这个EMAIL是我刚收到的，写这个EMAIL的老美DEALING WITH THE NUCLEAR INDUSTRY。
Below is a lot of information, but it should provide you with an adequate understanding of the situation in Japan at Fukushima Daiichi (at least as it is understood by me at this time). I’ve split this into two sections, Nuclear 101 and Fukushima Facts.
1) Nuclear 101
· Nuclear power plants are net positive power producers, meaning that they produce more power than they consume, but they do consume electricity in order to create electricity
a. A large portion of the consumption is used to run the reactor coolant pumps
· When a nuclear reactor undergoes an emergency shutdown, it is calling “scramming the reactor”
a. When a reactor is scrammed, the control rods are lowered into place stopping the reaction from going critical
b. An operating nuclear reactor is by design critical, meaning the reaction is self sustaining. “Going critical” is not a bad word in the nuclear industry. It is how they are designed to operate.
· After a reactor is scrammed, it takes approximately 3 to 4 weeks to remove all the decay heat from the system
a. The reactor coolant pumps must continue pumping or the reactor will overheat creating over pressurization and steam in the reactor pressure vessel (RPV)
· Nuclear power plants have multiple redundant safety features to help ensure coolant flow in an emergency
a. First are multiple redundant diesel generators to provide power for the coolant pumps and control room
b. Second (in a Boiling Water Reactor) are steam powered pumps called Reactor Core Isolation Cooling (RCIC) pumps which use steam to power pumps to cool the reactor
c. Third is plant specific. In the case of Fukushima, this is seawater injection where seawater and boron are pumped into the reactor to cool the system
i. In the case of seawater injection, seawater is continually pumped into the reactor and subsequently boiled off. The steam is collected, the radioactive materials are removed, and the clean steam is vented out of the top of the reactor
· The fuel rods in a nuclear reactor are made of zirconium tubes filled with enriched fuel pellets
a. During a nuclear reaction, several radioactive fissile gases are produced, but are contained in the fuel rods and RPV
· Zirconium undergoes a rapid oxidation reaction in the presence of steam and gives off hydrogen
a. In an emergency, the plants are designed to pipe hydrogen out of the RPV through a radioactive gas separator, then burn off the hydrogen at an external flare. Similar to what you see being flared at an oil refinery
· The GE Mark 1 and 2 nuclear power plant designs use a two stage containment system
a. Primary containment building (what we are used to seeing in the US-a big concrete domed structure)
b. Secondary containment, which is a steel superstructure. The superstructure is light weight and was designed to blow away, in this case explode, without imparting damaging loads on the primary containment
· Spent or used fuel is stored on site in two locations
a. The newest used fuel sits in a storage pool to cool down for 10 to 20 years
i. As long as the pools have water in them, there is little appreciable risk from used fuel
b. The older used fuel is stored in dry storage casks
2) Fukushima Daiichi Facts & Timeline
· The Fukushima Daiichi Nuclear Power Plant has six nuclear reactors on site, all of which are Boiling Water Reactors (BWRs)
o Unit #1, 1971, 460MW, GE design
o Unit #2, 1974, 784MW, GE design
o Unit #3, 1976, 784MW, Toshiba
o Unit #4, 1978, 784MW, Hitachi
o Unit #5, 1978, 784MW, Toshiba
o Unit #6, 1979, 1100MW, GE design
· All six plants were designed to handle the perceived worst case scenario earthquake and resulting tsunami
o The earthquake design basis is estimated to assume a worst case earthquake of between 6.5 and 7.2 on the Richter Scale
§ The earthquake that hit on Friday at 2:46pm (Japan time) registered 8.9 and was later upgraded to a 9.0
§ 9.0 is 250 times more powerful than what the plant was designed to handle
§ For Reference the Northridge Earthquake in California (1994) was a 6.7
o Japan and its 55 operating reactors, have experienced seven aftershocks so far that were equal to or greater than the estimated design basis for the plant
o The tsunami design basis is estimated to assume a worst case maximum wave height of 22 feet
§ The actual tsunami that hit the Fukushima plant was upwards of 30 to 32 feet high
· Approximately one minute before the earthquake shook Japan, their early warning systems worked and all 6 reactors were scrammed (shut down)
· When the tsunami hit land the Japanese electric grid began failing
· The Fukushima plant switched over to diesel generators
· As the tsunami passed the plant (inland and outward) it damaged the diesel storage tanks for reactors 1, 2, and 3, thus shutting down the diesel backup
· Reactors 4, 5 and 6 diesel generators continued to function as designed
· When the diesel generators stopped, reactor #1 experienced a small loss of coolant on the core, creating hydrogen which was vented to the flue system
· The RCIC pumps kicked in and continued to cool the reactors
· The RCICs use DC (battery powered) valves. After eight hours of RCIC cooling the batteries were consumed
· Seawater injection began as necessary in reactors 1, 2 and 3
o Once seawater is injected the reactors, they cannot be used again
· The flue systems were damaged during either the earthquake or the aftershocks, causing hydrogen to escape to the secondary containment building
o When the hydrogen reached ~20% in the secondary building, itself combusted and caused the first explosion
· Reactor #3 then had a loss of coolant on the core, creating hydrogen which was vented to the flue system
o Similar to reactor 1, its secondary containment then exploded
o The difference between reactors 1 and 3, is that the Japanese knew that 3 was going to blow when the hydrogen levels reached a critical point
· Portable diesel generators were installed on site and some power was restored
· The Japanese are working to locate and install additional heat exchangers so they can stop venting steam and more rapidly remove decay heat
· The USS Ronald Reagan measured radiation (mostly in form of Cesium) 60 miles off the coast of Japan
o The levels measured were not sufficient to cause a health concern
· Reactor #2 had a loss of coolant, measured at 80-cm
o The Japanese immediately told the world that secondary containment on reactor 2 was likely to follow suite with 1 and 3
· Several of the buildings around the onsite storage pools were destroyed by the tsunami and subsequent events
o The Japanese have positioned fire trucks at the storage pools. Their purpose is to flood the pools with water if they notice their water levels beginning to drop
· A release valve stuck on reactor 2 caused a pressure fluctuation in the RPV
o This lead to 2.7-m of the core (1/2 the core) being uncovered and exposed to steam
· At this point, no radiation levels had been released that would cause a health risk
· A fire began at reactor #4 near the storage pool
o The fire was an oil fire caused by a leak in water recirculation system
o Fire fighters worked to put out the fire. It is releasing radioactive substances into the air, but as of this morning they are not at an unsafe level
· Reactor 2 had an explosion or blast, but it was not the secondary containment
o They do not know what happened as of yet, but fear it was something inside the primary containment building
o The blast corresponded with a release of higher radiation, approaching levels that could cause health concerns for humans
· The fire was contained and/or extinguished at reactor 4
· 800 workers remained on site, 750 of which are dedicated to cooling reactors 1, 2, and 3
· Reactors 1 and 3 are now stable and cooling is being maintained via seawater injection
· Radiation levels in the control rooms of reactors 1, 2 and 3 exceeded safe limits
· All but 50 plant personnel have been evacuated from the site
· Work is now focused on reactor 2, attempting to bring it to a more stable position
I can’t reiterate enough that facts are few and far between. We are not nuclear experts, so be very careful how you frame any information that you relay to others. The media is intermixing hypothesis, facts and conjecture and portraying them all as facts.
