Beyond Three Mile Island
The U.S. Seventh Fleet reports that on Monday, 17 members of three helicopter crews from the U.S. Ronald Reagan aircraft carrier, providing disaster assistance off the coast of Japan, returned with measurable radiation contamination and underwent decontamination procedures. Their aircraft also had measured radiation contamination and were washed down for decontamination. The radiation is believed to be from a plume of material released from the Fukushima Daiichi Power Plant.
The U.S. Navy ships relocated to avoid being directly downwind of the damaged plant. News media report that naval operations continue to work around areas of heightened radioactivity. On Tuesday, a no-fly zone with a 32-kilometer (20-mile) radius around the Fukushima Daiichi plant has been established for commercial aviation.
It is likely that Fukushima Daiichi is in the midst of a triple-Three-Mile-Island level of accident, but not as of Tuesday morning Tokyo time yet close to the level of a Chernobyl-type accident. (The threshold for that higher level of nuclear disaster would be a significant, sustained breach of one or more of the reactor containment vessels, with a widespread distribution of nuclear material.)
The ongoing outcome of the triple-reactor nuclear accident will likely be determined by the degree of nuclear fuel damage probably already very significant at all three reactors at present, and how much further fuel melting can be prevented by emergency cooling efforts.
The emergency cooling with seawater that is currently underway is an open-loop process (unlike normal closed-loop reactor cooling), and it creates heightened radiation releases because the water pumped into the reactor vessel is contaminated there, and then as the water boils, pressure has to be relieved, and the radioactive steam is vented into the atmosphere.
Furthermore, seawater is more corrosive than the purified water usually circulated through the reactor. In addition, under partial meltdown conditions, damaged fuel rods can include additional radionuclides generated in the uncontrolled nuclear reactions, and the nuclear material in damaged fuel rods is more likely to react with the coolant.
All these conditions make the ongoing venting to the atmosphere of steam from seawater cooling dangerously problematic. However, at this point, apparently only the emergency cooling with seawater is preventing further nuclear fuel core melting, and the possibility of a runaway meltdown in any of the three crippled reactors.
The emergency procedure of cooling with salt water has apparently never been used before at a commercial reactor, over the 57-year history of the nuclear power industry (World Nuclear News (WNN)).
Nuclear Crises Continuing
Fukushima Daiichi Nuclear Power Plant (Fukushima Number One) includes six boiling-water-type reactor units. Reactor #1, which suffered a partial core meltdown (NHK) and lost roof and wall cladding in a hydrogen explosion on Saturday, seawater is being used to cool the nuclear fuel.
NHK World (Japan) reported at the stricken Fukushima Daiichi reactor #3, fuel rods were exposed "2.2 meters [6.5 feet] above water for two hours". Any exposure of fuel rods is disastrous. As of Monday morning, seawater was also being used for emergency core cooling at Fukushima Daiichi reactor #3. Around 11:01AM om Monday, Tokyo time, a significant hydrogen explosion occurred at reactor #3 that destroyed much of the walls and roof of the containment building, with reports of additional worker casualties. The hydrogen explosion reportedly did not damage the reactor containment vessel.
Several people working on the Fukushima plants are reported to have radiation sickness, and the increasing radiation conditions have greatly increased the risk to plant workers. At least one nuclear plant worker is dead (WNN), perhaps from the explosion on Saturday that destroyed the roof of the reactor #1 building.
Fukushima Daiichi reactor units 4, 5, and 6 were already on scheduled shutdown at the time of the earthquake. These units were believed to be stable in shutdown mode, until fire erupted at reactor unit #4, and TEPCO acknowledged cooling problems in the onsite spent fuel storage pools.
At the Fukushima Daiichi Nuclear Power Plant reactor #2, cooling problems were reported off and on since Friday or Saturday. As of 5:00PM Monday in Japan, cooling had again become ineffective, fuel rods had become significantly exposed (80 cm (31 in.) or more), and around 8:00PM seawater injection to the reactor #2 was "resumed" (NHK). The crisis at this reactor is continuing.
It is now clear this third reactor to break down badly is also permanently crippled. Like Fukushima Daiichi reactors #1 and #3, #2 is now also in an unstable state, with operators trying to get it cooled down enough to reduce the risk of an accelerating core meltdown a challenging process that is likely to continue for days and weeks, even if the fuel melt situation does not get any worse along the way.
Reactor #3 at the Fukushima Daiichi Nuclear Power Plant contains some fuel rods of "MOX" or mixed-oxide fuel (NIRS). This type of nuclear fuel includes plutonium, has a lower fuel-rod melting point, and can be significantly more toxic when released.
It is not clear if there is MOX fuel, and therefore plutonium, in the spent fuel storage pool at reactor #3, or in any of the five other spent fuel storage pools at the plant.
Additional releases of radioactive material were detected outside the plant late on Monday, and then measured radiation level oustide the plant spiked on Tuesday morning. Radiations levels near the reactors were high enough on Wednesday and Thursday to prevent direct access for urgent cooling water make-up and fire-fighting.
At Fukushima Daini Nuclear Power Plant (Fukushima Number Two), where quake-related cooling problems had also been reported for three operating reactors, official reports on Monday were that cooling systems are returning to proper function. (That had also been reported for reactor #2 at Fukushima Daiichi, which went on to completely lose normal operation.)
Reported numbers of evacuees from the area surrounding the ongoing nuclear accidents range from 60,000 to 200,000, in a 20-kilometer (12-mile) radius. Evacuees are being screened for radiation exposure, and some are now being sent through field decontamination procedures.
Widespread Shortage of Electric Power
In addition to the crippled nuclear power plants that are now permanent liabilities, conventional thermal powerplants have been impacted by the earthquake and tsunami and are also offline.
The utility company Tokyo Electric Power Company (TEPCO) called for conservation efforts and announced rolling power blackouts starting Monday morning, with current generating capacity at 31 million kilowatts, compared to typical demand of 41 million kilowatts.
Planned outages in the TEPCO service area, including Tokyo except its central area, and including the prefectures of Chiba, Gunma, Ibaraki, Kanagawa, Tochigi, Saitama, Yamanashi and part of Shizuoka, are currently expected to continue until the end of April. Ongoing announcements are providing changing details as the situation evolves (NHK).
Intentional power outages started around 5:00PM on Monday, and affected four prefectures during Monday evening.
If you have firsthand information or images of the situation in Sendai, Tokyo, or elsewhere in Japan, or in other areas with earthquake or tsunami damage, please submit a comment or email to "email@example.com" to share with the design community.
Technical Reference Chart for Fukushima Reactors
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Kevin Matthews is Editor in Chief of ArchitectureWeek. More by Kevin Matthews