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Anti-Nuclear Kagoshima Network

Study of Warm Water Released from Sendai NPP as Citizens' Science

By Takeo Hashizume*

Members of Anti-Nuclear Kagoshima Network (author left)

Kyushu Electric Power Company is carrying out environmental studies with a view to building a third reactor at the Sendai Nuclear Power Plant. Meanwhile, each month since February last year, we have been conducting a citizen-side study of the warm water released from the existing Sendai reactors.

Our study was motivated by discoveries beginning the year before last (2006) that the temperature of water released from nuclear power plants around the country had been falsified. Although I call it a "study", actually all we have been doing is measuring the water and air temperature once a month at the warm water outlets and the surrounding area. It is not as if we expect this to lead immediately to any significant discoveries. However, while at first it seems impossible to come to grips with a nuclear power plant, by continuing to monitor the warm water released, we hope to get some physical sense of the plant.

On Kyushu Electric's web site "Due to the fact that the temperature of the warm water released from the power plant (the temperature rise is no more than 7oC) drops quickly as it spreads over the surface of the water, is radiated into the atmosphere and mixes with the surrounding sea water, the area in which the temperature of the sea water rises 1oC or more is mostly confined to within about 2 kilometers of the shore. No impact has been recognized on marine organisms living within this area."

About 130 cubic meters of warm water, its temperature raised by 7oC, is released each second from Sendai NPP's two 890 MW reactors. Compare this to the average 80 cubic meters per second that flows from River Sendai. In other words, the warm water released from the NPP in one day is enough to raise the temperature by 7oC of a region of sea one kilometer square by 10 meters deep.

Kyushu Electric says the temperature rise does not exceed 7oC, but in March the water released from Sendai NPP was measured at 26.7oC, compared to 19.1oC at Kushikino, 15.5 kilometers to the south, and Nishikata, 15 kilometers to the north. That represents an increase of 7.6oC. Nearer to the NPP, at Tsuchikawa, 6.5 kilometers to the south, the temperature was measured at 19.4oC, while at Karahama, 5 kilometers to the north, the temperature was 19.5oC, suggesting that the nearer you get to the NPP the more the temperature is raised. In July, even though only one reactor was operating, we were surprised to find that the temperature of the water released was 31.4oC, compared to 23.8oC at Kushikino, representing a difference of 7.6oC. Given that the temperature at Nishikata was 25.4oC, it might be inferred that at a distance of 15 kilometers the sea temperature is raised by 1.6oC. The temperature of the sea around the NPP is not influenced by the warm water from the reactors alone. It is also related in complex ways to currents and tides and the temperature and quantity of water flowing from River Sendai. Seen from the waterfront, it is clear that you can't draw the simplistic conclusion, as Kyushu Electric does, that the warm water released from the NPP has no effect.

Furthermore, it is hard to believe that killing plankton with chlorine to prevent barnacles and the like from adhering to cooling pipes has no impact on marine organisms. The quantity of carcinogenic substances produced, such as trihalomethane, is on a totally different scale to what you get in tap water. Just because humans don't consume it directly, doesn't mean we shouldn't be worried about it. Old fishermen grumble, "When the nuclear power plant came along, oysters opened their mouths and died. And you can't catch fish any more either."

*Takeo Hashizume is the Director of Anti-Nuclear Kagoshima Network and a Professor of Physics at Kagoshima University.

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