Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

so I don't understand how anyone there could make such a definitive statement.

There is a list of caveats at the top of the document, which I summarized as:

Let's translate the core fuel removal 9 steps of http://www.aec.go.jp/jicst/NC/tyoki/sakutei/siryo/sochi2/siryo1.pdf . First of all, Tepco insists that this is only an example and that no firm decision has been taken yet. On difficult technological problems, alternative solutions will be studied and whenever necessary the alternative solution shall be used.

Also "Depending on the damaged fuel distribution" means that the statements that follow are conditional.

 

[tsutsuji]

It seems that Tepco could keep some contaminated water in the turbine building basements for longer than was previously planned:

TEPCO has also begun considering a review of its plan to remove all highly radioactive water at the Fukushima No. 1 plant by the end of this year. Once the quantity of radioactive water has been reduced to such levels that heavy rains would not cause an overflow, the rate of water treatment will be adjusted to minimize the amount of waste generated.
http://www.asahi.com/english/TKY201109020275.html

 

[NUCENG]

To reduce speculation here is the report onn the TMI2 cleanup

http://pbadupws.nrc.gov/docs/ML1111/ML111100641.pdf

 

[zapperzero]

I'd like to see their sources, or at least know where they are and ask tsutsuji to provide a translation.

http://www.yomiuri.co.jp/dy/national/T110607005367.htm

It's in English. Quotes the NISA report to IAEA.

 

[LabratSR]

For what its worth...

Page IV-48

"Considering the results of RPV temperature measurements, it is likely that a considerable amount of the fuel cooled in the bottom of the RPV."

http://www.kantei.go.jp/foreign/kan/topics/201106/pdf/chapter_iv_all.pdf

That line is repeated for all the Units

 

[clancy688]

"Considering the results of RPV temperature measurements, it is likely that a considerable amount of the fuel cooled in the bottom of the RPV."

http://www.kantei.go.jp/foreign/kan/topics/201106/pdf/chapter_iv_all.pdf

That line is repeated for all the Units

Well, that assessment is several weeks old. In the beginning they told us that there's no meltdown. Then they told us that there's partial meltdown (Their radiation reading instruments told them that only XX% of the core could be damaged, so there's no total meltdown. According to the instruments, there's still no total meltdown. But reality is different, and so I'd say we should treat those "temperature tells us that all the stuff is still in the vessels" statements with care). Then they told us that there's a fullscale meltdown, but WITHOUT massive RPV breaches.
They have so often revised their statements regarding the vessels conditions that I wouldn't take anything as definite. Also, the article zapperzero provided says

If the report is released as is, it would be the first official recognition that a melt-through has occurred.

So it's yet a new report and it isn't released so far. Did anyone notice that all those reports and assessments keep getting worse over time? Funny, isn't it...
But so far the Yomiuri report only speaks of a "possibility", not a definite fullscale RPV breach. Thx @ NUCENG for the TMI document

 

[zapperzero]

Well, that assessment is several weeks old.

Weeks? Here's the report...

http://fukushima.grs.de/sites/default/files/NISA-IAEA-Fukushima_2011-06-08.pdf

pp 13

Concerning Units 1 to 3 of Fukushima Dai-ichi NPS, as the situation where water injection to each RPV was impossible continued for a certain period of time, nuclear fuels in each reactor core were not covered by water but were exposed, and led to a core melt. A part of the melted fuel stayed at the bottom of the RPV.

EDIT: and another part left, of course.

pp 173

Therefore, at the present moment it is estimated that the
fuel has melted and an considerable amount of it is lying at the bottom of the RPV.
However, the bottom of the RPV is damaged, and it is thought at the present stage it is
possible that some of the fuel has fallen through and accumulated on the D/W floor
(lower pedestal).

This stuff is OLD, people, and it's official... there is nothing much to debate here.

 

[clancy688]

Um, what point are you trying to make? ^^;

Are you supporting my consideration that the age (three months) of the official report indicates that part of that assessment could be wrong? (Especially the "some of the fuel" line, which, according to that yomiuri report, could actually be something like "most of the fuel")
Since they already state in their report (albeit very sneaky), with that "at the present moment" line, that future assessments may come to different (worse?) conclusions...?

 

[Rive]

Regarding this 'where is the core?' discussion: the core spray in U3 works, as it seems.
http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11090306_temp_data_3u-e.pdf

So this core - or at least those parts of it which keeps the U3 RPV hot - is reachable by the core spray system.

Ps.: while it is not effectively reachable through the feedwater line.

Ps2.: it'll be interesting to see the next few nuclide analysis results for U3 basement.

 

[NUCENG]

Let me throw a couple of thoughts into the works.

Earlier injection through the feedwater nozzles adds water outside the shroud. The idea is to fill the area and let water flow down through the jet pumps intp the lower plenum. If the recirculation piping is leaking or if the pump seals are blown due to high temperature this water may be leaking out of the vessel and not reaching the core except for what is on the floor of the drywell. If the vessel is failed (likely), the water will leak into the drywell floor. Another consideration for the feedwater line is that this path was used with seawater and there may be some nozzle clogging.

Core spray adds water inside the shroud above where the core was originally located. If the slumped core has blocked or reduced flow (like happened at TMI2) this water may just sit on top of the debris and not cool debris in the lower plenum or below the vessel. If the shroud is damaged it may leak out and not keep the debris submerged. If the core support plate has failed core spray will be onto the lower plenum directly.

They are using both paths and that is intended to cool core debris wherever it is. Wherever the water is meeting hot debris it will boil. Since the vessel and containment are apparently vented the temperatures will remain cllose to 100 degC. Unit 3 suppression chamber pressure is above ambient. It is possible this is due to submergence pressure.

It is clear that nobody knows for certain what the exact conditions are inside unit 3, but it appears to me TEPCO is covering the potential cooling paths. The data shows a drop of a couple of degrees, if that continues it will be a good sign.

 

[rmattila]

Not knowing the American BWR design very well, I've been wondering since the beginning of the event, whether it would have been possible to use the scram system hydraulic lines to inject water to the bottom of the core. I know this is one alternative emergency injection route for some of the newer BWR:s.

As I've understood, the recirculation pump seals of the GE type BWRs are not very reliable in severe accident conditions, and once they fail, it may not be possible to get any water to the core using feedwater lines (especially if the shroud happens to be intact). The scram lines might also have the additional benefit that they might be located in a different section of the reactor building from most emergency cooling pumps, which typically lie in the basement in order to ensure sufficient suction head.

 

[NUCENG]

Not knowing the American BWR design very well, I've been wondering since the beginning of the event, whether it would have been possible to use the scram system hydraulic lines to inject water to the bottom of the core. I know this is one alternative emergency injection route for some of the newer BWR:s.

As I've understood, the recirculation pump seals of the GE type BWRs are not very reliable in severe accident conditions, and once they fail, it may not be possible to get any water to the core using feedwater lines (especially if the shroud happens to be intact). The scram lines might also have the additional benefit that they might be located in a different section of the reactor building from most emergency cooling pumps, which typically lie in the basement in order to ensure sufficient suction head.

Your understanding is correct about recirc pump seals. Typical leakage at full vessel pressure from complete failure of the seals is around 60 gpm in a typical BWR. The ECCS systems are sized to account for this leakage.

In the early days of the accident there was no power to run the CRD system to use this path for injection. Once major core damage was suspected including potential vessel failure at the CRDMs the integrity of this path would be highly suspect.

 

[rmattila]

In the early days of the accident there was no power to run the CRD system to use this path for injection. Once major core damage was suspected including potential vessel failure at the CRDMs the integrity of this path would be highly suspect.

I was thinking of the firewater system they improvised during Saturday March 12: if it could have been hooked up to the scram system lines, they might have had a better change of getting water to the core than with the feedwater system which has the risk of outflow through the recirculation pump seals, or with the core spray system that might have gotten clogged due to use of the seawater, or was badly accessible due to its location within the plant.

But as I said, I don't know the GE BWRs well enough to estimate whether it would have been a relevant option or not.

 

[NUCENG]

I was thinking of the firewater system they improvised during Saturday March 12: if it could have been hooked up to the scram system lines, they might have had a better change of getting water to the core than with the feedwater system which has the risk of outflow through the recirculation pump seals, or with the core spray system that might have gotten clogged due to use of the seawater, or was badly accessible due to its location within the plant.

But as I said, I don't know the GE BWRs well enough to estimate whether it would have been a relevant option or not.

I looked up the fire system connection for injection into the vessel for a BWR3 and a BWR4. Both plants connect the fire protection system through the General Service Water System into the Residual Heat Removal System which injects into the Recirculation system piping to the vessel. I didn't find a direct connection between the Fire Protection System and CRD. I cannot speak for Fukushima specifically, but using CRD would have taken more than valve manipulation. If they used feedwater they may have done something similar.

 

[zapperzero]

Um, what point are you trying to make? ^^;

Are you supporting my consideration that the age (three months) of the official report indicates that part of that assessment could be wrong? (Especially the "some of the fuel" line, which, according to that yomiuri report, could actually be something like "most of the fuel")
Since they already state in their report (albeit very sneaky), with that "at the present moment" line, that future assessments may come to different (worse?) conclusions...?

No. I am not supporting your consideration.

However.

The report was written at NISA based on TEPCO-provided data. Both entities have zero incentive to over-estimate the problems. If they believe in RPV bottom head breaches, I believe too.

So, there is no need to (with all respect to Astronuc) be beating around the bush and wondering IF there is fuel on the floors of the PCVs. It's a matter of how much and how efficiently it is being cooled.

 

[tsutsuji]

In http://www.aec.go.jp/jicst/NC/tyoki/sakutei/siryo/sochi1/siryo4.pdf contributed by Tepco for the 3 August meeting of the middle and long term special committee, one can read: "It can be thought that some part of the damaged fuel at units 1~3 has flowed out into the primary containment vessel".

 

[hbjon]

Question. If the gas Krypton is formed, how far would it travel from it's place of origin? Would it mix and settle into the ocean? Would it travel with the wind for long distances and settle in crack in the earth? Is it true that Krypton will not normally react chemically with other substances? Not to be confused with Kryptonite, how harmful is the gas?

 

[tsutsuji]

I have tried to translate the 19 research and development topics of the JAEA, Toshiba, Hitachi-GE http://www.aec.go.jp/jicst/NC/tyoki/sakutei/siryo/sochi2/siryo2.pdf document.

Middle and long term measures special committee (second meeting), Document No. 2.

Atomic Commission of Japan, Special Committee for the Study of Middle and Long Term Measures at Tokyo Electric Power Company (K.K.) Fukushima Daiichi Nuclear Power Plant

Necessary Research and Development Topics and Contents, 31 August 2011, by Japan Atomic Energy Research and Development Agency (independent body), Toshiba (K.K.), Hitachi-GE Nuclear Energy (K.K.)

1. Foreword
This document is dealing with the the research and development topics that are necessary in the future, based on the technical problems mentioned in the special committee's first meeting Document No.4 contributed by Tokyo Electric Power Company: "Technical problems for the middle and long term measures at Fukushima Daiichi nuclear power plant" [ http://www.aec.go.jp/jicst/NC/tyoki/sakutei/siryo/sochi1/siryo4.pdf ] and the discussions at the special committee.

2. Necessary research and development topics to solve problems
The core having been damaged at three commercial light water reactors, with building damages thought to be the consequences of hydrogen explosions and with pollution, this is a situation without precedent in the world. While referring to past experience, including in other domains, new techniques and findings are necessary. The new technologies that need to be developed incorporate several kinds of elemental technologies, which include breakthrough technologies overcoming several different difficulties. These breakthrough technologies requiring creativity, time and funds are the following:
* Decontamination inside buildings by way of remote control under radiations that do not allow human presence.
* Remote-controlled equipment to inspect inside PCV and RPV where low accessibility is expected and fuel debris sampling techniques.
* PCV leak stopping techniques to be performed while closed loop cooling water is running
* Remote-controlled cutting, handling techniques to remove fuel debris and reactor structural parts including from inside the PCV
In addition, coordination between the plant site and research and development is indispensable during fuel removal operations, as one can easily imagine progress through trial and error, with a feedback to the research and development teams of the results obtained after applying to the real plant technologies developed after the Three Mile Island experience.
The research and development topics that respond to each technical problem are presented on the following pages.

SFP fuel removal (topics 1,2,3)

Technical problem (topics 1,2,3) : Study of methods to deal with damaged fuel surrounded by salt (handling, cleaning, testing, reprocessing ability)

1. Assessment of long term integrity of fuel assemblies removed from SFP
Measures to secure integrity of fuel assemblies in the midst of storage term are studied as follows:
(1) assessment of long term integrity of fuel assemblies in the midst of storage term
(2) choice of fuel assembly cleaning criteria

2. Study of reprocessing ability criteria
With the consequences on debris handling, chemical processing, etc. in mind, selection criteria are organized and a standard is prepared for deciding whether reprocessing is possible or not.

3. Study of fuel debris reprocessing method
The following studies are undertaken in order to secure the reprocessing of fuel debris etc.
(1) Fuel debris case study
(2) Study of the consequences on chemical processes for fuel debris etc.
(3) Study on the handling of fuel debris etc.

Continuous measures toward stabilization and decommissioning (topics 4,5,6)

Technical problem (topics 4,5,6):
* Study of remote-controlled methods in order to improve human accessibility in the high radiation areas of the buildings.
* Assessment of corrosion in RPV and PCV and undertaking of corrosion limiting countermeasures where necessary
* Study of processing and disposal of high level radiation secondary waste produced by the water treatment facility

4. Study of cleaning methods to improve access to the buildings
To smooth the recovery operations, worker access being necessary, the following research and development is undertaken using effective cleaning techniques adapted to each case:
(1) inferring and surveying the contamination, a cleaning plan base is built
(2) the decontamination techniques are sorted, the decontamination plan is built
(3) Decontamination test on simulated contamination
(4) Development of remote-controlled equipment: Development of such equipments and systems that are necessary to install the measurement and decontamination technical candidates on the wheel platform.
Breakthrough technology: equipment for remote-controlled high radiation, narrow space, etc. decontamination.

5. Assessment of RPV, PCV integrity against corrosion
RPV and PCV materials being imperilled by high temperature sea water and radiations, corrosion speed data in this environment are found using quantitative methods, thus contributing to structural integrity assessment of RPV, RPV pedestal and PCV.
(1) corrosion tests on RPV and PCV materials
(2) corrosion test of RPV pedestal rebars
(3) test of corrosion inhibitors for RPV, PCV, RPV pedestal
(4) assessment of RPV, PCV, RPV pedestal life expectancy and life expectancy increase
(5) test use of corrosion inhibitor on the real thing (target is the PCV material)

6. Research and development toward stable disposal of secondary waste produced by the water decontamination facility
For the long term storage and disposal of spent zeolite, sludge, concentrated liquids, etc. produced by the high radiation, seawater-components-including contaminated water, the following research and development is performed:
(1) assessment of behavior of spent zeolite, sludge, concentrated liquids, etc.
(2) assessment of safety in relation with hydrogen production and heat
(3) study of long term storage method, considering seawater, heat, high radiation, etc.
(4) study of the transformation of spent zeolite, sludge, concentrated liquids into waste bodies
(5) assessment of the characteristics of waste bodies
(6) study of optimization of waste disposal

Core fuel debris removal preparation and removal (topics 7 ~ 17)

Technical problem (topics 7,8): Because, for radiation shielding purposes, the most rational approach is to undertake the removal of damaged fuel underwater, development of methods and techniques to undertake water filling after repairing, waterproofing, setting up boundaries at PCV and other leakage points.

7. Development of equipments and strategies to inspect PCV leakage points
The following research and development is undertaken in order to understand the PCV situation and the locations of PCV leaks.
(1) Wash out of the assumed leakage points
(2) Review of existing techniques
(3) Development of special techniques for PCV leakage points
(4) Development of remote-controlled equipments to inspect the PCV surroundings
Breakthrough technology: remote-controlled inspection equipment adapted to PCV leakage points in high radiation, narrow space conditions

8. Building of water filling strategy (repair, filling, etc.) and development of methods and equipments
In order to repair the assumed leakage points (torus chamber, PCV penetrations, bolt joints, resin seals inside PCV, etc.), the following repair methods and techniques are developed:
(1) cataloguing of existing techniques
(2) review and development of repairing materials and equipments (sealing agents, grout, etc.)
(3) development of methods and techniques to repair (watertight) assumed leakage points
(3-1) development of waterproofing methods and techniques to fill the torus chamber or suppression chamber with grout
(3-2) development of waterproofing methods and techniques for the gap between the penetration sleeves and the biological shield
(3-3) development of repair methods and techniques for the resin seals in the PCV penetration flange, electrical penetrations, etc.
(3-4) development of repair methods and techniques for the PCV shell main body
(4) development of remote-controlled PCV repair equipment
Breakthrough technology: methods and repair equipments for remote-controlled repair (waterproofing) of PCV leakage points under high radiation while water is running

Technological problem (topics 9,10): development of a method for the remote-controlled survey of the inside of RPV and PCV.

9. Development of strategies and equipments to inspect inside PCV
With the goal of understanding the status of the PCV inside, of inspecting the RPV leaks, and of studying a fuel removal method, research and development of equipments and methods to inspect inside PCV is undertaken. The basic plan being that after workers or robots get access to the outside of PCV, remote-controlled inspection equipments enter the PCV through though-holes or other ways, the following research and development is undertaken:
(1) inspection plan building based on the results of calculated assumptions of the situation
(2) development of access method and remote-controlled equipment
(3) countermeasures against the release of radioactive substances
(4) development of remote-controlled inspection tools and techniques
Breakthrough technology: remote-controlled inspection techniques enabling to enter PCV whose accessibility is low due to the high radiations and the fact that the situation inside is unclear. Remote-controlled techniques to collect samples of fuel debris inside PCV.

10. Development of strategy and equipments for RPV preliminary inspection
Research and development of methods and equipments for a preliminary inspection aiming at understanding the status of the RPV inside, and of studying the specifications of the core fuel removal methods and tools. The basic plan being that after workers or robots get access to the operation floor, remote controlled inspection equipments are inserted from the reactor top through the PCV/RPV head, and an inspection is performed inside the RPV, the following research and development is undertaken:
(1) review of existing techniques
(2) inspection plan building based on the results of assumptions made after analysing the PCV inspection results etc.
(3) study of access method
(4) development of remote-controlled inspection techniques under high radiations
(5) development and construction of remote-controlled core fuel debris sampling techniques
Breakthrough technology: remote-controlled inspection techniques enabling to enter RPV whose accessibility is low due to the high radiations and the fact that the situation inside is unclear. Remote-controlled techniques to collect samples of fuel debris inside RPV.

Technological problem (topics 11,12,13,14): Development of higher level fuel removal methods and techniques than those of Three Mile Island where fuel damage was limited to inside the RPV.

11. Development of methods and equipments for the removal of fuel and reactor structural parts
The following research and development is undertaken in order to develop methods and equipments for the removal of core fuel debris and reactor structural parts
(1) cataloguing of existing techniques (including confirming equipments that have a good record at Three Mile Island)
(2) building of removal method based on the results of the preliminary inspection
(3) development of remote-controlled removal techniques for fuel debris inside RPV
(4) development of remote-controlled removal techniques for fuel debris inside PCV
Breakthrough technology: remote-controlled removal techniques for fuel debris inside RPV, adapted to the fuel debris distribution. Remote-controlled removal techniques for fuel debris inside PCV.

12. Development of criticality control techniques inside reactor
For the development of criticality control techniques inside reactor, the following research and development is undertaken:
(1) criticality assessment
If conditions change inside the reactor during fuel removal, criticality control assessment is undertaken, making predictions on the plant and fuel conditions and conducting an analysis based on the latest findings.
(2) reactor recriticality detection techniques
study of neutron detection techniques and short lived fission products measurements.
(3) recriticality prevention techniques
In order to prevent recriticality during fuel removal, transportation, and storage, neutron absorbing materials and construction techniques related to these materials are developed.
Breakthrough technology: recriticality assessment and prevention adapted to the diversity of characteristics that is expected among the core fuel debris

13. Characteristic test using mock-up core fuel debris
In order to study fuel removal and fuel processing after removal, the following data acquisition etc. is undertaken:
(1) construction of mock-up core fuel debris
construction of mock-up core fuel debris (including simulation assessments) reflecting melting duration, core structure, seawater injection, etc.
(2) mock-up core fuel debris characteristic test
The following tests and assessments are performed with the mock-up fuel debris:
(2-1) basic properties measurement and assessment
(2-2) chemical properties measurement and assessment
(2-3) physical properties measurement and assessment
(3) Comparison with Three Mile Island core fuel debris
Breakthrough technology: construction of mock-up core fuel debris approximating the real conditions such as melting duration and seawater injection.

14. Analysis of properties of the real core fuel debris
Analysis of the properties of the real core fuel debris is undertaken in order to confirm the debris retrieval techniques, to study the processing of removed fuel, and to contribute to accident analysis. Besides, reflecting transportation conditions, analysis equipment is installed as needed.

Technological problem (topics 15,16,17):
* Development of techniques (storage containers) for stable storing of fuel debris that include salt
* Study of suitable processing and disposal strategy

15. Development of core fuel debris storage containers
Development of storage techniques adapted to core fuel debris assumed to be corroded by seawater injection
(1) review of existing techniques
(2) study of core fuel debris custody system
wet storage in pools and dry storage systems are studied
(3) Development of safety assessment techniques based on preliminary inspection (sampling) results. Development of an assessment method taking criticality, shielding, waste heat, sealing, structure into account.
(4) Development of storage techniques for core fuel debris
(5) Development of transportation and storage techniques for the storage containers
Breakthrough technology: storage techniques for core fuel debris taking the influence of seawater etc. into account

16. Study of core fuel debris processing strategy
In order to contribute to the studies concerning how to deal with the future long term storage or disposal of the temporary stored core fuel debris, storage technology studies are undertaken concerning the suitability of already available disposal techniques with direct disposal also in sight.
(1) Study of suitability of existing techniques (wet, dry etc.) for core fuel debris made of melted fuel, reactor structural parts and salt.
(2) Study of disposal suitability and transformation into waste bodies of the waste produced by processing (including the case of direct disposal of core fuel debris)
Breakthrough technology: techniques for transformation into waste bodies and disposal of core fuel debris made of melted fuel, reactor structural parts and salt.

17. Study and development of accountancy method for core fuel debris
In combination with the characteristic tests of the mock-up debris, and with the analysis of the real damaged fuel in the reactor, etc., together with the development of quantitative analysis techniques, a nuclear substance accountancy method that shall be used when debris removal is performed, is developed.

Radioactive waste processing and disposal (topic 18)

Technological problem (topic 18): Study concerning the suitable processing and disposal strategy, taking into consideration the produced quantity prospects and the properties of each waste object.

18. Radioactive waste processing and disposal
Understanding the present circumstances, it is necessary to sort and analyse the properties of the radioactive waste that can be expected in the future. Then each radioactive waste's processing and disposal technique is studied.

Accident progression elucidation (topic 19)

Technological problem (topic 19):
* Development of techniques to infer the conditions inside the PCV, using analysis and surveys from outside the PCV
* Upgrading of event analysis methods based on PCV and RPV inspections, fuel debris sampling and analysis results

19. Accident progression elucidation, in order to understand the conditions inside the reactor
While performing plant behavior analysis and accident progression code analysis based on Fukushima accident real plant data, or event elucidation tests, meltdown progression behavior or behavior inside PCV are determined using upgraded severe accident analysis code. Analysis code upgrading also contributes to assess the integrity of equipments, and to predict fuel debris behavior when planning RPV and PCV internal surveys.

 

[etudiant]

Question. If the gas Krypton is formed, how far would it travel from it's place of origin? Would it mix and settle into the ocean? Would it travel with the wind for long distances and settle in crack in the earth? Is it true that Krypton will not normally react chemically with other substances? Not to be confused with Kryptonite, how harmful is the gas?

Krypton and xenon are two of the noble gases that are byproducts of the fission process. While xenon has received by far the most publicity because it is routinely monitored by the CTBT network, krypton is at least as abundantly emitted. However, because neither gas is taken up by the biosphere, there is little or no effort to limit their release. These emissions simply increase the global contamination. They could be captured at the source, but that would require a gas condensing facility able to process radioactive gas reliably for a long time.
That does not exist and there is no desire to install such anywhere, afaik.

 

[joewein]

20 August Fukuichi Live camera, west side steel truss assembly
26 August Fukuichi Live camera, north side steel truss assembly

The vertical parts of the frame on the west side now extend to the full height of the unit 1 building and are connected via two horizontal beams.

There also seems to be a crane at work at unit 3, probably for removing rubble in preparation for the cover work.I'm also pleased to see that temperatures at the bottom of the unit 3 RPV have been dropping at a rate of about 1 deg C every 6 hours since starting up the core spray. Besides demonstrating that the core spray is useful, it also suggests that there was still fuel inside the RPV.
http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11090506_temp_data_3u-e.pdf

If it had all been splattered on the containment floor the core spray would not have made that much difference.

 

[joewein]

Krypton and xenon are two of the noble gases that are byproducts of the fission process. (...) They could be captured at the source, but that would require a gas condensing facility able to process radioactive gas reliably for a long time.
That does not exist and there is no desire to install such anywhere, afaik.

Back in the 1980s I attended a presentation by Professor Armin Weiß (chemistry, Munich university) about nuclear power.

One of the points I remember from his presentation was that cryogenic air liquification was just about the only way to capture noble gases, but that under the influence of radiation from the noble gases ozone was formed in any oxygen present, which liquifies along with noble gases and is highly explosive in that state.

His bottom line was that there was no realistic method of filtering noble gases at the time.

 

[hbjon]

So in the case of a large mass of molten corium being constantly sprayed with water, does the kr85 get liberated into the air, or does a large portion stay in the water? The gas is hot, so that would make it airborne, right? I imagine that it gets caught in the currents of other hot gasses rising with high volocity into the atmosphere. However, what interests me right now is that when half of all the Kr85 decays within the next 10 years to Rb85, the Rb85 will bond to almost any matter that it is next to at the time. Does that reaction concern anyone in the science community? Is there really zero intake into the biosphere? Has there been any studies on this?

 

[zapperzero]

So in the case of a large mass of molten corium being constantly sprayed with water, does the kr85 get liberated into the air, or does a large portion stay in the water? The gas is hot, so that would make it airborne, right? I imagine that it gets caught in the currents of other hot gasses rising with high volocity into the atmosphere. However, what interests me right now is that when half of all the Kr85 decays within the next 10 years to Rb85, the Rb85 will bond to almost any matter that it is next to at the time. Does that reaction concern anyone in the science community? Is there really zero intake into the biosphere? Has there been any studies on this?

Rb-85 is stable, is it not? Why would it be a continuing concern? It's not even very poisonous.

 

[etudiant]

So in the case of a large mass of molten corium being constantly sprayed with water, does the kr85 get liberated into the air, or does a large portion stay in the water? The gas is hot, so that would make it airborne, right? I imagine that it gets caught in the currents of other hot gasses rising with high volocity into the atmosphere. However, what interests me right now is that when half of all the Kr85 decays within the next 10 years to Rb85, the Rb85 will bond to almost any matter that it is next to at the time. Does that reaction concern anyone in the science community? Is there really zero intake into the biosphere? Has there been any studies on this?

The ongoing emissions of krypton now are on the order of 0.01% of the initial emissions at most, as the 3 reactors are now producing less than 10 megawatts total decay heat, versus about 10 gigawatts thermal while in operation and the accumulated krypton which was stored in the fuel rods was released on the meltdown.
The emitted gas gets mixed into the atmosphere pretty evenly within a couple of months. As the eventual decay product is not radioactive and is in part per trillion or lower quantities, no biological effect is expected.
Rubidium is absorbed as a potassium alternate by the body and is usually found in the body at the 3-4 parts per million level. The airborne increment of rubidium from krypton decay would be too small to measure, even statistically.

 

[Rive]

⑦ Filling primary containment vessel / reactor pressure vessel with water ⇒ reactor pressure vessel cap opening

After sufficient radiation shielding is provided by filling both the primary containment vessel and the reactor pressure vessel with water up to the suitable level, the reactor pressure vessel cap is taken off.
・The boundary construction as provided by ⑥ is a major prerequisite

First, very thanks for all those translations.

Second: OK, water is often used for radiation shielding - but am I right that water with high amounts of radioactive cesium in it is not the best for this purpose?

I see no real way to 'wash out' all the cesium from the corium before opening the RPV cap.

 

[hbjon]

The ongoing emissions of krypton now are on the order of 0.01% of the initial emissions at most, as the 3 reactors are now producing less than 10 megawatts total decay heat, versus about 10 gigawatts thermal while in operation and the accumulated krypton which was stored in the fuel rods was released on the meltdown.
The emitted gas gets mixed into the atmosphere pretty evenly within a couple of months. As the eventual decay product is not radioactive and is in part per trillion or lower quantities, no biological effect is expected.
Rubidium is absorbed as a potassium alternate by the body and is usually found in the body at the 3-4 parts per million level. The airborne increment of rubidium from krypton decay would be too small to measure, even statistically.

It has been noted that half of a big number is still a big number. Then why doesn't it follow that half of half of a big number is still a big number? I thought we were talking about half of every fission that occurred? Or was it half of half of every fission that occurred. My math may be off. I will admit. Perhaps it is half of half of all the mass that has been lost to fission. Another interesting point is that potassium and rubidium come to us by vastly different origins. Potassium is formed in the universe by nucleosynthesis from lighter atoms. The stable form of potassium is created in supernovas via the explosive Oxygen-burning process. And rubidium is born from the decay of Kr85? It seems to be a fact that human biology needs potassium to function, hard to believe that biology can substitute an entirely different element to perform the same functions. Sorry if this is slightly off topic. I know most of you are chomping at the bit to get back to technical engineering issues in Fukushima. Happy holiday from Minnesota.

 

[etudiant]

It has been noted that half of a big number is still a big number. Then why doesn't it follow that half of half of a big number is still a big number? I thought we were talking about half of every fission that occurred? Or was it half of half of every fission that occurred. My math may be off. I will admit. Perhaps it is half of half of all the mass that has been lost to fission. Another interesting point is that potassium and rubidium come to us by vastly different origins. Potassium is formed in the universe by nucleosynthesis from lighter atoms. The stable form of potassium is created in supernovas via the explosive Oxygen-burning process. And rubidium is born from the decay of Kr85? It seems to be a fact that human biology needs potassium to function, hard to believe that biology can substitute an entirely different element to perform the same functions. Sorry if this is slightly off topic. I know most of you are chomping at the bit to get back to technical engineering issues in Fukushima. Happy holiday from Minnesota.

Good point on the size issue.
However, the ongoing emissions are truly small. The nuclear decay now taking place is not from uranium decay, but from various fission fragments decaying in turn. Few of these reactions produce krypton, so there is a not only a more than a thousand fold reduction in fission, but also a further comparable cut in the krypton production, to a millionth of the initial rate or less.
It is worth noting that krypton on emission immediately becomes a global, not a local, problem.
On a global basis, the major source is the reprocessing of spent nuclear fuel, because the krypton is vented to the air. The best known reprocessing site is in France, at the Hague. The 58 reactors powering France have their fuel processed there. Assuming a very generous 10 year refueling cycle, the plant emits a Fukushima's worth of krypton every 6 months.
The rubidium issue is not a worry. Rubidium is an abundant element, comparable to zinc in terms of occurrence. Biology is pretty flexible in terms of tolerating different elements in its processes, which is why strontium is such a hazard because the body incorporates it into bone in lieu of calcium. Rubidium is well accepted by the body processes and a few more parts per billion are of no account when the body already incorporates several parts per million.

 

[nikkkom]

The best known reprocessing site is in France, at the Hague. The 58 reactors powering France have their fuel processed there. Assuming a very generous 10 year refueling cycle, the plant emits a Fukushima's worth of krypton every 6 months.

For how long do French cool down spent fuel before reprocessing?

It seems that longer cooldown has a lot of pros wrt reduction of emissions, and only a relatively small con of the necessity to pay for spent fuel storage. Since MOX fuel from reprocessing is not yet economically advantageous (uranium is still cheap), I'd think spent fuel waits many tens of years before going into reprocessing.

 

[etudiant]

For how long do French cool down spent fuel before reprocessing?

It seems that longer cooldown has a lot of pros wrt reduction of emissions, and only a relatively small con of the necessity to pay for spent fuel storage. Since MOX fuel from reprocessing is not yet economically advantageous (uranium is still cheap), I'd think spent fuel waits many tens of years before going into reprocessing.

According to this site http://www.areva.com/EN/operations-1092/areva-la-hague-recycling-used-fuel.html
the fuel at The Hague is allowed to cool for 3-5 years before being reprocessed. That cuts the krypton load by perhaps 30%, given the half life is a bit over 10 years.
A 50 year storage program would have more benefit. It can be argued that the US failure to implement the proposed nuclear waste storage has had that effective result.

 

[Most Curious]

A 50 year storage program would have more benefit. It can be argued that the US failure to implement the proposed nuclear waste storage has had that effective result.

Not to mention all the fissionable material that is wasted by not reprocessing!

 

[MiceAndMen]

It seems that TEPCO (and by extension the Japanese government) are gradually preparing the way for a decade long cleanup effort.

My WAG is that between 15 and 20 years will be required. Assuming the reactor buildings survive that long. One would hope that structural engineers have been analyzing them and carefully considering each's chance of survival for however long they think it's going to take given typhoons and the potential for more earthquakes.

 

[joewein]

My WAG is that between 15 and 20 years will be required. Assuming the reactor buildings survive that long. One would hope that structural engineers have been analyzing them and carefully considering each's chance of survival for however long they think it's going to take given typhoons and the potential for more earthquakes.

The plan is to enclose the buildings, first with the steel frame and plastic covers, later with something more substantial. It remains to be seen how well the first cover will cope with typhoons, since they probably won't be completed before this year's typhoon season ends, but that's just the first temporary solution.

They will also need to deal with the salt water in the basements soon, or all sorts of corrosion-related issues will occur.

 

[nikkkom]

Not to mention all the fissionable material that is wasted by not reprocessing!

This material (mostly Pu) is not going anywhere, you know. It is still inside those rods.

 

[nikkkom]

My WAG is that between 15 and 20 years will be required. Assuming the reactor buildings survive that long. One would hope that structural engineers have been analyzing them and carefully considering each's chance of survival for however long they think it's going to take given typhoons and the potential for more earthquakes.

These plants survived typhoons for 40 years. It's not like now they will crumble into dust in a year or two. If decontamination will be successful, the damaged upper portion can be cleaned up and built again.

 

[zapperzero]

These plants survived typhoons for 40 years. It's not like now they will crumble into dust in a year or two. If decontamination will be successful, the damaged upper portion can be cleaned up and built again.

It's not like they are not at the end of their design life, you know?