Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jim hardy]

here's from a real old Oak Ridge report. sounds like they'll be okay if they keep it wet.
I wouldn't even worry about temp somewhat above boiling - like a stove burner heating water from below, it has to be hotter than the pot

http://www.osti.gov/bridge/servlets/purl/6124656-R8y05j/6124656.pdf
cover page says distribution unlimited so i guess it's okay for us to read.
moderator scrub post if it violates anything, I'm still learning my way here.

[q]After structural deformation and downward relocation of molten control
blade, channel box, and candling clad material (in that order) onto the
dry core plate [2], local creep rupture failures of the core plate would
introduce relocating material into the lower plenum water and begin the
accumulation of quenched debris in the reactor vessel bottom head
[3,4]. Relocation of the metal structure of the core is expected to
leave the fuel pellet stacks standing until weakening, by overtemperature,
of the ZrO2 sheaths surrounding the fuel pellets and similar loss
of strength by the previously molten material that tends to weld the fuel
pellets together. It should be noted, given the progressive relocation
methodology outlined above, that the majority of the debris entering the
lower plenum is expected to be in the solid state when it enters the
water.
As the relocated core material accumulates in the 3WR reactor vessel bottom
head, it is expected that the composition of the quenched debris bed
would vary with height. Lowermost in the bed would be the mostly metallic
debris (control blades, canisters, candled clad and dissolved fuel)
that had either accumulated on the core plate before local core plate
failure or had subsequently relocated downward above the core plate failure
locations before fuel pellet stack collapse. Higher, within the
middle region of the bed, would be the collapsed fuel and ZrO2 from the
central region of the core. The initial local core plate structural
failures would cause temporary bursts of steaming as the relocated
metallic debris was quenched; however, with the collapse of the central
core fuel pellet stacks, a constant heat source (the decay heat
associated with the pellets) would be introduced to the lower plenum
reservoir, initiating a rapid continuous boiloff of the lower plenum
water.[/q]

stuff at bottom of pile protects vessel from the corium in middle of pile?

it's only a flesh wound...

 

[IowaNewbie]

it's only a flesh wound...

That's how gangrene starts ...

 

[rmattila]

Didn't the amount of radionuclides found outside the plant area show massive damage to fuel early on?

Large amount of cladding failures, yes. But concerning the max temperature of the core, information regarding the quantities of elements that evaporate between 1000 and 1500 degrees Celsius would be really important. It would help to see the results (besides the easily-evaporating I and Cs nuclides) of the analyses of the water found at different locations at the plant buildings (or even better, the raw gamma spectra) in order to see what has come out and how much.

Soil and air samples found at the site can be largely explained by the explosion at unit 3 service floor and don't thus tell much about the condition of the cores.

 

[rowmag]

Very interesting. Particularly the timing between the magnitude 7.1 earthquake and the CAMS d/w data. Keep in mind that there have been a large number of aftershocks/earthquake ongoing near Fukushima.

I've attached a screenshot from the QuakeZones iOS app which I've filtered to earthquakes of magnitude greater than 5 and within the last 30 days. The red pins are earthquakes greater than magnitude 6. Sorry, I am sure there is an online resource to achieve the same but this was easily within reach.

If you would like the data for further analysis and there isn't an easy way online to pull the date/time and intensity of each of these occurrences, I'd be happy to manually transcribe.

We have had such an insane number of aftershocks (still ongoing, though no large ones recently), that it may be an embarrassment of riches to look for a likely culprit. But if such an attempt is made, it may be useful to filter on shindo rather than magnitude. Shindo shows how much shaking a particular location felt. This might be a place to start to look for such data:

http://www.jma.go.jp/en/quake/quake_singendo_index.html

I think they are calling shindo "seismic intensity."

I would filter out anything below a shindo 5 for starters.

 

[TCups]

Find attached my assessment of the state of the roof structure of unit 3, after the explosion.

Based on visual inspection of photos, each field in a 16x24 matrix covering the entire roof structure was assessed to one of five categories of damage, see legend. The method used gives the assessment a resolution of about 1.5 meter.

Fragments found on the roof of unit 3 were assessed, as were fragments of the roof structure locatable to the south and the east side of the building. Due to poor photo coverage and their inter-mixture with other debris fragments which ended to the north of the building could not be inspected. Those parts of the structure from the N end and from the SE corner which could not be inspected were assessed based on plausibility, judging from visually inspected close-by or bordering fields.

Excellent! Now, add the overlay of the floor plan of the top floor. BTW, you should be marking this kind of work "copyright, 2011" and put your name on it, MadderDoc. There may be a publication in your future.

 

[MadderDoc]

I've overlay and added some labeled

I do believe that we can see an original steel structure between A and B

Nice job, |Fred. That conclusion about A and B is tempting, seeing there _is_ apparently a traverse in what appears to be the original position.

From a plausibility viewpoint one could say, why should it be in the orginal position considering the utter damage around it. However, more to the evidential, the interpretation leaves another structure unexplained, which I have marked in blue here:

I believe what is marked in light blue there is in fact the sorry remains of the original steel traverse between A and B.

In that interpretation the traverse that gives the illusion of being the original AB-traverse, is a loose traverse from uphill the roof structure further east, which has come to rest in this position - not quite incidentally, seeing that the trusses at both point A and B are kinked downwards, producing the nearest low resting position for it to come to rest in after having come loose. The high resolution photos looking in from the west also indicates that the traverse we see between A and B, may actually not be affixed to point A, but rather is resting close to and on top of it.

 

[RealWing]

New TEPCO media release:
http://www.tepco.co.jp/en/news/110311/images/110512_1.jpg"

- Does anybody knows how are those indicators works? Pressure difference, maybe?
- yeah, some more rods

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

 

[mscharisma]

TEPCO has responded that the photos from the previous time was steam from the spent fuel pools of reactor #3 and #4.

http://www.digtriad.com/news/national/article/174708/175/Japan-New-Smoke-At-Nuclear-Plant

The linked article here may also hold the answer/confirm what the memos/emails were about discussed here a few pages back.

"TEPCO also decided to open the reinforced door of the troubled No. 1 reactor building on Sunday, making way for engineers to work inside to stabilize it."
"We are trying to be as courteous as possible, so we will directly call our neighboring countries to let them know and the countries that are assisting us, such as the United States," Hosono told reporters at the joint news conference."

 

[jlduh]

In a BWR, there's plenty of room below the core to accommodate the control rods (which are as high as the core and are completely withdrawn during operation). Thus, if the core would melt, it would easily fit in the region below the core bottom plate.

Well you are right: the control rods are inside the RPV so the bottom of fuel rods must have been at a minimum 4m above the very bottom of RPV which is spherical, and in fact probably more so the peripheral rods can still enter 4m inside the core.

But on the other hand, we must add in the inventory of masses the mass of all the push rods mecanism (control rod drives = stainless steel?) as the core has been scrammed (control rods inserted).

Anyway, with a density of between 5 and 9 for the main materials, i think it is obvious that there must be enough room at the bottom to locate a fully melted core below the initial core position, or even 1m below it.

Assuming that the bottom of fuel rods was:

-> 5m above bottom of RPV, we get roughly (pi d2/4 * h) = 90 m3, one meter below gives 72m3,

and if I start with:

-> 4m above bottom of RPV, i get 72m2 and 54m3 one meter below.

So 58m3 is a possible number (even removing the volumes of the pushing rods but I don't know how big they are in dia?)

58 m3 with a density of 5 to 9 enables something like 290 to 522 tons of corium if fully liquid (lava) which is much more than we could imagine the inventory of molten material is (my guess is around 80/90 tons with the fuel assemblies, some plates, the control rods and their push rods and some other small stuff) . But this is assuming of course 100% liquid corium filling every space available, which can hardly be the case of course.

So based on what tepco said, it's possible that damaged core is still inside the RPV in an "undertermined" (but BAD) state.

 

[M. Bachmeier]

Please Note:

I understand that this thread is being monitored for political content, and I don't want to start sifting through soap boxes or diatribes, but the politics (corporate & nationalistic) are impacting directly on the effort to bring some scientific understanding.

I assert that political criticism, where it applies to the data and possible reasons for obfuscation, should have greater latitude in this thread with links to the more political thread for expression in detail. My reasoning is that the questionable political control of data flows is a legitimate reference when attempting to form hypothesis and speculation on substitute data.

I think it would make for a more concise presentation of hypothesis' if a persons primary reasoning were contained in the same block of statements. If another member wishes to argue they can state their primary objection with link to external thread (if needed) for more verbose communication. There's no mistaking that the politics have become a factor in the science of understanding and corrective action.

I have a second point...

Speculation:

The term 'unprecedented' seems wholly inadequate to describe these crisis' and the attempts to control them. I also believe this thread has enjoyed a greater latitude than nearly any other on this forum WRT speculation. I advocate even more speculation, provided unwarranted conclusions are not bandied about in that effort.

I've had ideas offered to me (while looking for a technical solution) by customers or friends that appeared to be utterly stupid (revealing their shear lack of technical understanding), only to realize that their ideas have lead to a completely new approach to the problem and the solution. "Brainstorming" is one thing I love about this thread and think it too needs more latitude from moderators and members alike.

I realize moderators have been working overtime to try and justly allow elements of political consideration and speculation, so I apologize for asking them to go further, but believe the asserted direction to be of value and the correct approach.

 

[Rive]

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

So, we have a reactor with probably a decent amount of solid salt, peppered with some debris and corium, boiled in unknown amount of water against an unknown reference pressure/level to calibrate some differential pressure sensor.

Bummer.

 

[pdObq]

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

Yes, I was also thinking that, how can they be sure their recalibration is correct...

And I don't understand, why they don't have a whole armada of specialized remote controlled robots like the KHG ones on site checking every corner of the buildings?

Maybe they don't want to know? I mean it really leaves the impression that they are not trying hard enough.

So, as to face wild hypothetical worst-case scenarios, if the one of the cores was on its way to "China" (in some sense taking care of its own long-term waste storage facility), would there be any easily detectable signs for that? How could one tell, apart from plausibility arguments based on reactor sensor readings, that it would not be happening?

 

[pdObq]

The linked article here may also hold the answer/confirm what the memos/emails were about discussed here a few pages back.

"TEPCO also decided to open the reinforced door of the troubled No. 1 reactor building on Sunday, making way for engineers to work inside to stabilize it."

Why can't they say more specifically which one they are talking about. The one of the refuelling tunnel/entrance on the SW corner? That would be most likely from their plan, I guess.

 

[clancy688]

Lets just get the facts straight, http://k.min.us/ikop60.JPG" that 200GJ of energy is required for a melt through we can then calculate using the formulas provided that the time for melt through is using Po=1380MW
0 minutes after shut down - 4hours
01 hours after shut down - 5 hours
02 days after shut down - 11 hours
30 days after shut down - 26 hours
60 days after shut down - 36 hours

So it is very unlikely that the core has melted through and is digging itself to the centre of the earth. We can forget that.

Reactors 2 and 3 Po=2380MW and the times will be proportionally less.

I don't think that "200 GJ" figure is about "melt through" but rather "melt down" - the energy needed to totally transform a normal core into corium. Failure of the RPV would be another issue.
And there is failure, otherwise it's unplausible as to where the water goes. They pump 6 tons water per hour, yet the water level is still 1 m below the fuel rods. There must be some kind of big leak at the very bottom of the core.

I've come across a very interesting Caltech presentation, here it is:

http://www.galcit.caltech.edu/~jeshep/fukushima/ShepherdFukushima30April2011.pdf

One thing to mention is that Unit 1 has, according to this source, a different passive emergency cooling system than Unit 2 and 3. Unit 1 has an "isolation condenser", which's using a water pool on the fuel loading deck as heat exchanger. Once the pool is boiled dry, cooling is gone. 2 and 3 are using an RCIC which's working with a steam turbine and the condensation chambers. Emergency cooling in Unit 2 and 3 was probably more effective than in Unit 1!

So, now we know that the water level sensor was "lying". We don't know when he began sending bogus data, but I think it probably happened when the readings got frozen. That would be 12/3, 15:28 ( http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/wlev-un1.txt ). The explosion was at 15:36. What a coincidence...
At 11:20, the core was uncovered 90 cm already. Seawater injection started with 2 tons per hour at 20:20. According to IAEA-TECDOC-955, you need around 20-15 tons/h to cool a 3000 MWt plant during days 1-10 after shut down. Unit 1 is half the size, let's make it 10-7. So, the water level gauge started malfunctioning at -1,7m and first seawater injection started five hours after this, but with not enough water.

On page 120 of the presentation I posted there's a paragraph about pressure vessel failure by molten core.
The time given for RPV penetration / rupture is 4-10 hours if the drywell is NOT flooded. And TEPCO told us today that it isn't.

So I think it's totally possible that during the time Unit 1 was not cooled or not cooled appropriate, the whole core could've molten down and failed the pressure vessel.

 

[maddog1964]

Please Note:

I understand that this thread is being monitored for political content, and I don't want to start sifting through soap boxes or diatribes, but the politics (corporate & nationalistic) are impacting directly on the effort to bring some scientific understanding.

I assert that political criticism, where it applies to the data and possible reasons for obfuscation, should have greater latitude in this thread with links to the more political thread for expression in detail. My reasoning is that the questionable political control of data flows is a legitimate reference when attempting to form hypothesis and speculation on substitute data.

I think it would make for a more concise presentation of hypothesis' if a persons primary reasoning were contained in the same block of statements. If another member wishes to argue they can state their primary objection with link to external thread (if needed) for more verbose communication. There's no mistaking that the politics have become a factor in the science of understanding and corrective action.

I have a second point...

Speculation:

The term 'unprecedented' seems wholly inadequate to describe these crisis' and the attempts to control them. I also believe this thread has enjoyed a greater latitude than nearly any other on this forum WRT speculation. I advocate even more speculation, provided unwarranted conclusions are not bandied about in that effort.

I've had ideas offered to me (while looking for a technical solution) by customers or friends that appeared to be utterly stupid (revealing their shear lack of technical understanding), only to realize that their ideas have lead to a completely new approach to the problem and the solution. "Brainstorming" is one thing I love about this thread and think it too needs more latitude from moderators and members alike.

I realize moderators have been working overtime to try and justly allow elements of political consideration and speculation, so I apologize for asking them to go further, but believe the asserted direction to be of value and the correct approach.

Thank You !

 

[mscharisma]

Cooling has been by spraying, by a flow. It has always been clear that water was disappearing.

Michio Ishikawa was right: http://ex-skf.blogspot.com/2011/04/fukushima-i-nuke-plant-ishikawa-of-jnti.html

Sorry to be so ignorant, but could someone please tell me what Ishikawa might mean by "building a bridgehead"? Many thanks.

 

[zapperzero]

So, as to face wild hypothetical worst-case scenarios, if the one of the cores was on its way to "China" (in some sense taking care of its own long-term waste storage facility), would there be any easily detectable signs for that? How could one tell, apart from plausibility arguments based on reactor sensor readings, that it would not be happening?

Chile, actually. Yes, you'd see either lots of black and gray smoke from burning soil and concrete or a huge steam explosion, possibly followed by same.

 

[jim hardy]

""So I think it's totally possible that during the time Unit 1 was not cooled or not cooled appropriate, the whole core could've molten down and failed the pressure vessel. ""

that requires that the pressure sensors were lying too, in the direction of high?

Which is not impossible, but speculative at this point? Their sense elements are built to measure hundreds of psi not just a few psi. I too am anxiously awaiting reports of their condition.

 

[rowmag]

So, as to face wild hypothetical worst-case scenarios, if the one of the cores was on its way to "China" (in some sense taking care of its own long-term waste storage facility), would there be any easily detectable signs for that? How could one tell, apart from plausibility arguments based on reactor sensor readings, that it would not be happening?

I wonder if flowing through holes in the RPV and landing in the containment vessel might not actually make the core easier to cool. Less "water entombment" depth in the containment vessel needed, for one thing...

Late-night thought.

 

[PietKuip]

Sorry to be so ignorant, but could someone please tell me what Ishikawa might mean by "building a bridgehead"? Many thanks.

Figurative speach, a war metaphor.

The first thing that is needed is "intelligence" (in war terms) - information about the status of the reactors. Two months after the tsunami, we still discover that the "enemy" has been capable of deception with regard to water levels etcetera.

 

[pdObq]

Oops, missed that. From the floor to the bittom of the crane support girders is 24 ft (7.3 m). The shroud would be light enough that the would use the secondary hook on the RB crane. Depending on the size of the lifting ring it might be close. There is also plenty of room on the refueling floor for a purpose built crane to do the lift if the RB crane is too low. The bottom of the roofing girders is about 40 feet above the floor (12.2 m).

NUCENG, thanks for your detailed answers. So, from what you wrote it seems most likely to me that they brought the core shroud in through the refueling tunnel/entrace. It seems to involve fewer complications to use the existing building features than to construct new openings in the building. Also, no such round hole in the roof can be seen in unit 4. Further, a square hole would probably have been easier to cut into the roof than a round one.

Follow-up question (just curious): Do we know what was the status of the core shroud replacement in unit 4?

Also, NUCENG, with all your inside knowledge, would you mind commenting on my question about why the SFPs in these type of BWRs are apparently not covered with concrete shield plugs during normal operation, which I had already brought up twice in this thread, but no one has picked up on it yet?

 

[clancy688]

that requires that the pressure sensors were lying too, in the direction of high?

They must have. Water in Unit 1 has been disappearing. TEPCO keeps pumping and pumping and today they discover that it's 1 m below the fuel bottom.
Either there are low lying leaks in both RPV and containment through which the water escapes and the pressure sensors are sending bogus data, or some kind of magic is letting that water disappear.
Water leak AND rising pressure together is impossible. But water leakage has been confirmed, so the pressure readings must be wrong.

 

[NUCENG]

Chile, actually. Yes, you'd see either lots of black and gray smoke from burning soil and concrete or a huge steam explosion, possibly followed by same.

First the corium needs to melt through the vessel lower head or cause failures in the CRDM penetrations. Then depending on how that happens the corium will melt through the drywell shell and start to interact with concrete. This will release significant amounts of carbon dioxide, carbon monoxide, hydrogen gas, and tellurium. The signature of corium concrete is significantly different from the previous releases. There may be steam explosions if there is sufficient water, but if the release from the vessel is in drips rather than a sudden significant release of liquid corium the steam release may not be explosive.

 

[SteveElbows]

Why can't they say more specifically which one they are talking about. The one of the refuelling tunnel/entrance on the SW corner? That would be most likely from their plan, I guess.

I read a press report that stated very specifically that this door was between the reactor building and the turbine building. Unfortunately I do not recall where I read it, but it seemed to make sense at the time.

 

[mscharisma]

Figurative speach, a war metaphor.

The first thing that is needed is "intelligence" (in war terms) - information about the status of the reactors. Two months after the tsunami, we still discover that the "enemy" has been capable of deception with regard to water levels etcetera.

I assumed that, but since I completely lack technical knowledge (although I'm learning thanks to everyone posting here), I wanted to make sure it's not a term referring to something technical. Many thanks.

 

[M. Bachmeier]

Thank You !

For what its worth, your welcome.

I've always felt that science is an evolving art in the process of understanding and sometimes a single incident can force that understanding to take large and uncomfortable leaps.

If you search this thread for the word "impossible", you might be surprised how many times the contextual assertion has been negated.

 

[pdObq]

I read a press report that stated very specifically that this door was between the reactor building and the turbine building. Unfortunately I do not recall where I read it, but it seemed to make sense at the time.

Yes, the door you are referring to was the "airlock" later called "double door" they opened during the May-8th-mystery-possible-readiation-release event. There was a pdf posted as an attachment by someone many posts back with quite detailed information on what TEPCO plans to do to get the cooling of unit 1 back to work. From that one could see that in a second step they will have to open the door in the SW corner, which they called "big equipment hatch" back then.

I guess one always has to double check what they are talking about or try to infer from the context.

 

[AntonL]

I don't think that "200 GJ" figure is about "melt through" but rather "melt down" - the energy needed to totally transform a normal core into corium. .

Thanks for that correction - I will edit the post accordingly.

 

[MadderDoc]

Chile, actually. Yes, you'd see either lots of black and gray smoke from burning soil and concrete or a huge steam explosion, possibly followed by same.

That sounds a bit like the history of unit 3.

 

[|Fred]

thx MadderDoc, I don't have time to finish that now.. but I'm in the process of doing this

[PLAIN]http://i.min.us/jlgANw.jpg

grr.. i got one color wrong.. on the right picture "the reconstructed thing..

 

[yakiniku]

Any sources of infos?

This link mentions 34 中性子計装管 "neutron instrumentation pipes". Sorry I don't know how to translate this properly and whether it is relevant to your calculations. Maybe someone can translate it better and shed more light on the relevancy.

http://headlines.yahoo.co.jp/hl?a=20110512-00001114-yom-sci

 

[pdObq]

First the corium needs to melt through the vessel lower head or cause failures in the CRDM penetrations. Then depending on how that happens the corium will melt through the drywell shell and start to interact with concrete. This will release significant amounts of carbon dioxide, carbon monoxide, hydrogen gas, and tellurium. The signature of corium concrete is significantly different from the previous releases. There may be steam explosions if there is sufficient water, but if the release from the vessel is in drips rather than a sudden significant release of liquid corium the steam release may not be explosive.

Thanks. In terms of the signature being different from current observations, do you mean different isotopes/nucleides of tellurium should be seen? Haven't there been some traces of tellurium seen in some samples a while ago? I guess the production of CO2, CO and H2 won't be a strong signature unless they measure the full make-up of the air around and inside the reactor buildings (not considering pressure created from that... high pressure readings despite water disappearing, hmmm...), so isotopes would be the strongest, clear signature?

 

[pdObq]

That sounds a bit like the history of unit 3.

Damn, you are right ... :

 

[NUCENG]

NUCENG, thanks for your detailed answers. So, from what you wrote it seems most likely to me that they brought the core shroud in through the refueling tunnel/entrace. It seems to involve fewer complications to use the existing building features than to construct new openings in the building. Also, no such round hole in the roof can be seen in unit 4. Further, a square hole would probably have been easier to cut into the roof than a round one.

Follow-up question (just curious): Do we know what was the status of the core shroud replacement in unit 4?

Also, NUCENG, with all your inside knowledge, would you mind commenting on my question about why the SFPs in these type of BWRs are apparently not covered with concrete shield plugs during normal operation, which I had already brought up twice in this thread, but no one has picked up on it yet?

I haven't seen any reports other than the reason they did a full core offload at Unit 4 was to support the shroud replacement. The reactor was shutdown in October so by March they could have had quite some time to offload the core and get started.

I will see what I can find about SFP design.

 

[Borek]

That sounds a bit like the history of unit 3.

From what I remember (early Astronuc posts) emissions of dust from corium melting through the concrete have easy to detect combination of isotopes, my understanding is this was not observed so far.