Japan’s Nuclear Power Plants Damaged but, So Far, a Safety Success

The Fukushima 1 NPP

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The damage to several of Japan’s nuclear power facilities is a big economic loss to a nation so dependent upon them.  But despite that damage and the problems we’re read about in controlling it, the design and expertise of the Japanese operators warrants praise.  The outer structure of the facility has been badly damaged but the containment vessel remains intact.  The lack of water flow has caused the most significant problems with cooling, but the Japanese operators have used the fire system to pump sea water and boric acid into the vessel trying to stabilize the plant.

If ever we needed a demonstration of the need for redundant systems and precision engineering this is it.  Japanese nuclear plant builders will certainly emerge from this horrific experience with bragging rights and plenty of customers eager to give their designs another look.

To be sure, the danger has not passed and this is no time to relax, but it is useful to put this incident into context.  While several workers were injured at the plants by falling debris during the earthquake or aftershocks there have been no deaths. The radiation is less than 1 REM per day. It takes 600 REM to kill.  Compared to other disasters this is remarkable.

Below is the latest report from NucNet, the trade press of the nuclear power industry:

Cooling System Fails At Fukushima-Daiichi-3, Venting ‘A Success’

13 Mar (NucNet): Tokyo Electric Power Company (Tepco) says it successfully vented the inner or primary containment vessel (PCV) at Fukushima-Daiichi unit 3 this morning after the high pressure reactor core coolant injection system stopped working.

Tepco said the venting was completed at 08:41 local Japan time. Venting is a controlled release of gases including radioactive substances via a filter system to the outside air in order to stop pressure building up.

Tepco said it then began injecting water containing boric acid, which absorbs neutrons, into the reactor system using a fire pump.

A statement said workers at the plant in northern Japan had attempted to restart the unit’s cooling system, but had failed.

Unit 3 at the plant, a boiling water reactor of 760 megawatts, uses mixed-oxide (MOX) fuel and according to the Japan Safety Agency coolant levels were 2 to 3 meters below the top of the MOX fuel rods.

Tepco said it has been seeing a rise in pressure at unit 3 and there is a risk of damage to the facility, but it is working to prevent this.

Chief cabinet secretary Yukio Edano said the core of the unit-3 reactor may have been deformed due to overheating, but denied it had led to a “meltdown”, a critical situation where fuel rods have melted.

Mr Edano said at a news conference that a hydrogen explosion might occur at the unit 3 reactor building because hydrogen may have accumulated during a period when cooling of the reactor was insufficient.

He said there might be a similar explosion to the one which occurred at unit 1 yesterday, but said even if an explosion occurs, the impact should not affect the pressure vessel and containment vessel.

Unit 1 at the six-unit plant has been shut down and is being inspected following yesterday’s explosion. Japanese authorities confirmed last night that the explosion occurred outside the PCV, not inside. Tepco said the integrity of the PCV remains intact.

Tepco said it has been injecting seawater mixed with boric acid into the reactor in an effort to cool the nuclear fuel. This measure was approved by Japan’s Nuclear and Industrial Safety Agency (NISA) and the injection procedure began at 20:20 Japan time.

Unit 2 is shut down but the backup cooling system is not working, Tepco said. Workers are trying to install equipment in order to enable cooling with seawater.

Tepco also confirmed last night that containment remains intact at Fukushima-Daiichi units 2 and 3. Units 4, 5 and 6 were already shut down for scheduled maintenance when the earthquake struck.

Unit 2 is shut down and the reactor core isolation cooling system has been injecting water to the reactor. Tepco said the reactor water level is lower than the normal level, but the water level was “steady”.

Radioactivity at the boundary of Fukushima-Daiichi has exceeded statutory limits and the incident has been rated as level 4 on the IAEA’s International Nuclear and Radiological Event Scale (INES).

Japan has also confirmed the safety of all its nuclear research reactors.

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

Tepco Confirms Venting Of Unit 1, ‘Reactor Not Affected’ By Explosion (News in Brief No. 55, 12 March 2011)

Japan Says Containments Are Intact At All Fukushima-Daiichi Units (News in Brief No. 57, 13 March 2011)

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

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