Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[clancy688]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111013/0500_kunren.html The drill assumed that tanks and pumps had been broken by an earthquake. 40 people installed fire trucks and 300 m of hoses, so that cooling was restored to one reactor in 1 hour 10 minutes. In the future Tepco will perform other drills assuming a tsunami with debris spread on roads, and occurrences at times when gathering people is more difficult, such as on holidays and during the night.

So if I understand everything correct, they are installing an auxiliary cooling system from mobile devices which doesn't use any plant hardware (except the reactor internal pipes of course).

Just wondering, now that we know that there are probable station blackout scenarios which may lead to major accidents, especially with older plants, wouldn't it be a wise idea to employ such mobile hardware throughout the world near older plants with similar designs and design faults like Fukushima?
If there would've been such a, how should we call it, "emergency cooling restoration team", close to Fukushima I, they probably still wouldn't have been able to save Unit 1, but there should've been enough time for such a team to restore cooling functions on Units 2 and 3.

At least I'd consider it as pretty awkward if there'd be a similar SBO ten years or so in the future and the whole world has to helplessly watch a reactor popping again because nobody thought of bunkering a couple of mobile pumps and hoses... Just a little example from Germany again (yeah, I like examples...):
We have a pretty decent highspeed railway system and throughout the whole network there are some big tunnels. So what happens if a train crashes inside a 10 km long tunnel? How the hell are the rescue workers supposed to arrive on scene? Walking?
So there are a six special tunnel rescue trains on call throughout Germany. They are specifically engineered for that task and they are always on readiness for duty, they can respond to the scene within five minutes after alert.

 

[Most Curious]

"Down for maintenance" and "failed" are two very different things. Media has an agenda and truth is not counted for much with them.

Failure to maintain is a guarantee of failure in the future! Agreed it is a little problematic when 1 unit of 3 or 4 is on scheduled maintenance when an emergency arrises and then one of the remaining units fails. Of course, that is why there are 4 units to provide power when only one needs to work to accomplish the task.


A requirement to shut down any plant at 35 while not building new ones to replace them is a receipe for blackouts. If we want power, we MUST build new plants whether nuclear, coal or other fuel. The "pie in the sky" renewables and over reliance on conservation will NOT get the job done, no matter HOW MUCH the "green weenies" and anti everythings WANT it to be so.

Everything has risk, particularly doing nothing. I for one have no desire to cook over an open fire while freezing in the dark! That being said, I recognize much is to be learned from the Japanese disaster and hopefully that new knowledge will be used to improve American facilities. No doubt there are weak spots in US systems that MUST be addressed but in a calm, well engineered manner. To be sure, no plant owner want to see his investment destroyed by an accident that could have been prevented. Much of Japan's problem originated in government, just as ours does. What we do NOT need is the environmental whackos meddling in engineering matters they poorly understand and have no desire to learn - that has contributed to major problems in siting, delays and blocking of needed facilities. Those needed NEW facilities could have allowed retirement of OLD facilities sooner. Place the blame where it properly belongs!

 

[clancy688]

A requirement to shut down any plant at 35 while not building new ones to replace them is a receipe for blackouts. If we want power, we MUST build new plants whether nuclear, coal or other fuel. The "pie in the sky" renewables and over reliance on conservation will NOT get the job done, no matter HOW MUCH the "green weenies" and anti everythings WANT it to be so.

Just for the protocol:

We (Germany) shut down our eight oldest nuclear plants immediately after 3/11. http://www.spiegel.de/images/image-204764-galleryV9-xxmj.jpg" what happened.
We basically only lost the power we would've exported anyway. Some time later, in May, there were 13 out of 17 nuclear plants total out of action (because of maintenance and the moratorium). All plant operators began warning of possible blackouts. And again exactly nothing happened.
I can't speak for other countries. But at least Germany has absolutely nothing to fear from abolishing nuclear power. We have the capacity to compensate. Even now. And there are many new conventional plants under construction.

 

[WhoWee]

Just for the protocol:

We (Germany) shut down our eight oldest nuclear plants immediately after 3/11. http://www.spiegel.de/images/image-204764-galleryV9-xxmj.jpg" what happened.
We basically only lost the power we would've exported anyway. Some time later, in May, there were 13 out of 17 nuclear plants total out of action (because of maintenance and the moratorium). All plant operators began warning of possible blackouts. And again exactly nothing happened.
I can't speak for other countries. But at least Germany has absolutely nothing to fear from abolishing nuclear power. We have the capacity to compensate. Even now. And there are many new conventional plants under construction.

If the plants are viable - wouldn't it be better to operate?

 

[NUCENG]

Not the first time I've said it, but its (way past) time to decommission all NPPs that over ~35 years old. More 'unforseen' events WILL occur, a combination of time, luck, human error and chaos theory will ensure it.

Also,

4 generator failures hit US nuclear plants [AP] http://www.guardian.co.uk/world/feedarticle/9886829

The information in that article quotation about Browns Ferry is incorrect or misleading. I was unable to retrieve the original article, but assume that the quote was accurate.

The event report of the severe weather event at Browns Ferry is available at: http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2011/20110428en.html

The preliminary Notification of Event or Unusual Occurrence is available at:
http://pbadupws.nrc.gov/docs/ML1111/ML111180005.pdf

On initial demand seven of eight emergency diesel generators started and carried load as designed. One EDG was out of service for maintenance. One offsite 161 kV source remained available. The following day the three reactors were in cold shutdown.

One diesel developed an oil leak on its governor and was declared inoperable. But it was still considered available, meaning that it could be started and carry loads under manual control. See:
http://pbadupws.nrc.gov/docs/ML1111/ML111190004.pdf
http://pbadupws.nrc.gov/docs/ML1111/ML111180005.pdf
http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2011/20110502en.html

About 4-5 days after the storm a diesel generator output breaker tripped causing a short power loss. The trip was a result of a false sensed diesel overspeed condition.

Additional details of the event can be found in Licensee Event Reports available through the NRC ADAMS web based document system under accession numbers:
ML11188A154
ML11180A007
ML11180A267
ML11180A056

Bottom line - plant safety functions were successful. If your expectation is a zero failure rate, that is not how the defense in depth principle works.

 

[cockpitvisit]

We basically only lost the power we would've exported anyway. Some time later, in May, there were 13 out of 17 nuclear plants total out of action (because of maintenance and the moratorium). All plant operators began warning of possible blackouts. And again exactly nothing happened.

What happened ist that instead of exporting power, Germany started importing it from neighboring countries (mostly France) during peak demand times. I doubt the same is possible in the US, since a neighboring country with a huge supply of energy would be required.

Abolishing nuclear power by constructing more conventional nuclear plants is of course possible, at the cost of a higher CO2 output and higher pollution.

 

[nikkkom]

No, I cannot speak for all countries. But I can speak from experience in the US. If you can't do the same then perhaps your opinion may be just that - opinion, and uninformed at that.

Proposing a fix that works is good, but I have explained why that fix may not be what you are asking for. Instead of discussing the reasoning I provide you imply that I am justifying doing nothing. Nothing could be further from the truth. I agreed with the concept of some external response teams to support emergency response in my initial response. But I am convinced that your more expansive red team needs a lot more discussion.

For the third time - it's not *me* who proposed red team to replace station personnel, it was zapperzero who said that. I told you twice that I propose red team to *augment* station personnel. Maybe with authority to order disaster prevention measures even it they damage the plant - regular station personnel may be hesitant to do that because management will be unhappy with the resulting losses, with repercussions to careers of those who caused them.

So if you will stop dismissing my motives

What motives? I did not talk about your motives at all. I just asked what do you propose, apart from crossing fingers and believing that station personnel in US is better than in Japan.

we can carry on a reasonable discussion including venting capabilities.

Please do. What's the status of venting capabilities at US plants?

IIRC vents were reinforced sometime ago to be more resistant to seismic damage and such, so at least venting will not pour hundreds of tons of 200+ Celsius hot steam through the cracks in the piping into the reactor building, which is a good thing to know.

But do they have any meaningful scrubbers? Simple answer, "yes" or "no"? In F1 there were no scrubbers.

 

[clancy688]

Abolishing nuclear power by constructing more conventional nuclear plants is of course possible, at the cost of a higher CO2 output and higher pollution.

I basically had the same discussion with NUCENG months ago. Since this is going offtopic, I'll just link you to it.

https://www.physicsforums.com/showpost.php?p=3357626&postcount=176

 

[Bodge]

Replace the old plants with passively cooled Generation III designs, invest in the Thorium fuel cycle, triple investment in solar and fusion research.

The risks of running the old plants is an increased cancer burden for the world.

 

[tsutsuji]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111015_04-e.pdf Infrared pictures of top parts of unit 1 and unit 3

 

[tsutsuji]

http://www.jnes.go.jp/jyohou/kouhyo/kaiseki_published.html The analysis documents released by JNES

http://www.jnes.go.jp/content/000119660.pdf Analysis of criticality safety of metal casks: in order to find out how the humidity inside casks can bring criticality, an analysis was made based on constant assumptions. It was found that criticality is not reached even if there is humidity, etc.

http://www.jnes.go.jp/content/000119661.pdf Causes of 15 March unit 4 explosion/blaze: At unit 4 it is possible that fuel pool water declined, spent fuel was exposed, hydrogen was produced from a reaction between steam and fuel cladding tubes and exploded. Adding water in pools and cooling is also needed at other units.

http://www.jnes.go.jp/content/000119662.pdf Radioactivity of the spent fuel pool releases: Two sets of hypothesis were used to calculate conservative estimates of the spent fuel pool releases.

http://www.jnes.go.jp/content/000119663.pdf What happens if the present water injection at units 1,2,3 stops: Analysis of the time taken for fuel exposure, RPV damage, PCV damage under a set of hypothesis such as being 144 hours after reactor shutdown.

http://www.jnes.go.jp/content/000119664.pdf Reactivity effects of injecting seawater into spent fuel pools: Even if only seawater is injected, 600 ppm borated water is effective, as it can reduce reactivity by about one half.

http://www.jnes.go.jp/content/000119665.pdf Reactivity control by injecting boron or seawater in storage pools: a major criticality control effect is obtained when seawater or boron is injected in spent fuel pools.

http://www.jnes.go.jp/content/000119666.pdf INES level based on fuel damage proportion: Inferring from the fuel damage proportion, INES level 5 is estimated. An estimate of the proportion of Zr reaction needed for hydrogen explosion is found for each unit.

http://www.jnes.go.jp/content/000119667.pdf Whether criticality can occur with the mist produced at unit 4 SFP. If the racks are lost, criticality is possible.

http://www.jnes.go.jp/content/000119668.pdf Boric acid quantities needed for recriticality prevention: Using the most severe hypothesis, the quantity of boric acid needed to maintain subcriticality is 18.3 tons.

http://www.jnes.go.jp/content/000119669.pdf Risk assessment of cooling methods at units 1,2,3: Assessment of hydrogen explosion risk, steam explosion risk, salt damage risk encountered in plant cooling operations.

http://www.jnes.go.jp/content/000119671.pdf Temperature rise in spent fuel pools (water-zirconium reaction): temperature behavior of fuel in steam atmosphere when water level declines in the perspective of fuel meltdown.

http://www.jnes.go.jp/content/000119672.pdf Quantities of salt deposits in unit 2: assesment of salt deposits caused by seawater injections. As the salt concentration for saturation is not reached, there is no salt deposit.

http://www.jnes.go.jp/content/000119673.pdf Estimate of Fukushima Daiichi radiation releases. Based on remote monitoring values, the releases are reverse calculated using a simple model.

http://www.jnes.go.jp/content/000119683.pdf Unit 1 leakage area estimate (about the conditions on the morning of 12 March before the wet well vent and hydrogen explosion): As the reactor water level is declining, because the RPV pressure is not increasing, it is thought that all the generated steam is leaking and the leak's area is estimated.

http://www.jnes.go.jp/content/000119682.pdf Quantities of salt deposits in unit 2 (revised version): Estimate of the salt deposit quantities resulting of seawater injection. With a 410 l/min water injection rate, it is thought that there is enough margin, and salt deposits are not created.

http://www.jnes.go.jp/content/000119681.pdf Estimate of radiation from drywell vent pipe and temporary pit at units 1,2,3: Estimates of dose rates from temporary pit, from drywell venting pipe, and in the flowing water.

http://www.jnes.go.jp/content/000119681.pdf CCI study: Judging from the situation at the plant until now, the melted fuel has fallen little by little. The heat flux of crust dryout exceeds decay heat, so that the solidification of melted objects occurs.

http://www.jnes.go.jp/content/000119679.pdf study of criticality of unit 4 fuel pool: assessment of criticality after the fuel assemblies are damaged, the fuel rod pellets fall to the bottom and are spread or form compact bodies. In a very conservative assessment, criticality is possible, but with a realistic credit (U235x07), even if the pellets fall down criticality does not occur.

http://www.jnes.go.jp/content/000119678.pdf Answer about the Evacuation prepared zone (EPZ) if the release quantity is changed from one to three reactor cores. Taking into account the external radiation dose of the whole body, the EPZ is extended by about 19 km. If the thyroid equivalent dose of children is taken into account, the EPZ is extented by about 16 km.

http://www.jnes.go.jp/content/000119677.pdf conversion of unit 3 PCV releases (permeability). The release (permeability) is calculated with a simple Bernouilli equation, without taking critical flow into account.

http://www.jnes.go.jp/content/000119676.pdf Answer about the Evacuation prepared zone (EPZ) if the release quantity is changed from one reactor core to two or two and a half reactor cores. With two and a half reactor cores, taking into account the external exposure of the whole body, the EPZ is extended by 15 km. Taking into account children equivalent thyroid doses, it is extended by 12 km. With 2 reactor cores the EPZ is extended respectively by 11 and 8 km.

http://www.jnes.go.jp/content/000119675.pdf Answer about the concentrations of core materials in the suppression pool (boron, cesium). concentrations of core materials in the suppression pool (boron, cesium) in a scenario of damage by excess of temperature.

http://www.jnes.go.jp/content/000119674.pdf possibility of PCV damage caused by hydrogen explosion. Even if explosion occurs, the design maximum pressure of reactor vessel is high and the resistance to pressure is sufficient. A break of the top part of the reactor vessel causing PCV damage is not thought to be possible.

http://www.jnes.go.jp/content/000119684.pdf radiation releases caused by unit 1 venting. If venting is performed in the future, the added release into the atmosphere is thought to be small.

http://www.jnes.go.jp/content/000119685.pdf assessment of hydrogen and oxygen concentrations at unit 1: Using conservative hypothesis, oxygen concentration is 2.1% and the combustion limit of 7% in steam atmosphere is not exceeded.

http://www.jnes.go.jp/content/000119686.pdf core-concrete reaction (MCCI) possibility and consequences: assessment of progression possibility of core-concrete reaction (MCCI) and concrete erosion consequences.

http://www.jnes.go.jp/content/000119687.pdf Answer to NRC recommend. (MELCOR analysis results in case of loss of all AC power): Past results of MELCOR analysis in case of loss of all AC power). Estimates of the time it takes for RPV and PCV damage in cas of loss of all AC power.

http://www.jnes.go.jp/content/000119688.pdf confirmation of the presence or absence of core recriticality: Study of the causes of neutron measurement data above the detection level revealed at Fukushima Daiichi monitoring points.

http://www.jnes.go.jp/content/000119689.pdf About the neutron leak at unit 4 storing pool: From 14 March to 15 March, neutron measurement data above detection level have been revealed at the Fukushima Daiichi monitoring points. Study of the causes of these measurements.

http://www.jnes.go.jp/content/000119690.pdf Comment about Tepco document "countermeasures against leaks during the storage of highy radioactive water in the concentrated waste tratment facility buildings". Comment about Tepco's assessment of cesium diffusion. That assessment is nearly valid.

http://www.jnes.go.jp/content/000119691.pdf Forecast of radiation doses in each area and at at each time, based on an analysis of the real measured values. In order to understand radiation exposure consequences before a monitoring system is secured, estimates are given for each area from 14 March to 18 March.

http://www.jnes.go.jp/content/000119692.pdf recriticality prevention at unit 1 during the shift to closed loop cooling: Based on the survey results obtained after the Three Mile Island accident, recriticality is analysed assuming the debris are in a conic shape and surrounded by borated water.

http://www.jnes.go.jp/content/000119693.pdf forecast of radioactive substances released from Fukushima Daiichi: calculated estimate of fission products from unit 1. Presentation of needed data for fission products in other units.

http://www.jnes.go.jp/content/000119694.pdf quantity of gaseous iodine releases at Fukushima Daiichi. Calculation using reference books of gaseous iodine releases from unit 1 polluted water to the gaseous part of the building.

http://www.jnes.go.jp/content/000119695.pdf About the validity of the operator's assessment of the improvement of working environment at unit 2: confirmation of the validity of the operator's assessment, using a calculation of the radioactive substances' concentrations in the air in the plant premises.

http://www.jnes.go.jp/content/000119699.pdf Possibility of hydrogen explosions at units 2 and 3. Study of possibility of hydrogen explosion occurrence if reactor cooling is not carried out, and if reactor cooling is carried out.

http://www.jnes.go.jp/content/000119698.pdf Time it takes for meltdown at unit 4 fuel pool: Calculation of the time taken until meltdown, for the fuel with the highest decay heat, based on real heat insulation conditions.

http://www.jnes.go.jp/content/000119697.pdf Study of earthquake safety of unit 4 reactor building in the present conditions. Study intended at confirming the validity of the operator's assessment of earthquake safety in the present conditions of the building, assuming the greatest aftershock of the present earthquake.

http://www.jnes.go.jp/content/000119696.pdf Study of earthquake safety of unit 3 reactor building in the present conditions. Study intended at confirming the validity of the operator's assessment of earthquake safety in the present conditions of the building, assuming the greatest aftershock of the present earthquake.

 

[Shinjukusam]

Tsutsuji, that is an incredible amount of information, once again we are in your debt.

 

[etudiant]

http://www.jnes.go.jp/content/000119660.pdf Analysis of criticality safety of metal casks: in order to find out how the humidity inside casks can bring criticality, an analysis was made based on constant assumptions. It was found that criticality is not reached even if there is humidity, etc.


This represents a mountain of work.
It is just stunning that all this industriousness is so wasted, analyzing what went wrong rather than working to minimize the impact on the Japanese people.
The technicians are certainly performing well, it seems the problems are in the executive suite. For instance, the management of contamination beyond the 50km radius as well as the policies on foodstuff safety just seem entirely ad hoc, with no overall leadership or direction.
Is individual leadership a la Soichiro Honda or Akio Morita such a rare commodity in Japanese politics?

 

[Bodge]

A document was given to the press in June, which included estimates of radioactive releases in the 1st 100 hours of the crisis.

On page 13 a table is given with the following header:

解析で対象とした期間での大気中への放射性物質の放出量の試算値

"Estimated amount of radioactive material released into the atmosphere over the time period covered by the analysis" {google translate}

It shows 1.2254x10^12 becquerels of Plutonium 238, 239, 240, 241 combined, 99% of which was Pu-241

I have 3 questions:

1.) Is there a way to convert the 1,225,400,000,000 becquerels into number of grams of Plutonium released?

2.) Is this estimate referring to "releases into the environment" or "releases into the atmosphere", i.e. air or water or both?

Google translate suggests that this is just for the first 100 days into the air only.​

3.) What will happen to the 7.6x10^13 becquerels of Neptunium-239 shown on the same table - what mass of Plutonium-239 will result?



http://www.meti.go.jp/press/2011/06/20110606008/20110606008-2.pdf

 

[NUCENG]

For the third time - it's not *me* who proposed red team to replace station personnel, it was zapperzero who said that. I told you twice that I propose red team to *augment* station personnel. Maybe with authority to order disaster prevention measures even it they damage the plant - regular station personnel may be hesitant to do that because management will be unhappy with the resulting losses, with repercussions to careers of those who caused them.



What motives? I did not talk about your motives at all. I just asked what do you propose, apart from crossing fingers and believing that station personnel in US is better than in Japan.



Please do. What's the status of venting capabilities at US plants?



IIRC vents were reinforced sometime ago to be more resistant to seismic damage and such, so at least venting will not pour hundreds of tons of 200+ Celsius hot steam through the cracks in the piping into the reactor building, which is a good thing to know.

But do they have any meaningful scrubbers? Simple answer, "yes" or "no"? In F1 there were no scrubbers.

I went back to see if I owe you an aplology and I stand by what I wrote in response to your post. For the second time I agreed with your discussion of external SUPPORT teams. I questioned the practicality and workability of external teams being able to be effective based just on training and drawings and procedures. I already responded to zapperzero on that point.

You twisted my motives when you said " In other words, you propose to accept the theory that all other NPP operators in the world are much better than Tepco." I never said anything of the kind and I have been very clear that I speak from experience in the US nuclear industry. I resoect that you disagree.

Then you add.
"Apparently, the system needs serious fixing. I propose a fix which adds another layer of accident response, one decoupled from NPP operator and its possible arrogance/stupidity/greediness/lapses in preparedness.

What do you propose? Basically nothing apart from minor patching-up of some safety rules?"

And then you talk about "crossing your fingers and believing" US operators are better than Japan. You may not be questioning my motives, IN YOUR MIND, but you are definitely not engaging in intellectually honest discussion.

In spite of that fact, I will try one more time.

The short answer is that US BWR hardened vent systems, that I have studied, are not filtered. These systems were classified for use in a beyond design basis event. That is the last ditch effort to minimize releases to the environment in a severe accident once it is impossible to prevent those releases. Now, your turn. Keep it respectful.

 

[zapperzero]

http://www.jnes.go.jp/content/000119688.pdf confirmation of the presence or absence of core recriticality: Study of the causes of neutron measurement data above the detection level revealed at Fukushima Daiichi monitoring points.

http://www.jnes.go.jp/content/000119689.pdf About the neutron leak at unit 4 storing pool: From 14 March to 15 March, neutron measurement data above detection level have been revealed at the Fukushima Daiichi monitoring points. Study of the causes of these measurements.

Thank you for your great and selfless work.

Now it only remains for jnes to translate these into English. I am very curious as to why neutrons were detected "at unit 4 storing pool". I had no idea that there was such a detection. I only remember the talk about neutron beams detected at the plant perimeter.

 

[zapperzero]

A document was given to the press in June, which included estimates of radioactive releases in the 1st 100 hours of the crisis.

On page 13 a table is given with the following header:

解析で対象とした期間での大気中への放射性物質の放出量の試算値

"Estimated amount of radioactive material released into the atmosphere over the time period covered by the analysis" {google translate}

It shows 1.2254x10^12 becquerels of Plutonium 238, 239, 240, 241 combined, 99% of which was Pu-241

I have 3 questions:

1.) Is there a way to convert the 1,225,400,000,000 becquerels into number of grams of Plutonium released?

FWIW, wolframalpha says 1 g of Pu-241 is 3.84E+12 Bq. So roughly 0.3 grams.

EDIT: perhaps when comparing this with the total inventory of a NPP it is easier to understand the seemingly cavalier attitude of some industry insiders who are dismissing Fukushima as "not a big deal". It's not so big a deal, in truth, from that perspective. Could have been orders of magnitude worse, easy.

 

[tsutsuji]

Thank you for your great and selfless work.

You are welcome.

Now it only remains for jnes to translate these into English. I am very curious as to why neutrons were detected "at unit 4 storing pool". I had no idea that there was such a detection. I only remember the talk about neutron beams detected at the plant perimeter.

In my previous post I merely translated the titles and summaries on the main menu page at http://www.jnes.go.jp/jyohou/kouhyo/kaiseki_published.html without having a look at the pdf documents themselves.　

Now, if I try to look a them, I find at the bottom of http://www.jnes.go.jp/content/000119689.pdf (dated 27 April 2011) that the last sentence is "Concerning the reason why neutron data above detection level were measured at Fukushima Daiichi monitoring points from 14 March to 15 March, for unit 4 SFP to be the cause, it is necessary that the water level declines below top of fuel".

The last sentence on page 2 of http://www.jnes.go.jp/content/000119688.pdf (dated 13 April 2011) is "Concerning measurement data above neutron detection level at Fukushima Daiichi monitoring points from 14 March to 15 March, there is almost no possibility that they are caused either by core recriticality or pool water level decline. Also, under the hypothesis that those measurements are valid, the possibility of neutron discharge from volatile substances of delayed neutron precursors caused by venting of units 1, 2, 3, can be thought".

http://www.sfgate.com/cgi-bin/article.cgi?f=/n/a/2011/10/15/international/i025338D61.DTL English article about the JNES documents.

 

[Astronuc]

From the translation of the JNES documents provided by tsutsuji, it is still not clear about the 'neutron source'.

The delayed neutron precursors have very short half-lives, less than one minute as shown below:

Nuclide Half-life
         (sec)
 Br-87    55.7
 Cs-141   24.9
 I-137    24.5
 Te-136   19.0
 Br-86    16.0
 I-138     6.5
 Rb-93     5.86
 Br-89     4.38
 Te-137    3.5
 Rb-94     2.76

At 10 minutes from shutdown, they have decreased by a factor of 1000, and in a half-hour, they have decreased by a factor of 1 billion from shutdown, so all but the longest lived have decayed away, and the longest is less than 1 billionth of a small amount to begin with. In the SFPs, the fuel hadn't operated for months, so essentially, there are no delayed neutron sources. The only possible neutron sources would be transuranics, e.g., Pu, Am, Cm, Cf

Draining of the SFP would reduce moderation, so criticality would be rather impossible. However, neutrons could escape without the shielding of the water, but the source would rather weak.

 

[nikkkom]

The short answer is that US BWR hardened vent systems, that I have studied, are not filtered. These systems were classified for use in a beyond design basis event. That is the last ditch effort to minimize releases to the environment in a severe accident once it is impossible to prevent those releases. Now, your turn. Keep it respectful.

To me, this is one of Fukushima "lessons learned".

IIRC Sweden constructed a 10000 m^3 filtration/buffer in their hardened vent with the goal of capturing most of emissions, and up to F1 disaster it was not clear whether this effort makes (economic) sense.

Today we can say that it definitely does make sense. In F1, it could have captured a large fraction of release, saving tens or even hundreds of billions of dollars.

If NRC would have proposed adding systems like this one to NPPs in US, I'd have reasons to think NRC took F1 disaster seriously enough.

So far I don't see it.

 

[etudiant]

To me, this is one of Fukushima "lessons learned".

IIRC Sweden constructed a 10000 m^3 filtration/buffer in their hardened vent with the goal of capturing most of emissions, and up to F1 disaster it was not clear whether this effort makes (economic) sense.

Today we can say that it definitely does make sense. In F1, it could have captured a large fraction of release, saving tens or even hundreds of billions of dollars.

If NRC would have proposed adding systems like this one to NPPs in US, I'd have reasons to think NRC took F1 disaster seriously enough.

So far I don't see it.

It does seem that the idea of hardening the vent without also making provisions for filtering the possibly extreme emissions is a possibly damaging half measure. A severe accident plume clearly exceeds the natural dilution capacity of the environment and it seems ill advised to raise the emission point several hundred feet on top of that.
In this context, the UK experience in the 1950s with the Windscale accident deserves more attention. Filters were installed on that site and saved the country from an enormous disaster when the nuclear pile (graphite moderated) caught fire. Filtering a reactor accident in a water moderated reactor with massive steam generation will however be a much more challenging task.

 

[Bodge]

...

2.) Is this estimate referring to "releases into the environment" or "releases into the atmosphere", i.e. air or water or both?

Google translate suggests that this is just for the first 100 days into the air only.​

3.) What will happen to the 7.6x10^13 becquerels of Neptunium-239 shown on the same table - what mass of Plutonium-239 will result?



http://www.meti.go.jp/press/2011/06/20110606008/20110606008-2.pdf

Anyone help?

 

[NUCENG]

The decision to add filtration to a hardened vent is not so simple. The purpose is to protect containment by releasing pressure from containment. Protection of the coolant piping and vessel barrier, and the cladding barrier keeps the plant out of a major release and generation of significant hydrogen concentrations.


Charcoal filtration requires a fairly low velocity of the filter stream to permit it to work. Having sufficient flow for the period immediately after shutdown requires a large surface area. The larger the system is physically, the more likely is its need for force ventilation flow (fans that require emergency power).


Activated charcoal is quickly saturated if the humidity id too high. So filtration systems heat the stream to lower humidity. That requires emergency power or some form if heat source. Failure of either of these design requirements will result in backpressures that could result in containment overpressure.I have not studied the Finnish or Swedish filtration systems designs so I can't say they have solved those problems (particularly the power issue). In any case, those systems have the same experience level as US and Japanese hardened vents up until March 11, 2011. They have not been tested by a real severe event.


Let's turn to Fukushima specifically. Possibly due to operator error in securing isolation condenser flow early in the event, Unit 1 quickly wound up with no makeup and fuel was uncovered. Fuel damage and hydrogen generation were well underway within hours of the SBO - even before batteries were exhausted. Containment pressures were more than twice design limits so containment leakage was probably significant even before the venting was attempted.


Units 2 and 3 also had significant problems attempting to vent. I can't confirm this from the information I have seen here or released by TEPCO, but it is possible that attempts to keep the cores covered were unsuccessful and fuel damage was underway before attempting to vent those units as well. They maintained the reactors at pressure longer in order to use the RCIC and HPCI steam driven systems despite knowing that they would be lost when the batteries died.


Basically, I believe Fukushima units 1, 2, and 3 were already leaking and already building explosive levels of hydrogen before they attempted to vent. They had already lost the war.


The alternative is that in an extended SBO where it is clear the plant will not regain AC systems for makeup and cooling, the reactor should be manually depressurized early. This will permit external low pressure makeup sources (fire pumps, fire trucks, or, in the US, B.5.b systems) to be used to keep the core covered, reducing or preventing fuel damage and oxidation. Priority should be to use the core spray system for injection since it is the most direct path to the core. Pressure relief from the reactor to the torus should be maintained via the SRV system. Containment pressure relief by the hardened vent system. Preventing or reducing core damage reduces the need for hardened vent filtration.


Now, for my caveats. This discussion is based on current knowledge and understanding of Fukushima. It is not carved in stone. At a minimum we need to learn more about why the operators had trouble venting and ensure that won’t happen again. It is clear that the duration of SBO coping periods should be reevaluated and possibly lengthened. Unit 1 problems with reinitiating isolation condenser operation needs to be examined to see if it is more than operator error. In view of the reports that other countries have Filtration systems on the hardened vent systems, this potential should be considered. I believe US BWRs need to reconsider the need for hydrogen ignition systems to prevent explosive concentrations.


The international nuclear industry needs to continue to support Japanese recovery efforts to ensure we can mine every possible lesson that this accident can teach. I don’t think we know anywhere near enough about what happened yet, and that is why it is important that we don’t get bored and quit watching and discussing. That process will only be useful as long as the discussion stays respectful.

 

[etudiant]

The decision to add filtration to a hardened vent is not so simple. The purpose is to protect containment by releasing pressure from containment. Protection of the coolant piping and vessel barrier, and the cladding barrier keeps the plant out of a major release and generation of significant hydrogen concentrations. ...

Thank you for a very coherent and cogent response.
The comments about depressurizing the reactor as a means to allow more easily feasible emergency cooling make great sense. Presumably there would still be noticeable emissions as the reactors would essentially be boiling in the open, but if the fuel rods remain intact, the contamination damage is relatively minute. Indeed, if the reactors are depressurized, water could be injected by a hydraulic or pneumatic pressurizer, somewhat similar to the existing emergency cooling systems but with more backup. Is there a good reason such an approach is not already SOP?

 

[nikkkom]

Charcoal filtration requires a fairly low velocity of the filter stream to permit it to work. Having sufficient flow for the period immediately after shutdown requires a large surface area. The larger the system is physically, the more likely is its need for force ventilation flow (fans that require emergency power).

Activated charcoal is quickly saturated if the humidity id too high. So filtration systems heat the stream to lower humidity. That requires emergency power or some form if heat source. Failure of either of these design requirements will result in backpressures that could result in containment overpressure.

Charcoal filters are probably not what's needed when you plan to vent hundreds of tons of steam relatively quickly.

To my non-specialist eye, a bubbler tank with mass of cold water no less than five times the mass of total reactor coolant inventory should be sufficient.

If F1 would vent their contaminated and overheated coolant through such a bubbler tank, most of Cs-134/137 would be that tank now instead of hundreds of square miles of Japan territory.

Such tank would be a large, but relatively simple, low-tech construct. How much can it cost?

 

[zapperzero]

Anyone help?

2) Np-239 decays to Pu-239 with a half life of 2.3 days. Starting quantity is 0.009 grams, again according to wolframalpha (makes sense, shorter half life means higher activity).

 

[zapperzero]

Charcoal filters are probably not what's needed when you plan to vent hundreds of tons of steam relatively quickly.

To my non-specialist eye, a bubbler tank with mass of cold water no less than five times the mass of total reactor coolant inventory should be sufficient.

If F1 would vent their contaminated and overheated coolant through such a bubbler tank, most of Cs-134/137 would be that tank now instead of hundreds of square miles of Japan territory.

Such tank would be a large, but relatively simple, low-tech construct. How much can it cost?

And now you have re-invented the suppression chamber, haven't you?

 

[zapperzero]

The delayed neutron precursors have very short half-lives, less than one minute

At 10 minutes from shutdown, they have decreased by a factor of 1000, and in a half-hour, they have decreased by a factor of 1 billion from shutdown, so all but the longest lived have decayed away, and the longest is less than 1 billionth of a small amount to begin with. In the SFPs, the fuel hadn't operated for months, so essentially, there are no delayed neutron sources. The only possible neutron sources would be transuranics, e.g., Pu, Am, Cm, Cf

Draining of the SFP would reduce moderation, so criticality would be rather impossible. However, neutrons could escape without the shielding of the water, but the source would rather weak.

Now, if I try to look a them, I find at the bottom of http://www.jnes.go.jp/content/000119689.pdf (dated 27 April 2011) that the last sentence is "Concerning the reason why neutron data above detection level were measured at Fukushima Daiichi monitoring points from 14 March to 15 March, for unit 4 SFP to be the cause, it is necessary that the water level declines below top of fuel".

The last sentence on page 2 of http://www.jnes.go.jp/content/000119688.pdf (dated 13 April 2011) is "Concerning measurement data above neutron detection level at Fukushima Daiichi monitoring points from 14 March to 15 March, there is almost no possibility that they are caused either by core recriticality or pool water level decline. Also, under the hypothesis that those measurements are valid, the possibility of neutron discharge from volatile substances of delayed neutron precursors caused by venting of units 1, 2, 3, can be thought".

So, it is either uncovered fuel in SPF #4 or recriticality in 1, 2 or 3, but probably the former?

 

[jim hardy]

""" the possibility of neutron discharge from volatile substances of delayed neutron precursors caused by venting of units 1, 2, 3, can be thought"."""

i spent a LOT of time back then trying to figure that out.

from plant logsheets those measurements co-incided with water injection and venting

so i assumed particulates went up the vents

looking for my old link to those plant logsheets
seems they had wind direction also and i decided nasty particulates wafted by measuring point which was main gate.
fuel probably was crackling and sputtering good - ever pour water on hot coals? you get covered with ashes.

had to be an awful scary time for those fellows.

 

[westfield]

And now you have re-invented the suppression chamber, haven't you?

Only if emergency venting was exclusively from the suppression chambers which it certainly wasn't at F1.

From my laymans perspective it seems like a great solution to enable emergency scrubbing from the hardened vent. Additionally, we know that venting from the drywell\s took place at F1, bypassing the torus completely, so its not reinventing the S\C, it's actually putting an adhoc one in line. We also know that the torus of at least F1-2 exceeded its capacity to shed pressure and heat which would seem to add another possible use for an additional standby volume of water.

So an external emergency freshwater tank, a backup suppression chamber if you must, sounds like a very elegant solution to the issue, particularly in the case of drywell venting.

NPP engineers, is there any reason from an engineering point of view why that might not be be feasible or effective? On the face of it it does seem to be "cheap insurance" for this type of NPP.