Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Reno Deano]

As for salvaging the plant, the primary cooling system has been been exposed to seawater for about 2 weeks. There may be enough corrosion, particularly of the core components, such that they cannot be used again. The fuel is damaged (so the core would have to be replaced), but more importantly, the control rods and the drive mechanisms would have to be replaced. And likely the recirculation systems have been compromised, so essentially, much or all of that needs to be replaced. All those components would have to be decontaminated and scrapped. Given the contamination at the plant, that will take years.

Good speculation, but items submerged in seawater tend to exhibit faster corrosion when removed from seawater and oxygenated air helps the corrosion (many examples, such as the Titantic and WII ships in the Pacific. The navy pulled a sunk unfueled nuke sub from a seawater river in Vallejo, CA and saved the reactor. It was a stinky mess.

Basically, the end cost will not justify the outlay by the bean counters. They will treat it as we did the TMI reactor.

 

[Joe Neubarth]

I read somewhere (sorry for not being able to provide link right now) that the EDG's was swamped by the wave - e.g. the air intake was flooded - which leads to immediate flooding of EDG's - e.g. hydrolock of the cylinders.

http://en.wikipedia.org/wiki/Hydrolock

Gross stupidity from an engineering standpoint. Who in his right mind is going to design a plant with the Emergency Diesel Generators placed where they can get douched by the ocean?? ? ? ? ?

 

[Astronuc]

Not just for the monitoring systems, but also for managing power-operated valves - such as those needed for reducing the reactor pressure (blowdown system), providing steam for the RCIC turbines and enabling the feedwater to be pumped into the core. I'm not sure how the Japanese plant is equipped in this respect, but it appears that loss of DC could have been one factor contributing to the core uncovery.

I should have indicated instrumentation and control functions. Yes - the loss of power (AC or DC) resulted in a loss of coolability of the core - and some degree of uncovering. The complete loss of power (LOOP) was certainly unanticipated. As far as I know, accident analyses of LOOP and LOCA to date all assume that there is some power (EDGs) available minutes and hours after the accident, such that the core is cooled appropriately and there is sufficient margins to the various design limits.

 

[jlduh]

Well, I'm trying to keep up with the flow of informations on this thread and it's not that easy, one day absence for me and i got 7 or 8 pages to read to try to be up to date!

But anyway, thanks to everybody for the great collaborative effort deployed here to better understand what's happening and what could happen...

Thanks especially to those who have knowledge about isotopes and stuff like that, i have NONE on this but it's very important to have people who can analyse this material because it can give as important information for the health of the reactors than we can get from a blood analysis for a human, as i understand it. Please, try always to add at least a sentence of summary to clarify your conclusions or hypothesis because sometimes what is obvious for specialists are not that obvious for others... which starts to be many here writting, and even more i think reading, and trying to get a feeling of what's going on there.

I've read several times here people saying that the press is mixing very often (and maybe more and more) numbers expressing doses of radioactivity (in millisieverts for example) with those expressing flows of doses of radioactivity (in millisieverts/h for example, or per 24h, or per year) and that they compare oranges to apples by doing so, and that's something I've been seing since the first days of the accidents. But are these "mistakes" only from the press or is the press just reproducing some foggy ways of presenting the situation by the autorities (and Tepco)?

I see more and more informations also from the autorities where the conclusions are in fact biased because on one side they compare one flow in millisieverts/h with legal limits that are in fact doses per year, which ends up very often to a situation where annual legal limit will be reached in few hours or days... Very often, i see sentences in their declarations where basically they measure something close to or higher than "limits" (and often limits are for doses over one year!) but keep saying there will be no health effects!

In fact they make as if the exposure were just transitory and wouldn't continue for long... which confirms day after day to be untrue based on our analysis of the situation at the plant that will last AT BEST stable for a very long time, but could get even worse at this point of time.

I give two examples of this strange language.

Look at this article for example.

http://www3.nhk.or.jp/daily/english/27_01.html

In this case, everything is said quite clearly (in one day you get 40% more than he annual limit) BUT no health problems BUT stay in alert because the situation will last... Quite a strange way of communicating on this...

Second example, this text has been on Ibaraki prefecture for several days.

http://www.pref.ibaraki.jp/bukyoku/seikan/kokuko/en/data/radiation_no_danger.pdf

In this case you have a perfect example of first giving some true info, then start mixing radioactivity/h and dose per year, and then giving comparisons between oranges and apples to conclude with the misleading title of the declaration for the public: "Radiation no danger. No need to worry about radiation accompaniying Fukushima power plant accident" !

I read now that Tepco just says that the high measurement in water from reactor 2 was not credible, ok maybe there has been a mistake we will see, but really i DON'T SEE ONLY MISTAKES, i see oriented datas and conclusions from the autorities and this is not a good way to create confidence in the public opinion. Meanwhile, confidence is of absolute necessity in such moments.

I heard yesterday i think the mayor of Minamisoma (I think it's the right name) which is in the 30 kms limit zone (between 20 and 30 kms) and he was completely upset because national government was just "advicing people to voluntarily leave the area" (so no order to evacuate). In fact 10 000 were still in this zone, some were afraid of not been able to leave later because no more gas but at the same time some other ones were coming back because they were concluding that since there was no offcial order to evacuate (for several days) then it would mean it is quite safe (which is the strange conclusion of many declarations...).

That's a pity because crisis management can create more victims because of bad or misleading communication.

 

[Joe Neubarth]

Actually they garnered a heck of a lot of information from Chernobyl and Three Mile Island. AT Chernobyl, the Lava that was generated from the melt down actually flowed through pipes under the reactor and out onto a basement corridor floor. Photos are available all over the Internet, but the easiest one to locate is a Wiki. Three Mile Island had accumulation at the base of the reactor vessel.

That mass was analyzed for content and it consisted primarily of Zirconium and Uranium with far smaller amounts of Steel, Nickle (Inconel), and Chromium. When I read that report I was wondering what happened to the control rods. It turns out the Boron (If the control rods have melted) eventually becomes Boric Acid in solution. As the Japanese were pumping sea water into the reactor, they were diluting the Boric Acid and it was flowing out into the building. Do that long enough, and you can make your corium glow with numerous fissions, especialy if it started out as an old core operating at a high rate of power when the troubles began.

When the Japanese announced that they were feeding sea water into the plants, I was wondering if they knew they could be diluting the boron inside the plant, but figured that the engineers there knew what they were doing. Now, I think they did not consider what they were doing after the explosions.

 

[Astronuc]

Gross stupidity from an engineering standpoint. Who in his right mind is going to design a plant with the Emergency Diesel Generators placed where they can get douched by the ocean?? ? ? ? ?

Fourty+ years ago, they anticipated a tsunami (something like 6 m). However, fourty+ later, the tsunami that struck was greater (14 m). Ideally, the fuel tanks would have been buried or placed on the other side of the plant (same with EDGs), or hardened such as not to be vulnerable to a tsunami.

 

[Astronuc]

When the Japanese announced that they were feeding sea water into the plants, I was wondering if they knew they could be diluting the boron inside the plant, but figured that the engineers there knew what they were doing. Now, I think they did not consider what they were doing after the explosions.

The seawater was borated. Soluble boron is not normally used in the cooling system in a BWR. It is added in the case of an emergency, but the complement of control rods is designed to shutdown the reactor (core) without the introduction of soluble boron. The reactors were shutdown normally - before the tsunami hit - at least according to what I read. The operators started normal shutdown procedures in response to the seismic activity.

When the connection to the grid was lost, the EDGs came on-line, ran for about one hour, then they were knock out by the tsunami.

 

[Joe Neubarth]

The seawater was borated. Soluble boron is not normally used in the cooling system in a BWR. It is added in the case of an emergency, but the complement of control rods is designed to shutdown the reactor (core) without the introduction of soluble boron. The reactors were shutdown normally - before the tsunami hit - at least according to what I read. The operators started normal shutdown procedures in response to the seismic activity.

When the connection to the grid was lost, the EDGs came on-line, ran for about one hour, then they were knock out by the tsunami.

You are not following me. The BORON from the rods (if they melted) is GONE!

 

[AntonL]

When the Japanese announced that they were feeding sea water into the plants, I was wondering if they knew they could be diluting the boron inside the plant, but figured that the engineers there knew what they were d
oing. Now, I think they did not consider what they were doing after the explosions.

Pure speculation and false accusations!
With a destroyed plant they took the right decisions at the right time otherwise we would have seen a complete meltdown by now.

The only mistake in my opinion is why there is not a huge team of international expertise working in Japan as a think tank, checking the decisions and predicting outcome from the action taken to save the situation.

 

[Astronuc]

The real consideration is self sustaining criticality. Any time you have a Uranium atom split from a neutron strike and it releases its 2+ Neutrons and at least one of them causes another Uranium atom to split and that goes on for a few seconds, you have a continuing chain reaction..

In the present state it can not be sustained even if they are flushing all of the BoricAcid out of the reactor and creating an ideal situation for a hot box for a hundred years.

Not necessarily - there are isotopes of Pu (Pu-240 and 242), Cm and Am that undergo spontaneous fission - as a low level. Those neutrons are then available to activate other elements or cause a fission of a nearby U-235 or Pu-239 atom.

Again, the seawater was borated, and the control blades were inserted.

 

[rmattila]

What I would like to know is whether they have added extra boron after switching to the freshwater injection. One explanation for flooding the turbine hall basement is flow of water through steam/feedwater/emergency feedwater pipelines through an untight isolation valve. The presence of Ce-144 in the water found in turbine hall of unit 1 (the containment of which is said to be intact) might be an indication that the flow has been in the form of water rather than steam. Since you probably can't trust the level gauges any more due to salt deposits in their impulse pipes, it could be that they have overfilled the reactor, and thus possibly driven some of the boron initially added out of the reactor.

 

[Astronuc]

You are not following me. The BORON from the rods (if they melted) is GONE!

Does one know they melted?

There certainly would be a concern of boron leaching out of the control rods - if they cracked or melted.

But then the seawater was borated.

 

[Joe Neubarth]

When I went through Naval Nuclear Power School I asked about the rods melting in a reactor accident and was assured that they would melt at the same time the fuel plates melted.

No study of that had been conducted and put in our physics classes or in our books, so I was always a cynic. (That was way back in 1968 - 1969). To date I have not seen that in the Reactor Lava any substantive Boron is found. The answer, of course, is that it goes into solution as Boric Acid. By flooding the reactor with sea water the Japanese were flushing their poison away from the Reactor Lava that was eating through the bottom of the vessel. (If a melt down occured.)

 

[Angry Citizen]

The BORON from the rods (if they melted) is GONE!

Just because a substance is soluble doesn't necessarily mean it's going to violate conservation of mass. It's in there somewhere.

 

[Astronuc]

What I would like to know is whether they have added extra boron after switching to the freshwater injection. One explanation for flooding the turbine hall basement is flow of water through steam/feedwater/emergency feedwater pipelines through an untight isolation valve. The presence of Ce-144 in the water found in turbine hall of unit 1 (the containment of which is said to be intact) might be an indication that the flow has been in the form of water rather than steam. Since you probably can't trust the level gauges any more due to salt deposits in their impulse pipes, it could be that they have overfilled the reactor, and thus possibly driven some of the boron initially added out of the reactor.

The presence of solid fission products like Ce-144, and isotopes of Y, Zr, La, Ba, . . . would indicate fuel washout, which could simply mean breached cladding, but not necessarily melting of the cladding. I would like to know if they detect Np-239.

I would hope that the fresh water is borated.

 

[rmattila]

When I went through Naval Nuclear Power School I asked about the rods melting in a reactor accident and was assured that they would melt at the same time the fuel plates melted.

Boiling water reactor has different control rod design from that of the naval PWRs. The BWR CRs are in the form of a cruciform blade that is inserted in between the assemblies. Different designs and materials have been used, and I'm not sure which is the one used in Japan. One typical material is stainless steel, which melts at around 1700 C, whereas the UO2 in the fuel rods remains solid until 2800 C. Therefore, recriticality in a severe BWR accident is a well known risk, and thus boron injection is one countermeasure used when preparing for an eventual core meltdown.

 

[Joe Neubarth]

Not necessarily - there are isotopes of Pu (Pu-240 and 242), Cm and Am that undergo spontaneous fission - as a low level. Those neutrons are then available to activate other elements or cause a fission of a nearby U-235 or Pu-239 atom.

Again, the seawater was borated, and the control blades were inserted.

I can not find where they say the sea water was being borated. Do you have a link?

I understand that the control rods were inserted when they scrammed. That is not the issue that I am talking about. Remember, I have been trained to operate nuclear reactor plants.

The questions raised on this board about why in the heck we are finding fission products that have a short term half life in the adjoining buildings. As I have posted, my conjecture is based upon the possibility of a Reactor melt down. Conjecture only as I understand this forum does not want to say that that is the only possible explanation to all of the recent findings. I am convinced that we had a full reactor melt down two weeks ago, but as I have stated to be politically correct, that is just my opinion and is not stated as known fact.

 

[Astronuc]

When I went through Naval Nuclear Power School I asked about the rods melting in a reactor accident and was assured that they would melt at the same time the fuel plates melted.

No study of that had been conducted and put in our physics classes or in our books, so I was always a cynic. (That was way back in 1968 - 1969). To date I have not seen that in the Reactor Lava any substantive Boron is found. The answer, of course, is that it goes into solution as Boric Acid. By flooding the reactor with sea water the Japanese were flushing their poison away from the Reactor Lava that was eating through the bottom of the vessel. (If a melt down occured.)

Um - we have to wait for the evidence that the CRBs and fuel melted. SS304 has a melting point of 1400 - 1455 °C, and Zircaloy-2 has a slightly higher melting point of about 1800°C. It's not clear yet that those temperatures were realized. The control rods are not strongly heated (there is some gamma heating related to decay products in the core), and they sit between fuel assemblies and their Zircaloy channels. The steam between the channels might have been somewhat superheated, but it's not clear that the steam would superheat to > 1000°C.

Nevertheless, the seawater was reportedly borated.

 

[RealWing]

The presence of solid fission products like Ce-144, and isotopes of Y, Zr, La, Ba, . . . would indicate fuel washout, which could simply mean breached cladding, but not necessarily melting of the cladding. I would like to know if they detect Np-239.

I would hope that the fresh water is borated.

The latest TEPCO update for Unit 2 states: -"From 10:10 am on March 26th, freshwater (with boric acid) injection was initiated. (switched from the seawater injection)"

No mention of borating in the other 2 units.

http://www.tepco.co.jp/en/press/corp-com/release/11032708-e.html

 

[PietKuip]

This is from the Tepco retraction. What are they writing on the blackboard?

Identification of iodine-134 should be unambiguous from the gamma spectrum. Tepco should publish their data.

 

[Joe Neubarth]

Boiling water reactor has different control rod design from that of the naval PWRs. The BWR CRs are in the form of a cruciform blade that is inserted in between the assemblies. Different designs and materials have been used, and I'm not sure which is the one used in Japan. One typical material is stainless steel, which melts at around 1700 C, whereas the UO2 in the fuel rods remains solid until 2800 C. Therefore, recriticality in a severe BWR accident is a well known risk, and thus boron injection is one countermeasure used when preparing for an eventual core meltdown.

The Uranium Pellets go wherever the Zirconium flows.

 

[rmattila]

The Uranium Pellets go wherever the Zirconium flows.

I agree that's the most probable course of action, but in principle in might be possible that some kind of "heap" of UO2 would remain higher than the already-molten cladding. (Not very probable, though.)

 

[Astronuc]

I can not find where they say the sea water was being borated. Do you have a link?

I understand that the control rods were inserted when they scrammed. That is not the issue that I am talking about. Remember, I have been trained to operate nuclear reactor plants.

The questions raised on this board about why in the heck we are finding fission products that have a short term half life in the adjoining buildings. As I have posted, my conjecture is based upon the possibility of a Reactor melt down. Conjecture only as I understand this forum does not want to say that that is the only possible explanation to all of the recent findings. I am convinced that we had a full reactor melt down two weeks ago, but as I have stated to be politically correct, that is just my opinion and is not stated as known fact.

The addition of borated seawater was mentioned numerous times in this thread starting with post 13. That was a reference to a video, but a link was not cited.

However, Fukushima Nuclear Accident Update (14 March 2011, 00:30 UTC) - Clarified
http://www.iaea.org/newscenter/news/2011/fukushima140311.html

Unit 1 is being powered by mobile power generators on site, and work continues to restore power to the plant. There is currently no power via off-site power supply or backup diesel generators being provided to the plant. Seawater and boron are being injected into the reactor vessel to cool the reactor. Due to the explosion on 12 March, the outer shell of the containment building has been lost.

Unit 2 is being powered by mobile power generators on site, and work continues to restore power to the plant. There is currently neither off-site power supply nor backup diesel generators providing power to the plant. The reactor core is being cooled through reactor core isolation cooling, a procedure used to remove heat from the core. The current reactor water level is lower than normal but remains steady. The outer shell of the containment building is intact at Unit 2.

Unit 3 does not have off-site power supply nor backup diesel generators providing power to the plant. As the high pressure injection system and other attempts to cool the reactor core have failed, injection of water and boron into the reactor vessel has commenced. . . . .

I bolded for reference. How many references/citations does one wish before accepting the seawater was added with boron?

Fukushima Nuclear Accident Update Log
http://www.iaea.org/newscenter/news/tsunamiupdate01.html

 

[PietKuip]

At higher resolution. Is there anything interesting on the whiteboard?

 

[Astronuc]

Two more references one referring to borated freshwater, and the older one referring to borated seawater:

http://www.tepco.co.jp/en/press/corp-com/release/11032706-e.html
-We have been injecting sea water into the reactor, but from 10:10 am on March 26th, we started injecting fresh water (with boric acid) into it.

Back on March 13 -
http://www.tepco.co.jp/en/press/corp-com/release/11031312-e.html

Unit 1(Shut down)
- Reactor has been shut down. However, the unit is under inspection due to the explosive sound and white smoke that was confirmed after the big quake occurred at 3:36PM.
- We have been injecting sea water and boric acid which absorbs neutron into the reactor pressure vessel.

Unit 2(Shut down)
- Reactor has been shut down and Reactor Core Isolation Cooling System has been injecting water to the reactor. Current reactor water level is lower than normal level, but the water level is steady. After fully securing safety, measures to lowering the pressure of reactor containment vessel has been taken, under the instruction of the national government.

Unit 3(Shut down)
- Reactor has been shut down. However, as High Pressure Core Injection System has been automatically shut down and water injection to the reactor was interrupted, following the instruction by the government and with fully securing safety, steps to lowering the pressure of reactor containment vessel has been taken. Spraying in order to lower pressure level within the reactor containment vessel has been cancelled.
- After that, safety relief valve has been opened manually, lowering the pressure level of the reactor, which was immediately followed by injection of boric acid water which absorbs neutron, into the reactor pressure vessel.

I bolded for emphasis.

 

[seasponges]

If one of the reactors at Fukushima underwent a full meltdown, how devastating an effect would it have on the region?

 

[rhody]

The only mistake in my opinion is why there is not a huge team of international expertise working in Japan as a think tank, checking the decisions and predicting outcome from the action taken to save the situation.

Anton,

I agree, however, given the sensitive nature of the situation, how can you be sure that it is not happening. I will say this, I would feel much better knowing that it is in fact happening without being privy to the details. Fair enough ? When I asked Astronuc who I have a great deal of respect for a question like this and do not get a yes or no answer, it may be that he cannot discuss even the existence of what I am asking about. That in and of itself is telling, interpret it as you wish, but I feel better even with a "silent" response knowing of its potential positive implications. Enough said.

Rhody...

 

[dtaipei]

Tepco press conference now live on uStream - began 4 minutes ago. Japanese no subtitles though.

 

[AntonL]

This is from the Tepco retraction. What are they writing on the blackboard?

Identification of iodine-134 should be unambiguous from the gamma spectrum. Tepco should publish their data.

Spot On - here is the NHK report

TEPCO retracts radioactivity test result
Tokyo Electric Power Company has retracted its announcement that 10 million times the
normal density of radioactive materials had been detected in water at the Number 2 reactor
of the Fukushima Daiichi nuclear plant.

The utility says it will conduct another test of the leaked water at the reactor's turbine
building.

The company said on Sunday evening that the data for iodine-134 announced earlier in the
day was actually for another substance that has a longer half-life.

The plant operator said earlier on Sunday that 2.9 billion becquerels per cubic centimeter
had been detected in the leaked water.

It said although the initial figure was wrong, the water still has a high level of radioactivity
of 1,000 millisieverts per hour.

Sunday, March 27, 2011 22:02 +0900 (JST)

 

[Astronuc]

If one of the reactors at Fukushima underwent a full meltdown, how devastating an effect would it have on the region?

If a core meltdown, it should be confined to containment. The immediate effect is a highly contaminated containment and loss of generation. Currently, TEPCO has lost 4 units, with 3 units have some degree of core damaged (any melting is undetermined at this time).

Now, if there is severe core damage, which appears to be the case, the matter becomes one of how much of the fission products are released to the environment. The containment of Units 1,2,3 are heavily contaminated. Some of that contamination (fission products) has been released to the environment. The short and long term effects depend on which and how much of those radioisotopes have been released.

Unit 4 may have damaged fuel in the SFP. Fission products, primarily Xe and Kr, and volatiles, I and Cs, have been released to the atmosphere. Again it is a matter of determining how much fuel has been damaged, and how much of the inventory of fission products has been released to the environment.

There is clearly a significant release of fission products from the core of Units 1, 2 and 3, and likely the SFP of Unit 4. There may be some damage to fuel in SFPs of U 1, 2, and 3, but the focus has been on the cores and contaminate water in the respective containments.

We do not know the extent of the damage to the cores of U 1, 2 and 3, or the extent of damage to the fuel in the SFPs. We are waiting for TEPCO to stabilize the units, so that they can start clearing out the debris and damaged structures, and then they can start thinking about how inspect the SFPs and cores. Removing the damaged fuel will be a challenge, since the eight of the fuel rods form the structure (connection between upper and lower tie plates), and it is the upper tie plate that is used to lift the fuel assembly as a unit. The channels are not mechanically connected to the bottom tie plate (although one design not used at Fukushima does use the channel as a structural element).