Radioactive substance found leaked in quake-hit plants

TOKYO — A small amount of radioactive substance was found to be leaked at the nuclear power plant No. a in Fukushima due to the powerful earthquake which rocked northeastern region of Japan Friday.

An official of safety affairs of the nuclear power plants at the Japanese Ministry of Economy and Industry said in a press conference Saturday that a small bit of radioactive substance was leaked due to problems of cooling system at the ractors, Kyodo News reported.

Earlier, Japan declared states of emergency for five nuclear reactors at two power plants after the units lost cooling ability in the aftermath of Friday's powerful earthquake. Nearly 14,000 residents were ordered to evacuate as workers struggled to get the reactors under control to prevent meltdowns.

Operators at the Fukushima Daiichi nuclear power plant scrambled ferociously to tamp down heat and pressure inside two of its reactors after the 8.9-magnitude quake and the tsunami that followed cut off electricity to the site and disabled emergency generators, knocking out the main cooling system.

The government declared a state of emergency — the first at a nuclear plant in Japan's history — at the Daiichi plant, and hours later, the Tokyo Electric Power Co., which operates the Daiichi site in northeastern Japan, announced that it had lost cooling ability at three reactors at its nearby Fukushima Daini site.

Initially, 3,000 people within two miles of the Daiichi plant were told to leave their homes, but the evacuation zone was more than tripled to 6.2 miles after authorities detected eight times the normal radiation levels outside the facility and 1,000 times the normal radiation inside a control room.

In addition, people within a 16.2-mile radius were told to stay indoors, according to the website of the International Atomic Energy Agency's Incident and Emergency Center.

Japan's nuclear safety agency said the situation was most dire at Fukushima Daiichi's Unit 1, where pressure had risen to twice the normal level in the reactor. Officials at the Daiichi facility began venting radioactive vapors from the unit to relieve pressure inside the reactor case.

The International Atomic Energy Agency said that diesel generators that normally would have kept cooling systems running at the Daiichi plant had been disabled by tsunami flooding. Plant workers labored to cool down the reactor core. They were temporarily cooling the reactor with a secondary system, but it wasn't working as well as the primary one, according to Yuji Kakizaki, a Japanese nuclear safety official.

Emergency power supplies were brought in, authorities said; it was unclear if that meant portable generators.

Even once a reactor is shut down, radioactive byproducts give off heat that can ultimately produce volatile hydrogen gas, melt radioactive fuel or even breach the containment building in a full meltdown belching radioactivity into the surroundings, according to technical and government authorities.

Despite plans for the intentional release of radioactive vapor, Chief Cabinet Secretary Yukio Edano said there was no risk. "With evacuation in place and the ocean-bound wind, we can ensure the safety," Edano said at a televised news conference early today.

The outside measurement of radiation at Daiichi was far below the allowed limit for a year, other officials said, reporting that it would take 70 days standing at the gate to reach the yearly limit.

Dr. Irwin Redlener, a pediatrician who runs a disaster preparedness institute at Columbia University, said the reported level of radiation outside the plant wouldn't pose an immediate danger, though it could lift the risk of thyroid cancer over time.

However, he called the reported level of radiation inside the plant extraordinarily high, posing acute health risks.

"I would personally absolutely not want to be inside," he said.

Defense Ministry official Ippo Maeyama said that dozens of troops trained for chemical disasters had been dispatched to the plant in case of a radiation leak, along with four vehicles designed for use in atomic, biological and chemical warfare.

If temperatures inside the reactor were to keep rising to more than 2,000 degrees Fahrenheit, it could set off a chemical reaction that begins to make brittle the metallic zirconium that sheathes the radioactive uranium fuel.

That reaction releases hydrogen, which can explode when cooling water finally floods back into the reactor. That was a concern for a time during the 1979 Three Mile Island reactor accident in Pennsylvania.

If the reactor temperature reaches about 4,000 degrees, the fuel could melt outright, and the reactor could slump into the bottom of the containment building in a partial meltdown. Then the crucial question would be whether the building would stay intact.

"The last line of defense is that containment — and that's got to hold," said Arnold Gundersen, a nuclear engineer who used to work in the U.S. nuclear industry.

If it doesn't, the radioactive material inside the reactor can pour out into the surroundings.

Technical experts said the plant would presumably have hours, but probably not days, to try to stabilize things.

In addition to the efforts to get Tokyo Electric's nuclear reactors under control, a fire broke out at the nearby Onagawa nuclear power plant, but it was later extinguished. A water leak was reported in another Onagawa reactor. No radioactive releases were reported at any of those plants.

As one of the most seismically active countries in the world, Japan has strict sets of regulations designed to limit the effect of quakes on nuclear power plants. Even so, 10 of Japan's 54 commercial reactors were shut down because of Friday's quake, and Japanese media said a fifth of the country's total nuclear generating capacity was offline because of the quake.

Additional material from Bloomberg News and The New York Times. (Kyodo, AP)

일본 원전 방사능 물질 소량 누출 확인

강진 피해를 입은 일본 후쿠시마 제 1원전에서 소량의 방사능 물질이 누출된 것을 일본 정부가 12일 공식 확인했다.

교도통신 등에 따르면 일본 경제산업성 산하 원자력 안전보안원은 이날 기자회견에서 지진에 따른 냉각장치 이상으로 소량의 방사능 물질이 외부로 누출됐다고 밝혔다.

안전보안원 측은 다만 외부로 누출된 방사능 물질의 양이 인근 주민들의 건강에 직접적인 위협이 되는 수준은 아니라고 설명했다.

원전 운영자인 도쿄전력은 이와 관련해 후쿠시마 원전의 압력을 낮추기 위한 조치의 일환으로 증기를 원자로 건물 밖으로 배출하는 작업에 착수했다.

그러나 배출 증기에 방사성 물질이 포함돼 있을 가능성이 높다는 지적이 나오고 있다.

후쿠시마 제1원전 2호기의 방사능 누출은 11일 지진으로 원자로의 전력공급이 끊기면서 냉각수 순환체계에 이상이 생겼고, 이에 따라 연료봉을 담은 냉각수의 수위가 낮아진 때문이다.

즉, 냉각수 수위가 낮아지면서 연료봉이 냉각수 밖으로 노출돼 방사능이 새어나간 것으로 보인다.

이에 앞서 원자력 안전보안원은 "후쿠시마 제1원전 1호기 원자로 내부의 중앙통제실 방사선량이 평상시보다 1천배 이상 높아진 상태"라고 밝혔다.

보안원에 따르면 평상시 중앙통제실 방사선량은 시간당 0.16 마이크로시버트였지만지금은 150 마이크로시버트를 보이고 있다.

이런 가운데 일본 정부는 12일 오전 후쿠시마 제1 원전에 이어, 남쪽으로 약 8킬로미터 떨어져 있는 제2원전에 대해서도 재해긴급사태를 선포했다.

제2 원전 1,2,3호기 압력 제어실의 온도가 100도를 넘어 원자력의 압력을 억제할 수 없게 됐기 때문이다.

이에 따라 후쿠시마 제 2원전 반경 3km 이내 주민들에게는 대피지시를, 반경 10km 이내 주민들에게는 옥내 피난령이 내려졌다.

일반적으로 원전에서는 건물내 원자로 격납용기에서 방사능이 누출되지 않도록내부 기압을 낮추고 있지만 만일 이 기능이 고장났다면 방사성 물질이 외부로 누출됐을 가능성이 크다.

앞서 일본 정부는 지난 2000년 원자력재해특별조치법 제정 이후 처음으로11일 원자력긴급사태를 선포했다.