Radiation level in Fukushima’s No. 1 reactor building rises
Jun. 6, 2011
The operator of the crippled Fukushima Daiichi nuclear power plant said Saturday it has detected high-level radiation of around 4,000 millisieverts per hour at the building housing the troubled No. 1 reactor -- the highest reading taken in air inside the complex.
Tokyo Electric Power Co. also suggested the possibility that the March 12 hydrogen explosion at the plant's No. 1 unit may have been caused by a reverse flow of steam intended to be sent into the air through the exhaust stack after radioactive gases were vented, but a company official later said such a reverse flow was unlikely.
The high amount of radiation was observed during measurement taken using a robot Friday. Steam was seen rising from an opening in the floor for a pipe that runs through the building, but the utility known as TEPCO said it found no damage to the pipe.
The reading means that a worker would be exposed to the maximum limit of 250 millisieverts, set for the ongoing emergency at the plant, after less than four minutes. TEPCO said its workers have no plan to work in that area of the plant, but added that it will carefully monitor developments using robots.
The company also said the pressure measurement inside the No. 1 unit's reactor pressure vessel, taken using a newly installed device, was about 1.26 atmospheres, slightly above the atmospheric pressure. ''The vapor is inside the vessel, and it looks like there are no big holes,'' a TEPCO official said.
On Friday, nine workers entered the building to attach a pressure indicator to the vessel, with the workers exposed to up to about 4 millisieverts of radiation, according to TEPCO.
The pressure suppression containment vessel is located under the building and highly radioactive contaminated water generated by the reactor is believed to have accumulated there, TEPCO said.
Regarding the hydrogen explosion at the No. 1 unit, which occurred a day after the plant was struck by the magnitude 9.0 earthquake and subsequent tsunami, the company initially suggested Saturday that a reverse flow of steam after the start of the venting operation there could be one of the possible causes.
TEPCO earlier said the steam, along with hydrogen, might have flowed back into the No. 1 unit building through a pipe instead of going out of the exhaust stack into the air, but quickly added that more detailed investigations are needed to determine the cause or whether there was a design error.
But on Saturday afternoon, it said such a reverse flow is unlikely as one of the valves in the reverse route is believed to have closed based on the design. The company had said earlier in the day that it was not known whether the valve was open or closed.
Unlike the No. 2 and No. 3 units at the plant, there is no valve for preventing reverse flows of steam at the No. 1 unit. But under the design of the No. 1 reactor, the valve in the reverse path would have closed with the loss of power, thereby preventing a reverse flow, TEPCO said.
The utility said it will check to see whether the valve has actually closed.
TEPCO had said earlier that hydrogen gas that leaked through damaged parts of the containment vessel caused the explosion around 3:36 p.m. on March 12. The venting operation began shortly past 2 p.m. that day to try to prevent the reactor vessel from exploding due to increasing pressure inside it after the quake-tsunami disaster knocked out the plant's cooling functions.
(Distributed by Kyodo News on June 4, 2011)
Tokyo Electric Power Co. also suggested the possibility that the March 12 hydrogen explosion at the plant's No. 1 unit may have been caused by a reverse flow of steam intended to be sent into the air through the exhaust stack after radioactive gases were vented, but a company official later said such a reverse flow was unlikely.
The high amount of radiation was observed during measurement taken using a robot Friday. Steam was seen rising from an opening in the floor for a pipe that runs through the building, but the utility known as TEPCO said it found no damage to the pipe.
The reading means that a worker would be exposed to the maximum limit of 250 millisieverts, set for the ongoing emergency at the plant, after less than four minutes. TEPCO said its workers have no plan to work in that area of the plant, but added that it will carefully monitor developments using robots.
The company also said the pressure measurement inside the No. 1 unit's reactor pressure vessel, taken using a newly installed device, was about 1.26 atmospheres, slightly above the atmospheric pressure. ''The vapor is inside the vessel, and it looks like there are no big holes,'' a TEPCO official said.
On Friday, nine workers entered the building to attach a pressure indicator to the vessel, with the workers exposed to up to about 4 millisieverts of radiation, according to TEPCO.
The pressure suppression containment vessel is located under the building and highly radioactive contaminated water generated by the reactor is believed to have accumulated there, TEPCO said.
Regarding the hydrogen explosion at the No. 1 unit, which occurred a day after the plant was struck by the magnitude 9.0 earthquake and subsequent tsunami, the company initially suggested Saturday that a reverse flow of steam after the start of the venting operation there could be one of the possible causes.
TEPCO earlier said the steam, along with hydrogen, might have flowed back into the No. 1 unit building through a pipe instead of going out of the exhaust stack into the air, but quickly added that more detailed investigations are needed to determine the cause or whether there was a design error.
But on Saturday afternoon, it said such a reverse flow is unlikely as one of the valves in the reverse route is believed to have closed based on the design. The company had said earlier in the day that it was not known whether the valve was open or closed.
Unlike the No. 2 and No. 3 units at the plant, there is no valve for preventing reverse flows of steam at the No. 1 unit. But under the design of the No. 1 reactor, the valve in the reverse path would have closed with the loss of power, thereby preventing a reverse flow, TEPCO said.
The utility said it will check to see whether the valve has actually closed.
TEPCO had said earlier that hydrogen gas that leaked through damaged parts of the containment vessel caused the explosion around 3:36 p.m. on March 12. The venting operation began shortly past 2 p.m. that day to try to prevent the reactor vessel from exploding due to increasing pressure inside it after the quake-tsunami disaster knocked out the plant's cooling functions.
(Distributed by Kyodo News on June 4, 2011)
