)
24 Mar 11 10:15
@rcchap

Your comments here (and in the hindsight thread) are right on. And you are right, decay heat removal in a submarine PWR vs a land based BWR are completely different. I used the submarine PWR example only because (a) I was personally familiar with it and (b) it shows that decay heat removal without electrical power is a practical proposition. Whether it is cost-effective in a given situation is a matter for regulators and business managers, not engineers.

Fukushima physically survived a greater than design basis seismic event only to lose control of the plant because comparatively fragile electrical systems failed.

I think a relevant question (that will be heard frequently) is, "What will your plant conditions be after a long term site blackout?" The list of correct answers will not include statements that start out, "A long term SBO couldn't happen here because..."
 
Good or bad, the long term SBO has just made the list of foreseeable events, at least in the public eye. Doesn't matter what kind of inconceivable circumstances cause it. The genie is out of the bottle. IMHO, the nuclear industry must acknowledge that if it is to overcome the loss of public trust resulting from this tragic event.

And yeah, Rickover had it right. (I just read an interesting first-hand account about the first full power runs that were done on the Nautilis prototype. When you consider the limited prior art knowledge base they were building on (none), how successful they were, and how much it influenced reactor designs that followed, it was an amazing achievement.)    

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

printing724 (Electrical)
24 Mar 11 10:57
@rcchap

I just re-read your post above. The steam generators had nothing to do with the decay heat removal system (XC system, for emergency cooling). It was a standalone heat exchanger that tapped into the primary loop inside the main coolant cutout valve boundary as I recall. A thermal siphon of primary coolant flowed through it, and it was cooled by a seawater thermal siphon (under loss of all power conditions, with power available it was cooled by the RPFW fresh water system). The thermal siphons are only possible because the heat sink (ocean) is at a level above the heat source (reactor core).

 

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

rcchap (Mechanical)
24 Mar 11 14:18
printing724:

I agree completely.  A long term SBO is no longer beyond design basis.  This will our affect our entire industry.

Your XC system sounds unique to a sub plant.  Land based PWRs (at least the ones I have worked at) don't have that.  It makes sense to have this on a sub.


Trottiey:

Most of the hydrogen production is a result of the zirconium-steam chemical reaction.

After they lost power from their batteries, the RCS pressure would be instreasing from the continued core decay heat and exothermic zirconium-steam chemical reactions.  They vented the RCS into the primary containment.  Then, to protect the primary containment from overpressurization, they vented it through a series of ducts with filters to remove radioactivity.  The vent path would have discharged this at an elevated release point.  The hydrogen detonation occurred during venting shortly after an aftershock.  The prevailing thought is that a spark ignited the hydrogen during the venting process.

Venting of H2 was of great concern during TMI.  I remember reading somewhere that the containment pressure spike did occur, so it is possible that there was an explosion inside containment.  But their containment held (a PWR only has one containment, not two like a BWR) and thus there was no significant radiation release.
rmw (Mechanical)
24 Mar 11 22:26
Printing724,

Is what you read about the Nautilus prototype testing a publicly available book or document?

rmw
Zogzog (Electrical)
25 Mar 11 7:56
Here is a link to the article (I assume) he was refering to. I tourded this plant when I was stationed at A1W, it was shut down and if I recall they were removing the vessel at the time.

http://www.theatlantic.com/technology/archive/2011/03/first-person-account-of-powering-up-one-of-the-worlds-first-nuclear-reactors/72870/
owg (Chemical)
26 Mar 11 10:23
Gillespie asked the following a few days ago. I did not see an answer.
"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?"

I have been reviewing the reactor circuit and I note that the primary cooling water is normally radioactive. It leaves the containment building as steam, drives the turbine, gets condensed, and goes back to pick up more heat from the reactor. What circuit is used for the emergency seawater? Is it also radioactive? Does it just vent radioactivity to atmosphere after it goes through the reactor? Thanks.

HAZOP at www.curryhydrocarbons.ca

trottiey (Nuclear)
26 Mar 11 13:21
The primary cooling circuit you describe is normally driven by feedwater pumps. Those pumps need megawatts of electricity to run, and they may have been damaged by the tsunami since they reside in the turbine hall. Or the condenser pumps might not be running, depriving the condensers of cold seawater. There may be additional back-up pumps, or the system may have some ability to thermosiphon, but basically the cooling system hasn't been running adequately for the last couple of weeks.

The primary coolant is still boiling or evaporating, and that endothermic process still cools the fuel just like it does during normal operation. But with the cooling circuit handicapped, the condensers can't keep up and the water level starts to fall. So to keep pressures down and keep the core covered with water, it sounds like they have been venting steam from that primary coolant circuit and replacing it with seawater.

Any water that flows over the fuel is going to pick up some radioactivity, much more so if the fuel is damaged. At least some of that radioactive steam has been vented to primary containment and condensed to water there. Excess gases and steam could normally be piped through filters that capture most of the contaminants and then released through a high smokestack to dilute any remaining fallout before it reaches the workers. In the case of Fukushima, the filters have evidently been overwhelmed or damaged.

Yesterday's newspapers indicate that they have released a large amount of radioactive water in liquid form. That could be a result of primary containment breach or leakage, or it might have been an intentional release of the condensate from primary containment, which would be consistent with Fermi2's earlier analysis here:
http://warships1discussionboards.yuku.com/topic/15893/8-9-Earthquake-Tsumani-in-Japan?page=3

I don't think we'll know much more specific details of which pipes and pumps they used until much later. There's lots of plumbing in a nuclear reactor, there's a recirculation circuit you might be interested in, there's water in the torus that also needs to be kept cool, etc. And we can presume that they also have a lot of broken pipes, stuck valves, and temporary bypasses at this point.  
zlindauer (Structural)
26 Mar 11 13:22
What's the worst case scenario?  What would be the likely outcome if everyone just walked away from the plant?
owg (Chemical)
26 Mar 11 16:29
Thanks very much Trottier. What you suggest sounds reasonable. The only phrase I did not understand was "vented to primary containment and condensed to water there". I thought the primary coolant was already in primary containment. Wouldn't venting it put it into some other containment or just to atmosphere? However I appreciate that we don't have access to the full process flow scheme. Keep up the good work.

HAZOP at www.curryhydrocarbons.ca

owg (Chemical)
26 Mar 11 17:19
After a couple of passes at Fermi2's notes, I think the steam gets vented to the Tora. It goes in underwater so that is how it gets condensed. There is some thermosyphon during normal cooling but not if the condensers after the turbogenerators have no cooling water flow. I am also wondering how Fukushima normally gets rid of low grade heat, I don't see any cooling tower in the pictures. Could they be warming the sea?

HAZOP at www.curryhydrocarbons.ca

itsmoked (Electrical)
26 Mar 11 17:30
owg; You have it.  NORMALLY the cooling loop is closed and none of it is released to the atmosphere.  Now since there is no functioning condenser system the only thing left to remove the steam, really the pressure it builds, is to directly vent it to the atmosphere.  Normally that isn't particularly bad as the normal nucleotides that would be in that are fairly short lived.  However as the core becomes damaged the resulting products get substantially worse/different and more concentrated.

zlindauer; Worse case?  Walk away?  Think Chernobyl.  All the spent full pools would empty. The fuel in them would melt and probably burn off their jackets.

Probably 3 reactor vessels would eventually rupture.  There would be fires.  They would carry radioactive dusts having half lives up to thousands of years. All this carried away on the smoke particles.

The smoke would be going in any weather driven direction and probably dangerously contaminate anywhere and everywhere with-in something like 200 miles.   Out to perhaps a thousand miles you would have areas of serious contamination with islands of notable contamination depending on local air and wind patterns and shadows.

Ultimately approaching the site would be extremely hazardous.

That's why this fantasy will not be happening.  

Keith Cress
kcress - http://www.flaminsystems.com

trottiey (Nuclear)
26 Mar 11 20:49

The primary coolant is normally kept at very high pressures (say 100 atmospheres) inside the reactor pressure vessel. (RPV) That's the blue pill-shaped thing in the picture. The RPV resides inside the light-bulb shaped primary containment, which is not normally pressurized and is only supposed to take 2-3 atmospheres in an accident scenario. The torus (also called "wetwell") is connected to the primary containment, so overpressure is supposed bubble through that water. That traps particulates and some gases, and condenses the steam. I believe primary containment also has its own cooling systems, although they're not shown on this diagram. If these cooling systems are overwhelmed, the torus water can eventually get so hot that it evaporates away, which might have happened intermittently in Fukushima.

The low-grade heat is ditched to sea, which is represented by that green pool at the bottom right-hand of the diagram.

Defining worst-case scenarios at this level of complexity is a sucker's game, because it depends on where you want to draw the line on low-probability events. Itsmoked's assessment feels somewhat too bleak to me, but I don't feel I can make more precise predictions.
786392 (Petroleum)
27 Mar 11 6:09
Hello/Good
Afternoon Although many very much learned &knowledgeable people are around.
I have mentioned in another forum seawater's with very high NaCl contents has severe corrosive and imaginable consequential impacts all around the reactor primary containment,secondary containment and even on to main core itself(although may not be exactly estimated very correctly as per close vicinity radioactivity exposure threat).
It has already done great harm and now being planned for replacing with fresh water which seems too late.

A safer activity right now is to start one by one covering the reactors at risk(starting from most damaged two reactors) with targeted concrete & sand mixtures covering till the radio activity subsides to very safe levels.
This is the safest for Japan and the whole world as otherwise the "Grave Consequences are really foreseeable"

Best Regards
Qalander(Chem)

owg (Chemical)
27 Mar 11 6:14
Thanks again Trottiey. I had that diagram but without the containments identified. I thought that green wavey stuff looked suspiciously like seawater. So if the blue primary cooling water gets quite radioactive, I suppose the green secondary cooling water would get slightly radioactive. So it should be no surprise to find radioactivity in the neighbourhood ocean?

HAZOP at www.curryhydrocarbons.ca

zeusfaber (Military)
27 Mar 11 7:45

Quote (owg):

So if the blue primary cooling water gets quite radioactive, I suppose the green secondary cooling water would get slightly radioactive. So it should be no surprise to find radioactivity in the neighbourhood ocean?  
That doesn't sound right to me.  The loop through the condenser is all to do with normal plant operation.  At the moment, I don't think there's any circulation through it (especially on the seawater side), so the fission products they're finding in the sea (fission products implies a release of water that's been in direct contact with broken-down fuel rods inside the reactor pressure vessel) probably escaped some other way.

A.
trottiey (Nuclear)
27 Mar 11 9:19
The alpha/beta/gamma ionizing radiation that we're talking about here is not contagious. (Neutron radiation is contagious in some situations, but it's not relevant here.) During normal operation, the green secondary cooling water does not get radioactive. (Except from fugitive emissions such as leaks, spills, maintenance activities, etc.) The high levels of radioactivity that they're measuring now can only be due to fission products (contaminants) that originated in the core or in the spent fuel bays.

There are many ways in which the radioactive contaminants could have reached the sea. They might have been carried by steam that was vented to primary containment, condensed in the torus, and then released to sea (with as much filtration as they can do) per Fermi2's analysis. Or the contaminated torus water might have leaked out through a primary containment breach and bypassed the filters. Or the steam vented straight to atmosphere might have carried particulates and low-volatility liquids with it, and these would have fallen out in the neighboring area. But I suspect that the most likely possibility is simply that water leaked or overflowed out of the spent fuel bays.

But regardless of how the water is getting out, this is the essential reason why blindly dumping sand and concrete would accomplish little: contamination would still leak out into the groundwater. The stress of an unpredictable and poorly controlled event tends to push people to rash physical exertions. That stress mechanism was useful in the wild, but please keep in mind that this is a technological problem that can only be solved by clear level-headed thinking. In the end, the stress and depression may have a greater public health impact than the radiation. (At least no one here has suggested sending in an air strike to bomb the place. I've seen that in the comments section of some news websites.)   
owg (Chemical)
27 Mar 11 11:34
Thanks again for all the help.

HAZOP at www.curryhydrocarbons.ca

rmw (Mechanical)
27 Mar 11 15:36
What Trottiey says is generally true, but again we have to remind ourselves that we are dealing with the aftermath of a 9.0+ earthquake that literally moved Japan 8" closer to the USA plus some very unusual and unpredicted after effects so there is nothing to guarantee that the integrity of anything hasn't been compromised in this plant, including the normal and usual isolation of the seawater cooling system from the "hot" side.

I can't really see that being the reason for radioactivity in the sea, but I remind that we can't think this through with rational thought.

rmw
itsmoked (Electrical)
27 Mar 11 16:09
I believe it was actually fourteen feet.

Keith Cress
kcress - http://www.flaminsystems.com

electricpete (Electrical)
27 Mar 11 16:55
While we're talking numbers, the Tsunami was originally reported at around 7m.  TEPCO now says it was around 14m:

http://www.nextlevelofnews.com/2011/03/tepco-fukushima-was-hit-by-14-meters-high-tsunami-but-built-for-a-max-of-57.html

=====================================
(2B)+(2B)'  ?

rcchap (Mechanical)
28 Mar 11 8:49

Just to clarify a couple of points:

 - zuesfaber is right.  In the diagram above, the condenser shown in only used when they are making electricity.  The turbines, condenser, and the circulating water system is not used if offsite power is lost.  They would likely have another seawater cooling system used to reject core decay heat and spent fuel decay heat to the ocean.  There are no cooling towers because the plant is right on the ocean and uses once-through cooling.  All heat will ultimately be rejected to the ocean.

 - I am not a BWR expert, but I am pretty sure that they have a recirculation cooling system with heat exchangers that are cooled by another cooling system (not shown in the figure).  I believe that the wetwell also has a cooling system.

 - Most of the fuel in the SFP has been sitting long enough that it will not melt.  Only the more recently used fuel assemblies are at risk of melting.   
owg (Chemical)
28 Mar 11 9:27
rcchap - Thanks for the additional information. But I was wondering, if they have power to run a backup cooling circuit, would they not have power to run the regular cooling circuit? Maybe they have some power now but not not enough for the big stuff.

HAZOP at www.curryhydrocarbons.ca

owg (Chemical)
28 Mar 11 9:37
Here is a clip from a March 28 newspaper report. "The water must be removed and safely stored before work can continue to power up the plant's regular cooling system, nuclear safety officials said." So this may be the reason that the main cooling circuit is not yet back on in one or more of the units.


 

HAZOP at www.curryhydrocarbons.ca

BJC (Electrical)
28 Mar 11 11:42
The diagram shows only the power producing si side of the plant.
The two pumps and piping shown inside the containment are the reactor recirc pumps.  They were used to vary power output but not for ememgency cooling.
There are four RHR  and two core spay pumps not shown. There would also  be 2-4 emergency service water pumps to provice RHR cooling via heat exchangers and cooling for the emergency generators.
The diagram does not show the HPCI and RCIC systems.  

I can't tell from the pictures but I would suspect the refueling cranes are gone and the reactor building bridge crane as well.

trottiey -  What can the reactor water clean up system do?


 
trottiey (Nuclear)
28 Mar 11 18:52
I found this document which shows a lot more plumbing:
www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf

It mentions the reactor water clean up system and has a diagram for it, but I don't have any more detailed information.
itsmoked (Electrical)
29 Mar 11 1:20
That was interesting.  Thanks.

Keith Cress
kcress - http://www.flaminsystems.com

rcchap (Mechanical)
29 Mar 11 12:37

owg:

The "normal" cooling circuit with the circ water system would not be used without offsite power available.  The circ water pumps are very large and require a large amount of power.  These pumps would not be able to be supplied from the emergency diesel generators.  The EDGs would only feed the safety related busses, and the circ water pumps are non safety related and designed to reject the 60-65% of the full power heat production for the steam turbine (Rankine) cycle.

The safety related cooling system used for shutdown cooling would be relied upon in a loss of offsite power scenario such as this.  These pumps are smaller, would be safety related, and would be powered by the EDGs and would be designed to only reject decay heat, which would be just a few percent of the full power.  When they talk about restoring power to the "regular" cooling system, this is what they are talking about.

BJC:

The reactor water cleanup system would be used during normal power operation to keep contaminants out of the water and control pH (and numerous other parameters) within spec.  To keep normal operating dose down and to ensure proper operation of the plant, it is very important to keep the water extremely clean.  This system will have a series of demineralizers to do this.  At this point, this system would have very little use, and may not be powered from safety related busses.
cloa (Petroleum)
4 Apr 11 20:37
What suits do Japanese nuclear workers use? Hopefully they have Demron. They have been around for 10 years.

http://www.gizmag.com/demron-lightweight-lead-free-radiation-proof-suit/9300/
owg (Chemical)
5 Apr 11 7:04
Thanks rcchap.

HAZOP at www.curryhydrocarbons.ca

trottiey (Nuclear)
5 Apr 11 9:51
Don't be fooled by advertising. "Shielding test results indicate that two layers of Demron, with [...] a thickness of 0.4 mm each, [...] would have equivalent shielding power as lead with [...] a thickness of 0.2 mm."
http://www.radshield.com/pdf/mars_material.pdf

So what does 0.2 mm of lead buy you? Well the half-thickness value for lead shielding on typical radioactive waste is about 13 mm, so I = Io / 2^(0.2/13) = 0.989 Io. Wearing two demron suits one on top of the other will cut down your external gamma exposure by about 1.1%.

Personal protective gear does not provide much protection from external radiation exposure. The plastic suits are worn primarily to stop radioactive vapours from being absorbed through your skin. They also prevent radioactive dust from clinging to your clothes or skin and being dragged back to clean areas with you.
itsmoked (Electrical)
8 Apr 11 2:16
Thanks for the link.  

Keith Cress
kcress - http://www.flaminsystems.com

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