Monday, 14 March 2011

Japanese Reactor Radiation - The Numbers

I'll quote the measured doses as reported by the Japanese Nuclear and Industrial Safety Agency (NISA) bulletin #22.

First, a "normal baseline" :
MP1 (Monitoring at the North End of Site Boundary)
0.036 microSv/h(19:00 March 13)
→0.038 microSv/h(05:00 March 14)
MP3 (Monitoring at the North/West End of site boundary)
0.038 microSv/h(19:00 March 13)
→0.037 microSv/h(05:00 March 14)
MP4 (Monitoring at the North/West End of Site Boundary)
0.036 microSv/h(19:00 March 13)
→0.038 microSv/h(05:00 March 14)
MP5 (Monitoring at the West End of Site Boundary)
0.04 microSv/h(19:00 March 13)
→0.042 microSv/h(05:00 March 14)

So the normal background around a fully functional nuclear powerplant is about 0.038 microSieverts per hour.

OK, so what's a Sievert? It's an SI (Scientific standard) unit which is 100 Rem. The biological effects of radiation are based on the number of Rem in the dose. In most places, a dose of 0.3 Rem per year is what you'd get just from normal background.

That's 0.003 sieverts, or 3,000 micro-sieverts. Divide by 8766 hours in a year, call it 0.035 microsieverts per hour, though being 500m altitude above sea level or having granite rocks nearby could easily double it. So would wearing a watch, or living in a brick rather than timber building.

The Health Physics Society figures for the US
External Background Radiation60 mrem/yr, US Average
Natural K-40 and Other Radioactivity in Body40 mrem/yr
Air Travel Round Trip (NY-LA)5 mrem
Chest X-Ray Effective Dose10 mrem per film
Radon in the Home200 mrem/yr (variable)
Man-Made (medical x rays, etc.)60 mrem/yr (average)
Call it 360 mrem - or 0.36 Rem.

From the NDT Resource Centre:
The dose limit to non-radiation workers and members of the public are two percent of the annual occupational dose limit. Therefore, a non-radiation worker can receive a whole body dose of no more that 0.1 rem/year from industrial ionizing radiation. This exposure would be in addition to the 0.3 rem/year from natural background radiation and the 0.05 rem/year from man-made sources such as medical x-rays.

OK, now we have numbers established for "normal". For radiation workers, 5 Rem per year is considered safe. Actually, there's evidence that a little more might be more healthy due to stimulating the immune system - there's a J-curve effect at such low doses, we think, but we really, really, really want to be Conservative with a Capital C here. The evidence says that 5 rem is as healthy as 0.3 rem anyway. 5 rem is 57 microsieverts/hr over the course of a year.

Now let's look at the Bad News(tm). The radiation at the perimeter of the Fukushima Dai-ichi Nuclear Power Station, otherwise known as Ground Zero. And it's worse than I'd thought.
MP2 (Monitoring at north- northwest of Unit1 and northwest of the
End of Site Boundary for Unit 1 ) :
450 microSv/h(20:10 March 13)
→680 microSv/h(3:50 March 14)
MP4 (Monitoring Car at North West Site Boundary for Unit 1)
44.0 microSv/h(19:33 March 13)
→56.4 microSv/h(04:08 March 14)
(Surveyed by MP2 as MP1 is in the top of the cliff)
MP6 (Monitoring at the Main Gate)
5.2 microSv/h(19:00 March 13)
→66.3 microSv/h(02:50 March 14)

60 or so vs 0.035. About 1800 times normal. Stand there for a year, and you'd get your annual dose for a radiation worker. Do it for a week, and you'd get the annual dose for a civilian. Not too bad so far.

But look at Monitoring station 2. That's over 10 times more. More concerning, the trend is increasing. That means radioactive material is slowly leaking from the containment vessels, in amounts certainly indicative of severe damage to the rods - a partial meltdown - and maybe even the far more severe meltdown, involving about half the fuel, found in 3-mile island. Since the reactors are now poisoned, very little additional fission should be occurring, yet external levels are still rising. That suggests a more severe meltdown, and a consequently a longer cooling-off period.

Reactor #1 might not be the culprit. I think it's worse than that, it's dead, Jim. Moving towards room temperature. An ex-reactor. Bereft of fission, it rusts in pieces. Reactor #3, the one which burns a plutonium-uranium mix, and is nearly twice the size, that might have really gone pear-shaped.

I could be wrong here, I'm working off limited information.

UPDATE : Turns out they had problems develop with reactor #2 - it boiled dry, which explained the temporary peak. Now it too is scrap metal. From Bulletin #23:
MP3 (Monitoring at North West of Site Boundary for Unit 2) : 231.1 micro Sv/h (14:30 March 14)
MP4 (Monitoring at north- west of Site Boundary for Unit 2 : 56.4 micro Sv/h(04:08 March 14)
→29.8 micro Sv/h(14:14 March 14)
MP5 (Monitoring at north-west Site Boundary for Unit 2)
6.1 micro Sv/h(14:02 March 14)
MP6 (Monitoring at the west –southwest Site Boundary for Unit 2)
3.70 micro Sv/h(16:10 March 14) (typo in original - should be March 13)
→4.2 micro Sv/h(12:34 March 14)
MP7 (Monitoring at the west –southwest Site Boundary for Unit 2)
6.1 micro Sv/h (12:16, March 14)

So now it's down to 1/10 of the values of 12 hours previously.


Not your friend said...

Given Asian's need to save face, are we sure the numbers are honest?

Of course we don't know the numbers are accurate.

Cameron said...

I found it through and see what you think...

a female Faust said...

Thank you so much: I recommended you, for the much needed context, in a recent post.

a female Faust said...

and, Not Your Friend, before this crisis I'd always considered the Need To Save Face more of a Western Malady. Certainly, if Asian, not so much Japanese. See List of war apology statements issued by Japan.

Wherever the malady originated, it is one of the biggest obstacles to the safety and continued evolutionary growth of homo sapiens, in my honest opinion...

Dakuro said...

Wow seeing this data I can see the radiation levels are extremetly high, one person exposed to this radiation can die in 2 or 3 days as long, looks like that part of japan is gonna be the second chernobyl, I laugh because human's like to play with fire and I wonder, they really know that they can burn ? and because of there stupidity many other people will suffer, just like chernobyl...
Realize that human's can't play with nuclear energy because in a situation like this they can't control what could happen.

Zoe Brain said...

Dakuro - 3 days - 72 hours - the lowest dose anyone's ever died from is 250 rem - 2,500,000 microsieverts.

So a dose of 3500 microsieverts/hour for 72 hours might kill someone, but almost certainly wouldn't

It's currently 60.

Dakuro said...

Thanks for the clarification.
Been sick by radiation is like being dead anyway :S

Anonymous said...

"An ex-reactor. Bereft of fission, it rusts in pieces."

Like the Monty Python reference. So you could say then if the control room for #1 were empty the sign would read "Gone Fission".

(And no, I am not lampooning a serious potentially tragic situation. I would probably find something funny in my own death.)

Anony Mouse

Sarah Murphy said...

As much a fan of nuclear energy as I am, I'm starting to rethink the sensibility of reactors near major fault lines.


Zoe Brain said...

Dakuro - for actual effects of acute radiation exposure, see Project Rho.

Summary: Less than 25 Rem, and there's no detectable effect. It now appears that no-one has taken that high a dose.

Zoe Brain said...

The peak reading according to Kyodo News:
Prior to the second full exposure of the rods around 11 p.m., radiation was detected at 9:37 p.m. at a level twice the maximum seen so far -- 3,130 micro sievert per hour
Now down by at least a factor of 10.

100 hours continuous exposure at that level might just be enough to cause biological effects detectable by a lab. 15 hours at that level, and you'd reach your allowable annual dose.

Di said...

Thanks so much for the explanation.

Not your friend said...

the Japanese government has been consistently lying about the level of exposure. The USS Ronald Reagan had to leave the aria due to unacceptable levels of radioactivity.

Get your Iodine while you can.

nader paul kucinich gravel mckinney said...

The elevated spent fuel pools have also been compromised by the explosions.
Israeli dependents and non-essential embassy staff removed several days ago.