[ RadSafe ] WG: NucNet Japan Update / Brief No. 76 / 21 March 2011

[Franz Schönhofer]

Some more facts.

 

Franz Schoenhofer, PhD

MinRat i.R.

Habicherg. 31/7

A-1160 Wien/Vienna

AUSTRIA

 

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Subject: WG: NucNet Japan Update / Brief No. 76 / 21 March 2011
 


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Betreff: NucNet Japan Update / Brief No. 76 / 21 March 2011

THE NUCLEAR COMMUNICATIONS NETWORK
Japan Update / Brief No. 76 / 21 March 2011

Efforts Continue To Restore External Power

21 Mar (NucNet): Electrical installation work began this morning at units
3 and 4 of the Fukushima-Daiichi nuclear plant in an effort to return power
to the units and restart the primary cooling systems.

Spraying seawater onto the spent fuel pools (SFPs) at the two units was
temporarily suspended so the work could be carried out, Japan’s Nuclear and
Industrial Safety Agency (NISA) said.

The International Atomic Energy Agency (IAEA) said progress has been
achieved in restoring external power to the plant, although it remains
uncertain when full power will be available to all reactors.

Off-site electrical power has been connected to an auxiliary transformer and
distribution panels at unit 2 and work continues toward energising pump and
cooling systems within unit 2.

Yesterday 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.

In a statement at 09:00am on 21 March Japan time (01:00 central European
time), the Japan Atomic Industrial Forum (JAIF) said the Tokyo Fire
Department had finished pumping water into the SFP at unit 3 at around
04:00 this morning after 6.5 hours of operation. The national Self-Defence
Force pumped water into the SFP at unit 4 from 06:37 to 08:30 this morning.

NISA has also confirmed that the pressure inside the primary containment
vessel (PCV) of unit 3 has continued to decrease. After a peak value of 3.2
bar yesterday noon, it fell again to 2.2 bar last night and was at 1.6 bar
early this morning. Tepco said that because the pressure had fallen there
was no need for venting.

JAIF said damage to fuel in the SFPs is still a potential threat, although
the pumping of seawater into the pools at units 3 and 4 seems to have had
some effect. The IAEA said authorities remain concerned about the condition
of the SFP at unit 4.

A construction company has been helping with the pumping of seawater using
two special vehicles usually used for pumping concrete at construction
sites, JAIF said.

Units 5 and 6 at the plant were shut down for routine maintenance before the
earthquake and both reactors achieved cold shutdown on 20 March. The
reactors are in a safe mode, with cooling systems stable and under control,
and with low temperature and pressure within the reactor.

The IAEA said instrumentation from both spent fuel pools had shown gradually
increasing temperatures over the past few days. Officials configured two
diesel generators at unit 6 to power cooling and freshwater replenishment
systems in the spent fuel pools and cores of units 5 and 6.
As of 20 March, temperatures in both pools had “decreased significantly”
down to about 30 degrees Celsius.

Workers have opened holes in the roofs of both buildings to prevent the
possible accumulation of hydrogen, which is suspected of causing explosions
at other units.

The Ministry of Defence announced that a Self-Defence Force helicopter had
measured surface temperatures at Fukushima-Daiichi from the air and found
that the temperature of each unit is below 100 degrees Celsius.

Yesterday JAIF said the maximum ground acceleration near unit 3 of the plant
from the earthquake that struck 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.

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.

>>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)

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