THE NUCLEAR COMMUNICATIONS NETWORK
News in Brief/ No. 81 / 26 March 2011
Japan Update: Slow Progress In Efforts To Secure External Power
26 Mar (NucNet): Progress is slow in efforts to secure an external AC power supply for essential systems at units 1 to 4 of the Fukushima-Daiichi nuclear power plant because so many areas are heavily contaminated and spraying of the spent fuel pools (SFPs) is continuing, which makes decontamination difficult, Tokyo Electric Power Company (Tepco) said today.
However, lights and some of the instrumentation in the control rooms are now functional. Units 1 and 2 share a combined control room, as do units 3 and 4.
One of the next challenges will be a detailed radiological assessment of the entire site, after which decisions will be made on what work will follow, including repairs and cleaning.
Yesterday, a temporary cable for external power was connected at the plant making electricity available to all six units for the first time since the earthquake and tsunami struck on 11 March 2011, the Japan Atomic Industrial Forum (JAIF) said.
Test runs of each item of electrical equipment will need to be carried out before vital systems such as instrumentation, and core and spent fuel pool cooling can be turned on.
Tepco said today it has started to inject fresh water instead of seawater into the primary reactor systems of units 1 and 2. This is to avoid the accumulation of too much salt in the primary systems.
The fresh water is provided by the US Navy because the tsunami destroyed most of the infrastructure for local fresh water supplies.
Tepco said it plans to switch to fresh water injection at unit 3 and could also do so at unit 4 if it becomes necessary.
Radioactive Materials Found In Seawater Sampling
Japanese authorities said today that iodine-131 concentrations measured in seawater samples collected at eight points 30 kilometres from the coastline of the Fukushima-Daiichi nuclear plant were about at Japanese regulatory limits, with caesium-137 levels in the same samples “well below those limits”, the International Atomic Energy Agency (IAEA) said.
The IAEA said its marine environmental laboratory in Monaco has received the data and concluded in a preliminary analysis that dilution, both into deeper layers of water and by dispersion along the prevailing ocean currents, will lead to “a rapid decrease of the initial surface contamination”.
In the short term, iodine-131 will be the relevant radionuclide as far as doses are concerned, but in the long term, caesium-137 will be the more important radionuclide in the marine environment. It will be possible to follow this nuclide over long distances for several years.
The IAEA said radionuclides will probably take months or years to reach other shores of the Pacific. The main transport of contamination takes place by atmospheric transport over long distances.
Seawater samples taken by Tepco at about 300 metres from the southern discharge channel at Fukushima-Daiichi showed a much higher radioactivity level of about 1,250 times above the limit for iodine-131 and 80 times above the limit for caesium-137.
Unit Status At Fukushima-Daiichi 25 March 2011:
Unit 1
Core and fuel integrity damaged.
Reactor pressure vessel integrity: unknown.
Core cooling requiring AC power: not functional.
Building integrity severely damaged by hydrogen explosion.
Water level in the rector pressure vessel (RPV): fuel partially or fully exposed.
Pressure of the RPV: now decreasing after initial increase.
Temperature of the RPV: now decreasing after initial increase.
Water injection to core: continuing. Now using fresh water instead of seawater.
Water injection to containment vessel: to be confirmed.
Containment venting: temporarily stopped.
Unit 2
Core and fuel integrity: damaged.
Reactor pressure vessel integrity: unknown.
Core cooling requiring AC power: not functional.
Building integrity slightly damaged.
Water level in the rector pressure vessel: fuel partially or fully exposed.
Pressure of the RPV: unknown.
Temperature of the RPV: stable.
Water injection to core: continuing. Now using fresh water instead of seawater.
Water injection to containment vessel: to be confirmed.
Containment venting: temporarily stopped.
Unit 3
Core and fuel integrity damaged.
Reactor pressure vessel integrity suspected damaged.
Core cooling requiring AC power: not functional.
Building integrity severely damaged by hydrogen explosion.
Pressure of the RPV: unknown.
Temperature of the RPV: now decreasing after initial increase.
Water injection to core: continuing. Use of fresh water under consideration.
Water injection to containment vessel: to be confirmed.
Containment venting: temporarily stopped.
Unit 4
Shut down at the time of the earthquake, no damage to fuel (which had already been removed from the reactor and transferred to the pool), core or containment. Building integrity severely damaged by hydrogen explosion.
Unit 5
Shut down at the time of the earthquake, no damage to fuel, core or containment. Vent hole opened in roof as precaution against hydrogen explosion.
Unit 6
Shut down at the time of the earthquake, no damage to fuel, core or containment. Vent hole opened in roof as precaution against hydrogen explosion.
Spent Fuel Pool Status At Fukushima-Daiichi 25 March 2011:
Fuel integrity unknown at units 1 and 2, possible damaged at units 2 and 3, safe at units 5 and 6.
Unit 1
Seawater injection being considered.
Unit 2
Seawater injection carried out on 20 March.
Unit 3
Water level low, seawater injection continues.
Unit 4
Water level low, seawater injection continues. Reactor building damaged by explosion and fire on 15 March.
Unit 5 & 6
Pool cooling capability recovered.
Common Spent Fuel Pool
Seawater was sprayed over this pool on 21 March. Pool cooling was restarted after successful installation of an external power supply line on
24 March.
Dan Yurman
Email: dan.yurman@usa.net
Mobile: 208-521-5726
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