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Monday, March 14, 2011
No signs yet of a Chernobyl-type catastrophe
By JUN HONGO and KAZUAKI NAGATA
While the outcome of the crisis at a nuclear power plant in Fukushima Prefecture remains uncertain, experts Sunday were quick to stress there are no signs of a critical meltdown, let alone a catastrophe comparable to the 1986 Chernobyl disaster.
"I think the worst scenario has been avoided," said Hiromi Ogawa, a former engineer at Toshiba Corp. who managed its nuclear power generation project.
Other pundits dismissed the notion of comparing the Fukushima crisis to Chernobyl, noting that the two plants differ in basic construction, including the setup of the reinforced containment vessel.
Ogawa said that the seawater poured into the Fukushima No. 1 reactor had halted the nuclear reaction and that cooling was under way.
Ogawa added that the reactor's pressure vessel and container appear to be sound, indicating its fuel has been confined.
"It is clearly different from the case of Chernobyl, in which a reactor itself exploded and fissile substances spread outside," he said.
Chief Cabinet Secretary Yukio Edano also offered assurances, telling a news conference Sunday that the government "has confirmed that pumping of seawater is being processed as scheduled."
The nuclear rods are now completely covered with water and radiation levels around the facility are not rising, the government's top spokesman said, adding that the release of pressure through vents and cooling the reactor with water will "allow us to manage the nuclear reactor safely and under a stable condition."
According to the nuclear power safety agency, the accident at the Fukushima plant has been assigned a status of level 4 on the International Atomic Energy Agency scale. The IAEA defines level 4 as an incident including a minor release of radioactive material that does not involve any significant risks beyond the facilities.
The Chernobyl accident in 1986 remains the only level 7 accident to meet the IAEA scale.
The release of radioactive material there had widespread health and environmental impacts that required extensive countermeasures.
The crisis at Three Mile Island in 1975, which saw a partial meltdown and release of radioactive gas into the atmosphere, was rated as a level 5 incident.
"I think the accident has been handled in a level-headed way," said Ogawa, the former Toshiba engineer.
While the Nuclear Power Safety Agency said as many as 160 Fukushima Prefecture residents may have been exposed to radiation, the government has repeated that the situation appears to be under control.
Pundits say that although exposure to radioactivity may sound serious, a radiation level of 1,015 microsieverts per hour — the highest level detected inside the power plant since the earthquake — isn't as grave as it sounds.
While it is equivalent to the allowable amount for an individual to receive in one year, a regular X-ray used in hospitals exposes the patient to about a one-third or one-quarter of that, said Tetsuo Sawada, associate professor of reactor engineering at the Tokyo Institute of Technology, during an appearance on a Fuji TV program.
According to the Nuclear and Industrial Safety Agency, evacuees can reduce the risk of radiation exposure by wearing long-sleeve shirts and masks, staying out of the rain, which is likely to contain high amounts of radiation, and taking iodine if necessary. Those staying near the site should shut all vents where they are sheltering, close the windows and keep food and water covered.
Radiation Emergency Medicine Network Cancel, a group of experts who treat those exposed to radiation, said it has dispatched 20 doctors and nurses to back up local hospitals in Fukushima Prefecture in case the number of such patients rises.
The group played a pivotal role during the fatal 1999 criticality at the Tokai uranium-processing plant in Ibaraki Prefecture.
"We have experts from Hiroshima University joining us," a spokeswoman for the group said.
Yet, some of Tokyo Electric Power Co.'s measures indicate it is too early to relax.
For example, pumping seawater and boric acid into a nuclear reactor is considered a last resort because it renders the reactor useless.
Secretary General Yukiya Amano on Sunday released a video statement praising Japan's measures but also said "there continues to be concerns over Fukushima No. 1 plant."
Ogawa, the engineer, stressed that the media should not alarm the public by reporting that the situation is dangerous, saying that calm and accurate reports are needed since many people are sensitive to the term radiation but are generally not familiar with the details.