The terror of an aging nuclear power plant
Genkai Nuclear Power Plant is "the most dangerous" power plant of all in Japan
Via Tokyo Shinbun "Kochira Tokuhoubu" written by Tomohiro Okuni
July 2, 2011
Area map of radius of 30 km within Genkai Nuclear Power Plant in Saga Pref.
(Map replaced with English version from Google Earth)
What happens when a nuclear reactor shatters like a glass cup?
A scientist warns of the inherent danger of this happening in Japanese nuclear power plants (NPPs), in which case, a series of uncontrollable nuclear reaction will cause a massive explosion that will disperse an enormous amount of radioactive materials throughout the region. This could result in a disaster of enormous scale that would dwarf the Fukushima Daiichi's nuclear incident. Reactor No.1 of the Genkai power plant is now the top most dangerous nuclear power plant in Japan.
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| Dr. Hiromitsu Ino |
"The most dangerous nuclear power plant in Japan is Kyushu Electric's Reactor 1 of Genkai Nuclear Power Plant (in Saga Prefecture)," says
Dr. Hiromitsu Ino, University of Tokyo professor emeritus on metal materials (
Original report). Reactors 2 and 3 of Genkai power plant are currently not operating for regular inspections. While Economic Minister Banri Kaieda has called for early restart, Governor Yasushi Furukawa and his associates have shown signs of approval of the restart (
Related). Although there are existing opposition towards the restart of reactors 2 and 3, Dr. Ino points out that reactor 1 also has a big problem (
Related).
Nuclear power plants are equipped with ECCS or Emergency Core Cooling System that stops the operation of the reactor during anomalies such as earthquakes and incidents to rapidly cool down the reactor. The Fukusihma Daiichi incident was a result of the failure of ECCS due to loss of all power. But in the case of Genkai Reactor No. 1, the exact opposite is feared: that an enormous incident is expected if the ECCS functions properly.
Genkai's Reactor 1 started its operation 36 years ago in 1975.
It is the oldest of Kyushu Electric or KEPCO's power plants.
"Through aging, the steel walls of the reactor's pressure vessel is becoming weak. If you cool this too rapidly, it could rupture," says Dr. Ino.
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| The Genkai Nuclear Power Plant |
Imagine a glass cup shattering
Dr. Ino equates the phenomenon to a shattering glass cup. When you poor a cold water into a hot glass cup, it breaks due to rapid changes in external and internal temperatures. According to Dr. Ino, the same thing could happen in the pressure vessel.
The inner walls of the pressure vessel are constantly exposed to neutron rays generated from nuclear fission. The more the steel is exposed to neutron rays, the weaker it gets. It loses its ductility and causes a phenomenon equivalent to human blood veins becoming weak due to hardening of the arteries. Normally, steel does not rupture even due to application of certain amount of force. It is only deformed. However, when its temperature is below a certain level, it breaks like a work of pottery. This temperature is called ductile-brittle transition temperature or DBTT. The weaker it gets, the higher the DBTT gets.
According to Dr. Ino, the DBTT of supercruiser Titanic which sunk into the North Atlantic Ocean during its voyage was 27 degrees centigrade due to the poor-quality steel material used for its body. Her hull broke when she crashed against the iceberg.
Electric companies measure the DBTT in order to estimate the durability (service life) of power plants. They place about four to six sets of specimen made of the same material as the pressure vessel to the far-inner layer of the vessel, and retrieve them after every few years to a decade for inspection. Because these specimens are placed in the far-inner side of the internal walls closer to the reactor's core, they are exposed with more neutron rays and thus their brittleness is accelerated. They predict how weak it will be in the future by inspecting the specimens.
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| Genkai's Reactor No. 1 |
What about the DBTT of Reactor No.1?
When Reactor No.1 launched its operation in 1975 the DBTT was - 16 degrees centigrade. This gradually rose to 35 degrees in 1976, 37 degrees in 1980, and 56 degrees in 1993.
"This was within our projection. What was astonishing was the number KEPCO announced October last year (2010)," says Dr. Ino. The DBTT jumped to 98 degrees.
Pressure vessels for pressurized light-water reactors (PWR) like Genkai's Reactor No.1 are operated under a high-pressure and high-temperature environment with internal atomic pressure of 150 with over 300 degrees in internal temperature. If there is a crack in the vessel, it leads to a destructive explosion that would disperse enormous amount of radioactive materials into the air; a catastrophe of an unimaginable scale.
Inspection results not reported to the authorities by KEPCO
Last December, Dr. Ino and his team of experts asked the authorities at the Nuclear and Industrial Safety Agency (NISA) of the Ministry of Economy, Trade, and Industry (METI) for explanation.
"Astonishingly, the NISA didn't have any information on it. KEPCO didn't tell them because they weren't 'obligated to report'," claims Dr. Ino.
Why did the DBTT increase so rapidly in Reactor No.1?
"It could have been the rate of content of lead within the steel. The reactor could be suspected to be made of a faulty material depending on where the material is applied," suspects Dr. Ino. "In order to find out the causes, specimens should be provided to universities to conduct a micro-organic-level inspection. The reactor should be at least stopped until the results are shown."
According to the projection curve find in a report submitted by KEPCO in 2003, the DBTT of Genkai's Reactor No.1 was 65 degrees centigrade or 75 degrees with tolerance. DBTT of 98 degrees is well beyond the scope of the adjusted projection curve.
"DBTT of 98 degrees found in specimens was the expected temperature after 66 years of operation. The temperature of the vessel itself was expected to be at 80 degrees. If it was operated for 60 years, it would be 91 degrees. This is below the industry's standard set for new reactors by the JEA (Japan Electric Association)," KEPCO's Public Affairs Department explains. "There is no issue of safety."
Still, Dr. Ino contends.
"It is way too beyond the scope of the projection curve. The projection formula is not suited anymore. It has to be fundamentally reviewed, and strict safety inspections must be imposed."
Dr. Ino strongly fears that there may be other aging reactors that may have the same problem as Genkai's Reactor No.1.
"Japanese nuclear power plants begun their operations more than 10 years after the Americans did. All power plants that begun its operation in the 1960's in the United States and Germany have been shut down. You could say Japan's the forerunner in operating aged nuclear power plants."
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| Projected range of dispersed radioactive materials in case of explosion of Genkai's Reactor No.1 |
A whole lot more aging reactors to come due to extension of service life
Initially, nuclear power plants were designed with a life span of thirty to forty years. Reactor No.1 at Atsuga nuclear power plant in Fukui Prefecture begun its operation in 1970. It was to be shut down by 2010 but it hasn't. Factors such as the opposition of the residents that rendered impossible to build new reactors, and that it would be cheaper to extend the life of existing reactors, the government decided to extend the life of this aging reactor. For those reactors that exceed 30 years in operation, the electric companies first submit a report on aging countermeasures to the government's Aging Countermeasure Examination Committee. The Committee examines the report and when approved they are granted up to 60 years of extension by 10 years interval.
There are most twenty reactors that have been operating exceeding the 30-year threshold, including reactors No.1 at Genkai, No.1 at Atsuga, Nos.1-3 at Mihama, and Nos. 1-6 at Fukushima Daiichi. No.1 reactors in Atsuga, Mihama, and Fukushima Daiichi have already been granted approval to operate beyond the 40-year threshold.
In few years there may be reactors that would be pushed to operate beyond 50 or even 60 years.
Abusive operations causing ware and tare
"The more it ages, the more defects and problems would be found, making maintenance a tough task. Abusive operations will only increase the ware and tare [in the reactors]," Dr. Ino points out.
Genkai's Reactor No.1 tops the rest with 98 degrees, but there are seven reactors that have DBTT of over 50 degrees. There are also reactors that have not gone through the inspection for more than 10 years.
"If they are all inspected, the DBTT of some pressure vessels could 'jump' as it did with Genkai's Reactor No.1. You can't deny that possibility," warns Dr. Ino.
"All aging reactors should be placed under comprehensive inspection, and reactors that show sign of an unprojected level of embrittlement should be shut down immediately."
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Dr. Hiromitsu Ino is professor emeritus at the University of Tokyo. Having served on the government's nuclear safety panel, Dr. Ino is also a member of "Study Group on Nuclear Aging Issues," a research group consisting of scientists, engineers, and legal experts.
Editor's Note: On the issue of restart of the Genkai reactors, Economic Minister Kaieda has obstinately insisted that the government "would take full responsibility in the unlikely event." The people in Fukushima must be saying, "Then be responsible and bring back our homeland!" Of course, no one can. If anyone says they can, even a child would understand it's a lie. And voters don't forget politicians who lie.
Addendum:
According to a report submitted by the Kansai Electric to the Osaka Prefectural Government on April 20 2012, reactor No.1 of Takahama nuclear power plant now ranks second in the list of power plants in Japan exceeding the projected DBTT level. According to the report a 2009 survey found that DBTT of the Takahama reactor No.1 rose from 68 to 95 degrees centigrade. An increase of 27 degrees. Here are the list of the rest of power plants with notable increase in DBTT. (Original source:
Study Group on Nuclear Aging Issues)
98 degrees / Genkai Reactor No.1 / Kyushu Electric / PWR
95 degrees / Takahama Reactor No.1 / Kansai Electric / PWR
81 degrees / Mihama Reactor No.1 / Kansai Electric / PWR
78 degrees / Mihama Reactor No.2/ Kansai Electric / PWR
51 degrees / Atsuga Reactor No.1 / Japan Atomic Power / BWR
Source: Tokyo Shinbun, Morning ed. July 2, 2011.
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