The PJ Tatler

IAEA Updates from Fukushima

IAEA report 21 March 2011 at 1530Z (11:30AM EDT, 8:30AM PDT) (if only the IAEA knew about permalinks):

1. Current Situation

We are seeing some steady improvements, but the overall situation at the Fukushima Daiichi nuclear power plant remains very serious. High levels of contamination have been measured in the locality of the plant.

The restoration of electrical power to Unit 2, which we reported yesterday, is good news. AC power is available and an electrical load check to pumps, etc. is currently on-going. Work on the restoration of off-site power to Units 3 and 4 is also underway.

Seawater is still being injected into the reactor pressure vessels of Units 1, 2 and 3.

Pressure in the reactor pressure vessel and the containment vessel drywell at Unit 3, which had been rising yesterday, has again fallen.

Water is being sprayed periodically into the spent fuel pools at Units 2, 3 and 4. The Agency still lacks data on water levels and temperatures in the spent fuel pools at Units 1, 2, 3 and 4.

Following the restoration of cooling at Units 5 and 6, temperatures in the spent fuel pools continue to decline.

So power is on for Unit 2, which means they can power pumps etc without using the mobile diesel generators, and progress is continuing for Units 1 and 3. Notice that since work is continuing, the short evacuation reported earlier today has clearly ended, although I don’t see any particular mention of it specifically.

2. Radiation Monitoring

As I reported yesterday, the IAEA radiation monitoring team took measurements at distances from 56 to 200 km from the Fukushima nuclear power plant. At two locations in Fukushima Prefecture gamma dose rate and beta-gamma contamination measurements have been repeated. These measurements showed high beta-gamma contamination levels. Measurements by the IAEA and the Japanese authorities were taken at the same time and locations. The Japanese and independent IAEA measurements gave comparable results.

Notice, since this has been a subject of some debate, they make specific mention that these measurements are being made independently by IAEA; IAEA is not simply accepting Japanese measurements.

Measurement of gamma dose rate and beta-gamma contamination were taken on 20 March at more locations. The dose-rate results ranged from 2-160 microsieverts per hour, which compares to a typical natural background level of around 0.1 microsieverts per hour. High levels of beta-gamma contamination have been measured between 16-58 km from the plant. Available results show contamination ranging from 0.2-0.9 MBq per square metre.

I’ve seen several news reports now that quoted this in millisieverts rather than microsieverts; watch out for that. As a reminder, a microsievert, abbreviated μSv, is 1/1000 of a millisievert (abbreviated mSv.)  Also, since there has already been an attempt in comments to make this sound like a big scary dose rate, do remember that a CT scan is 15 mSv or more.  That’s 15,000 μSv. What they’re saying is that these particularly contaminated areas would still take between 100 and 7000 hours to add up to the dose from an abdominal CT.

Further measurements are needed to assess possible contamination beyond the area currently monitored – both closer to the facility and further way. We have no contamination measurements showing that that contamination levels are high at greater distances than 58 km from the plant, but this cannot be excluded.

I have no further information available regarding the measurement of alpha radiation. As I reported yesterday, from the measurements taken within the evacuation zone (20 km), no significant alpha radiation had been detected at that time.

This is important for two reasons: first, it tells us that no unexpected radionuclides are getting away from the plant; and second, because alpha particles are more damaging than beta and gamma.

In the coming days, the IAEA monitoring team will continue to take measurements in the Fukushima prefecture. We are seeking data from Japan on radioactivity contamination measurements for the rest of Japan.

Some results on the monitoring of foodstuffs have been made available by Japan to the IAEA and FAO. Results provided recently by the Japanese authorities range up to 55 000 Bq per kg of I-131 in samples of Spinach taken in in the Ibaraki Prefecture. These high values are significantly above Japanese limits for restricting food consumption (i.e. 2 000 Bq/kg). I understand that the Japanese Government is actively considering relevant precautionary measures and has instructed four Prefectures (Ibaraki, Totigi, Gunma, Fukushima) to refrain, for the time being, from distributing two types of vegetables (spinach and kakina) from these Prefectures and milk from Fukshima.

A Becquerel (Bq) is one atomic disintegration per second. It’s basically a very tiny number in terms of radiation dose. By comparison, a banana has about 14 Bq of radiation normally.

If these units are confusing, don’t despair; they’re not really hard. I’ll have an explainer about them up by tomorrow I hope.