Fukushima: Unit 2 Discharge - Why Differs from Units 1 & 3?

[westfield]

<snip>

Anyway there is no really obvious pathway that I can think of for lots of this stuff getting into reactor 2 torus room, and plenty of other candidates for what the white stains are caused by.
<snip > .

I certainly wasn't suggesting that beige stuff they sprayed around could be in the torus room of RB2. You went there by yourself :)

In a sentence - I was wondering if there is something in the water tepco had used to cool everything (RB2 and the SFP of RB 4) that has precipitated out of the steam onto various surfaces leaving the whitish coating.

Edit: While I'm here, I apologise if I am doing to much thinking while I'm posting, all I can bring to this party is some years working as a fitter in the paper manufacturing and mining industries before I became a sound engineer. I'm looking for informed opinions which is why I love this forum.

 

[jim hardy]

So a question I have is - is there any likely substance in the water TEPCO used in the emergency that could leave the whitish deposits deposited via steam?

Perhaps Boric Acid , if it carried over .

It leaves a white coat. In quantity it looks like snow.

We sent them 17 tons of it early on.
http://www.vandenberg.af.mil/news/story.asp?id=123247390

 

[SteveElbows]

Was it a small leak from a valve\minor gasket in a flange or was it a massive failure of the torus? This is what I'm curious about in RB 2 ( along with the did it dry vent or not question)

Well the initial exploration into the torus room seems to have lead them to conclude that there was a really massive failure, which is why in subsequent stories we see them leaning more towards damage to the top of the drywell than anything to do with the s/c.

But of course some S/C damage is still well possible, its mostly the explosive scenarios which have faded at this stage.

In recent posts I have tried to focus on the idea that its the fact they couldn't wet vent a lot of substances before containment failed that made reactor 2 such an environmental polluter, rather than the location of the containment damage being the key factor.

 

[MadderDoc]

<..>
In a sentence - I was wondering if there is something in the water tepco had used to cool everything (RB2 and the SFP of RB 4) that has precipitated out of the steam onto various surfaces leaving the whitish coating.<..>

I can't think of any such thing.

I suggest the whitish coated area might coincide with upper facing surface areas of the torus which throughout events have been direct heat sources to the torus room atmosphere. That would be those areas of the torus outer surface which were left unflooded, unaffected by torus leaks, and happened to be close to the heat source(s) of the internal space of the torus.

Unlike the climate of the torus room generally (which must have been warm and humid) the climate at such areas of the torus wold have been hot and dry, favorable for deposition.

 

[SteveElbows]

http://www.tepco.co.jp/en/news/110311/images/110412_1f_tsunami_6.jpg (This is the earliest dated photo I know of showing steam coming from Unit 2.)

I was just looking again through the well-known chapter 4 of the government report to the IAEA. ( http://www.iaea.org/newscenter/focus/fukushima/japan-report/chapter-4.pdf )

On page IV-66 there is a table of events and it has the following entry which fits quite nicely:

8:25 White smoke (seemed to be steam) was observed near the fifth floor of the reactor building.

 

[MadderDoc]

I was just looking again through the well-known chapter 4 of the government report to the IAEA. ( http://www.iaea.org/newscenter/focus/fukushima/japan-report/chapter-4.pdf )

On page IV-66 there is a table of events and it has the following entry which fits quite nicely:

8:25 White smoke (seemed to be steam) was observed near the fifth floor of the reactor building.

Yes, that fits nicely to the photo of the steam taken half an hour later, at 08:59.


Looking otoh at the image taken an hour earlier, with exif time 07:33, there is no sign of steam coming from unit 2:

IMO, judging from the visibility and direction of the plumes from unit 3 and 4,
a plume from unit 2 of a magnitude as shown in the photograph from 08:59
would have also been visible in the photo above from 07:33, if it had been present.

So, what we have is: no visible steam emission present at 07:33, steam first observed/reported at 08:25, and, clearly visible steam evolution present at 08:59.

 

[clancy688]

http://www.tandfonline.com/doi/abs/10.1080/00223131.2012.669237#preview "A scenario of large amount of radioactive materials discharge to the air from the Unit 2 reactor in the Fukushima Daiichi NPP accident"

Unfortunately it's behind a paywall.

 

[NUCENG]

http://www.tandfonline.com/doi/abs/10.1080/00223131.2012.669237#preview "A scenario of large amount of radioactive materials discharge to the air from the Unit 2 reactor in the Fukushima Daiichi NPP accident"

Unfortunately it's behind a paywall.

Reading the summary, the author proposes a two stage release. First the suppression chamber (torus) fails due to either earthquake or hydrodynamic loads. This pathway is then open for release of the radioactivity being transported to the suppression chamber from the SRV valve operation.

The second stage is direct release from the drywell through failed electrical pentrations from high temperatures caused by corium outside the reactor vessel.

It sounds like he is assuming that the other units did not have the large early releases from the suppression pool and that explains the higher releases from unit 2. But that is based on reading only that first page.

 

[SteveElbows]

Yes I agree that is what it sounds like he is saying.

Certainly both TEPCO and NISA accident analysis results had a problem where they could not get the model to give the same results for drywell pressure in the first days of the crisis as the actual measured pressure values were. This is why we got stories in the press a long time ago about assumptions of drywell and wet well leaks of a certain diameter, its what they fed into their model in order to get results that more closely matches the measured values. A lack of actual measured suppression chamber pressure before late on the 14th makes it hard to determine the reality of a s/c leak, but there is drywell pressure data for the period.

However I don't know what difference this assumption actually makes to radioactive release. As I understand it they were extremely concerned about the state of S/C by the time they wanted to open the SRV, since the RCIC water source had been changed to the S/C on the 12th, and they had doubts about the S/C ability to deal with the steam from SRV. They weren't concerned about it already being damaged, but rather the possibility of it failing once they opened SRV. The interim committee report covers this well, since the manager of the plant on site had a different idea about priorities compared to someone from the government/ministry. Site manager wanted to focus on wet venting first, due to fear of big containment failure, government man wanted to just get on with reactor depressurisation as the top priority. I will point to the specific page this is discussed later.

Anyway my point is that from the point of view of radioactive release, does it make any difference if the suppression chamber fails early on, or not till during or after the SRV opening? As you know I have found myself moving in the direction of the failure to vent being the main problem that sets reactor 2 apart from the others. Either because a failure to vet vent stopped some of the worst substances from being scrubbed, or because of the pressure the drywell was under when it failed. I don't know if the suppression chamber breaking actually makes much difference to this equation really, its loss of suppression function and inability to vent it seem more significant than whether it failed. And it wouldn't be surprising to learn that reactor 3's suppression chamber may also have failed, yet the consequences there seem a little different (or they were as bad but wind direction made it easier to underestimate releases from 3).

Perhaps you can help me with a question. Given that they switched the source of water for RCIC to the suppression chamber on March 12th, if the suppression chamber was damaged at the time what impact might we expect this to have on RCIC? This is the only remaining line of enquiry I can follow with currently available data & observations when trying to work out of s/c got damaged early.

 

[zapperzero]

Steve, I have written this elsewhere as well. I think I just had a minor brainwave.
I have been obsessed with how there could have been a dry venting at #2. I thought maybe the torus was cracked and lost all/most of its water.

What if it's simpler? What if one of the steam downcomers got cracked, ABOVE the water level? What TEPCO thought was a wet venting may have been a dry venting!

The SRV opens, the downcomer fails comprehensively (where it was just cracked beforehand) and what was a trickle of radioactive steam becomes an outpour, that somehow (perhaps even through the hardened vent) goes out into the atmosphere?

 

[SteveElbows]

Well I think I know what you mean, but what I don't quite understand is your question 'how there could have been a dry venting at reactor 2'.

If there was no successful wet venting or dry venting at reactor 2, the high emissions and contamination can still be explained. We have no shortage of candidates for leaks in both the drywell and suppression chamber, or the links between the two.

So in many ways I don't think we are lacking all the pieces necessary to explain what happened, in fact we have too many pieces, we aren't sure which ones to rule out. I think the only thing we can rule out at this stage is an explosive event in the torus room that caused total devastation, but smaller events in that area are still well possible.

Certainly by the time they did the SRV release reactor 2 had been in a very bad state for hours, and they were very worried about the suppression chamber. The interim committee report makes it sound like part of the reason why they told the world that the explosive sound came from reactor 2 torus room area was because they were expecting trouble there.

I will post a timeline of some relevant events in a bit, as it may help when discussing this stuff.

 

[SteveElbows]

An attempt at a timeline which does not cover every reactor 2 event, but mostly ones which are relevant to recent discussions:

March 12th 04:20-05:00 RCIC water source changed, now uses suppression chamber water.

March 12th 12:00 This is about the time that TEPCO modelling of the accident assumes a small drywell leak in order that their model results more closely match the drywell pressures that were recorded. This also explains why we see preparations for venting in a moment, they were expecting greater containment pressure than actually happened.

I also have a note that says a government report assumes that steam flowed from the S/C to the D/W as a result of RCIC using suppression chamber as a source.

March 12th 15:00 PCV vent valve opened 25%
March 12th 17:30 Told to prepare for PCV venting
March 12th 19:10 Ordered to close PCV vent as there was a concern about hydrogen building up in pipes in the period before pressure was high enough for rupture disc to go.

March 13th 08:10 PCV vent valve opened 25%
March 13th 10:15 Order to complete vent line path (except rupture disc)
March 13th 11:00 PCV vent line complete but rupture disc pressure not reached
March 13th 15:18 Estimates of potential radioactive release in the event of venting sent by company to authorities.

March 14th 04:30 First S/C pressure measurement taken, 0.476 MPa abs.
March 14th 07:00 First S/C water temperature taken, 146 degrees C.
March 14th 12:00 Water level measurement in reactor vessel starts to fall from about now
March 14th 13:25 RCIC judged to have failed as the water level has been declining for a while.

OK after this point a lot happens and its too much for one post, and I need to double check my facts. As you can already see from the above part of the timeline, there are a few places where there are possible conflicts with the timing or order of events mentioned in different source documents, and it doesn't get any easier as we head into the crucial hours at reactor 2. There are a variety of vent and SRV operations going on at times when failure of RPV or S/C are also possible, and part of the reason I tried to make one timeline was to see if any co-incidences of timing stuck out. But it seems I need to give myself more time to fully absorb the timeline as its probably quite easy to make a mistake.

 

[zapperzero]

What I don't quite understand is your question 'how there could have been a dry venting at reactor 2'.

If there was no successful wet venting or dry venting at reactor 2, the high emissions and contamination can still be explained.

I have this notion that we should maybe think of the minimum necessary number of concurrent failures.

I like the idea of a small break in the steam downcomer (S/C side) because that vent path is the exact one intended by the operators - only it bypasses the water in the S/C.

 

[clancy688]

I like the idea of a small break in the steam downcomer (S/C side) because that vent path is the exact one intended by the operators - only it bypasses the water in the S/C.

That would also explain why the rupture disk didn't fail. But wouldn't the operators still notice a drop in reactor pressure during the intended vent?

 

[MadderDoc]

<..>
March 14th 13:25 RCIC judged to have failed as the water level has been declining for a while.

OK after this point a lot happens <..>

Yes, certainly. :-) Looking at the radiation level from the Main gate of the plant:

it demonstrates a major contamination event at about 21:30 on March the 14th, which brought the contamination at the main gate from the 0.01 mSv/h level to the 1 mSv/h level. Interestingly, this event tails into what appears to be a monotonous and rather swift decay phase, indicative that the deposited contamination included shortlived isotopes.

Then, in the morning hours of March 15th the down trend was interrupted by af further and even larger contamination event, which took the conditions at the main gate to the 10 mSv/h level. So, from the viewpoint of the main gate -- if unit 2 is to be considered a serious contender to the title of major culprit -- Unit 2 must necessarily claim responsibility for a major part of the massive contamination received at the main gate in the morning of March 15th.

 

[SteveElbows]

I have this notion that we should maybe think of the minimum necessary number of concurrent failures.

I like the idea of a small break in the steam downcomer (S/C side) because that vent path is the exact one intended by the operators - only it bypasses the water in the S/C.

We should also consider whether there was much water in the s/c by this point. It had been used as the RCIC water source for days by this point, and the temperature measured was well over 100 degrees C.

 

[SteveElbows]

That would also explain why the rupture disk didn't fail. But wouldn't the operators still notice a drop in reactor pressure during the intended vent?

We don't actually know whether the rupture disc failed or not, as discussed a few pages ago on this thread.

The failure to see substantial pressure drops seems to be the main reason why they doubt the success of various venting attempts.

I will be studying the pressure data again more closely soon, especially as there is an interesting blip much earlier on, a very temporary drop in drywell pressure that may coincide with the March 12th vent preparation.

 

[MadderDoc]

<..>there is an interesting blip much earlier on, a very temporary drop in drywall pressure that may coincide with the March 12th vent preparation.

In it's context the blip appears suspiciously outlier-ish, and I believe I've seen it explained by Tepco as being coincident with the run-down and change of a battery used for measurements.

 

[SteveElbows]

Yes, certainly. :-) Looking at the radiation level from the Main gate of the plant:

it demonstrates a major contamination event at about 21:30 on March the 14th, which brought the contamination at the main gate from the 0.01 mSv/h level to the 1 mSv/h level. Interestingly, this event tails into what appears to be a monotonous and rather swift decay phase, indicative that the deposited contamination included shortlived isotopes.

Im not quite ready to discuss this period in detail yet, but there are several events around this time which are of interest. My notes say that small S/C vent was temporarily opened at 21:00, 2 SRV opened at 21:20. There are not enough S/C pressure readings recorded at this point, but the S/C pressure measured at 22:50 is notably lower than it was at 04:30.

I'll ut this stuff into a more comprehensive timeline when I get the chance.

And we must remember to factor in the weather, since we know that on the evening of March 14th the wind direction changed so that stuff was no longer going out to sea.

 

[MadderDoc]

Im not quite ready to discuss this period in detail yet, but there are several events around this time which are of interest. My notes say that small S/C vent was temporarily opened at 21:00, 2 SRV opened at 21:20. There are not enough S/C pressure readings recorded at this point, but the S/C pressure measured at 22:50 is notably lower than it was at 04:30.

I'll ut this stuff into a more comprehensive timeline when I get the chance.

And we must remember to factor in the weather, since we know that on the evening of March 14th the wind direction changed so that stuff was no longer going out to sea.

The period before the evening of March 14th would seem irrelevant. Unit 2 can't claim to have vented large amounts of radioactivity, hidden by going seawards, during the period preceding its experiencing fuel damage.

 

[SteveElbows]

The period before the evening of March 14th would seem irrelevant. Unit 2 can't claim to have vented large amounts of radioactivity, hidden by going seawards, during the period preceding it's experiencing fuel damage.

True but there are other reactors to consider, and some hours before 21:30 to think about too.

I do expect that dramatic events that were occurring at that time had a big influence on the site monitoring point, but I still have to include wind direction when analysing the data for clues about precise timing of events.

Anyway I am closer to talking about this period in detail, but first I will just go back to cover the earlier pressure blip.

In my timeline of earlier events, I have the following sequence of events on the 13th from reports:

March 13th 08:10 PCV vent valve opened 25%
March 13th 10:15 Order to complete vent line path (except rupture disc)
March 13th 11:00 PCV vent line complete but rupture disc pressure not reached

If I look at reactor & drywell pressure measurements from this date I see the following:

05:30-09:25 reactor pressure falls slightly from 6.14 to 6.08
09:55 reactor pressure now measured as being 1.283
15:30 reactor pressure back up to 5.85

05:30-09:25 D/W pressure rises slightly from 0.33 to 0.365
09:55 D/W pressure now 0.16
10:30 D/W pressure now 0.1
10:35 D/W pressure now 0.01
11:35 D/W pressure back up to 0.38
15:30 D/W pressure 0.4

This could be some problem with the measurements or the recording of them, but as there is some overlap between these readings and vent preparation I thought I should mention them before moving on to the more interesting periods of 14th & 15th March.

 

[MadderDoc]

True but there are other reactors to consider, and some hours before 21:30 to think about too.

I do expect that dramatic events that were occurring at that time had a big influence on the site monitoring point, but I still have to include wind direction when analysing the data for clues about precise timing of events.

Anyway I am closer to talking about this period in detail, but first I will just go back to cover the earlier pressure blip.

In my timeline of earlier events, I have the following sequence of events on the 13th from reports:

March 13th 08:10 PCV vent valve opened 25%
March 13th 10:15 Order to complete vent line path (except rupture disc)
March 13th 11:00 PCV vent line complete but rupture disc pressure not reached

If I look at reactor & drywell pressure measurements from this date I see the following:

05:30-09:25 reactor pressure falls slightly from 6.14 to 6.08
09:55 reactor pressure now measured as being 1.283
15:30 reactor pressure back up to 5.85

05:30-09:25 D/W pressure rises slightly from 0.33 to 0.365
09:55 D/W pressure now 0.16
10:30 D/W pressure now 0.1
10:35 D/W pressure now 0.01
11:35 D/W pressure back up to 0.38
15:30 D/W pressure 0.4

This could be some problem with the measurements or the recording of them, but as there is some overlap between these readings and vent preparation I thought I should mention them before moving on to the more interesting periods of 14th & 15th March.

All right. Here is a plot of the doserate measurements on March 13th. Note: log scale.

General caveat: there is little to no data published from monitoring posts north of the reactors until about 8 am on March 13th.

This lack of data is particularly a pity here, since the wind in the morning of March 13th appears to have come mainly from the south. However, the earliest data from northern posts we have do seem to indicate a relatively recent additional deposition in the morning hours up to about 8 am. There could be a window of opportunity here for some reactor or other to make claims.

However, after 8 am, during the morning of March 13th, Unit 3 might have been the major player involved in the observed raising of doserate: there is operation record of venting in unit 3 about 9 am, and satellite photo, and webcam evidence, show emission from its stack at 9:50 and10:00 respectively.

Similarly, during the afternoon, the webcam shows emission from the unit 3+4 stack at 13:00 and at 14:00. Unit 3 could reasonably claim responsibility for any incremental contamination seen at monitoring posts during this period.

 

[tsutsuji]

Reading the summary, the author proposes a two stage release. First the suppression chamber (torus) fails due to either earthquake or hydrodynamic loads. This pathway is then open for release of the radioactivity being transported to the suppression chamber from the SRV valve operation.

The second stage is direct release from the drywell through failed electrical pentrations from high temperatures caused by corium outside the reactor vessel.

It sounds like he is assuming that the other units did not have the large early releases from the suppression pool and that explains the higher releases from unit 2. But that is based on reading only that first page.

http://mainichi.jp/select/jiken/news/20120403ddm016040021000c.html Eastern Japan mega seismic disaster: Fukushima Daiichi NPP accident: Was unit 2's PCV damaged by the earthquake?

Among the discussions about Tokyo Electric Fukushima Daiichi nuclear power plant accident, there is a controversy regarding whether unit 2's PCV was broken by the earthquake. Large amounts of radioactive substances were released from unit 2 in the morning of the 5th day of the accident, the 15 March of last year, and there is a high probability that Earth contamination spread wider to Iitate village, Fukushima prefecture and other places. Elucidation of causes is crucial to recurrence prevention. We present the discussion that took place last month at the Japan Atomic Society meeting in Fukui.

(...)

However, in December of last year, Tokyo Electric revised its position, saying that the seismometer data generated at the same time as the damage came from unit 4's hydrogen explosion. Concerning the suppression chamber's pressure gauge, it judged that "there is a high probability that it is broken". It inferred that radioactive substances leaked after part of the PCV top part, whose resistance to high temperatures is weak, was damaged. Actually, the PCV pressure, which was 7.3 atmospheres at 7:20 AM on 15 March declined to 1.5 atmospheres in 4 hours' time. Plant premises surrounding radiations also rose.

In contrast with this, former JAEA senior chief researcher Fumiya Tanabe (66) insists that "there is a phenomenon which cannot be explained solely [1] by the melting of the junction parts in the PCV top part". This phenomenon is that, after the core melt down after 01:00 AM on 15 March and during the 5 hours that ensued, in consequence of the fuel that melted and fell from the RPV to the PCV, while the radiation dose rose by a factor of 2.1, the suppression chamber's radiation dose, conversely, declined by 40%.

This is where Mr Tanabe explains: "If one assumes that the suppression chamber was damaged by the earthquake, it is possible to explain the reason why the suppression chamber radiation declined". As water is contained in the suppression chamber, it is difficult for the suppression chamber to reach high temperatures, and to suffer damage by melting, he says.

About the status of the suppression chamber, Tepco says "minimal damage might have taken place, but if it had suffered major damage it would not have been able to maintain a 7.3 amosphere pressure".

[1] Edit: I had forgotten to translate this one word : "solely".

 

[MadderDoc]

<..> after the core melt down after 01:00 AM on 15 March and during the 5 hours that ensued, in consequence of the fuel that melted and fell from the RPV to the PCV, while the radiation dose rose by a factor of 2.1, the suppression chamber's radiation dose, conversely, declined by 40%.

<..>

I didn't think that is a mystery, but is it? What I thought is that while the fuel melted down, RPV was loosing pressure, so the safety relief valve naturally stopped transporting radioactivity to the suppression chamber, and the natural decay of shortlived isotopes took over . But the RPV of course kept leaking to the PCV only more than ever.

 

[SteveElbows]

However, after 8 am, during the morning of March 13th, Unit 3 might have been the major player involved in the observed raising of doserate: there is operation record of venting in unit 3 about 9 am, and satellite photo, and webcam evidence, show emission from its stack at 9:50 and10:00 respectively.

Similarly, during the afternoon, the webcam shows emission from the unit 3+4 stack at 13:00 and at 14:00. Unit 3 could reasonably claim responsibility for any incremental contamination seen at monitoring posts during this period.

I agree, I mention the pre March 14th stuff in regard to reactor 2 only because there are a couple of questions about possible damage well before it melted-down, but I wouldn't expect any notable radioactive emissions from reactor 2 during this period.

But as its more than a year since the disaster I think any time we want to refresh our understanding of events it is worth discussing detail, even if it doesn't turn out to be directly relevant.

 

[SteveElbows]

In contrast with this, former JAEA senior chief researcher Fumiya Tanabe (66) insists that "there is a phenomenon which cannot be explained by the melting of the junction parts in the PCV top part". This phenomenon is that, after the core melt down after 01:00 AM on 15 March and during the 5 hours that ensued, in consequence of the fuel that melted and fell from the RPV to the PCV, while the radiation dose rose by a factor of 2.1, the suppression chamber's radiation dose, conversely, declined by 40%.

This is where Mr Tanabe explains: "If one assumes that the suppression chamber was damaged by the earthquake, it is possible to explain the reason why the suppression chamber radiation declined". As water is contained in the suppression chamber, it is difficult for the suppression chamber to reach high temperatures, and to suffer damage by melting, he says. .

Interesting stuff. I am not sure that I think very much of this analysis though.

Firstly I don't think that possible evidence of suppression chamber leaking between 1am and 6am is evidence that damage must have happened during the earthquake. e.g. the suppression chamber may have been damaged at 9.20PM on the 14th, or midnight, or some other time well after the earthquake but before 6am on the 15th.

I don't quite understand his point about suppression chamber water and damage by melting. They had been using the suppression chamber as water source for RCIC for several days, which is going to affect conditions of the suppression chamber, amount of water etc. And melting is not the mode of failure that we often think of for the suppression chamber anyway (rather over pressure, hydrogen burn, or forces caused by steam) although from the article I can't quite tell what sort of melting he means (melting of chamber itself or melting of seals etc).

I don't know enough about CAMS readings to say how useful they are in a severe accident. I am sure this is the data he refers to when taking about a rising trend in the drywell but falling radiation trend in suppression chamber. But if he wants to use CAMS as a guide, I don't know why he picks 1am as a start time. Because actually the CAMS D/W readings are first recorded as being rather high earlier, at 21:55 on the 14th its recorded as 5.36 Sv/h. By 23:54 the D/W CAMS has reached 24.5 Sv/h, and when it is next measured at 01:18 15th its risen higher but not a huge leap, 28.88 Sv/h. Its actually the pressure readings of the reactor that could point to a significant failure around 1am, not the CAMS, so either his timing is wrong or CAMS is actually not a good guide to explain events on this level.

But perhaps lower S/C CAMS readings at reactor 2 do mean something, as you can tell I do not place too much faith in CAMS measurements as being able to tell the whole story, but if the S/C CAMS at reactors 1 & 3 were far more consistent with the D/W CAMS at those reactors, then this is a difference that should be noted I guess. But it certainly doesn't help that in these first days the CAMS readings have some gaps where measurements were not recorded, and also only 1 D/W and one S/C reading are recorded, rather than both A & B sensors.

 

[SteveElbows]

An additional area of doubt regarding S/C CAMS comes from the fact that when they finally started reporting & publishing data from the S/C CAMS B sensor on April 15th 2011, it was very much higher than the A sensor they had been recording for the prior month. But the values of this CAMS S/C B sensor fluctuate quite a lot, so its not clear if it is faulty. It still leaps up sometimes to this day, I think it has been higher again for weeks, but I cannot take this data very seriously.

 

[SteveElbows]

I checked the CAMS data for the other reactors and unfortunately they did not start receiving CAMS data soon enough for us to see any trends during the initial melting events at those reactors. Reactor 3 data shows much higher levels for D/W CAMS than S/C CAMS. At reactor one the S/C CAMS reading is lower than the D/W CAMS but not by very much order of magnitude, much less difference than at reactors 2 & 3.

Anyway for now I will only safely assume that CAMS is good for alerting you to fuel damage, but perhaps not much else.

 

[MadderDoc]

<..> for now I will only safely assume that CAMS is good for alerting you to fuel damage, but perhaps not much else.

CAMS is designed for normal as well as post-accident _monitoring_ of gamma radiation, it is certainly meant to yield quantitative measurements, not just a binary yes/no answer to the question whether there is fuel damage. The uncertainty of CAMS data should be reflected by the number of significant digits given. Assuming invalidity of such data is a serious matter and one must have specific reasons to do so. In the case of the CAMS readings from unit 2 in the period we are talking about there are afaics no such reasons.

 

[SteveElbows]

OK well they used CAMS data to estimate fuel damage ratio and only time will tell if these estimates are any good. At this stage all we can say is that some people will accuse these estimates of being part of the 'much too positive' spin from the company, but I cannot judge what the reality is. The damage ratios sound a bit low given the estimates about meltdown we have seen since. Obviously this is old data and I mention it now only in connection with the way this particular discussion has evolved.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e19.pdf

The graphs in that document are another good visualisation of what I was saying about reactor 3 S/C CAMS being low too. And reactor 1 isn't exactly seeing huge numbers in the S/C.

I am left assuming that the analysis I questioned is using only the differing trends of D/W and S/C CAMS at a key moment to make a point, rather than the difference in magnitude of D/W and SC measured levels, and that it is to be expected that S/C levels will be lower than D/W ones? In this case the lack of measurements during crucial times for reactors 1 & 3 make it impossible to look for similar or dissimilar patterns at the other reactors, making it harder for me to evaluate the plausibility of his argument.