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3 Fukushima nuke plant workers blasted with beta radiation
At least two workers at the crisis-stricken Fukushima No. 1 Nuclear Power Plant were blasted with more than 15 millisieverts of beta radiation on Aug. 28, plant operator Tokyo Electric Power Co. (TEPCO) has announced.
Two of the men were replacing parts of a system for decontaminating radioactive substance-contaminated water when they were irradiated. One other worker with them at the time also likely absorbed a high radiation dose, and his exposure level is now being checked. The men will undergo diagnostic tests beginning on Aug. 30 to assess their condition.
According to the TEPCO announcement of Aug. 29, the three men were replacing the filters on the decontamination system between 10 and 11:30 a.m. on Aug. 28, pulling out submerged components to replace the filters. The maximum beta radiation exposure to workers during this task is capped at 15 millisieverts, but two of the men absorbed doses of 23.4 and 17.1 millisieverts, respectively.
Beta rays are a type of radiation that can penetrate through the skin and into the body, and total exposure is legally limited to 1,000 millisieverts. The three men involved noticed they had gone over the 15-millisievert limit for their task on Aug. 28, but did not report it to their supervisor until the following day as they thought the exposure level was within legal limits.
“They were doing the replacement for the first time so inexperience may have played a part, but I’d like to examine whether we need to improve our procedures and equipment,” said TEPCO representative Junichi Matsumoto.
Mainichi Shimbun , August 30, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/30/20110830p2a00m0na012000c.html
Gov’t to lower Fukushima nuclear workers’ radiation exposure limit
TOKYO (Kyodo) — The government plans to lower a radiation exposure limit from 250 millisieverts to a usual level of 100 millisieverts possibly this fall for workers dealing with the Fukushima Daiichi nuclear plant crisis, a Cabinet minister said Tuesday.
’’The limit must be lowered,’’ Health, Labor and Welfare Minister Ritsuo Hosokawa told a press conference. ’’We may have to make a decision as soon as this fall.’’
The ministry raised the allowable radiation exposure limit to 250 millisieverts as an emergency measure soon after the March 11 earthquake and tsunami led to a series of catastrophic explosions and release of a massive amount of radiation.
The ministry intends to implement the exposure limit reduction after examining actual radiation exposure as crisis management efforts by plant operator Tokyo Electric Power Co. have entered the ’’step 2’’ phase of achieving a cold shutdown of the damaged reactors at the plant.
Kyodo, August 30, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/30/20110830p2g00m0dm095000c.html
Nuclear plant worker dies of acute leukemia
TOKYO (Kyodo) — A worker in his 40s who had been engaged in recovery work at the crisis-hit Fukushima Daiichi nuclear power plant has died of acute leukemia, plant operator Tokyo Electric Power Co. said Tuesday.
Tokyo Electric said the worker’s death is not linked with his work at the plant, citing results of medical examination by doctors.
The man had been exposed to 0.5 millisievert of radiation at the plant and showed no internal exposure to radiation, said the power company, known as TEPCO.
The dosage is much smaller than 5 millisieverts or higher per year — the benchmark for recognizing a death as work-related — TEPCO said, citing the Ministry of Health, Labor and Welfare’s criteria on work-related deaths. The ministry’s criteria also put the incubation period to develop symptoms of acute leukemia at one year.
TEPCO said the man had been involved with duties on radiation control at the plant for a week starting in early August. He later complained of poor health and underwent medical checkups before his death.
TEPCO said it received the report on the worker’s death on Aug. 16 from one of its contractors whose subcontractor hired the worker.
The utility said it had no information on the man’s work career before being engaged in the recovery work at the nuclear power plant which was crippled by the March 11 earthquake-tsunami disaster.
Kyodo, August 30, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/30/20110830p2g00m0dm084000c.html
Workers enter containment vessel at Fukushima Daini reactor
FUKUSHIMA (Kyodo) — Workers began inspections Monday inside the containment vessel of the Fukushima Daini nuclear plant’s No. 4 reactor to prepare for investigations into the impact caused by the March 11 quake-tsunami disaster, according to operator Tokyo Electric Power Co.
The Daini plant is located about 10 kilometers south of the crippled Fukushima Daiichi nuclear power plant.
The group of about 10 workers will check the radiation levels and other conditions inside the vessel of the reactor, which automatically halted operations after the magnitude 9.0 temblor.
It is the first time since the disaster that workers have entered reactor containment vessels at either the Daini plant or the Daiichi plant.
Among Fukushima Daini’s four reactors, the No. 4 reactor was the first to successfully have its cooling systems activated in the aftermath of the quake. In addition, gauges at the reactor show no abnormalities at present, prompting TEPCO to decide to conduct the inspections Monday.
The utility said it also plans to send workers into the containment vessels of the other three reactors at the Fukushima Daini plant in the near future.
All four reactors at Fukushima Daini have been brought into a stable condition called “cold shutdown” following the March disaster.
Meanwhile at Fukushima Daiichi’s No. 2 reactor, a thermometer located on the upper part of the pressure vessel showed a rapid rise in temperature to 120 C on Monday, up from 72 C the previous day.
But TEPCO said the reading was likely due to malfunctioning of the thermometer, as other thermometers and barometers showed no abnormalities inside the vessel.
The thermometer in question is located close to a cover which serves as the opening when removing fuel from the vessel.
Fukushima nuke plant workers irradiated on job ignored alarm: TEPCO
Two workers exposed to high doses of beta radiation at the crisis-stricken Fukushima No. 1 Nuclear Power Plant on Aug. 28 were ignoring their dosimeter readings, plant operator Tokyo Electric Power Co. (TEPCO) announced on Aug. 30.
The two men were both blasted with beta radiation while they and one other worker were replacing filters on a water decontamination system at the plant — a task that requires pulling components out of the water. TEPCO stated that they ignored the radiation count on their dosimeters and continued to do the filter replacement despite absorbing radiation doses of 23.4 and 17.1 millisieverts respectively, exceeding the 15-millisievert limit for the operation.
According to TEPCO, the men’s radiation alarms sounded when their doses exceeded the 15-millisievert maximum, but they decided to complete the task with the help of the third worker as they had very little left to do. The utility also said the men’s radiation control manager was not present at the time. Testing revealed the third worker absorbed a 1.1-millisievert dose.
Beta rays are a type of radiation that can penetrate the skin and enter the body, and total exposure is legally limited to 1,000 millisieverts.
Mainichi Shimbun , August 31, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/31/20110831p2a00m0na001000c.html
State of the plant...
Fukushima No. 3 reactor bottom’s temperature falls below 100 C
TOKYO (Kyodo) — Tokyo Electric Power Co. said Monday that the temperature of the crippled No. 3 nuclear reactor at the Fukushima Daiichi atomic power plant has fallen below 100 C, signaling progress toward the plant’s cold shutdown.
It is the first time that the temperature measured at the bottom of the No. 3 reactor pressure vessel dropped below 100 C since the nuclear crisis began at the complex in March due to a devastating earthquake and tsunami. The No. 1 reactor is already below 90 C.
The plant operator known as TEPCO said using an additional cooling method of showering water to the reactor core is likely to have helped lower the temperature of the No. 3 reactor pressure vessel.
TEPCO is considering applying the same method to the No. 2 reactor.
The utility has said the Nos. 1 to 3 reactors’ cores are assumed to have suffered meltdowns and the melted fuel is believed to be solidified at the bottom of the pressure vessels.
Cooling the pressure vessels of the plant’s damaged Nos. 1 to 3 reactors is part of the key conditions to realize the plant’s cold shutdown, which the government and TEPCO hopes to achieve by January at the latest.
The cold shutdown is also defined by the government and TEPCO as a state in which the release of radioactive materials from reactors is under control and radiation exposure dose is significantly held down.
Kyodo, September 6, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/09/06/20110906p2g00m0dm019000c.html
Potent radiation leak halts water decontamination operations at Fukushima plant
Operations to decontaminate highly radioactive water at the crisis-stricken Fukushima No. 1 Nuclear Power Plant came to a 13-hour halt when a section of pipe emitting 3 sieverts of radiation per hour in one decontamination system was discovered, plant operator Tokyo Electric Power Co. (TEPCO) has announced.
According to TEPCO, the high radiation emissions from the pipe section were discovered at just after 7 a.m. on Aug. 22 while workers were doing the first ever change-out of a decontamination system part for absorbing radioactive cesium. Work on the part change was stopped immediately. After washing radioactive mud away from the area, radiation levels dropped, and decontamination operations resumed at about 8:15 p.m., though the delay pushed replacement of the cesium absorption component back to Aug. 23. TEPCO officials apparently still do not know what caused the radiation leak.
The water decontamination system, called “Sally,” was built by electronics and heavy machinery giant Toshiba Corp. There are high expectations for Sally’s performance after two other decontamination systems at the site — one made in the United States and the other in France — continued to have problems and delays.
This is the third time for high radiation emissions to be discovered at the plant in August. On Aug. 1, emissions of 10 sieverts per hour were detected coming from the substructure of exhaust pipes in the No. 1 and 2 reactor housings, while on Aug. 2 emissions of more than 5 sieverts per hour were found in the air conditioning room in the No. 1 reactor building.
Mainichi Shimbun , August 23, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/08/23/20110823p2a00m0na019000c.html
Groundwater around Fukushima nuke plant to be protected by underground steel barrier
Construction of an underground barrier at the stricken Fukushima No. 1 nuclear plant to prevent leaking radioactive materials from reaching ground water will begin this year and be completed in about two years, plans released on Aug. 31 revealed.
The plans, announced by plant operator Tokyo Electric Power Co. (TEPCO), include use of a workboat and a temporary pier by the plant to speed up construction. According to the utility, the barrier will be built of between 600 and 700 22-meter-long steel sheet piles driven into the ground and stretch some 800 meters. The approximate 10-meter space between the steel barrier and the existing dike will also be filled with concrete.
Simulations conducted using benign substances that mimic the properties of radioactive materials showed the barrier at the coastal plant would stop the dangerous materials from reaching the ocean. The barrier is expected to last for 30 years.
The barriers are specifically intended to prevent contaminated water in buildings housing reactors 1 to 4 and their turbine buildings from seeping into the local ground water. TEPCO will continue to monitor ground water conditions both during and after the barrier’s construction.
Mainichi Shimbun , September 1, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/09/01/20110901p2a00m0na008000c.html
TEPCO eyes removing melted fuel after filling reactors with water
TOKYO (Kyodo) — Tokyo Electric Power Co. said Wednesday that it plans to take out the melted nuclear fuel from inside the crippled reactors at the Fukushima Daiichi power plant after repairing the reactor containers and filling them up with water.
But the plant operator did not go further into details, only saying that the plan, unveiled during a meeting of a government panel on nuclear energy policy, is just “an image at the current moment.”
The process is expected to start with the removal of radioactive substances inside the plant’s buildings housing the reactors, which would be followed by repair work on the primary containment vessels. Workers are then expected to fill each primary containment vessel with water to a level above the fuel and open the lid of the inner pressure vessel holding the fuel.
The utility known as TEPCO said it believes that flooding the container is necessary before removing the fuel because water would help block the radiation so that workers will be able to pinpoint the position of the melted fuel.
But the company also noted that it may have to seek alternatives because an “advanced technological development” is likely to be required to carry out the planned procedures.
The Nos. 1 to 3 reactor cores are assumed to have suffered meltdowns in the early days of the crisis, possibly damaging the bottom of each reactor pressure vessel and partially accumulating in the outer primary container.
Kyodo, September 1, 2011
http://mdn.mainichi.jp/mdnnews/national/archive/news/2011/09/01/20110901p2g00m0dm011000c.html
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