[ RadSafe ] WG: WG: NucNet Japan Update / Brief No. 75 / 20 March 2011

[Franz Schönhofer]

For those who are interested in hard numbers and facts instead of
speculations of „experts“ and journalists.

 

 

 

Franz Schoenhofer, PhD

MinRat i.R.

Habicherg. 31/7

A-1160 Wien/Vienna

AUSTRIA

 

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WG: NucNet Japan Update / Brief No. 75 / 20 March 2011


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NUCNET 75

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Betreff: NucNet Japan Update / Brief No. 75 / 20 March 2011

THE NUCLEAR COMMUNICATIONS NETWORK
Japan Update / Brief No. 75 / 20 March 2011

Figures Released On Fukushima-Daiichi Seismic Design Reference Values

20 Mar (NucNet): The maximum ground acceleration near unit 3 of the
Fukushima-Daiichi nuclear plant from the earthquake that struck northern
Japan on 11 March 2011 was 507 gal – or 507 centimetres per second squared
– which is above the plant’s design reference values of 449 gal, the Japan
Atomic Industrial Forum (JAIF) said today.

It was also announced that the University of Tokyo has re-evaluated the
maximum height of the tsunami wave and it had a peak height of at least 23
metres when it hit Miyagi and Fukushima prefectures. The plant design
reference value was 10 metres.

Meanwhile, external power is available onsite at the plant and teams from
the Tokyo fire service and national Self-Defence Force are continuing to
pump seawater into the reactor pressure vessels (RPV) and primary
containment vessels (PCV) at units 1, 2 and 3 in an effort to cool the
nuclear fuel.

The International Atomic Energy Agency said workers were continuing
efforts to restore plant systems at units 1, 2 and 3.

At unit 2, external power has been established to the control room meaning
essential surveillance and control systems are again operational, Japan’s
Nuclear and Industrial Safety Agency (NISA) said.

NISA said workers were preparing to connect an external power supply to
the residual heat removal systems of unit 2 and then unit 3. If the systems
have not been damaged, this will allow cooling and feeding of the reactors
and the spent fuel pools (SFPs).

Seawater spraying into the SFP at unit 3 has begun and while the pressure
in the PCV went up early today, it was not sufficiently high to justify
venting. The local dose rate close to this unit is decreasing
At unit 4, where there is no fuel in the reactor, seawater spraying of the
SFP started today at 09:40 Japan time (01:40 central European time). An
external power supply connection is being prepared, NISA said.

At units 5 and 6, diesel generators were repaired yesterday and there is
now enough power available to each unit for the residual heat removal
system pumps. NISA said the temperature has fallen in both SFPs and the
units were now in cold shutdown. Workers were today preparing to connect an
external power supply to both these units.

Cold shutdown means the reactors are in a safe mode, with cooling systems
stable and under control, and with low temperature and pressure within the
reactor.

Air Sample Analysis

Plant operator Tokyo Electric Power Company (Tepco) said today it made the
first spectral analysis of air samples taken on the Fukushima-Daiichi site
at noon on Saturday local time and found volatile iodine and particulate
caesium isotopes as follows:

Iodine-131: 5900 becquerel per cubic metre (Bq/cubicm), above the limit of
1000 Bq/cubicm;

Iodine-132: 220 Bq/cubicm, below the limit of 70,000 Bq/cubicm;

Cesium-134: 22 Bq/cubicm, below the limit of 2000 Bq/cubicm;

Cesium-137: 24 Bq/cubicm, below the limit of 3000 Bq/cubicm.

The limits are for air being breathed by workers under surveillance, but
Tepco said workers were wearing charcoal masks and no internal
contamination is expected.

Environmental Radiation Monitoring

The Ministry of Education, Culture, Sports, Science and Technology (MEXT)
has published updated data from its surveillance network of automatic
measurement posts (MPs) at a distance of more than 20 kilometres from the
plant site.  Inside the 20 km  zone, Tepco is responsible for the network,
but under NISA’s surveillance.

The downward trend of all measurements has continued since yesterday.

Today (Sunday), the highest dose rates were measured at the north-eastern
Fukushima Mountains (summit 864 m, 30 km from the plant site), with values
between 45 and 110 microsieverts per hour (microSv/hr) at 12:00 noon Japan
time today in comparison with 60 to 170 microSv/hr on Thursday.  

In the valleys, where most people live, the readings range from 1 to 6
microSv/hr in a distance of 35 to 60 km from the plant site. This is 25
percent less than on Thursday.

All these readings refer to an area north-west of the plant. This was the
direction in which prevailing winds were blowing during the first days of
the accident when the main releases occurred.

In the Tokyo area, the dose rate stayed very low at 0.05 microSv/hr.
Yesterday the government’s chief cabinet secretary Yukio Edano said
radiation exceeding the government-set radiation level was detected in
sampled milk in Fukushima Prefecture and in six samples of spinach in
neighbouring Ibaraki Prefecture. 

He said the radiation measured from the samples posed “no immediate
threat” to health. 

>>Related reports in the NucNet database (available to subscribers)

Authorities Order Evacuation Around Fukushima-Daiichi Nuclear Plant (News
in Brief No. 52, 11 March 2011) 

EC Calls For Information On Back-Up Power Systems At European NPPs (News
In Brief No. 66, 15 March 2011)

Japan Releases Radiation Data From More Than 50 Monitoring Posts (News in
Brief No. 71, 17 March 2011)

The NucNet database contains more than 15,000 reports published since
1991. To subscribe or ask for any further information email
info at worldnuclear.org

Source:    NucNet
Editor:    david.dalton at worldnuclear.org



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