Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Pakman]

Would anybody by a chance happen to have information, how much the water level in the reactor normally sinks after closure of the MO-3 valves?

I see you're tightly in subject, neighbor! I counted 10 cubic meters. About. You think this is for both IC or only for B?

However, I bet nobody else here even know what tubes you are talking about.

 

[Pakman]

I guess the answer to your question is "yes". But I would be glad that Tepco provides a map showing where all these airlocks are located. What do they mean by "turbine building airlock"? Is it an airlock between the turbine building and the outside, or between the turbine building and the reactor building ?

BWR has quite contaminated steam-water circuit loop, including the turbine flow, so the turbine set in maintenance-free room with airlock to outside. Almost like secondary containment of the reactor building. Therefore one doesn't simply walk into turbine hall.

 

[Pakman]

What's the point in wearing a dosimeter if it goes off at radiation doses considered to be normal every five minutes?

Who knows how far is our knowledge? What's the point in fail-saving the emergency cooling system due to DC power loss, which most likely means something unexpected is happened?

 

[rmattila]

I see you're tightly in subject, neighbor! I counted 10 cubic meters. About. You think this is for both IC or only for B?

As both trains were operating until 15:03-15:04 and then both of them were closed by shutting the MO-3 valve, I suppose both of them would continue taking steam until they fill up to a stable level. But I have no idea of the amount of space available for the steam to get condensed into water.

 

[rmattila]

However, I bet nobody else here even know what tubes you are talking about.

Well, theoretically (=if the level measurement reference line is very close to the reactor temperature) it would be possible that while the IC is operating and the reactor pressure is dropping, the hot condensate at the top of the level measurement reference tube would flash to steam, causing the level measurement to show too high a value, and after the IC is closed and the pressure rises again, the reference tube would fill up and the level measurement would drop to the correct value.

But i doubt it, since the pressure transients caused by operation of the IC were not very large. However, as I said, I have never seen an IC operating, so I can't say for sure.

 

[Gary7]

Interesting story about a plan to use muons to take a virtual x-ray of the reactor cores.

http://www.yomiuri.co.jp/dy/national/T120107003539.htm

 

[jim hardy]

"" the hot condensate at the top of the level measurement reference tube would flash to steam, causing the level measurement to show too high a value, and after the IC is closed and the pressure rises again, the reference tube would fill up and the level measurement would drop to the correct value. ""

that's one reason it's recommended to depressurize quickly in station blackout.
depressurizing reduces reactor temperature
which reduces heatflow from vessel to containment, ( which has no cooling in blackout, )
where the 'reference legs' are located.
the containment temperaturre needs to be kept low
both for sake of electronics in there and you don't want the containment's metal wall to expand from the heat, buckle and crack
not to mention reference legs.

reference legs depend on steam moving into condensate pot, condensing and running back out the sloped sense pipe toward vessel, to keep condensate pot full.
so the condensate pot will be at saturation temperature.
that's how you check them - feel and if they're not scalding hot they're "gas bound", ie filled with noncondensables that keep the steam out.
we had vents atop ours to let out the noncondensibles.

the cooler water in reference leg can carry dissolved noncondensibles, just like carbonated soda does.
If the reference legs got hot enough to boil out some of the water or drive out dissolved noncondensibles
at a time when there was significant noncondensibles in the vessel (hydrogen? )

i believe the reference legs would become gas-bound and not refill.

just an old instrument guy's estimate.

 

[Pakman]

The reason for increased radiation at the reactor building airlock could be the SVR's operation. It drains inventory from RPV, which is in the drywell, to suppression pool which is out in the room with less thicker concreate walls than drywell has. So the radiation from the thorus inventory could affect the measurement at the airlock.

Without denying written above, as a simpler explanation may be the lack of ventilation in the reactor building. Did you know if you shut the vent hole in the bathroom and turn on the shower, radiation inside rapidly increases up to 2 mkSv due to Radon? Such was certainly here but in a more rigid form.

Everything about the attempt to enter the reactor building rests on the fact that the dosimeters were not suitable for this job, even there wasn't any damage to the equipment inside the building, and certainly if there was. Why then the report does not blame operators for this? This is a real bug, unlike the lack of knowledge of the fail-safe automatic functioning imposed by the report.

 

[jim hardy]

we might be over-focused on dosimeters. i don't know what they had.

surely they had survey meters good for a few R/hr?

the Inpo report mentions water deeper than their boots, i'd have turned back too.
water can carry reeally nasty stuff, recall the electrical workers who got radiation burns from walking through water. presumably dissolved beta emitters because field above water wasn't too bad.

decisions have to be judged by the facts they were based on, ie what was known at that time & place.

i'd wager too much credence was put on the reactor level instrument.

 

[rmattila]

i'd wager too much credence was put on the reactor level instrument.

I've been wondering about the level measurement systems since the very beginning, even started a thread in March to get some justification for the trust that seemed to be put on the level instrumentation.

A rule of thumb is that 10 kg/s decay heat evaporation rate (typical about 1 hour after shutdown) will cause the level in the tank to drop about 3 cm per minute (=about two meters per hour), and as there was no cooling for several hours, it should have been obvious that the core will have been uncovered during the evening of March 11.

(And, by the way, I am still somewhat uncertain whether the GE level instrumentation will work at all, when the level drops below -1200 mm).

Diversification of the low level instrumentation with a binary signal based on floats is one way to improve reliability of data concerning the level drop in situations where impulse pipes might not work properly (rapid depressurisation etc.) My understanding is that such plant modifications/improvements have already been implemented at some European BWRs, and are currently being carried out at least in the Finnish plants.

 

[Pakman]

decisions have to be judged by the facts they were based on, ie what was known at that time & place.

It's a fact that at that time&place the reactor cooling status was unknown. Is it not enough to enter the reactor building by any cost? Especially because there was no high radiation alarm to the reactor building rooms after quake and before SBO.

By the way, abut deep contaminated water it was in the turbine hall.

 

[zapperzero]

It's a fact that at that time&place the reactor cooling status was unknown. Is it not enough to enter the reactor building by any cost? Especially because there was no high radiation alarm to the reactor building rooms after quake and before SBO.

By the way, abut deep contaminated water it was in the turbine hall.

Well they attempted to enter the building after the tsunami, when they had lost all power so I'm not sure those dosimeters that could have triggered an alarm were even online.

 

[Pakman]

Right because of this I wrote above there was no radiationn alarm BEFORE SBO.
You better read exactly what is written.

 

[zapperzero]

Right because of this I wrote above there was no radiationn alarm BEFORE SBO.
You better read exactly what is written.

I did read.

No radiation alarms implies no major pipe breaks or leaks before the tsunami, I guess. How does that tell me anything about the radiation field in the reactor building hours later?

 

[r-j]

What does SBO stand for?

 

[swl]

SBO = Station Black Out.

Loss of power to the power plant.

 

[Joffan]

What does SBO stand for?

Station black-out. No electrical power either from external sources or from site backups. I think it is usually limited to mean AC power availability but I believe in the case of Fukushima many DC sources (batteries) also failed (before exhaustion). Real experts here may elaborate on (or contradict) this response.

 

[NUCENG]

Station black-out. No electrical power either from external sources or from site backups. I think it is usually limited to mean AC power availability but I believe in the case of Fukushima many DC sources (batteries) also failed (before exhaustion). Real experts here may elaborate on (or contradict) this response.

Correct. SBO starts with a Loss of Offsite Power (LOOP) and failure of the Safety Related Emergency Diesel Generators (AC). In the case of Fukushima the Offsite AC supplies were lost during the earthquake Onsite EDGs failed due to flooding from the tsunami. Damage occurred to the fuel tanks and flooded some of the EDG rooms in the Turbine Building basements. Finally some of the AC switchgear which would allow EDG power to be applied to the safety equipment were also flooded.

However Fukushima accidents went one step further and some of the DC switchgear for the DC batteries were also damaged. So in that respect it was a beyond SBO accident.

 

[matthewdb]

BWR has quite contaminated steam-water circuit loop, including the turbine flow, so the turbine set in maintenance-free room with airlock to outside. Almost like secondary containment of the reactor building. Therefore one doesn't simply walk into turbine hall.

No, not even close. The airlock is for going into primary containment. The secondary containment and the turbine building are ventilated to the outdoors.

The turbine is not normally approached under power due to gamma from N-17. It has a bioshield around the turbine and main steam lines but the rest of the turbine hall can be entered under power.

 

[Pakman]

No, not even close.

Ok, I just guessed. So it needed to change "airlock" to "tightly closing door" in what I've written above. But then the talking was about the reactor building.

The secondary containment and the turbine building are ventilated to the outdoors.

Through the vent stack, I believe? What happens with level of radiation inside the building when ventilation stops?

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120110/index.html 10 litres of partly decontaminated water were found at around 10 AM on January 10 on the concrete below a tank. The leaked was stopped by tightening a junction bolt. Tepco says the water did not leak to outside the plant premises.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120110_03-e.pdf " Water leakage from the concentrated water tank of the water desalinations (reverse osmosis membrane)"

The turbine is not normally approached under power due to gamma from N-17.

What does N-17 stand for ?

 

[zapperzero]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120110/index.html 10 litres of partly decontaminated water were found at around 10 AM on January 10 on the concrete below a tank. The leaked was stopped by tightening a junction bolt. Tepco says the water did not leak to outside the plant premises.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120110_03-e.pdf " Water leakage from the concentrated water tank of the water desalinations (reverse osmosis membrane)"



What does N-17 stand for ?

Nitrogen.

 

[tsutsuji]

Nitrogen.

How is it generated ?

 

[rmattila]

It's N-16, not N-17, and it's produced by neutron irradiation of the oxygen O-16 from the steam in the reactor with (n,p) reaction (a neutron knocks out a proton from the oxygen). It has a very short half-life of about 7 seconds, but that's enough to make all pipelines containing steam difficult to approach during the operation of a BWR plant.

 

[tsutsuji]

I found the following via google:

In the EPR (a PWR) "the main radioactive sources responsible for external radiation near the primary circuit are nitrogen-16 (gamma emitter), nitrogen-17 (neutron emitter) and the core (gamma rays and neutrons)" http://www.epr-reactor.co.uk/ssmod/...pter 12.3 - Radiation protection measures.pdf

"The only case [of neutron decay] which is of some interest in nuclear technology is the neutron decay of nitrogen 17, formed by fast neutron irridiation of oxygen 17" http://books.google.com/books?id=E7Em_V7Zq9sC&pg=PA162

http://icanps.go.jp/111226Siryo2.pdf (Attachments for the cabinet investigation committee interim report, part II) A layout plan of Fukushima Daiichi unit 1's reactor building first floor is available on page 23, and that of the turbine building first floor is available on page 25. The north side (on the top of page 23 or on left of page 25) and south side (on the bottom of page 23 or on right of page 25) airlocks are clearly visible between turbine and reactor buildings. You may also want to have a look at the reactor building's fourth floor on page 21, where IC (A), IC (B) and the exhaust vents (pig nose) are represented.

 

[matthewdb]

Ok, I just guessed. So it needed to change "airlock" to "tightly closing door" in what I've written above. But then the talking was about the reactor building.

Not necessarily a tightly closing door - they are just high quality ordinary security doors. Plants rely on positive airflow from the ventilation systems. Airflow is arraigned to flow first to areas people will occupy and then is ventilated out from the areas of highest contamination.

Through the vent stack, I believe? What happens with level of radiation inside the building when ventilation stops?

All reactor building ventilation goes through the stack. As does the condenser vent and the turbine gland exhauster. The flow rate from the turbine building is VERY high to keep the building temperature in check so it doesn't go up the stack. We're talking flows on the order of 2 million m^3/h in a large plant.

 

[matthewdb]

I found the following via google:

In the EPR (a PWR) "the main radioactive sources responsible for external radiation near the primary circuit are nitrogen-16 (gamma emitter), nitrogen-17 (neutron emitter) and the core (gamma rays and neutrons)" http://www.epr-reactor.co.uk/ssmod/...pter 12.3 - Radiation protection measures.pdf

I was incorrect at stating it is N-17, thanks rmattila.

The N-16 is the majority of the immediate dose since the high energy gamma penetrates the piping. N-17 is a concern over time because it slowly activates the metal of the piping and turbines.

The N-16 is extracted at the condenser. After that the feed piping is quite low in activity so you won't see much shielding on the feed piping. The exhaust of the condenser is retained for 10 minutes by sending it through a long, folded up pipeline.

In a PWR the amount of N-16 in the steam is monitored as an indicator of the leak rate of the steam generators.

 

[matthewdb]

http://icanps.go.jp/111226Siryo2.pdf (Attachments for the cabinet investigation committee interim report, part II) A layout plan of Fukushima Daiichi unit 1's reactor building first floor is available on page 23, and that of the turbine building first floor is available on page 25. The north side (on the top of page 23 or on left of page 25) and south side (on the bottom of page 23 or on right of page 25) airlocks are clearly visible between turbine and reactor buildings. You may also want to have a look at the reactor building's fourth floor on page 21, where IC (A), IC (B) and the exhaust vents (pig nose) are represented.

I think we have multiple uses of the word "airlock" meaning quite different things. At the entrance to the reactor building there are double doors forming an airlock that prevents disruption of the normal airflow pattern to prevent undesired contamination movement. These are your typical industrial doors with weather-striping type gaskets. They are only able to withstand very low pressures generated by ventilation systems.

There are similar doors at the entrance to the control room to prevent entry of contamination in an accident.

To enter the primary containment there are bolted hatches with gaskets able to withstand rated containment pressure. Whenever I've heard the term "airlock" they are referring to the primary containment entry. In the pdf these are visible on page 27 between the reactor building and the primary containment.

 

[SteveElbows]

Talking of ventilation:

http://www.tepco.co.jp/en/press/corp-com/release/12011005-e.html

Operation of ventilation and air-conditioning system at reactor building
of unit 5 and 6 has been suspended since March 11, 2011. We have been
carrying restoration works and checks to repair the system to prevent the
equipment from degradation aiming for keeping the stable cold shutdown and
improve the high-humidity environment in the building. Now the system is
ready to operate and so we will start the operation of the system at 13:30
pm on January 11, 2012.
The operation of the system leads air inside of reactor building to be
exhausted through main exhaust stack of unit 5 and 6. However, we will
monitor the exhausted air by radiation monitor (exhaust monitor) that is
the same as the way we monitor them before March 11, 2011, and also we
will exhaust the air through newly installed high performance particle
filter placed at both intake and exhaust sides at air-condition equipment
in reactor building to reduce the level of radioactive.

 

[jim hardy]

""The N-16 is extracted at the condenser. ""

is there not a quite lengthy maze of pipe in main steam line between reactor and turbine, for purpose of delaying steam's arrival until n16 has mostly decayed away?

and that's why there's so much volume in some of those basements, they are huge rooms surrounding that pipe?

tsujitsu -
"How is it generated ? "
n16's halflife is in seconds as rmatlla said. so it's quite active because half of it decays every 7 seconds.
in pwr it's the reason we can't go around the primary loops at power. it has an energetic gamma ray accompanying its beta decay..


in case you've not tinkered with chart of the nuclides:
http://www.nndc.bnl.gov/chart/chartNuc.jsp
type n16 into "nucleus " box,
click "go" button then "zoom 1" above

have fun!

 

[matthewdb]

""The N-16 is extracted at the condenser. ""

is there not a quite lengthy maze of pipe in main steam line between reactor and turbine, for purpose of delaying steam's arrival until n16 has mostly decayed away?

No. The pipe routing in a BWR and a PWR are quite similar. The pipes are big and expensive and the owner of the plant doesn't want to buy more than they have to. They are around 3/4 m in diameter and there are 4 in parallel. 70 seconds of pipe would be an incredible maze.

and that's why there's so much volume in some of those basements, they are huge rooms surrounding that pipe?

The biggest item on the lowest level is the condenser. In a 1GW plant the condenser is around 12m tall, 20m wide and 40m long and there are three of them. The condensate pumps have to be in the basement to provide suction head (actually well below basement grade in a pit). Water in the condenser is at saturation temperature and the motive force is gravity; if a pump were to try and lift condensate it would just flash to steam.

If open feed heaters are used, the feed pumps must be located at the lowest level to provide suction head to them too.

 

[rmattila]

Steam velocity in the steam lines is typically some 50 m/s, so the steam does not spend a long time traveling to the turbine. There is some delay in the top of the reactor vessel, but all the steam lines up until the condenser ejectors are pretty active during operation. Some 10 mSv/hr is normal in the vicinity of the steam line outer isolation valves.

 

[gmax137]

is there not a quite lengthy maze of pipe in main steam line between reactor and turbine, for purpose of delaying steam's arrival until n16 has mostly decayed away?

No. The pipe routing in a BWR and a PWR are quite similar. The pipes are big and expensive and the owner of the plant doesn't want to buy more than they have to. They are around 3/4 m in diameter and there are 4 in parallel. 70 seconds of pipe would be an incredible maze.

Yeah, I think some PWRs have a run of 'delay pipe' in the letdown line for N-16 decay, maybe that's what jim hardy is thinking of. For 70 seconds at 132 gpm you'd need about 20 cubic feet of pipe.

 

[Pakman]

For PWR it's vital, yeah.

 

[Pakman]

Well. The conditions you mentioned above can tell you that more likely there's no significant threat to human's life in the reactor building as long as fuel is covered. You just need to know how long.

Of course, then you tell me that is not enough to enter the building, since there's no 100% gurantee. I skip this conversation and answered right to the last in terms, that who does not want to do their job, will always find an excuse.

 

[jim hardy]

bravado and big machinery is a bad combination.

if one wants to know the position of a valve he can lift leads in control room and read position switches with an ohm-meter
or find whether there's flow downstream of it
without endangering his co-workers (they'd have to go in and drag him out)

i won't criticize anyone's actions in a disaster zone without first-hand knowledge of the circumstances.

the trouble with harsh words is one so often has to eat them.

 

[Pakman]

Doubts and hesitancy is what really can not be combined with large machines. Or you're ready for taking action in the same plant conditions and you say this or you're polite.

Jim, you said you're an old instrument guy, so you're not an operator? Real operator, i mean, heat guy? May be because of this all your doubts are?

You think just like an instrument guy. Of course it's possible to check switches with ohm-meter. What if the valve position is not what you want? How will you operate it? Using ohm-meter's accumulator?

 

[r-j]

It takes a mixture of hydrogen and oxygen to be explosive. One or the other but not both doesn't give you an explosive mixture.

This reminds me of all the concern during the Three Mile Island accident concerning the "hydrogen bubble". The concern is that it was going to explode and breach the system piping.

Greg

Page 99 of the he Presidential Commission report says there was a hydrogen explosion inside the containment building.
http://www.threemileisland.org/virtual_museum/pdfs/188.pdf

Has anyone figured out what ignited the hydrogen/oxygen mix in the Fukushima explosion? I read that the first explosion happened right after they had hooked up power to the building.

 

[jim hardy]

Jim, you said you're an old instrument guy, so you're not an operator? Real operator, i mean, heat guy? May be because of this all your doubts are?

You think just like an instrument guy.

guilty as charged, Pakman. I am an old instrument guy.

i have highest regard for operators. they have a different psychology, ability to stand back and assess whole situation.
my makeup causes me to focus on small details.( google aspergers)
i would not make a good operator.

old men err by thinking too much before they'll act.
young men err by thinking too little before they act.

that's why one wants a mix of fresh thinking and experience.

in emergency, somebody with suitable talents chooses between the courses of action recommended to him.

if the shift supervisor asked me to go in, knowing the conditions were i might not come back out, i would go. I'm 65 and my kids are grown.
but i wouldn't place him in situation of having to answer "why'd you let him do that?"
and neither should a younger man

old jim

 

[Pakman]

I was an NPP operator. I can't imagine to myself the situation, when my shift supervisor being unaware about reactor cooling status wouldn't send me immediately anywhere he is thinking it is necessary, to check what he wants to be checked. He will never be guessing if the reactor is cooled or not. In case of high radiation, if we refused to do the task, he will go there personally by himself

 

[al2207]

Page 99 of the he Presidential Commission report says there was a hydrogen explosion inside the containment building.
http://www.threemileisland.org/virtual_museum/pdfs/188.pdf

Has anyone figured out what ignited the hydrogen/oxygen mix in the Fukushima explosion? I read that the first explosion happened right after they had hooked up power to the building.

i think what cause the water to be dissociated the beryllium tube will be the factor for the ignition because when burning it is creating flashes

 

[jim hardy]

if we refused to do the task, he will go there personally by himself

If you encountered drastically different radiation than he expected, surely you'd tell him? That sounds like an important indication as to state of things.

Morning of TMI an electrician brought an old fashioned bridge to the control room and read the millivolts comiing from incore thermocouples.
He observed they were well above 650 degrees, i think approaching a thousand (F).
(some ill advised person had programmed plant computer to display question marks when readings got that high, so operators were confused by disparate indications.)
He had Navy experience and advised control room operators "You need more water in there..."

i don't know why that key information was dismissed. Perhaps it didn't get to SS.

if we refused to do the task, he will go there personally by himself

just like you, i can't imagine that becoming necessary.

 

[matthewdb]

Has anyone figured out what ignited the hydrogen/oxygen mix in the Fukushima explosion? I read that the first explosion happened right after they had hooked up power to the building.

Hydrogen is phenomenally easy to ignite. With most fuels it is effective to control ignition sources to prevent explosions. With hydrogen it is irrelevant. You must prevent explosive mixtures from forming because minute static discharges from airflow can ignite it.

 

[matthewdb]

If you encountered drastically different radiation than he expected, surely you'd tell him? That sounds like an important indication as to state of things.

Morning of TMI an electrician brought an old fashioned bridge to the control room and read the millivolts comiing from incore thermocouples.
He observed they were well above 650 degrees, i think approaching a thousand (F).
(some ill advised person had programmed plant computer to display question marks when readings got that high, so operators were confused by disparate indications.)
He had Navy experience and advised control room operators "You need more water in there..."

I didn't think they had malfunctioning sensors at TMI, just a failure to understand their meaning. They didn't consult a steam table to realize that the pressure and temperature they had were for steam not sub-cooled water. Because of this all PWM plants in the US now have a subcooling calculator with a readout in the control room. That and not recognizing a rising temperature in containment and sump pump operation to indicate a LOCA.

They did get a surprise when they asked for a primary water sample. The chem tech reported brown primary water with incredible activity. At that point they realized they had a fuel melt.

Perhaps you're confusing this with the Browns Ferry U1 control room fire? They measured the RPV water level and pressure and the containment temperature and pressure using a multimeter in one of the electrical rooms. They then shut the plant down by operating the RCIC and containment cooling locally and operating the blow-down valves via a makeshift switch.

 

[djm51x]

senior nuke QA Engineer here...how are things going at the plant?

 

[djm51x]

what do you think about letting the cavity water boil for 48 hours, while the reginative heat exchangers are being repaired...the fuel pool was also boiling?Am I over reacting?

 

[jim hardy]

""I didn't think they had malfunctioning sensors at TMI, just a failure to understand their meaning. They didn't consult a steam table to realize that the pressure and temperature they had were for steam not sub-cooled water. Because of this all PWM plants in the US now have a subcooling calculator with a readout in the control room. ""



their plant computer wasn't malfunctioning, it was simply programmed to display question marks instead of readings that were higher than whoever programmed it thought possible.
That's why the fellow read them with a bridge type millivolt meter.
displaying question marks for beyond-expected thermocouple readings became an industry issue , we had to answer numerous inquiries and provide assurance that ours wasn't programmed that way.


indeed, i too read report they had no steam table in the control room.
It seemed to take forever to get an electronic subcooling meter bought and installed. Meantime i pulled the wide range pressure meter, which was an analog instrument with a needle and printed scale, and wrote alongside each major scale division the corresponding saturation temperature, put it back in panel...
works great because almost adjacent to that meter is the temperature indicator.

but I'm way off topic.

over and out.

 

[Rive]

what do you think about letting the cavity water boil for 48 hours, while the reginative heat exchangers are being repaired...the fuel pool was also boiling?Am I over reacting?

??
Can you please give me some links or something about this?

 

[elektrownik]

And what is with unit 2 temperature: http://www.tepco.co.jp/nu/fukushima-np/f1/images/12011612_temp_data_2u-j.pdf ?

 

[Pakman]

Corium runs down the control rod drive