Posts Tagged ‘Nuclear reactor technology’

Fukushima Dai-ichi nuclear plant: Reactor vessel integrity may be compromised

March 26, 2011

Leakage of water with high levels of radioactivity  raise the possibility that there may be cracks in the reactor containment vessels of Reactors #1,2 and 3.  One saving grace is that the pressure in the vessels remains high and would argue against a breach. However cracks below the water level that permit some water seepage  cannot be ruled out. It is also possible that the leakage of radioactive water is not from the vessel itself but from some of the surrounding valves or piping.

The Guardian:

A suspected break in the core of a nuclear reactor could have been responsible for a leak of large amounts of radioactive contamination at the Fukushima Daiichi power plant, Japanese nuclear safety officials said on Friday, in another setback to efforts to avert disaster at the stricken facility.

In the latest developments, officials have said seawater outside one of the units has registered 1,250 the normal level of radiation, while efforts are under way to pump radioactive water that has pooled around the reactor turbines into safe storage. The BBC has reported that short-term radioactive iodine has been detected at very high levels in the Pacific Ocean near the plant.

US naval barges have started rushing in supplies of fresh water amid concerns the seawater being used to cool down the reactors might be causing corrosion. …

On Thursday three workers were exposed to unusually high levels of radiation after stepping in contaminated water in the turbine building of the crippled No. 3 reactor, which they were trying to cool.

Two received possible beta ray burns to their legs. All three have been transferred to a special radiation treatment facility. Kyodo news reported that the two more seriously injured workers could have suffered internal radiation exposure.

“The contaminated water had 10,000 times the amount of radiation as would be found in water circulating from a normally operating reactor,” said Hidehiko Nishiyama, a spokesman for Japan’s nuclear safety agency.

Nishiyama said it was unlikely that the reactor had cracked, but conceded that the unusually high levels of radiation appeared to have originated from its core. “It is possible there may be damage somewhere in the reactor,” he said, adding that a leak in the plumbing or the vents could also be to blame.

GE BWR cutaway : image

NHK World reports:

A high level of radioactive iodine has been detected in seawater near Japan’s troubled Fukushima Daiichi nuclear power plant. The facility was hit by the March 11th earthquake and tsunami.

The Nuclear and Industrial Safety Agency said on Saturday that iodine 131 in excess of 1,250 times regulated standards was found in seawater collected 330 meters south of a plant water outlet at 8:30 AM on Friday.

The agency says there is no immediate threat to people within the 20-kilometer evacuation zone. The agency adds that as seawater is dispersed by ocean currents the contamination level will decline.

Iodine 131 at146.9 times regulated standards was detected in seawater in the area on Wednesday.

Saturday, March 26, 2011 12:44 +0900 (JST)

Kyodo News:

TEPCO, is currently injecting fresh water into the No. 2 reactor core to prevent crystallized salt from seawater already injected from forming a crust on the fuel rods and hampering the smooth circulation of water, thus diminishing the cooling effect. It has begun injecting fresh water into the No. 1 and No. 3 reactor cores.

At the same time, the firm is trying to remove pools of water containing highly concentrated radioactive substances that may have seeped from either the reactor cores or the spent fuel pools, while also trying to restore power at the No. 2 reactor.

On Thursday, three workers were exposed to water containing radioactive materials 10,000 times the normal level at the turbine building connected to the No. 3 reactor building. On Friday, a pool of water with similarly highly concentrated radioactive materials was found in the No. 1 reactor’s turbine building, causing some restoration work to be suspended.

Similar pools of water were also found in the turbine buildings of the No. 2 and No. 4 reactors, measuring up to 1 meter and 80 centimeters deep, respectively. Those near the No. 1 and No. 3 reactors were up to 40 cm and 1.5 meters deep. ..

The U.S. Department of Energy said in its radiological assessment released Friday that by comparing aerial measurement data from Thursday with previous measurements, the data indicate peak exposure rates in the western side of the Fukushima plant are lower.


Fukushima Dai-ichi nuclear plant: Reactor #3 control room powered up and cooling pumps to be switched on tomorrow

March 23, 2011

Progress at the Fukushima Dai-ihi nuclear plant continues steadily but slowly.External power is now available to all 6 reactors. Highlights today:

  • A high-powered water cannon truck has arrived from Australia at a US base in Tokyo to help recovery efforts at the Fukushima Daiichi nuclear power plant. The water cannon can shoot 150 liters of water per second at a target 150 meters away. It can also operate unmanned for 2 to 3 days while pumping seawater. It will be sent o Fukushima if needed.
  • A vehicle with a long spraying arm injected water into the No.4 reactor at the troubled Fukushima Daiichi nuclear power plant for about 3 hours on Tuesday. The vehicle, owned by a construction firm in Mie Prefecture in central Japan, began the operation at 5:17 PM Tuesday at the request of the Tokyo Electric Power Company. The vehicle is used in construction of high-rise buildings, and is capable of extending its arm more than 50 meters to pour concrete. The operation ended at about 8:30 PM.

Water spraying into Reactor #4: image nhk

  • Tokyo fire department started operation of spraying water to Unit-3 through cooperation with Osaka fire department. Water spraying  was conducted for one hour and finished around 16:00. Total amount of water sprayed is more than 3 times the pool capacity.
  • TEPCO said on Tuesday that it will restore power to the control rooms of No.3 and No.4 reactors as soon as water-spraying operations are completed to cool down fuel storage pools.
  • Defense Minister Kitazawa announced  that surface temperature measurement by helicopter will be conducted everyday, weather permitting, and not just twice a week in view of the smoke and steam that has been observed.

NHK World:

TEPCO has restored the electricity supply to the control room of the Number 3 reactor at the quake-damaged Fukushima Daiichi nuclear plant. Lights in the control room were switched on again on Tuesday night.
Eleven days have passed since the massive earthquake devastated northeastern Japan and cut off external power to the Fukushima Daiichi nuclear plant.
TEPCO reconnected power cables to the Number 3 and Number 4 reactors earlier on Tuesday.
TEPCO will now try to reactivate vital monitoring systems in the control rooms, such as those for measuring temperatures inside the reactors and water levels in the spent fuel storage pools. TEPCO says it will transmit electricity to the cooling pump for the Number 3 reactor on Wednesday. The company says if the pump functions normally, it will begin cooling the reactor and the spent fuel storage pool

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