The water is contamined, but it’s not the source of the radiation. The ultimate source of the radiation is the damaged reactor core itself. Pumping the water out gets rid of the radioactive water, but the core will remain, and now you will now have a buffer of water acting as insulation against the radiation.
Water is both erosive (see Grand Canyon) and corrosive (it reacts chemically with other substances). For a long-term structure you need things dry. Either they need to get all the water out, or somehow construct something that can store the water indefiniately without leaking into the environment. The former is much easier to accomplish than the latter, even if “getting all the water out” is extremely difficult.
Even if true, this doesn’t mean anything. All it indicates is that people are afraid. It says nothing about whether or not they have something to be rationally afraid of.
Like people who won’t let a black cat cross their paths. Nothing to actually be afraid of, but they do it anyway. That’s not to say there’s nothing to be afraid of in this situation, but evidence of fear is not evidence of actual danger.
Thank you! My understanding of this is embarrassingly poor, but trying to get a grip: this is not beta decay we’re talking about, but there were then plausibly some low intensity fission still producing neutrons after SCRAM, and that’s the reason for the boronated water?
[QUOTE=Broomstick]
The water is contamined, but it’s not the source of the radiation. The ultimate source of the radiation is the damaged reactor core itself. Pumping the water out gets rid of the radioactive water, but the core will remain, and now you will now have a buffer of water acting as insulation against the radiation.
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So if I understand this correctly the question is if there’s a chance for radiation levels to drop by themselves given time, e.g. is the “natural” progression wrt the core or what’s left of it that it will become less radioactive now that the fission process has long since been stopped? Iow, how alarming is it that the levels are as high as they are at the moment? It would seem to hinge on whether the situation is likely to get better or worse with time…
Yes - with time the mess left in the reactor will become less radioactive. A major problem with regard to this is that it will take a long time for the levels to drop to anywhere near safe for a human being to be near the mess, far longer than a human lifetime. This is because a nuclear reactor core, of necessity, is composed of stuff that gives off high levels of radiation.
If a working nuclear reactor is analogous to a bonfire then the Fukashima plant is like when the flames are put out but the coals are still hot - it takes time for them to cool down. This applies to both the actual temperature of the core and the radiation “cooling” off by decay over time.
What’s alarming is that these radiation levels are outside the reactor vessel. These radiation levels are normal (or nearly so) in a working reactor core, but a properly functioning reactor keeps all the fuel and its radiation contained behind multiple barriers. High radiation outside those barriers mean the barriers are no longer intact. There is concern because, first of all, that vastly complicates cleaning the place up and potentially endangers workers. Second, that means the nasty stuff might leak out of the plant into the environment, which would be bad. How bad depends on what isotopes, how much, and how long they take to decay. The iodine, for example, is of concern but it has a half life of I think 8 days so it rapidly goes away on its own. More dangerous is cesium, of which there is less quantity but its half-life is, um 20-30 years? Something in that time frame. So it will be around a lot longer and that’s one of the things that makes it more threatening. Some of the other isotopes present in the actual fuel last much longer, so even in minute quantities they can be dangerous.
Now, all of that nuclear stuff giving off radiation will, eventually, decay and stop doing so. Eventually. In the case of something like plutonium that might be tens of thousands of years, though, and that’s where it gets complicated. If it were a giant pile of radioactive iodine you could just rope the place off for a few months, then go back in safety. If it were a giant pile of radioactive cesium you need to stay away 150-300 years, but after that, no problem. Horribly inconvenient, but it’s not forever. 20,000 years? Well, that’s three times the length of written human history. 100,000 years? 200,000? Possibly longer than our species has even been in existence.
How long is corium actually dangerous? I have no idea, other than “longer than my life expectancy”. It depends on what exactly is in it.
So we have to do something to contain the really dangerous stuff inside Fukushima because it would be hazardous to let that nasty stuff leak out. Now, waiting a couple months, or entombing it for 20-30 years, or a century, will make an appreciable difference in the overall radioactivity as isotopes with shorter half-lives decay into harmlessness. This will make what’s left easier to handle. There is some benefit in waiting awhile before doing certain things, but it’s a trade off between “wait until it’s a little safer” and “risk more stuff leaking where we don’t want it to go”.
Well, fission is a little out of my forte, but I believe so. Boron isn’t terribly helpful at blocking beta emissions, water can do that fine by itself. Nor is there much worry about activation by anything other than neutrons. Or maybe Borax has TEPCO in their pocket.
[QUOTE=Broomstick]
So we have to do something to contain the really dangerous stuff inside Fukushima because it would be hazardous to let that nasty stuff leak out. Now, waiting a couple months, or entombing it for 20-30 years, or a century, will make an appreciable difference in the overall radioactivity as isotopes with shorter half-lives decay into harmlessness. This will make what’s left easier to handle. There is some benefit in waiting awhile before doing certain things, but it’s a trade off between “wait until it’s a little safer” and “risk more stuff leaking where we don’t want it to go”.
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First: thanx for all the info!
So what I’m trying to wrap my head around here is the fact that radiation levels in the reactor have already been measured at least at one spot so high that staying 30 minutes inside will literally make you sick and staying an hour and a half is likely to kill you. That tells me that if radiation levels can’t be brought down by any workable means such as pumping out water, then the situation is already pretty close to where you either just have to give up on ever restoring containment integrity or else accept that some people basically have to die to get it done.
So it looks to me we’re not terribly far from the point where TEPCO are just forced to give up on cooling the RPV and let the chips fall or else continue dumping water in it and let it just leak off to wherever…?
So if that’s the case they are probably starting to look at Chernobyl style entombment already..
I wish to emphasize, however, that extremely high levels of radioactivity aren’t inherently unmanageable. The isotopes and radiation sources used routinely in medical applications are high enough to cause illness or kill, but *properly *handled they are extremely useful and pose little risk.
Or, with another analogy - the level of heat inside a furnace making steel is enough to vaporize the human body, yet people can work nearby in relative safety. The key is to prevent the hazard (heat, radiation) from harming the nearby people. There are a variety of means to do this. In the case of radiation that can mean distance, or shielding (concrete, water, lead, etc.) or remote manipulating devices.
Another technique used is careful manage of time near a radiation source. That means, if an object puts out enough radiation in a half an hour to cause illness you might not allow anyone to be close enough to have that hazard for more than 15-20 minutes. Even in normally operating nuclear plants there might be some tasks where an outside contractor is hired to perform that task for 5-10 minutes, then that person is not permitted higher than normal background radiation exposure for a long interval - months, a year, whatever.
Thus, if something much be dealt with in Fukushima one of factors they will look at is how much time performing a needed task will take. It might make sense for a worker to run in, do something quickly, then run back out of the area. Workers at nuclear plants, whether in crisis or not, wear devices that measure how much radiation they are exposed to over time to help avoid excessive exposure.
Incorrect.
Pumping out water will reduce the amount of contaminated substances in the general environment. This will leave the highly hazardous stuff exposed. There will then be several alternatives for dealing with it. Some of them can be quite unusual. When scientists at Chernobyl wanted a sample of the corium there for analysis, but there was a problem with how long it would take to saw a piece off, an AK-47 was used to shoot the larger mass, then a few shards knocked off were carefully collected, put into shielded containers, and taken off for analysis in a manner that did not expose the people transporting it to unusual hazard although approaching the original mass would have been ludicrously dangerous.
So, again, depending on what you’re looking at there are ways to deal with the problem. Maybe you wait a few months, so some of the radiation will decay. Maybe you use remotely controlled equipment to deal with whatever it is. Maybe you encase it, in place, with concrete to provide shielding, then dig the resulting lump out of the ground and transport it as a very large, but not particularly dangerous (as long as it’s intact) lump to somewhere else for permanent safe keeping.
In other words, even if an object is lethally radioactive that doesn’t mean anyone “has to die” in order for it to be managed, moved, or contained.
However, analyzing the risks, coming up with a plan, and employing appropriate technology and care does take time. Although some people want TEPCO to DO SOMETHING! DO SOMETHING NOW! haste is not a virtue here. There are some dangerous items in the plant, no question, and they need to be handled carefully. Priorities also need to be set - stabilizing a teetering storage pool, for example, may be given higher priority than removing or entombing a lump of corium in a basement that, while extremely hazardous, isn’t likely to go anywhere or hurt anyone in the near future.
If they stopped pumping water on it it would, at this point, simply take longer to cool. There might be a slight initial rise in temperature but it’s not going to get hot enough to remelt. Another thing keeping the damaged core covered with water does is provide radiation shielding. Without it, the technicians and engineers would have to be located further away from the core and damage. With it, they can get closer which makes studying the problems involved easier.
That’s certainly a possibility. Although it is hoped that if they do decide on entombment they’ll be able to make a much better structure than the Chernobyl sarcophagus, which was largely jury-rigged and unstable, and is deteriorating.
Entombing would still require construction work, and determining what exactly is going on so leaks and such can be prevented in the final structure.
Ok, so basically you’re saying that this long after SCRAM, decay heat emission is so low that the core material cant get hot enough to melt out of the RPV, even without cooling? That sounds a bit more encouraging! And thanks for all the info, once again.
That is my understanding, yes, at this point the core won’t remelt. I hasten to add I am not a credentialed expert in nuclear reactors, I do not have any special access to on-site data at Fukushima, I’m not even sure those who do are entirely clear what’s going on in the place, and my best-guess as related above might need to be revised if new information comes to light.
Your understanding is fine - there’s a lot to understand and there’s a lot of ramifications that take time to fully appreciate. Personally I’ve learned a huge amount since the Fukushima incident started! You’re playing catchup on material that people here have been reading up on for weeks.
Now, as to neutron radiation, some of the fission products in the fuel rods are themselves extremely fissile and release neutrons by spontaneous fission, so there is still a neutron flux after shutdown that decreases with time. Boronated water would have reduced this and may also have reduced the heat produced, since at least some of the spontaneous fission neutrons would have caused secondary fissions and released more energy. Boronated water would also prevent the momentary re-criticalities I talked about upthread.
That’s correct, but it depends what isotopes we’re talking about. The three big bad boys of radioactive contamination are iodine 131, caesium 137 and stronium 89 and 90.
Iodine 131 is a fiercely radioactive beta-emitter that is very dangerous if it contaminates food, especially to children. It is concentrated by the body into the thyroid gland where it causes thyroid cancer. Children seem to be very much more vulnerable to this for some reason. The good news is that iodine 131 decays relatively quickly with a half life of about 8 days, so after 80 days the amount of it (in the fuel rods, the cores, in the corium if there is any, in the water, on the ground, whereever it has ended up) is 1000 times smaller, and after another 80 days, a million times smaller, another 80, a billion times smaller etc. And since the reactors are shut down and fission has stopped, no more iodine 131 is being created.
The caesium and strontium isotopes are much less radioactive than iodine 131 but they last longer. (The two things go together. The more atoms emitting alpha/beta per second, the faster the atoms get used up.) Half-lives are around 30 years for both of them which means they hang around for a long time and they are radioactive enough to be a real hazard. They are both bioavailable and absorbed by the body. (IMO the much-maligned plutonium 239 is generally far less dangerous except under very specific circumstances.) If they contaminate large areas of land, there’s nothing much to be done except remove the topsoil and take it away, hope the rain washes them into rivers and out to sea, and quarantine the land for farming (or even habitation) for as long as it takes, which might be centuries. Levels of contamination by these elements outside the plant aren’t looking too disasterous yet, but the contaminated water has to be contained and disposed of, and the damaged cores will have to be either entombed or cooled down in a controlled manner and then buried.
The article goes on to explain how a small group of activists have fought a lonely and, unfortunately, a losing battle against the power industry in Japan to improve nuclear safely.
Many articles which I’ve read, both in English and Japanese, over the last two months have reiterated the hubris of the nuclear power industry and its refusal to take the known threat of earthquakes and tsunami seriously.
Many people, IRL and on this board, simply wave their hands and say that it was the gods of the earthquakes and tsunami, and nothing could have been done, but that simply was not true.
There were measures which could have made a significant difference without a budget-killing price tag, but neither the industry nor the lapdog “oversight” government agency had any interest in red-teaming the design to look for weaknesses.
There’s a new post up at Atomic Power Review, and blogger Will Davis writes in the comments section related to the issue of fission after SCRAM, that I asked about here, and also the issue of recriticality that was discussed earlier. I thought it was interesting, so I’ll repost it here:
[QUOTE=Will Davis of Atomic Power Review]
There should be a very tiny fission rate right now, at this time period after the full scram insertion, in a reactor whose core is not seriously deranged, partly or fully melted. If the core is seriously damaged to the point of melting into a mass of what we call “corium,” which is a mixture of the uranium fuel pellets, zirconium cladding, melted control rod material and so forth then you really get into a gray area as to what the fission rate.. if any .. really is. Without a lot of water to moderate neutrons there may not be a large inventory of thermalized neutrons to induce fission, but then again with the new and highly irregular geometry in the core area it’s hard to guess whether neutrons could thermalize in enough numbers to cause a sustained, instead of continuously lowering, rate. Recriticality has been the subject of much conjecture in accident studies. The results from this accident in Japan will greatly enhance future studies by allowing us to modify theoretical analysis with actual events. Hopefully there is data being collected on neutron leakage to get a handle on fission rate.
To me it seems more likely that exposed fuel was superheating water, causing the serious rise in feed nozzle temperature… but temperature increases at other times at the other plants in recent weeks didn’t trigger the use of boron. We must wait for more facts.
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Ok, so it’s likely then that the very high contamination levels found in e.g. water @ Fukushima where you get the 1-2Sv / Hr readings - a lot of that radiation is plausibly from Iodine 131 and is bound to decrease by half in eight days time..?
[QUOTE=TokyoPlayer]
Many articles which I’ve read, both in English and Japanese, over the last two months have reiterated the hubris of the nuclear power industry and its refusal to take the known threat of earthquakes and tsunami seriously.
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And yet they DID take both a tsunami and earthquake thread seriously. They had hardened the plant at Fukushima against earthquake (which it survived fine btw), and had built a protective wall against tsunami as well. The trouble was, they built it 20-30 feet lower than it turned out they needed it. They didn’t plan for the very worst case scenario of a mega-quake of 9.0 or higher, or for a mega-tsunami that would be 20-30 feet higher than the protective wall they had built. And since they thought their defenses were adequate to any reasonable disaster, they made their one REAL mistake…they put the freaking 2nd tier backup generators in a place that would be vulnerable if the worst happened and the sea wall was breached or over-topped, and if the infrastructure to get power into the area was trashed, and if all the roads and ways to logistically support emergency measures were completely trashed and there was no feasible way to rapidly get the men or material into the area to try and fix the problem.
And many people, IRL and on this board feel that every scenario needs to be addressed, regardless of how remote it might be, and if it’s not then they feel that proper care hadn’t been taken. Fukushima was coming to the end of it’s life when all this happened. It was an old design and it was a power plant built 40 years ago. It had some flaws that came out only in one of the worst earthquakes in recorded history…a perfect storm of disasters. Sometimes shit just happens. That’s not to say that the folks who built the thing shouldn’t have thought through what might happen if the worst possible scenario developed and everything went to hell…there was a lot they COULD have done, starting with putting those backup diesel generators someplace that would be protected if a big freaking wave of water breached the defenses.
If a disaster is big enough you get a cascade of problems until the system, no matter how well thought out, simply can’t handle it. Obviously this disaster overwhelmed the planning and design of this plant. Hindsight is always 20/20, and it’s easy to look back now and say that they should have done this or should have done that, or should have spent an additional billion or so to plan for the other. My point being that saying that neither your government nor the industry took earthquakes or tsunamis seriously is wrong. If they didn’t take them seriously at all then there would have been NO protection or contingency for either.
The citizens of Japan wanted and needed power. And I have my doubts they would have been too keen, pre-disaster, in paying a hell of a lot more for safety measures to the scale of what actually happened. Again, in hindsight they probably wish they had…and probably wish they had built large scale sea walls around many of the villages that were wiped out in the tsunami as well. THAT would have saved 10’s of thousands of lives, and my guess is that NOW the citizens of Japan would have been more than willing to pay any price some time in the past to save all those people. But disasters don’t work that way.
As per my post above, the masks are not used in Tokyo, but there are schools closer to the plant where they are required.
Unfortunately, the masks are not that effective. I looked into then when the SARS outbreak occurred in 2003, and I needed to fly back to the States.
The types of maskswhich are used do not form an airtight barrier, and a surprisingly high level of air comes in from the sides and around the nose.
I’m certainly not as expert, but from what I’ve read, the masks are designed for removing pollen (between 10 to 100+ microns) where radioactive particles will be getting a ride on dust particles which can be as small as a half of a micrometer or water particles, of similar size?
The masks are markets as 97% effective at removing pollen, but that is in a controlled lab with no leakage. From what I remember, the typical usage only reduces the intake by dismally low amounts, since air will quickly flow from the path of least resistance.
For flying during the early days of the SARS scare, I purchased N95 rated medical masks, which does provide a better level of protection.
The difference between wearing them and the off the shelf typical mask was remarkably different. Breathing was much more uncomfortable, which is a good indication that they were more air tight.
If it does come down to having to wear masks, you should also be wearing other protective clothes to keep the dust from settling in your hair or on your clothes, so you don’t track it into your house.
If it was all iodine 131, yes, but that is probably not the case. Additionally, more iodine 131 is being added from injected water flowing past the reactor cores and although the total amount in the cores is also decreasing, the initial amount would have been high.
Measurements of the radioactive water in the turbine halls and trenches only seems to be carried out sporadically so I haven’t got a clear picture of any trends there, but I’ve got the impression the measured levels fluctuate. Of course the pumping operations stir up any solids at the bottom and cause flow and otherwise complicate matters.
Measurements taken around the reactor area over time are given here, and they show a distinct exponential-type decay since March in all areas. On some of those graphs you can practically see the measurements halving every eight days. http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1303953470P.pdf
An example of this is that I have learned very recently why the spent fuel pools are snuggled up against the reactors. It’s because the entire refuelling operation is done under water so the hot spent fuel never sees air.
