More on the Fukushima #1 plant

Ah… wanted to write about some other stuff but theres been a lot of development here.  So let’s run things through…

• Back on Monday, NISA released the 100th version of their Seismic Damage Information, which i guess is a milestone of sorts.

• Yesterday some robots  from the US were able to go into the unit 1 and unit 3 buildings and make initial surveys and radiation measurements. As i think was expected, the radiation levels were rather too high for people to sensibly work in there (~50 mSv /hour; the total allowed dose for workers during an disaster is 250mSv if there is a need to protect people.)

• The biggest news is that on Sunday TEPCO presented their long term roadmap for stabilising the reactors at the plant.  I found it quite an interesting read.  It’s going to be a while yet.  The first half of the plan is to bring the release of radioative materials down so that ionizing radiation levels are closer or in line with the normal background. After that, step 2 is to switch over to a more permanent containment. Step one is estimated to take 3 months, step two to be about 3~6 months after completion of step one.

Well i guess i’m not suprised about the time it’s going to take.  There’s been a lot of water poured over various buildings, and that all has to be pumped away before some of the work can begin, which will take a month in itself. 

Earthquake update

Well i’t been a week or so since i last posted on here. Hum, i guess i’ll talk about the earthquake again.  These days i don’t know so much that you cant find in the news, but i’m a physicist so perhaps i can follow the stuff on the Fukushima #1  a bit better.  So this is going to be disproprtionatelt weighted towards that.

In and around Tōkai-mura, where i normally work, “lifelines” (ライフライン – an English loanword used to mean essential services) are mostly recovered.  There was a prohibition on babies drinking tap water about a week ago but that is lifted now.

I think the problem with drinking water comes about because of the rain that happened a few days before that: this brings with it the airborne radioisotopes (Iodine-131 mostly), and gets into resoviors and ground water and such. I-131 has a half life of 8.03 days, so if it’s only just above some legal limit (as it must presumably be if it only applies to infants are affected) it will drop down again in a few days unless more is brough into the system.

Which leads us to… I’m not  sure how much radioisotopes are still reaching the atmosphere from the plant. According to NISA’s 64th seismic damage report ‘white smoke’ (steam & water vapour, i suppose) is still being generated from all the units where water is being pumped in, which i guess is what you’d expect. I think the radioisotopes content is much lower than it was, because fission at the plant stopped three weeks ago, but  i can’t find data on this.  Perhaps there is none.

The big concern with the plant right now is the water coming in the bottom of the reactor buildings.  I don’t know excatly where this water has been, but the radioisotopes in it are iodine and caesium, which maybe means it’s  maybe from the water injected into the RPV… condensed water vapour maybe?  Thats a worry for the local area if it enters the ground water since it’s a much more efficient route than by rainfall.   Most of the time up to now the injected water has been sea water… i wonder if this water is also saline?  If so i’d have thought the biggest problem for groundwater would be the high salt content.

As i understand it though, the biggest problem with the pooling water is that it’s preventing access to the reactor buildings.  The plan a few days ago was to reactivate the heat exchangers for the reactors, so that the water in the RPV wouldn’t be boiling off anymore.  Untill that is done, keeping everything stable is a rather active process. But the water needs to be drianed off first, and because it’s radioactive it has to be stored safely or have the radioisotopes scrubbed from it.  Untill space is found to put all this water, work to stabilise units 1~3 is essentially stuck.   NHK is reporting some interesting measures being taken to store this water.

 

So back to Tōkai-mura.  Life seems to be returning to something like normal, with people starting to go back to work. Were getting to the point where people can start to make the first visual inspections of the lab.  It’s been a reminder of just what a big thing a magnitude-9 earthquake is.  In the parts of the vilage i saw, not many buildings were wrecked; the problem is more that everything is a bit damaged.  To use a specific example,  you can’t just go to the broken roads and fix them, you have to fix all the roads on the way between here and there.  It’s a staggeringly big job, but still nothing like the scale of what will be needed in the tsunami-hit areas.

Radiation and risk assesment.

So bear with me a moment, it’ll take a little while to get into what i actually wanted to say.  The preamble goes on untill you get to “But the…”

A day or so ago i  read (with regard to the Fukushima plant) a variation of  “if the XXX is so YYY why doesen’t the author of this piece  go and ZZZ there” device.

It’s tempting to answer that sort of comment by linking to ‘spEak You’re bRanes’, but instead of that, it set off a bunch of tangents in my head that i’m now going to follow.

Obviously the simple answer is:
“If i went onto the site without the expectation of being able to improve the situation, that would mark me out as a moron whos views on what is an acceptable risk should be ignored by all”

A different and personal answer: “Assuming i could usefully help, i would be prepared to do so.”  In my case though, i’m recovering from depression, and i know the balance between my desire to be more useful and my concern over my own saftey is slighly out-of-whack.

But the question, and the possible responses, remind me of the time i spent as a demonstrator for an undergraduate nuclear physics lab.  For most of the experiments the students require a radioactive source of some kind.  When these aren’t in use they are, of course, kept in the source cupboard (esentially a locked safe).  Some of the more penetrating sources also sit within their own lead holders inside.  When the labs begin, a demonstrator would unlock the cuboard, check all the sources were accounted for, and then the students would be allowed to check out sources for their experiments.  They then mount them in the experiments, which for most sources also meant they were then inside shielding  for the duration of the experiment (I should point out that these sources were pretty tiny, some were on a par with bananas and low-sodium salt).

The proper way to handle sources (which the students are all told about at the start of the day, on the off-chance the diddn’t already know) is to check the source out, carry it directly from the cuboard to your experiment, remembering to hold it away from your body, and install it straight away.  This is an example of the general procedures for radioactive sources, keep the vital parts of your body as far away as possible, and minimise the exposure time.

Thats what the students are supposed to do.  In practice, i noticed there was a range of behaviours, at one end some would not go near the sources and would get other people to carry them.  At the other end, some were totally relaxed about it, and would go as far as stuffing the source in the pocket of their jeans and chat to their friends for half an hour before going back to their experiments.  But as i said, these sources are tiny, and holding one in your hand to one for a day wouldn’t be a cause for concern.

So we have a bunch of people, all physicists, (almost) all perfectly capable of understanding the risks involved and still there are a huge range of behaviours.  So the first thing i learnt is that understanding the risks dosen’t mean people will deal with them appropriately.

The next thing, i always thought the students who were ‘scared’ of the sources were, in a way, more sensible than those who were completly relaxed about them. For the paranoid students their assesment of the risk was just inflated, and some of them even accepted that.  But for the students who were happy to put the sources in their pockets… why?  Theres no reason to do that. It’s no more convineint, no faster.  It’s ever so slightly more ‘risky’, (and by risk here they should also consider the posibility that we the demonstators were wrong about how weak  the sources are), but other than that there’s no difference.

However small, there’s no point in taking risk with no payoff at all.  In daily life everone understands that.  Crossing the road is dangerous, but if you need to get to the shop on the other side, it’s a risk well worth taking. If you don’t, then there’s no reason to do it ten times.   But somwhere between crossing the road and handling a tiny chunk of radioactive Caesium people’s ability to make sensible decisions breaks down, in both directions.

It’s can’t be attributed to the ‘invisible’ nature of ionising radiation.  Things that will eletrocute you are not obviously dangerous, but most people have got used to what is and what is not a safe way to deal with electricity (although i admit to being terified as a kid every time my dad changed a lightbulb).  My guess is it’s the long term nature of a radiation hazzard.  If it just killed or did not kill then i think people would be much more relaxed. Probably.

Earthquakes in the UK

My Japanese colleagues asked me how often we had earthquakes in the UK. So just below, courtesty of th BGS, is a list of the largest earthquakes in the UK in the past 35 years. They have intensites of around EMS 4~5, which is roughly equivalent to a Shindo 2.

http://www.earthquakes.bgs.ac.uk/macroseismics/macroseismic_surveys.htm

It’s difficult to compare, because the JMA doesen’t bother to report anything that small, but what the hell, i’ll give it a go anyway.

Japan is still getting regular aftershocks from the Magnitude 9 (Mw) Tōhoku earthquake. Yesterday there waer 14 quakes of Shindo 3 or higher. Between shindo 3 and shindo 4 the frequency drops by about an order of magnitude. So, for a threshold of Shindo 2, the frequncy is probably also about a factor of 10 higher.

So to compare to the UK:  with a similar reporting threshold, Japan had abut the same number of earthquakes between breakfast and lunch as the UK did in the last 35 years.  Admittedly, Japan is about twice the size of the British Isles.