Why is Japan injecting nitrogen into a damaged reactor?
to keep the fires down and help cool the reactor.
Japan’s Stricken Reactors Show No Damage from Latest Quake
April 07, 2011, 3:55 PM EDT
By Akiko Nishimae, Jim Polson and Ichiro Suzuki
(Updates with number of people injured in 17th paragraph.)
April 8 (Bloomberg) -- A 7.1-magnitude earthquake minutes before midnight spared the stricken Fukushima Dai-Ichi nuclear plant in Japan, although workers struggling to cool radioactive fuel were evacuated, Tokyo Electric Power Co. said based on its initial assessment.
The aftershock was the strongest since March 11 when a record 9-magnitude earthquake and tsunami devastated the coast of Northeast Japan. No unusual conditions were observed at the plant afterward, the utility, known as Tepco, and Japan’s Nuclear and Industrial Safety Agency said in statements.
No unusual measurements of water level, pressure or other operations were found at the No. 3 and No. 4 reactors at the six-unit plant, Tepco officials told reporters today.
“Indications of new leakage or a change in radiation levels will be the only way they’ll tell if there’s further damage,” Murray Jennix, a nuclear engineer who specialized in radioactive containment leaks and teaches at San Diego State University, said in a telephone interview. “You’ve got cracks that could have been made bigger.”
Tepco said April 6 engineers had plugged a leak of radioactive water into the ocean from a pit near the No. 2 reactor after several failed attempts. Concentration of radioactive iodine in seawater near the reactor discharge pipe fell by half, to 140,000 times the regulatory limit, the company said yesterday.
‘The Main Fear’
“The main fear is more structural damage, leading to additional cracks or reopening of the fixed crack,” Peter Hosemann, an assistant professor of nuclear engineering at the University of California at Berkeley, said in an e-mailed message. “Radioactivity can leak again if cracks open.”
A day may be needed to detect additional damage at the plant, he said.
Crews at the crippled nuclear station north of Tokyo will continue pumping nitrogen into the No. 1 reactor to prevent hydrogen explosions of the type that damaged radiation containment buildings last month. Injection of nitrogen, the inert gas that comprises most of air, may take six days spokesman Yoshinori Mori said before today’s quake.
“They are manually injecting nitrogen through a very narrow pipe,” Tadashi Narabayashi, a professor of nuclear engineering at Hokkaido University in northern Japan, said by phone yesterday. “High radiation levels in the building are also making it difficult as workers have to keep rotating.”
Cooling the Reactors
The March 11 tsunami flooded emergency generators at the Fukushima plant, triggering cooling-system failures at four of the plant’s six nuclear units.
Tepco is still using emergency pumps to cool the reactors and pools holding spent fuel, almost four weeks after the initial disaster. Three blasts damaged reactor buildings and hurled radiation into the air last month.
About 3.64 million households in six Japanese prefectures were without power following the aftershock, Kyodo News reported, citing Tohoku Electric Power Co., which operates in seven prefectures.
The Rokkasho nuclear-fuel reprocessing plant and the Higashidori nuclear power plant lost power and were operating on backup diesel generators, the nuclear safety agency said today in a statement. Two of three power lines to the Onagawa nuclear power plant also were disabled, it said.
Five other power stations were shut down by the aftershock, broadcaster NHK reported, citing Tohoku Electric.
“What occurred today is an aftershock in the same area and rupture zone to the magnitude-9 main shock that occurred about a month ago,” said Don Blakeman, a geophysicist in the U.S. National Earthquake Information Center in Golden, Colorado. “It is tremendously smaller than the main shock. The main shock caused about 80 times more ground movement.”
The 7.1 aftershock was the fourth of magnitude-7 or higher since the major quake on March 11, according to the Japanese Meteorological Agency. The largest measured 7.7, about 30 minutes after the record quake, according to the agency’s website.
Police and fire officials reported the number of people injured in today’s earthquake reached 82 as of 3:30 a.m. local time, public broadcaster NHK said on its website.
There have been 464 aftershocks of magnitude 5 or greater, counting today’s, according to agency statistics.
More than 27,300 people are dead or missing after the initial natural disaster in northeastern Japan, according to the latest figures from the National Police Agency.
--With assistance from Taku Kato, Tsuyoshi Inajima, Michio Nakayama and Takashi Hirokawa in Tokyo, Greg Chang and Mark Chediak in San Francisco and Brian K. Sullivan in Boston. Editors: Jessica Resnick-Ault, Susan Warren
This was the Best one I found..
When a water cooled reactor is not cooled properly even after it has been shut off by lowering the control rods containing boron that absorb neutrons released during radioactive decay of uranium and during the fission reaction and this mopping up of neutrons stops the nuclear chain reaction then hydrogen gas is released as a byproduct of the chemical reaction produced by the excessive heat interacting with the chemicals in the uncooled fuel rods in the reactor.
(When the reactor is working neutrons hit uranium atoms in the fuel rods and produce fission - meaning that the uranium atoms split and produces smaller atoms called isotopes and in the process converts a little mass into energy (heat) used to heat water that makes steam, and making turbines spin which generates electricity)
Hydrogen is explosive. Air contains 20% oxygen and oxygen is needed for an explosion to occur. If you replace normal air with nitrogen it displaces the oxygen and the chance of an explosion decreases greatly.
So the reason for the nitrogen is to prevent a hydrogen gas explosion as Alchemist said above.
To prevent the risk of a hydrogen explosion."It is necessary to inject nitrogen gas into the containment vessel and eliminate the potential for a hydrogen explosion,"
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