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.
Dan Yurman
Email: djysrv@gmail.com
Blog: ANS Nuclear Cafe Twitter: @djysrv
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