Thursday, March 17, 2011

Journal Of The Nuclear Mess In Japan

My ex-wife is Melinda Otte, a Nuclear Engineer currently working in the business.  She was kind enough to permit me to repost this from her Facebook page.  I will add that she is, well, brilliant.  Thanks to my daughter for obtaining said permission .  You can see that it covers several days.

NOTE:  Newer stuff is at the bottom.
I was at the offices of the Nuclear Energy Institute (NEI) in Washington, D.C. on Friday.  It was kind of strange being there, because the NEI folks were getting updates about every 15-30 minutes.

Monday morning about 7:35

The explosions the news has talked about are hydrogen explosions, NOT nuclear explosions.  There have been two (at Fukushima Daiichi plant, units 1 and 3).  Unit 2 has lost its cooling capacity, and they are working on removing hydrogen from the Unit 2 reactor building (to avoid a similar explosion there).

The explosions are in the secondary (outer) containment buildings, but the primary containment and the reactors themselves are safe (at this point)

All the reactors are “shut down,” but in a nuclear reactor, you need to continue to cool the fuel even when the reactors are “turned off.”  There were some issues with providing cooling water to some of the reactors (as a result of the 8.9 earthquake and a huge tsunami), and they are using sea water at some of the plants to ensure enough cooling water is available.

There was some mention of radiation exposures on the news.  Actual radiation levels at that time were 155 millirem per hour on site.  Millirem and rem are just units of radiation exposure.  To put this amount into perspective, federal regulations in the US limit radiation exposure to the general public from a nuclear plant to 100 millirem per year, but they allow nuclear workers to receive 5000 millirem (or 5 rem) per year.  If it was 155 millirem on site, it would have been MUCH lower outside the plant, because radiation dose decreases significantly as you increase the distance.  (Example—if you’re 1 foot away from the source of radiation and you’re getting 155 millirem per hour, at 10 feet away you’re only getting 1.55 millirem per hour of exposure.)  We have areas in our plant that are well above 155 millirem per hour, and people go in and perform work in those areas.

An additional reference point—you get and average of about 300 millirem per year from natural radiation (from rocks, bricks, the sun, natural radioactive gases in the air, etc.) every year, depending on where you live.  Medical procedures (like a CAT scan), range from about 150 millirem (for a Barium swallow procedure) up to about 5700 millirem for a full blown angioplasty (heart study).  

The plants in Japan were designed to withstand the force of powerful seismic events, and the containment structures did an awesome job of withstanding the earthquake (even this “mother of all earthquakes”).  At this time, the primary containments are all intact.  They were also designed to withstand tsunamis, but this one exceeded the design basis.  The force of Thursday’s tsunami flooded the diesel generators and their fuel.  Lack of emergency power is what is challenging the reactor cooling systems.  [No power to pump the water.]  They expect there has been some damage to the fuel in reactors 1 and 3, but with if the primary containments are intact, this does not pose a threat to the public.  (The steel and concrete containment vessels, with walls from 40 to 80 inches thick, are designed to contain the radioactive materials.)

Bottom line:  Japan is facing what literally can be considered a “worst case” disaster and, thus far, even the most seriously damaged of its 54 reactors has not released radiation at levels that would harm the public.

Some additional info: Nuclear power plant operators in the U.S. are trained to ensure that their plants will achieve and maintain safe shutdown during a station blackout scenario (loss of offsite power AND loss of onsite emergency AC power). They have operating procedures that guide them on actions to be taken in responding to this condition, and they practice this frequently in the plant simulator.

Monday evening at 7:50

Update on Japan. There has been a "blast" heard at the Fukushima Daiichi 2 plant, and they are concerned there there is a defect in the containment, possibly impacting the torus within containment.
The torus, or suppression pool, contains water and is used to remove excessive heat if steam is released (by condensing the steam). This is where my knowledge breaks down because I don't know much about Boiling Water Reactors (BWRs). I know about Pressurized Water Reactors (PWRs).  If it were a PWR with a crack in the coolant piping, we could [simplified] keep putting water in and letting it run out through the crack, carrying some of the heat with it.  I really don’t know what they can or can’t do with a BWR.  I know this is serious and they are working on continuing cooling.  Fuel most likely is damaged with some melting, but that is not the horrendous event that many fear mongers make it out to be.  There was some significant melting at Three Mile Island, and there was very little impact on the general public.
They are a far cry from being out of the woods.  Things will get more serious if something happens to the containment for the reactor with plutonium.  But even then, if they can keep cooling water to the reactors, that is more than half the battle.
I'm pretty impressed with the fact that they are keeping up with things in the face of the chaos in the aftermath of a major earthquake and that tsunami. Just getting around is challenging and they are having to deal with THIS? God bless them!! I'm praying for their continued fortitude and wisdom to make the right decisions, and to keep themselves safe as well as the public.

Tuesday, around noon

Ready for another Japan update?  I have seen some updated numbers released for radiation dose rates.  As of this morning (9:15 EDT), the radiation levels at the site boundary of Fukushima Daiichi were reported to be 821 millirem per hour.  This is much higher than they like—remember from earlier posts that regulations limit exposure to the public to 100 millirem per year.  They have evacuated the general public to a 12 mile radius around the plant.  If the radiation stayed at the plant, the public outside the 12 mile radius would be receiving essentially no dose.  But, it looks like the wind is blosing to the south, and has carried the radioactive “plume” along with it.  As it moves, it will disperse and be diluted.  They were seeing about 0.4 millirem about 200 km south of the plant (about 124 miles).

So, the measurement was 40 rem/hr (40,000 millirem) near the Unit 3 reactor, 821 millirem at the site boundary, and 0.4 millirem at 124 miles.  [NOTE:  without knowing what the wind is doing or the plume, we can’t make too many judgments about what is happening in the 124 miles between the plant and the measurement point.  If the radiation was released in a “puff”, it could be mostly contained in the “cloud” that is passing over the measurement point.  Or, it could be a plume that is stretching from the plant to 124 miles away. Without more information, I just don’t know.

So—what does this level of radiation mean?  The biggest impact, of course, is on the (about) 50 workers remaining in the plant.  (Again, God bless these folks—they are putting themselves out there to get this under control.)  You can work in a 40 rem/hour field for about half an hour with no detectable effects.  (You wouldn’t see anything on medical tests, etc.)  If the workers have to go into a 40 rem/hour field to take action, they will most likely “tag team” it, so no one person would be in the field too long.

If radiation is released in a “cloud” and a person is standing there when it passes, they get radiation exposure and they can become contaminated.  (This means that some of the radioactive dust can stick to them.)  About 150 people near the Fukushima Daiichi site were checked for contamination and 23 people had to be decontaminated.  [There were no contamination levels provided, so I can’t talk about how serious this was.]  This probably means that they got to take a shower and change clothes [and shoes].  Contamination is physically like any other dirt.  You wash it off.  (No wire brushes allowed—for you Silkwood fans!)

A major concern when a radioactive plume is passing through, is breathing in contamination.  (Once it’s inside of you, you can’t wash it off.  You have to wait for your “biological processes” to get rid of it.  They typically advise the public to “shelter,” i.e., go into a house or building until the plume passes, so it can’t deposit contamination on them and the won’t breath it in.  [Also, the exposure received is less because of the extra distance between you and the plume.]

One of the concerns about the plume is the radioactive iodine it contains.  Iodine collects in your thyroid.  This is why the Japanese officials were passing out potassium iodide tablets for people to take.  [Fill the thyroid up with “good” iodine, and if you breathe in radioactive iodine, no more will “fit,” so the body just gets rid of it.]

There was a question about the 400 millisieverts reported on the news.  This is the same as 40,000 millirem, or the 40 rem discussed above.  Just a different unit of measurement (like miles and kilometers).

Tuesday afternoon about 1:50

The fire reported on unit 4 was caused by an oil leak, and was NOT in the spent (used) fuel pool as reported by the media.  In addition, this unit was in a maintenance outage, and there is no fuel in the reactor at that unit.  (For those who have heard me talk about refueling outages and notice that I “disappear” for several weeks at a time, this should sound familiar to you!)

Question asked by friend:  I read a story about the workers who are still there.  It said they are wearing protective gear and taking turns to try to limit their exposure.  How effective is the protective gear? 

Answer:  The protective gear they are talking about is most likely to protect them from contamination. They are probably also wearing safety glasses which does protect their eyes from beta radiation. They may or may not be wearing respirators. (There is a tradeoff between the protection provided by respirators and the extra time it may take you to do the job because the respirators are kind of cumbersome.)

Question:  I have some friends in Canada who think that the radiation “cloud” could be moving their way and are worried that they are at risk for contamination. 

Answer:  There will most likely be very low levels of radiation detectable in some other countries, but I would not expect it to be a significant amount at this time.  Right now they are seeing about 0.4 millirem 124 miles south of the Japanese plants.  I don’t know if they only have those numbers because the winds are blowing in that direction, or if it’s because Japan is kind of long an narrow, and they can’t get that far away to measure in an east/west direction.  If your friend lives in western Canada, it might be detectable, but unless things get significantly worse, I doubt it.  [NOTE:  I don’t know weather conditions, etc., so it’s hard to even guess without more information.]  But, if the current “cloud” made it all the way to Canada, intact, and they actually measure 0.4 millirem per hour all the way over there, and it stayed there for an entire year, intact and at that same exposure level, then everybody would STILL get less than the annual limit allowed for radiation workers.  The workers that we stuff up inside steam generators to do some work get that much radiation all the time.  Year after year.  [NOTE:  the cloud that contains 0.4 millirem per hour in Japan will have dispersed and been diluted by the time it makes it to Canada, so it wouldn’t be anywhere close to 0.4 millirem when it got there.  And the radioactive material would decay throughout the year, so even if it ALL got there, it wouldn’t stay at that “strength.”  It would continue to disperse and decay.]

Radioactive iodine poses a threat to young children, because it collects in their thyroids, and young children are growing faster than the rest of us, which makes them more sensitive to radiation.  But, Iodine-131 has about an 8 hour half life.  (This means that in 8 hours, about half of it has undergone radioactive decay and is gone.  So after 16 hours, you would only have a fourth of the original, and after 24 hours, there would only be an eighth of it….)  They are probably giving potassium iodide to all the children around the Japanese reactors to protect their thyroids.  With an 8-hour half life, the amount of iodine-131 that reaches Canada would be minimal. 

Pregnant women are of concern (because the cells in the unborn child are reproducing at a tremendous rate, which again, makes them more sensitive to radiation).  But we have pregnant women working at nuclear plants.  The National Council on Radiation Protection recommends they be limited to 500 millirem for the entire term of pregnancy.  So again, barring significant changes, I wouldn’t expect enough radiation to make it as far as Canada to even begin to challenge that.

Tuesday evening, 7:50

I would recommend against wasting your time buying iodine tablets [if you are in the US/Canada].  See explanation on iodine in response to question directly before this.

It's a serious situation and certainly worthy of being nervous about, especially if you live in Japan. Impact on the US should be minimal for current conditions.

Thursday Morning about 11 am

There is concern about the condition of the spent (used) fuel pools at a couple of the reactors.  (One source says that in one, the fuel is completely uncovered.  Another source says it is not yet completely uncovered.)  Also, the radiation levels are high enough to prevent people from working in the immediate area.

They have begun using helicopters to drop water on reactors to provide cooling.  Each helicopter can drop about 7.5 tons of water.  (wow!)

Reports are that radiation levels at the plants are continuing to drop at the plant.  I did see a report that they measured 33 millirem per hour at about 12 miles from the plant.  (This would be the edge of the evacuation zone.)  This is probably why the US government is encouraging an US citizens to increase their distance to the 50 mile radius.  (And why they are being encouraged to just leave.)  But, you can stay in that field for about 151 hours and still be below the limits that US regulations allow workers to receive, and for more than 600 hours before any noticeable effects. 

Radiation Protection Primer, or Radiation Protection 101:

This can be summed up in three words:  Time, Distance and Shielding.

Time:  Reduce the time you're in a radiation area (OR, WAIT until the radiation levels have decreased).  This is why the workers are "tag teaming" different activities, so that no one individual is in the high radiation fields too long.  Also, why some activities are being resumed because radiation levels at the plant have decreased.

Distance:  Put more distance between yourself and the source of radiation.  This is why the general public is being evacuated from the areas immediately surrounding the plant (and out to 12 miles).  And why the US is telling its folks in Japan, "yeah, you might want to evacuate out to 50 miles, or better yet, just come home."

Shielding:  Put additional shielding between you and the source of radiation.  Inside the plants, we often use concrete or lead to provide shielding from the higher radiation areas.  This is another reason the water being lost from the spent fuel pools is not good.  In addition to cooling, it also provides a shield from the radiation.  Typically, spent fuel pools are open, meaning they are not a covered tank.  They are inside a building, but it sounds like the roof has been torn off by one or more of them at the Japanese reactors.  They keep enough water in them to provide enough sheilding that you can walk around the edge of the pool and look in.  (We even take some tours in to look at our spent fuel pool.)  But when you lose that layer of water, you lose both cooling and shielding.

I know NEI (Nuclear Energy Institute) plans their updates JUST to ensure that they priovide one AFTER I have updated my notes.... But here's another one.

Some information behind the decision to suggest that US citizens increase the evacuation distance to 50 miles vs. the 12 being recommended by the Japanese government:  According to NEI, this was more because of the lack of a lot of information concerning the dose rates in the area.  I know in the US, our emergency response organization includes Offsite Monitoring Teams that provide actual information on rad levels in the area around the plant.  Japan probably does the same thing, but remember, they've had an 8.9 level earthquake, and they probably can't just easily hop in the truck and zoom over to a spot 5 miles away to check the rad levels there.   Also, in part, the recommendation for non-Japanese citizens to leave is based on limited services, rather than concern on radiation releases.

Some info on radiation levels in neighboring countries following Chernobyl
I am NOT trying to imply that we have another Chernobyl here, but I've had questions about what some other countries (espcially the US and Canada) can expect to see from the current situation in Japan.  Not enough information is available right now for me to give a good answer to that.  But I CAN share what happened after Chernobyl:

Radiation levels in the aftermath of the Chernobyl accident were 1 millirem per year in the United States and in Canada. By comparison, each person receives the same radiation dose from watching television over a year’s time. Among countries neighboring the site of the Chernobyl accident, Bulgaria received the highest radiation dose at 76 millirem per year, followed by Austria at 68 millirem per year, Greece at 59 millirem per year, and Finland at 45.

If you've read the earlier information in this note, you'll know that all these values were considerably less than what you receive from natural background radiation (which averages about 300 millirem per year, depending on where you live).  So, even after Chernobyl (and we're nowhere near that level of concern at this point!) the radiation levels at the countries "right next door" were not that bad.

Reported status of Japanese plants as of 11:35 this morning:

The reactors at Fukushima Daiichi are in stable condition and being cooled by seawater.  They are still trying to provide additional cooling water to spent fuel pools at units 3 and 4.

Reactor 1:  Reactor in stable condition, primary containment intact.  Cooling with seawater.
Reactor 2:  Reactor in stable condition, cooling with seawater.  They are think now that the primary containment may still be intact (contrary to what was reported earlier).  They are still trying to get some offsite power restored to this site.
Reactor 3:  stable and being cooled by seawater.  Primary containment believed to be intact.  On one side of the spent fuel pool, the concrete structure has collapsed, but the stainless steel liner is still in place, based on aerial photos, and there is still some cooling water.  Helicopters are dropping additional cooling water here.
Reactors 5 and 6 were both shutdown and containments (both primary and secondary) are intact here. 
(Note:  Reactor 4 contains no fuel, as it had been offloaded for a maintenance outage.  Only concern here is for the spent fuel pool.)

Fukushima DainiAll four reactors at the Fukushima Daini plant have reached cold shutdown conditions with normal cooling being maintained using residual heat removal systems. 
Information on Spent Fuel Pools and why everyone is concerned about THEM.
Spent Fuel Pools store used nuclear fuel.  There are 7 of these at the Fukushima Daiichi plant—one for each reactor and a shared pool.  About 60% of the used fuel on site is in the shared pool that is in a building separate from the reactor building.  The rest is split between the 6 reactor storage pools and some dry storage containers.  The 6 reactor storage pools are located on top of the buildings.

The pools are designed to ensure enough water to provide cooling and radiation shielding.  Pools are designed so water cannot drain down because of breaks in the coolant piping.  (I.e., cooling water comes in at the top of the pool, so the pool can’t be drained through that piping.)  The only way to rapidly drain a spent fuel pool is to have structural damage to the walls and the floor.  (Note:  there was damage to the concrete structure on the walls of the unit 4 pool, but the stainless steel liner appears to be intact.) 

Spent fuel pool cooling is important because the used fuel continues to produce heat even after it has been removed from the reactor.  But, the rate that heat is produced is less and less the longer it has been out of the reactor.  If cooling to the pool is lost, you would expect a slow temperature increase, so the water would evaporate a little faster, and loss of cooling for extended periods could result in mild boiling.   This is slow, and would lower the pool level by only a few percent per day.  Plants typically keep AT LEAST 16 feet of water over the spent fuel for shielding purposes, so you should have a few weeks to find another way to add water to the pools (like using a fire hose or dropping it in from above) before the fuel is uncovered.

If the fuel does become uncovered, it’s not as serious as if the fuel in the reactors is uncovered, because, remember, this fuel is producing heat at a slower and slower rate the longer it’s been out of the reactor.  So it’s much less likely to melt.  There will probably still be some clad damage (clad is the metallic covering surrounding the fuel) and some reaction between the (now very hot clad) with the air to produce some hydrogen.  (Remember, hydrogen buildup was what caused the explosions earlier.)  Because the fuel in the spent fuel pools is producing less and less heat, the hydrogen production would be a lot less than that from fuel in the reactors. 

As the water level in the spent fuel pools decreases, the radiation levels in the area will increase because the water also provides a shield from the radiation.  This would be detected by radiation monitors in the area.

Current radiation levels update (Thursday at about 1:30 pm)

Radiation levels at the Fukushima Daiichi site boundary today were measured to be about 2 to 3 millirem per hour.  Is the situation over?  No, definitely not.  There is still the potential for the conditions to escalate.  I (personally) would be surprised, but very pleased, if there were not other releases of radiation still to come.  They are still working on ensuring a continued cooling supply to reactors and fuel pools and restoring electricity.

1 comment:

Dad29 said...

Thanx. Good stuff.