Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Reno Deano]

Old news, but insight to US Actions at West Coast Nuclear Pwr Plants (all PWRs):

http://pbadupws.nrc.gov/docs/ML1107/ML110700503.pdf"

 

[Astronuc]

"A little radiation is not necessarily bad. Cells can be repared, or dead cells are simply discarded and replaced. The more radiation, the more cellular necrosis, the more one can become seriously ill. Some damaged cells may mutate into cancers. Nerve cells are particularly sensitive to radiation, and they are not so easily replaced."

Considering human evolution occurred during higher levels of terrestrial radiation in the far past, More than a little radiation exposure is not that concerning, except for the weak. I and many of my fellows Nukes have life-time whole body doses exceeding 40 Rem, and are relatively healthy at our retirement ages.

I have also been exposed to radiation well beyond what the average person in the general population would receive, and I'm fine.

On the other hand, I've had one colleague develop thyroid problems, possibly related to exposure.

Still, the industry doesn't need to be unnecessarily exposing the general population (especially pregnant women, babies and children) to radiation - as is currently the case.

 

[Reno Deano]

Apparently the US 7th Fleet has detected radiation at sea and are moving out of the area.

Knowing the Navy they flew through the downwind radionuclide concentrations and brought it back aboard the ship. Some of the highest contamination found external of the reactor compartments on an aircraft carrier is the fresh air intake filters for the ship. When planes lands they shake off accumulated contamination (Cs-137 and other radionuclide's) from their high altitude flights, which is quickly sucked into the fresh air plenums outboard of the flight deck.

 

[marwood]

''When planes lands they shake off accumulated contamination (Cs-137 and other radionuclide's) from their high altitude flights ..."

Is the contamination distribution denser at high altitudes (and up into the jet stream) or do the planes come back with greater contamination because of their path length through the contaminated air being longer?

 

[intric8]

Latest reports of Japan officials bowing in unison to express their remorse and other discouraging comments about the status of all three reactors have me feeling like its game over.

No water>no coolant>2200F+ temperatures>?

Is it inevitable at this point?

 

[Reno Deano]

Is the contamination distribution denser at high altitudes (and up into the jet stream) or do the planes come back with greater contamination because of their path length through the contaminated air being longer?

Its the path length and time immersed. There is long lived 1950's & 1960's weapons testing contamination circulating around up there.

 

[jarvik]

Its the path length and time immersed. There is long lived 1950's & 1960's weapons testing contamination circulating around up there.

I don't think the fission products of the 50s and 60s tests contribute any relevant amount of contamination to these flights. My impression is that the fallout from the atmospheric tests (and other inputs) rain out to the earth’s surface largely within a year or so of their input. Events such as large forest fires can return small but measurable amounts of this 60s fallout back into the atmosphere.

However, I would bet that the current contamination of US aircraft spoken of is >99% sourced to current reactor issues in Japan and not appreciably due to 50s/60s era sources.

 

[turbo]

Is one referring to Onagawa plant? What is meant by enhanced?

There is some concern about the spent fuel pool at FK-I, Unit 1 and whether or not it went dry. I would hope they have checked that.

I have been looking for info on the risks of a dry spent fuel pool. Unfortunately, there is little middle-of-the road info out there. Lots of the worst-case scenarios, though many of them have the fingerprints of Fairewinds Associates on them. Phrases like "Chernobyl on steroids" etc. The NRC materials I found were comforting about the level of safety required, but very light on the risks.

This software simulator site quiz says that the severity of an SFP failure would be on a par with a "worst case power accident".
http://www.microsimtech.com/sfpquiz/default.htm

Can you help clarify, Astro?

 

[gmax137]

I think the worst case scenario for a 'dry spent fuel pool' is overheating to the point where the zirc cladding oxidizes rapidly (in other words, it burns). If you are old enough, you may remember seeing a zirconium fire - the old flashbulbs (think reporters with big crown graphic 4x5 cameras) used zirconium wire. The good news is that, as long as the pool is intact, all you need to do to prevent the 'dry' part of the scenario is add water to make up for any boiloff.

 

[rogerl]

In a nuclear reactor, there are as many as a thousand fuel rods. But there only appears to be a dozen or so control rods which are put amongst the thousands of fuel rods. How does this stop nuclear reaction within each rod? Or in a nuclear reactor. Do neutrons from different fuel rods hit other fuel rods at a distance and the control boron rods are supposed to block or absorb them? But how can the few control rods absorb the neutrons from thousands of fuel rods?

 

[falcon32]

Layman's question...doesn't the rate of radiation greatly increase when a core melts into a blob at the bottom of the reactor because of the inverse square law? So wouldn't a lone melted rod give off much less radiation than a bunch of them?

And at what time is the maximum amount of radiation released? Pre-core meltdown when all coolant is gone? Post?

Thanks for the help!

 

[Astronuc]

Layman's question...doesn't the rate of radiation greatly increase when a core melts into a blob at the bottom of the reactor because of the inverse square law? So wouldn't a lone melted rod give off much less radiation than a bunch of them?

And at what time is the maximum amount of radiation released? Pre-core meltdown when all coolant is gone? Post?

Thanks for the help!

No, the radiation source is independent of geometry, and only dependent on the fission products or nature of the radionuclides decaying. If one looks at the decay heat curve as a function of time, one sees that it is decreasing, and the radionuclides decay to long-lived radionuclides, or inert (non-radioactive) nuclides.

The maximum release would be dependent on a number of variables including the fission product inventory (source term) and the rate at which fuel rods are breached.

 

[Astronuc]

In a nuclear reactor, there are as many as a thousand fuel rods. But there only appears to be a dozen or so control rods which are put amongst the thousands of fuel rods. How does this stop nuclear reaction within each rod? Or in a nuclear reactor. Do neutrons from different fuel rods hit other fuel rods at a distance and the control boron rods are supposed to block or absorb them? But how can the few control rods absorb the neutrons from thousands of fuel rods?

In a BWR, there is one control rod for four fuel assemblies. Most modern BWRs use a 10x10 array of fuel rods, but some fuel rods are part-length rather than full-length (core height), and there are 'water rods' or 'water channels' within the assembly in order to introduce water for moderation in the interior rods of the assembly. So while a 10x10 fuel assembly has 100 lattice positions, some designs have 96 rods, some 91 rods, and other 92 rods, and some of those fuel rods might be 2/3 of the full-length or core height.

The are local differences in neutron flux and power generation, which is more or less proportional to local neutron flux (we call this power peaking, and we can describe local power in terms of an average power and local peaking factor). The fuel rods in the four assemblies are most affected by the control blades, while those on the opposite side of the fuel assembly are less affected - but that is only important when the reactor is critical, and then only when the reactor is at power.

We know the control rods were inserted, which means the fission reaction shutdown, i.e. the fission reaction or power geneation went to essentially zero. However as mentioned elsewhere, there is decay heat from the beta and gamma decay of fission products, which decay well after the fission reactions stop.

Control rods contain a neutron absorber B-10 and/or Hf, which is very efficient at absorbing neutrons. The B-10 is a much better absorber of neutrons than U-235 or Pu-239, so the cores are always designed such that when the control rods are inserted, minus the strongest control rod, the core goes subcritical. Core and fuel design is a very mature technology.

 

[Reno Deano]

Core covered with seawater, and still a continuing melt and release of vapors? Sounds like something is missing, such as a control rod or 2, or the core was never covered. BTW, salt water is a great neutron moderator. Remember BWR control rods need to be held "up" inplace by an intricate hydraulic system.

BWR system description: http://www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf"

 

[ferrelhadley]

Dumb question time (but its the right forum for it I guess)
Where have I gone wrong with this.
If the fuel rods in the core are about 1300K then pluggin into stefan boltman I get
At 1300K I a get c 1.62*10^5 J/s per square meter assuming emissivity of 1.
j = (1300K)^4* 1 * (5.67*10^-8)

So why has there not been a reasonable amount of cooling due to radiative rather than conductive heat transfer? Have I got the calculations wrong?

 

[promecheng]

Just read that there was a third explosion at unit-2. The article mentioned that the explosion created a "defect" in the torus pressure suppression pool. I'm trying to confirm this from a credible source. Isn't the suppression pool considered part of primary containment? I really hope they are mistaken.

http://www.ft.com/cms/s/0/cdc71436-4e59-11e0-98eb-00144feab49a.html#axzz1Gci1ultJ

 

[Astronuc]

I have been looking for info on the risks of a dry spent fuel pool. Unfortunately, there is little middle-of-the road info out there. Lots of the worst-case scenarios, though many of them have the fingerprints of Fairewinds Associates on them. Phrases like "Chernobyl on steroids" etc. The NRC materials I found were comforting about the level of safety required, but very light on the risks.

This software simulator site quiz says that the severity of an SFP failure would be on a par with a "worst case power accident".
http://www.microsimtech.com/sfpquiz/default.htm

Can you help clarify, Astro?

As gmax137 indicated, they plant personnel will make every effort to ensure that the spent fuel pools are filled and cooled. We have no info on that.

The consequence of an SFP fire could be comparable - give or take - to a core accident. But it's not so simple, and no one has done an actual test, although we know something about the physics behind Zr combustion. That's actually something we'll be looking at in more detail.

I have seen Zr alloys inductively heated to temperatures above 1000C, and the protective oxide prevents oxidation. A mass of Zr alloy, like tubing or sheet, is not the same as fine wire in a flash bulb. The oxide won't necessarily 'burn' - uncontrolled or rapid combustion.

I've done an demonstration in high school with magnesium ribbon. We put a flame/torch to an oxidized ribbon - and it just got hot. But once we scratched the oxide, we could burn the metal. In a spent fuel pool, the cladding already has a protective oxide, and it would have to get very hot before the oxide would break and rapid oxidation would occur. How hot the fuel would get depends on the burnup and how long it has been sitting in the pool (i.e., how much decay heat has dropped off).

 

[Astronuc]

Dumb question time (but its the right forum for it I guess)
Where have I gone wrong with this.
If the fuel rods in the core are about 1300K then pluggin into stefan boltman I get
At 1300K I a get c 1.62*10^5 J/s per square meter assuming emissivity of 1.
j = (1300K)^4* 1 * (5.67*10^-8)

So why has there not been a reasonable amount of cooling due to radiative rather than conductive heat transfer? Have I got the calculations wrong?

1300 K for what? Also, if two surfaces are at the same or similar temperature, there is not differential to drive radiative cooling - the two surfaces radiate to each other.

 

[CAC1001]

Quick question, but when they say a nuclear plant is for example "Designed to withstand up to a 7.0 earthquake," do they mean the plant could go into meltdown beyond that level of earthquake, or just that the plant is designed to keep operating up to that level of earthquake, but might have to be shutdown if the earthquake is greater?

Because everyone seems to assume it means beyond that level of quake, the plant could go into meltdown, but for all I know that could just mean the plant is designed to keep operating to that level.

 

[ferrelhadley]

1300 K for what? Also, if two surfaces are at the same or similar temperature, there is not differential to drive radiative cooling - the two surfaces radiate to each other.

I was working on open literature that stated an uncovered fuel rod would reach a temperature of 1100C, but thinking on the issue I've spotted a couple of flaws including that as you say most of the fuel rods will be radiating at other fuel rods so no net loss and as the rods are not really uncovered for all that long they are likely to be significantly cooler plus off course the containment vessel will heat up and radiate back at the fuel rods so this is not really an effective mechanism for losing heat.

I was just wondering why the rods had not lost significant amounts of heat over 3 days and still posed a melting risk unless the moderators had not been fully inserted.

Thanks anyway.

 

[Ferrus]

Can someone answer a basic chemistry question here: what is the redox potentials of the zirconium-water reaction? Is it thermodynamically infeasible under standard conditions, or does the oxide coating merely form a high activation energy barrier ala TST?

 

[edgepflow]

1300 K for what? Also, if two surfaces are at the same or similar temperature, there is not differential to drive radiative cooling - the two surfaces radiate to each other.

For this reason, the only place in the reactor core I could see radiation heat transfer being significant would be the fuel rods on the perimeter. These could radiate to the lower temperature of the vessel. The fraction of the total surface area of the rods is small however, and convenction to the fluid from interior fuel would probably still dominate. A view factor would need to be applied and you could assume the vessel is a blackbody. It would be interesting to calculate. Will try to find some time to do this. I will bet it will be a very small fraction of the decay heat.

 

[edgepflow]

I was just wondering why the rods had not lost significant amounts of heat over 3 days and still posed a melting risk unless the moderators had not been fully inserted.

Thanks anyway.

They have lost significant amounts of heat over 3 days, but the power output is still large. You can back-of-the-envelope estimate the decay heat power with infinite fuel exposure from (Ref. "Nuclear Heat Transport" El-Wakil):

P(t) = 0.095 Po ts ^ -0.26

Po = power before shutdown
ts = shutdown time is seconds

And you can integrate this to get the total energy released.

For ts = 2 days, and Po = 2000 MWt (not sure if this is the actual power before shutdown), there is still 8.3 MW of thermal power. And integrating to 2 days gives 22.3 MW-day of released energy.

 

[NeoDevin]

Why couldn't they have used the remaining heat/steam to run the generator to produce enough electricity to power the cooling system, once the diesel generators had failed?

 

[turbo]

Why couldn't they have used the remaining heat/steam to run the generator to produce enough electricity to power the cooling system, once the diesel generators had failed?

T-G sets are designed to operate in pretty narrow parameters regarding feed pressure, temperature, superheat, etc, and they have intermediate stages and controls. Also, the pressure drop across the turbines has to be enhanced by cooling/vacuum in final stages to make sure that the turbine actually operates at all. You can't pump wet steam into a turbine with insufficient stage-to-stage steam control and expect it to work without tearing itself apart. Please bear in mind that I am used to studying and documenting much smaller (often 30-60 Mw) turbines in single T-G sets, but I don't believe that the laws of physics can be violated when you scale up to larger turbines.

Edit: there are probably emergency pumps that can be driven by robust turbines with with less restrictive feed-quality requirements, like the line-shaft turbine driving my old paper machine, but you have to have electrical power to control those systems, too. If your battery backup fails and you have no access to the AC grid, good luck controlling those. I should mention that such really primitive turbines might be regulated by mechanical governors, but I don't know enough about nukes to know if that kind of low-tech was implemented 40 years ago.

 

[rogerl]

I'm wondering. Right after uranium fuel rods are manufactured in the factor. Do they start to fission and produce nuclear reactions? Then how do the manufacturers store the fuel rods before sending them out? By putting them in live reactor with boron control rods and water
to cool them? For example, when they are shipped out at sea. Do they have to be put in a reactor like configuration inside the ship with running coolant water and stuff just like in normal reactor or do they put them in wooden crate and send them out?? How then do the nuclear plant enable them or turn them on to begin the nuclear reactions?

 

[promecheng]

From NEI:

UPDATE AS OF 9:40 P.M. EDT, MONDAY, MARCH 14:
An explosion in the vicinity of the suppression pool at Fukushima Daiichi 2 just after 6:20 a.m. Japan Standard Time (5:20 p.m. EDT) may have damaged a portion of the reactor’s primary containment structure.

Pressure in the suppression pool has been reported to have decreased to ambient atmospheric pressure shortly after the blast. Plant operator Tokyo Electric Power Co. (TEPCO) has reported possible damage to the reactor’s pressure-suppression system. Radiation levels at local monitoring stations have risen but are still in flux. TEPCO has evacuated some workers from all three Fukushima reactors with the exception of approximately 50 workers involved in sea water pumping activities into the reactors as part of emergency cooling efforts.


Efforts to inject sea water into Unit 2 have been complicated by a faulty pressure relief valve. The fuel at Unit 2 has been exposed at least twice, before being re-covered with sea water.

Japan's Chief Cabinet Secretary, Yukio Edano, has said a partial defect has been found inside the containment vessel of reactor 2 at the Fukushima Daiichi nuclear power plant.

 

[Astronuc]

I'm wondering. Right after uranium fuel rods are manufactured in the factor. Do they start to fission and produce nuclear reactions? Then how do the manufacturers store the fuel rods before sending them out? By putting them in live reactor with boron control rods and water
to cool them? For example, when they are shipped out at sea. Do they have to be put in a reactor like configuration inside the ship with running coolant water and stuff just like in normal reactor or do they put them in wooden crate and send them out?? How then do the nuclear plant enable them or turn them on to begin the nuclear reactions?

BWR assemblies are shipped in pairs. They are in a dry sealed metal inner container in a outer container. They are subcritical.

Fission does not start occurring until the fuel is in the core, and the control rods are withdrawn to preset levels.

Shipments of fuel go by truck usually, sometimes by ship, or by cargo aircraft. Normally within a country, they go by truck.

 

[promecheng]

This situation keeps getting worse. I'm watching the live press conference on NHK and they are now saying unit-4 is on fire due to a hydrogen leak from the spent fuel and unit-4 may have also suffered a hydrogen explosion inside the reactor building.

Also, they are confirming a that there is a hole in the suppression pool structure of unit-2 which is releasing radiation.

The good news is that they think that units 1&3 are effectively cool due to seawater cooling operations. Now they need to figure out how to maintain cooling.

Radiation is now being measured at the plant as 400-800 milliSievert, not micro!

Edit: They've also increased the radius from 20 km to 30km from the plant where people should evacuate, or stay indoors.

 

[rogerl]

BWR assemblies are shipped in pairs. They are in a dry sealed metal inner container in a outer container. They are subcritical.

Fission does not start occurring until the fuel is in the core, and the control rods are withdrawn to preset levels.

Shipments of fuel go by truck usually, sometimes by ship, or by cargo aircraft. Normally within a country, they go by truck.

You mean to say if there are only 2 rods.. fission won't occur even without control rods? How many pieces together before they begin to fission?