Here's some more information on the injection of Nitrogen into the core of Reactor No. 1 at the Dai-ichi
facility in Fukushima-ken (Fukushima Prefecture).
Tokyo Electric Power Co. (TEPCO) has, as of April 8 2011, begun injecting Nitrogen into the core of the to try and prevent a hydrogen explosion.
TEPCO has said that some 70 per cent of the nuclear fuel rods in the reactor are damaged allowing Hydrogen gas to accumulate in the reactor core.
The Nitrogen gas is being injected to prevent the Hydrogen from reacting with Oxygen that would otherwise cause an explosion that could further damage the reactor core.
It is expected that a total of 6,000 cubic metres of Nitrogen will be injected into the core of Reactor No. 1 over the next few days.
This is a multi-reactor project, starting with No. 1, which is supposed to have the LEAST amount of damage to the nuclear reactor's containment vessel. When completed, Reactors No. 2 and No. 3 will be done next.
This is a multi-reactor project, starting with No. 1, which is supposed to have the LEAST amount of damage to the nuclear reactor's containment vessel. When completed, Reactors No. 2 and No. 3 will be done next.
The No. 1, No. 2 and No. 3 reactors were all operating when the 9.0 Magnitude Sendai earthquake and 10 metre-high (30-feet) tsunami hit on March 11, 2011. Power loss led to the reactor core cooling systems not functioning - meaning the uranium fuel rods were exposed above the cooling water line in each of the three reactors.
Based on calculations of radiation measured within the containment vessel on March 14 and 15, TEPCO officials estimated that 70 percent of the fuel rods in the No. 1 reactor were damaged, while 30 percent of the fuel rods in the No. 2 reactor and 25 percent of the fuel rods in the No. 3 reactor were also damaged.
Note that TEPCO's numbers do not state the condition of the nuclear fuel rods - or if melting occurred - though a partial meltdown seems likely to have occurred. The information from TEPCO does indicate that there is damage to the Zirconium metal alloy covering the fuel rods.
Hydrogen gas may have been created through a reaction between the metal alloy and steam within the core. Because of the higher percentage of damaged fuel rods in the No. 1 reactor, there is a greater possibility that Hydrogen gas was produced there.
Officials of the Nuclear and Industrial Safety Agency (NISA) also believe that radiation emitted from the fuel rods may have transformed water into separate gases of Hydrogen and Oxygen.
An explosion can occur if Hydrogen and Oxygen reach certain concentrations and thus cause a chemical reaction. During normal operations, the core containment vessel is filled with non-flammable Nitrogen gas, and of course, there is no Oxygen within the containment vessel.
If Hydrogen and Oxygen leak into the containment vessel through cracks in the damaged vessel, an explosion could occur.
It is believed that the Hydrogen explosions that occurred in the buildings housing the No. 1 and No. 3 reactor cores after the big earthquake were caused by Hydrogen produced in the containment vessels leaking out into the surrounding building and reacting with Oxygen in the air.
Neutron rays were also detected after a hydrogen explosion occurred at theNo. 3 reactor of the Fukushima plant. Neutron rays are emitted when nuclear fissionoccurs, but it was unclear whether this hadreally happened.
Neutron rays were also detected after a hydrogen explosion occurred at theNo. 3 reactor of the Fukushima plant. Neutron rays are emitted when nuclear fissionoccurs, but it was unclear whether this hadreally happened.
"Because the soundness of the pressure container and containment vessel of the No. 1 reactor appears to have been maintained, the injection of nitrogen should be done as soon as possible," explains Hisashi Ninokata, a professor of nuclear reactor engineering at the Tokyo Institute of Technology (TIT - not to be confused with MIT).
But there are dangers involved with the Nitrogen injection.
According to NISA officials, there's a chance Oxygen in the air could mix with injected Nitrogen and reach a concentration within the containment vessel that could cause a chemical reaction - and an explosion.
To minimize this, TEPCO will use non-electrical valves to inject the Nitrogen to avoid the Oxygen entering the piping.
The idea to inject nitrogen came from the U.S. Nuclear Regulatory Commission (NRC).
The NRC notes that the pumping of seawater to cool the nuclear reactors could cause the build up of Hydrogen, as it is more likely to be produced via saltwater than via freshwater.
The NRC guesses that the damaged Uranium fuel rods in the No. 1 reactor had fallen to the base of the container and had been covered by the saltwater sprayed in - which may have had the opposite intended effect, and may have prevented the cooling water from reaching the fuel rods - which is why it says the situation within Reactor No. 1 was the most dire.
NRC says the fuel rods in the No. 2 and No. 3 reactors may also have been damaged and likely accumulated at the bottom of the pressure containers.
Because the water level in the pressure container has not gone beyond the position that is connected to the recirculating pump in the core, despite the volume of water pumped into the container, the NRC believes that water is leaking from the sealing part of the pump. If a large volume of leaked water accumulates within the containment vessel, the vessel could be destroyed from the weight of the water should a strong earthquake aftershock hit the reactor.
Additional Information:
The fuel rods in Reactor No. 3 contain MOX - a Plutonium-Uranium mixture. Plutonium generates more heat than Uranium,which means these rods have the greatest riskof burning.
You should know that along with the active fuel rods, the facility also stored the spent fuel rods.
Dai-ichi has seven pools for holding spent fuelrods. Six of these are (or were) located atthe top of six reactor buildings. One common pool is at ground level in aseparate building.
Each reactor top poolholds 3450 fuel rod assemblies, while the commonpool holds 6291 fuel rod assemblies. Each assembly holds sixty-threefuel rods, meaning that the Dai-ichiplant may contain over 600,000 spent fuelrods.
Files compiled by Andrew Joseph
Another story should be up by the time you read this.
