– #Fukushima I Reactor 3: TEPCO Pouring Boric Acid to Prevent Recriticality:
Yomiuri Shinbun (10:02PM JST 5/15/2011):
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TEPCO announced on May 15 that it started to use boric acid in the reactor cooling water for the Reactor 3 at Fukushima I Nuclear Power Plant to prevent recriticality from happening. Boric acid absorbs neutrons.
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TEPCO plans to do the same for the Reactors 1 and 2.
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Recriticality is when the nuclear chain reaction is restarted. There is salt in the Reactor Pressure Vessels of the Reactors 1, 2 and 3, as TEPCO initially poured seawater to cool the RPVs. TEPCO thought the salt would absorb neutrons. TEPCO has decided to use boric acid in the cooling water because the level of salt in the cooling water may have decreased since TEPCO switched the cooling water from seawater to regular water.
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In the meantime, the temperature at the top of the Reactor 3 RPV has risen rapidly. TEPCO increased the amount of cooling water to 12 tons per hour on May 12 using two water feeding systems, then to 15 tons per hour on May 14. However, the temperature at the top of the RPV increased by 46.5 degrees Celsius in 24 hours to 297 degrees Celsius as of 5:00AM on May 15. TEPCO thinks there’s a problem with the pipes that feed water into the RPV.
In the latest measurement data (11:00AM 5/15) released by the Ministry of Economy, Trade and Industry (METI) , that temperature (the 4th column) appears to have dropped slightly to 291.7 degrees Celsius, although the data table is put up sideways and it is a bad scan and hard to see. The second digit could be 9, 8, or 3. An age-old trick by bureaucrats to discourage people from seeing the data… (My neck is hurting from trying to read the number.)