Long article but deffinately worth the time to read.....
Japanese Reactor Status Update
Explosion rocks third Fukushima reactor
14 March 2011
First published: 3.08am GMT
UPDATE 1: 3.25am Addition of background information
UPDATE 2: 3.49am Technical details on pressure
UPDATE 3: 4.34am Injuries, radiation rates and pressure data
UPDATE 4: 12:00pm Subsequent radiation readings
Another hydrogen explosion has rocked the Fukushima Daiichi nuclear power plant, this time at the third reactor unit. Initial analysis is that the containment structure remains intact.
The blast that occurred at 11.01am today was much larger than the one seen at unit 1 two days ago. An orange flash came before a large column of brown and grey smoke. A large section of the relatively lightweight roof was seen to fly upwards before landing back on other power plant buildings.
Chief cabinet secretary Yukiyo Edamo appeared on television shortly afterwards to identify the blast was a hydrogen explosion. He said contact had been made with the plant manager whose belief is that the containment structure, important to nuclear safety, remains intact. The rationale for that statement, Edamo said, was that water injection operations have continued and pressure readings from the reactor system remained within a comfortable range.
Pressure readouts from the period after the explosion were within a relatively normal range: 380 kPa at 11.13 and 360 kPa at 11.55am. These compare with comfortable levels yesterday of 250 kPa, reference levels of 400 kPa, and a high of 840 kPa recorded at unit 1 on 12 March.
Radiation readings on site remained low after the blast, albeit elevated from normal operation. In the service hall the reading was 50 microSieverts per hour. At the entrance to the plant the figure was 20 microSieverts per hour.
At 12:30pm, the radiation dose measured at a monitoring point on the Fukushima Daiichi site indicated a level of 4 microSieverts per hour. However, Tepco said that an increase in the radiation dose could not be confirmed at that time. A monitoring post at the Fukushima Daini plant – some 10 kilometres south of the Fukushima Daiichi plant – indicated no change in the radiation dose there.
Cooling and pressure control
Fukushima Daiichi 3 was yesterday the subject of sustained efforts by engineers working to ensure that adequate cooling water was available for decay heat removal. Seawater was being injected into the reactor vessel and pressure had been relieved to comfortable levels.
A statement from Tepco shortly after the blast said that pressure had risen again to 530 kPa by 6.50am. The company determined this was 'abnormal' at 7.44am and declared the matter officially to government. It began to gradually relieve the pressure, and carried out a "tentative evacuation" of the site, until it reached a level of 490 kPa at 9.05am.
Researched and written
by World Nuclear News
Reactor container not damaged in Japan's nuke plant blast: IAEA
English.news.cn 2011-03-14 15:59:09
This Oct. 2008 file photo released by Kyodo News Agency on March 13, 2011 shows the reactors of Japan's Fukushima No. 1 nuclear power station. Japan's Nuclear and Industrial Safety Agency said March 14, 2011 that hydrogen blast occurred at the No. 3 nuclear reactor (2nd from left) of Fukushima No. 1 nuclear power plant at 02:01 GMT (11:01 local time). (Xinhua/Kyodo)
VIENNA, March 14 (Xinhua) -- Explosion at the Fukushima No. 1 nuclear plant had not damaged primary containment vessel, the International Atomic Energy Agency said on Monday, quoting Japanese officials.
An IAEA statement said Japan's Nuclear and Industrial Safety Agency (NISA) provided the IAEA with further information about the hydrogen explosion, which occurred at the No. 3 reactor Monday following Friday's devastating earthquake.
All personnel at the site were accounted for, and six people were injured in the blast, the Vienna-based UN nuclear watchdog said.
The control room of No. 3 reactor remained operational, the statement added.
Second blast occurs at Japan's nuclear plant as death toll rises
TOKYO, March 14 (Xinhua) -- A second hydrogen explosion on Monday rocked the quake-stricken nuclear plant in Japan, as the government is going all-out to prevent a nuclear disaster.
Plumes of white smoke were seen coming from the Fukushima No.1 nuclear power plant following a loud explosion at the plant's No. 3 reactor, the Nuclear and Industrial Safety Agency (JNISA) said.
Tokyo Electric Power Co. said seven people went missing and 11 were injured after the explosion.
The agency said the wall of the reactor building collapsed, confirming eye-witness reports that only the building's skeletal structure remained.
The likelihood of high levels of radiation in the area is low, the agency said, but warned the 600 people who were still in the 20-km evacuation zone to leave immediately.
The agency also said large amounts of hydrogen have amassed in the upper parts of the reactor building, where the pressure remained unusually high, similar to that of the No. 1 reactor building, which also exploded on Saturday.
ANS: Japanese Nuclear Power Plant Update
Posted on March 13, 2011 by Steven B. Krivit
Source: American Nuclear Society
American Nuclear Society Backgrounder: Japanese Earthquake/Tsunami; Problems with Nuclear Reactors
3/12/2011 5:22 PM EST
To begin, a sense of perspective is needed… right now, the Japanese earthquake/tsunami is clearly a catastrophe; the situation at impacted nuclear reactors is, in the words of IAEA, an “Accident with Local Consequences.”
The Japanese earthquake and tsunami are natural catastrophes of historic proportions. The death toll is likely to be in the thousands. While the information is still not complete at this time, the tragic loss of life and destruction caused by the earthquake and tsunami will likely dwarf the damage caused by the problems associated with the impacted Japanese nuclear plants.
Recognizing that information is still not complete due to the destruction of the communication infrastructure, producing reports that are conflicting, here is our best understanding of the sequence of events at the Fukushima I‐1 power station.
- The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic power system worked.
- All external power to the station was lost when the sea water swept away the power lines.
- Diesel generators started to provide backup electrical power to the plant’s backup cooling
system. The backup worked.
- The diesel generators ceased functioning after approximately one hour due to tsunami induced damage, reportedly to their fuel supply.
- An Isolation condenser was used to remove the decay heat from the shutdown reactor.
- Apparently the plant then experienced a small loss of coolant from the reactor.
- Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were used to replace reactor core water inventory, however, the battery‐supplied control valves lost DC power after the prolonged use.
- DC power from batteries was consumed after approximately 8 hours.
- At that point, the plant experienced a complete blackout (no electric power at all).
- Hours passed as primary water inventory was lost and core degradation occurred (through some combination of zirconium oxidation and clad failure).
- Portable diesel generators were delivered to the plant site.
- AC power was restored allowing for a different backup pumping system to replace inventory in reactor pressure vessel (RPV).
- Pressure in the containment drywell rose as wetwell became hotter.
- The Drywell containment was vented to outside reactor building which surrounds the
- Hydrogen produced from zirconium oxidation was vented from the containment into the reactor building.
- Hydrogen in reactor building exploded causing it to collapse around the containment.
- The containment around the reactor and RPV were reported to be intact.
- The decision was made to inject seawater into the RPV to continue to the cooling process,
another backup system that was designed into the plant from inception.
- Radioactivity releases from operator initiated venting appear to be decreasing.
Can it happen here in the US?
- While there are risks associated with operating nuclear plants and other industrial facilities, the chances of an adverse event similar to what happened in Japan occurring in the US is small.
- Since September 11, 2001, additional safeguards and training have been put in place at US nuclear reactors which allow plant operators to cool the reactor core during an extended power outage and/or failure of backup generators – “blackout conditions.”
Is a nuclear reactor “meltdown” a catastrophic event?
- Not necessarily. Nuclear reactors are built with redundant safety systems. Even if the fuel in the reactor melts, the reactor’s containment systems are designed to prevent the spread of radioactivity into the environment. Should an event like this occur, containing the radioactive materials could actually be considered a “success” given the scale of this natural disaster that had not been considered in the original design. The nuclear power industry will learn from this event, and redesign our facilities as needed to make them safer in the future.
What's going on with the Japanese nuclear reactors: a primer
By News Desk on March 13, 2011 8:12 AM
Platts nuclear group, led by Tom Harrison and William Freebairn, published a story early Monday Japan time on just what is and might be happening with the damaged nuclear reactors in Japan. We are publishing it for Barrel readers below.
Washington--Tokyo Electric Power began injecting sea water into a reactor at its Fukushima Daiichi nuclear power plant Saturday in an effort to maintain cooling of the unit, which lost power following an earthquake and tsunami Friday.
Tepco reported higher-than-normal levels of radioactivity at the site but did not provide numbers. Tepco said one worker in the unit 1 reactor building was sent to the hospital after receiving a radiation dose that exceeded the threshold considered as low. Earlier that day, the IAEA said radiation levels at the plant, which rose earlier, had lessened. One worker at the adjacent Fukushima Daini station was reported killed, Tepco said, but did not give the cause.
The effort to use sea water at the coastal plant to cool the Fukushima Daiichi-1 reactor core was "an act of desperation," said Robert Alvarez, a senior scholar at the Institute for Policy Studies and a former US Department of Energy official. The effort may reflect a loss of water circulation capacity at the site, Alvarez said in a conference call sponsored by the anti-nuclear Nuclear Information and Resource Service.
Tepco said in an update on its website Saturday that injection of sea water into the reactor core, followed by addition of boron, which is used to reduce the rate of nuclear fission, began at 8:20 pm local time. The effort was later halted because of concerns about another tsunami brought on by an aftershock, Tepco said.
Tepco said it shut all its seven operating power reactors at the Fukushima stations following the earthquake. The six-unit Fukushima Daiichi station lost power, and emergency diesel generators that were designed as a backup failed about an hour after the earthquake, possibly in connection with the tsunami.
Japan's national government ordered the evacuation of residents living within 20 kilometers (12.4 miles) of Fukushima Daiichi, broadening an earlier order to evacuate those within 3 km.
Japan's nuclear regulator has confirmed the presence of radioactive cesium-137 and iodine-131 in the vicinity of the plant, the International Atomic Energy Agency said on its website. The presence of cesium could be an indication of damage to the fuel in the reactor, Alvarez said.
Tepco said an explosion at the site "near" unit 1 injured four workers earlier Saturday. That explosion affected the concrete building that covers the top of the reactor's steel containment vessel, which remains intact, the IAEA said.
The cause of the explosion is unclear, but could have been an accumulation of hydrogen in the concrete building from the interaction of fuel cladding materials and water, former US Nuclear Regulatory Commission member Peter Bradford said during the NIRS call. That hydrogen could have been vented into the containment vessel and then migrated to a building where it could ignite when mixed with oxygen, he said.
The accident could significantly reduce public support for nuclear power around the world, Bradford said. Those who advocate nuclear energy as a way to lower carbon emissions and fight climate change "will have to deal with greatly heightened skepticism," said Bradford, who has opposed policies promoting nuclear energy.
The nuclear industry will examine the root causes of the accident and seek to learn from it, Nuclear Energy Institute spokesman Tom Kauffman said Saturday. "The world nuclear industry will be paying close attention to this," he said. Tepco and its workers have done "a heroic job" attempting to control the reactor, he said.
Dale Klein, a former chairman of the NRC, said in an interview Saturday that using seawater to flood Fukushima Daiichi-1's reactor core--and containment as a precautionary measure--is part of the plant's emergency planning process. "If you're near the end of your options, that's one of them," he said.
Klein said such a procedure leads him to believe the condensate tank was broken or empty or the pipes leading to it were broken because it would have been used otherwise. The condensate tank is used to provide water to the emergency core cooling system.
Klein, who chaired the NRC from July 2006 to May 2009, said future operation of the reactor "would be an economic decision that Tepco would have to make." But he said that it was his guess that the company would consider building a new one instead. "It would be a major cleanup of contaminated components and water," he said. The 460-MW unit 1 at Fukushima Daiichi (or Fukushima I) began commercial operation in 1971 and is the oldest and smallest of the Fukushima reactors.
Klein said he would characterize the quake impact on Fukushima I-1 as "more like a Three Mile Island [but] with a lot more knowledge." Operators at the Japanese unit "knew early on what they had to do, they just had trouble doing it." he said.
During the accident at the Three Mile Island-2 unit in Pennsylvania on March 28, 1979, operators mistakenly turned off the emergency core cooling system, which had automatically activated, because they erroneously believed the core was covered. The TMI-2 accident -- in which there was a partial core meltdown -- is considered the worst in US commercial nuclear power plant history but led to no deaths or injuries to plant workers, according to NRC.
The workers at Fukushima I-1 set up emergency diesel generators to provide backup power for the cooling system, but they apparently ran for only a short time before being damaged by the tsunami, Klein said. Backup power could have been provided by batteries but that typically lasts only a few hours, and damage to the surrounding area appears to have cut off the option of bringing in additional emergency diesel generators, he said. "The earthquake had minimal impact; the tsunami had the impact," Klein said.
At early-afternoon EST Saturday, Klein said he believed there would be few fatalities due to the reactor itself, although he said the hydrogen explosion could have injured people in the plant. "I think this will be remembered for the fatalities from the quake and tsunami, not from the reactor," he said.
Officially an accident
The problem in cooling Fukushima Daiichi-1 was officially rated an accident on the IAEA scale Saturday. The event was reported on the IAEA website as having a rating of 4 on the International Nuclear Events Scale, meaning it was an accident with local consequences, according to the agency's website. Events can be rated from 1, an "anomaly," to 7, a "major accident."
The explosion of a reactor at the Chernobyl nuclear plant in Ukraine in 1986 was a level 7 event; the partial meltdown of the core at Three Mile Island-2 was rated at level 5, IAEA said. Events rated 4 or higher are considered accidents, IAEA said.
Japanese authorities were reportedly planning to distribute potassium iodide tablets to residents around the plant. In the event of a radiation release from an accident, potassium iodide can protect the thyroid gland from possible radiation damage by blocking the absorption of radioactive iodine.
The Fukushima Daiichi-1 reactor is a boiling water reactor design that has a large number of ways to get cooling water into the core, Ken Bergeron, a physicist and former Sandia National Laboratory scientist, said on the NIRS call. The design counts on steam-driven components that do not require offsite power except for controls, he said. "They have a lot of options and they're using them now," Bergeron said.
The use of sea water might have been a planned line of defense for the core, he said.
But the small metal containment vessel in which the reactor is located does not present as much protection in case the core of fuel rods should melt, Bergeron said. Unlike the containment at Three Mile Island-2, that of Fukushima Daiichi-1 might not survive a core melt, he said.
Nuclear reactors have various barriers -- including the containment building, reactor vessel and fuel cladding -- aimed at preventing the release of radioactivity in case of an accident or a terrorist attack.
Three of the Fukushima Daiichi nuclear units were shut at the time of the earthquake for inspection, Tepco said. Unit 2 was shut after the earthquake, and cooling water level was lower than normal but steady, Tepco said. Unit 3 was also shut and cooling water was being injected, the company said.
At the adjacent Fukushima Daini (Fukushima II) plant, all four units automatically shut down after the earthquake. Tepco reported all four had stable coolant levels, although the company recorded higher-than-normal pressure readings.
The NRC was sending two BWR specialists to Japan as part of a delegation of US Agency for International Development workers, the agency said Saturday. NRC has some of the top experts in BWRs and will assist Japan as much as possible, Chairman Gregory Jaczko said in the statement.
Japan Nuclear Fallout: How Bad Could It Get?
by Josh Dzieza
Josh Dzieza is an editorial assistant at The Daily Beast.
As Japan scrambles to cope with a nuclear reactor damaged in the quake, Josh Dzieza talks to Ron Ballinger, a nuclear expert at MIT about how the plants work, worst-case scenarios, and more. Plus, full coverage of Japan's catastrophe.
Shortly after Japan was hit with the double disaster of a magnitude 8.9 earthquake and subsequent tsunami, a possible third reared its head: nuclear meltdown. The quake caused 11 of Japan's nuclear reactors to shut down automatically, including three at the Fukushima Dai-ichi power plant, 170 miles northeast of Tokyo. But the quake also cut Fukushima off from the power grid, forcing plant operators to switch to emergency diesel generators in order to continue cooling the reactor core, generators that then failed shortly after the tsunami hit. By the end of the day Friday, Prime Minister Naoto Kan had declared a “nuclear emergency,” and 200,000 people near the plant had been told to evacuate.
Then, Saturday afternoon, a building at the plant erupted in a massive explosion, apparently the result of hydrogen from the superheated fuel rods interacting with oxygen as plant operators tried to vent increasing pressure inside the reactor. Officials say the reactor wasn't damaged in the blast, and that radiation levels have actually been declining since. Nevertheless, they took the extreme step of flooding the reactor with seawater in an attempt to cool it down, and news that the cooling system for a second reactor at the same plant has begun to fail did little to calm worries of a meltdown. As Japan copes with its worst nuclear mishap at least since the leak at Tokaimura, The Daily Beast spoke with MIT Professor of Nuclear Science and Engineering Ron Ballinger about worst-case scenarios, iodine tablets, and why he thinks everything is going to be fine. Plus, complete coverage of the quake.
What's the worst-case scenario?
Well, first off, we can't have a Chernobyl-like situation. The system is designed so that as long as we keep water in there to keep it cool, nothing will happen. There are three levels of protection here. One is the fuel cladding, and if that's damaged then it releases radioactive material into the pressure system, which is a steel container. Then there's a containment vessel around that. What likely happened is that you had fuel damage, damage to the first barrier, which produced hydrogen in the primary system, and then to keep the pressure down they vented the hydrogen into the building that was destroyed.
What happens if all the water boils off?
Hypothetically, if the water all boils and evaporates, then the fuel will stay molten and eventually melt through the steel vessel. But that's already beyond a hypothetical worst-case scenario for me. The steel vessel is four inches thick, and they could always put seawater around the vessel, and that would keep it cool, so it can't melt. If you put a frying pan in water, you could put a blowtorch on the other side and it won't make any difference. Then you have the other containment vessel, with a concrete faceplate underneath that's between four and 10 feet thick. But melting through that is hypothetical beyond normal reasoning.
Radiation spiked at 1,015 microsievert per hour before the explosion. Is that dangerous?
No, that's about 100 milirem. It's high, but you get about 35 milirems on a trans-Atlantic flight. And if you live in Denver, you get about 50 milirems per year.
What is the dangerous level, and what happens when that level is reached?
The LD50—that is to say, the point when 50 percent of the people exposed will meet Jesus—is in the order of 250 rem, or maybe 400. A big number. Keep in mind, what they've been exposed to is 0.1 rem, and about 50 percent fatality is on the order of 400 rem. What would happen with that kind of exposure is that they would get sick. Radiation damage destroys the immune system. Most people who die of radiation sickness die of pneumonia or a cold, they die of some disease which they have but their immune system can't fight off.
Why is Japan distributing iodine tablets?
One of the isotopes of fission products, when fuel melts, is an iodine isotope, and it goes in your body through your thyroid. So if you take iodine tablets, the non-radioactive iodine goes to your thyroid, you bulk up your thyroid with iodine and it prevents absorption of the radioactive iodine.
What failsafes are there to prevent a meltdown?
A lot. First there's the SCRAM system, it automatically ejects the control rods into the core and shuts the plant down. That happened right after the earthquake. Then there's a number of core spray systems, which inject water to keep things cool. Then, if the system needs to depressurize, there's something called a suppression pool that it vents steam into. Then, when the system is depressurized there are other systems that inject water at low pressure. And then, worst comes to worst, there are pumps that can take water from the local cooling water supply, in this case the ocean, and just pump water in there. As long as there's water in there, it might be expensive for the utility to get it cleaned up, but everything is going to be fine.
If they're pumping in seawater, does that mean all the other failsafes failed?
The earthquake plus the tsunami destroyed all the power sources to run pumps and things like that. There are diesel generators on the site that are supposed to run for that purpose, but for some reason they ran for a while and then stopped, maybe because of the tsunami. Then they hauled a bunch of portable generators to run the pumps.
How good a failsafe is pumping in seawater?
The ocean's pretty big. But it's salt water, so from an operational point of view you're pretty screwed. If you get saltwater into the primary system, it's very hard to get it cleaned up. Salt water's not good for the materials, it requires pure water. So if they have to put saltwater into the primary system, it would keep it cool, but it would damage a lot of things and there will have to be extensive cleanup.
How will we know when the crisis is over?
The fuel has to cool down to the point where the water that's cooling it is below the boiling point. Usually when they shut one of these plants down to refuel they have to open it up. It takes a couple days to get the plant shut down to the point where they can take the lid off and replace the fuel. It might be a financial disaster, but no member of the public has been hurt, and I doubt anybody will be.
Josh Dzieza is an editorial assistant at The Daily Beast.
The Neutron Economy
The nuclear fuel cycle, reactors, and everything in between
Sunday, March 13, 2011
Fukushima in layman's terms
This post started out as a facebook note to try and educate and inform my non-technical friends and associates about what's been going on in the situation with Japan post-quake with respect to the reactors at Fukushima Daiichi. I was surprised at how many people appreciated having the relevant issues explained to them in both a way that was factual (rather than sensationalist) and in a way they could understand.
With the help of my colleagues Alan and Cyrus, this post began evolving into a platform for communicating what's been going on since the initial response and digesting much of the information for a more general audience. Given that, it made sense to branch these updates out into a more flexible, updated format - in other words, a blog.
This post will cover some of the frequently-asked questions I posted on facebook, and following from this, we'll be covering the situation as it has evolved from there.
First, the most authoritative place for news would be the Tokyo Electric Power Company, which is releasing regular press releases on the situation. Likewise, ANS nuclear cafe is featuring constant media updates on the situation. Rod Adams at Atomic Insights also has a good summary of the situation. NEI also has a good fact sheet on the events at Fukushima that have occurred up until now and details as they unfold.
What happened in the earthquake?
When the earthquake struck, Japan's reactors were immediately shut down by a quick insertion of control rods, stopping the chain reaction responsible for producing fission (known as a "scram.") This was successful in all of the reactors. However, the reactor still remains "hot" for a short time after shutdown, because of very short-lived radioactive fission products which are in the fuel. As these fission products decay, they produce heat - this heat still must be removed from the reactor in order to keep the fuel cool. As my colleague Cyrus points out, this can be 6-7% of full power at shutdown - in a reactor like Fukushima, this can be 60-70 MW. However, the rate of heat produced decays exponentially; after 24 hours, it would be around 10 MW and falling. In other words, the first few days are the most crucial - keeping the fuel submerged over the next week is the highest safety priority.
Normally, when the power is cut off in an emergency such as this, a diesel generator serves as a backup system, which powers pumps in order to circulate coolant (much like in your car's radiator). However, it appears that these diesel systems were damaged during the earthquake - thus, the pumps had to operate on limited battery power until this was exhausted. Contrary to early reports, the USAF wasn't "flying in coolant" (as this just consists of ordinary water); however, a backup diesel generator was flown in and installed to get the pumps working again. (Cyrus points out that the diesel generator was working for about an hour until the subsequent tsunami struck, which is what disabled the diesel backup system.)
What is the big concern?
The biggest concern in this case is keeping the fuel cool - even though the reactor is "off" (e.g., not producing any more fissions), heat is still being produced which needs to be "wicked" away. Without the water circulating, what will happen is similar to in your car's radiator if the car's water pump fails - i.e., the coolant will continue to get hotter and hotter until it boils. This increases pressure inside containment (or your radiator). In each case, the pressure build-up can eventually cause a blow-out, where the containment (or your radiator) is breached. This is obviously undesirable.
To prevent this, some of the steam is being vented, to "bleed off" the pressure. The downside of this of course is that letting out steam means there's less water available for cooling now. Likewise, a very small amount of radiation may be released in the process (carried with the steam). However, the amounts are generally incredibly small - the largest dose indicated has been in the reactor building, where one worker received 106.3 mSv - elevated beyond regulatory limits, but far from fatal. Current estimates of the control room put the dose around 70 microsieverts/h, or about 7 mrem/h - elevated, but quite small. One would have to be exposed continuously for nearly an entire work year for it to begin to hit regulatory limits, which are themselves conservative.
The big concern about keeping the fuel cool is to keep the fuel intact. When fissions occur, almost all of the radioactive isotopes created are trapped in the ceramic fuel itself - this is a safety feature. Thus, the main concern about keeping the fuel cool isn't a "China Syndrome" type of situation (which itself is physically impossible), but rather a matter of keeping the radioactivity safely confined.
As water is boiled away from the reactor, there is a chance that the fuel can be "uncovered," which is where the risk of partial melting of the fuel exists. (i.e., nothing is left to wick away heat from the element itself). However, the fuel itself is only the first radiation containment barrier - the containment building itself is also designed to prevent the release of radiation to the environment, specifically under these types of circumstances.
Has there been a meltdown? (Is this like Three-Mile Island or Chernobyl?)
Basically, no. First, it's helpful to define the term "meltdown." Were the reactor completely devoid of coolant, eventually the entire core assembly would heat and melt - producing a large, very hot radioactive pool of metal on the floor of the containment building. (Rod Adams helpfully points out that it's unlikely it would even get this far - in Three Mile Island's case, a substantial portion of the core melted, however it cooled into a lump of metal - "corium" - at the bottom of the pressure vessel.) This is not what is happening, nor is it the danger. The risk is in "uncovering" fuel from coolant, where the top portion of the fuel may melt and release radioactive fission products.
What has happened is that the fuel in Unit 1 may have been exposed for some time due to loss of coolant, which may have resulted in some loss of radioactivity.
Three-Mile Island was a partial fuel melt due in part to operator errors - operators incorrectly believed the reactor was being flooded with coolant (when in fact a pump was stuck closed), turning off coolant to the reactor. While the core itself was rendered unusable and the unit shut down, the actual dose received by the public was extremely minimal.
Chernobyl was a reactor different than the kind operated in Japan or the United States (and in fact would be illegal to build in the U.S. for technical reasons). Chernobyl operators were conducting tests with poor communication and had bypassed several safety devices. This was a full "meltdown" in the true sense, resulting in an explosion in the containment reactor building and a release of radioactivity. However, it should be noted that the death toll was relatively small, and most of the dose received (and subsequent casualties) were in the first responders to the accident.
Update: Reader David helpfully points out the following about Chernobyl's lack of safety systems which are present in all U.S. and Japanese reactors:
Chernobyl didn't have a containment building. It was not designed to withstand internal pressure from the reactor, and relied on continuous atmospheric ventilation. Chernobyl was also graphite moderated, the graphite reacting with superheated steam to create the large explosion internal to the core that blew the roof off the place. No commercial reactors, in the US or Japan, make use of graphite, and all have containment buildings designed to withstand significant internal pressures. The GE Mark I suppression-pool containment design, their first, is arguably the weakest design (structurally) still in service. As design basis accidents evolved, Mark I containments were retrofitted with a venting system to limit containment overpressurization, and prevent catastrophic containment failure
In that sense, Fukushima could not be more different than the Chernobyl design; it has a containment designed to withstand high internal pressures, and does not rely upon air cooling with the outside. Likewise, it is a water-moderated reactor, rather than graphite, which has several key safety advantages, including a design which automatically "shuts down" the reaction as temperatures increase. This is known in technical parlance as a "void coefficient," which means how the reactor responds to an increasing fraction of steam-to-liquid, or in other words, "void." Unlike Chernobyl, all reactors licensed in the U.S. must have a negative void coefficient, meaning they "slow down" as the fraction of steam in the coolant increases, preventing a runaway acceleration of the core reaction rate as it heats up. Because the core is already shut down, any Chernobyl type of scenario is already off the table - the issue now is simply one of keeping the fuel cool and intact until the decay heat comes down over the course of a few days. (End update).
In the case of Japan, the operators have been doing things correctly - the fuel has been kept as cool as possible to prevent any possible overheating of the fuel. Everything they've done so far has been to minimize the risk of damage to the core or accidental release of radiation to the public.
Wasn't there a radiation leak at one of the reactors?
Fukushima Daiichi Unit 1 appears to have released a small amount of radioactivity when the containment was vented in order to relieve pressure (due to the buildup of boiling water). However, this release appears to have been very small and of no real danger to the public. The measured radiological levels near the plant have been reported to have been elevated from 0.007 rem/hr to 0.67 rem/hr. While this is elevated beyond normal acceptable limits, this is far below the levels of Three Mile Island (itself quite small) or Chernobyl (much larger). The IAEA has given the incident a 4 on its International Nuclear and Radiological Event Scale (on a scale of 1-7; TMI was a "5", and Chernobyl was a "7").
TEPCO has announced that it is venting containment in Unit 3 as the high-pressure coolant injection system - an emergency system designed to inject coolant into the core - has stopped and cannot be restarted. Like Unit 1, venting is a safety precaution to release pressure from containment.
To clarify: when the containment is vented, a very small amount of radioactivity is released into the environment. This primarily consists of nitrogen-16, which is created when atmospheric nitrogen is bombarded by neutrons. N-16 has an extremely short half-life (7.16 seconds), meaning that by the time any release would reach any member of the public, it would have already decayed back away into stable oxygen; thus, the exposure from nitrogen would be nearly non-existent.
One of the other major isotopes released would be tritium, an isotope of hydrogen with two neutrons (instead of none) which exists in trace quantities in nature, and is created in small quantities in reactors when hydrogen in water molecules absorbs hydrogen. Tritium is weakly radioactive - as a beta radiation emitter, it only poses a real issue if it is ingested into the body (and even then, in large quantities). (This is unlike gamma emitters, which are deeply penetrating, or alpha emitters, which can be stopped by the surface of the skin or a sheet of paper). Tritium actually is present in a lot of everyday applications, from exit signs (yes, really!) to glow-in-the-dark watch dials. Overall, this represents a very minor amount of radiation compared to that present in the fission products contained by the clad and fuel material itself.
Why are they evacuating the area?
This is done as a preventative precaution to protect the public. While so far there has been no known escape of radioactivity (save for what may have been released when the containment was vented), the evacuation is to ensure that this can be verified without putting anyone at risk.
My colleague Alan disagrees with my characterization somewhat, indicating that he thinks the evacuation may be more of a preventative measure against possibly larger failures. While I remain more optimistic, I don't fundamentally disagree with the idea that any such evaluation is fundamentally preventative in nature. My point here is more emphasize that no significant public danger currently exists (i.e., no known significant radiological hazard at the present time). However, Alan's contention is that he believes that a potential, undetermined radiological hazard would not warrant such an extreme evacuation alone (especially under these conditions), and thus the evacuation is a precautionary measure against potential larger failures.
What caused the explosion? (Is this a meltown?)
There was an explosion in the reactor building (not the reactor or the containment building). Official sources speculate that this was due to an ignition of hydrogen gas. Hydrogen gas can build up due to the extreme heating of the water and dissolution into hydrogen and oxygen. When the cladding which encases the fuel gets very hot, it can dissolve water into its components of oxygen and hydrogen. (This may have been caused by the fuel becoming "uncovered"). This hydrogen may have ignited as containment was vented, causing an explosion. However, this is not a meltdown - so far, there has been no good indication that any kind of catastrophic fuel failure (melt) has occurred.
Some further explanation: for this reactor, there are two "nested" containment buildings - "primary" containment, which houses the core itself and is the chief barrier against a release of radioactive materials if the fuel, clad, and pressure vessel fail. Then there is a larger building around this, "secondary" containment, which is the reactor building itself, including industrial equipment like cranes, etc. used to service the core. The explosion occurred outside of primary containment, in secondary containment. This diagram from NEI shows a diagram of the building, including the core and where the explosion occurred. You can see what happened from this photo to give you some perspective of what these buildings normally looked like, see here (you're looking at the tall, rectangular-looking buildings - light blue). Basically, an explosion is serious, but not an indication that primary containment has failed or that radioactive materials are being released from the fuel/core itself.
Why are they flooding the containment building with seawater?
Basically, they need to keep the temperature down in the reactor. Because they've been losing water to boiling, they need to quickly cool the reactor. In order to do this, the operators have made the decision to flood the containment building with seawater containing boron (boron is used to "quench" nuclear reactions by absorbing neutrons - the point here is as an added safety precaution). What this ultimately means is that Unit 1 is likely a total loss - i.e., it will never operate again. However, this appears to be the only reactor which was so significantly impacted. Again, the other reactors on the same site (along with other reactors in the general area) have shut down and been cooled normally.
Doesn't this prove nuclear power is fundamentally unsafe?
No no no. A thousand times no. First, bear in mind that earthquakes are part of the design basis for every single reactor built today. Second, after an magnitude 8.9 earthquake - the largest in Japan's recorded history, and the fifth largest earthquake in human history - and a subsequent tsunami, the integrity of the reactor (and all of the other units at this same site) are intact. While breaking reports indicate that this reactor may have been "ruined" by the catastrophe, the danger to the public has been extremely minimal - namely, because engineered safety systems worked as planned.
Let me re-emphasize: nuclear reactors are often over-designed for the point of safety. The very first safety system to kick in was to turn off the reactor. This worked for every single unit. The second safety system, a diesel generator, worked in most cases - it would appear that the severity of the quake / tsnunami damaged the diesel backup in the case of Unit 1. However, battery backup systems gave operators time to provide a contingency. Second, the physical containment itself has operated as designed in providing a means of containing potential releases. (As Cyrus points out, nuclear systems are designed with a "defense in depth" - with the fuel, clad, pressure vessel, and containment building providing multiple layers against a radioactive release. At the moment, the main concern is at the level of the fuel / clad - not beyond this.)
What this proves is that in the very worst scenario - a once-in-a-lifetime earthquake beyond the design basis - that the systems can safely contain the integrity of the reactor, particularly with well-trained personnel.
To put a further point to it, this is what is going on right now at a liquified natural gas facility in the same area. (More images of the devastation here.) Basically, no system out there is going to stand up favorably to a disaster like this, but nuclear systems are specifically engineered against situations like this - again, unlike natural gas.
The BWR/6 design manual gives a more detailed explanation of the emergency cooling systems being employed here, in pages 57-68 of the PDF (pages 4-4 to 4-15 of the manual). While the BWR/3 at Unit 1 is slightly different these details are discussed on page 11 (page 1-2).
Hopefully this clears up some of people's questions, but if you have more, by all means ask, and I'll update this post accordingly. (And of course, if my NE friends want to add anything, please do!)
And of course, a special thanks to my colleagues Alan and Cyrus who have been helping me compile information for these updates.
Posted by Steve at 9:31 AM
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Labels: Fukushima, Japan quake
Japan nuclear woes cast shadow over U.S. energy policy
Sun, Mar 13 2011
By Jeff Mason and Will Dunham
WASHINGTON (Reuters) - Anxiety over Japan's quake-crippled nuclear reactors has triggered calls from lawmakers and activists for review of U.S. energy policy and for brakes on expansion of domestic nuclear power.
President Barack Obama has urged expansion of nuclear power to help meet the country's energy demands, lower its dependence on imported fossil fuels and reduce its climate-warming greenhouse gas emissions.
But as engineers in Japan tried on Sunday to avert a meltdown at three nuclear reactors following Friday's massive earthquake, some U.S. policy makers were reevaluating their take on nuclear energy even as the industry itself offered assurances about the safety of new and existing plants.
"I don't want to stop the building of nuclear power plants," independent Senator Joe Lieberman, chairman of the Senate Homeland Security and Governmental Affairs Committee, said on the CBS television's "Face the Nation."
"But I think we've got to kind of quietly put, quickly put, the brakes on until we can absorb what has happened in Japan as a result of the earthquake and the tsunami and then see what more, if anything, we can demand of the new power plants that are coming on line," Lieberman added.
Since the 1979 accident at the Three Mile Island nuclear plant in Pennsylvania, many Americans have harbored concerns about nuclear power's safety. Controversy has also dogged the nuclear power industry due to its radioactive waste, which is now stored on site at reactor locations around the country.
The Nuclear Energy Institute, which represents the industry in Washington, said regulators already are reviewing license applications for 20 reactors that would be built over the next 15-20 years. Four to eight new reactors are slated to begin operating between 2016 to 2020, spokesman Steven Kerekes said.
"It is a fairly measured build-out program," he said. "We feel it would be premature at this point to draw any conclusions from the tragic events in Japan relative to the U.S. program."
In February 2010, Obama announced $8.3 billion in loan guarantees to build the first U.S. nuclear power plant in nearly three decades. The backing helps Southern Co build two reactors at a plant in the U.S. state of Georgia.
The White House said it was watching the events in Japan for lessons about nuclear safety but indicated that no major policy changes were imminent.
"Information is still coming in about the events unfolding in Japan, but the administration is committed to learning from them and ensuring that nuclear energy is produced safely and responsibly here in the U.S.," White House spokesman Clark Stevens said.
"The president believes that meeting our energy needs means relying on a diverse set of energy sources that includes renewables like wind and solar, natural gas, clean coal and nuclear power."
Environmentalists said Japan's example should be a wake-up call for Obama to reconsider his policies.
"Obama's request for additional loan guarantees for new nuclear reactor projects is now revealed to be a questionable approach given the inherent safety risks of nuclear reactors and resulting radioactive waste," said Tom Clements of environmental group Friends of the Earth.
"Congress should deny any additional funding," he said. The group was opposed to the expansion of nuclear power even before the Japan disaster.
Both Democrats and Republicans have embraced expanding nuclear power as a way to generate electricity and jobs. The recent spike in gasoline prices as well as the Gulf of Mexico oil spill have put a renewed focus on revamping U.S. energy policies to find more sources of fuel.
Senate Republican leader Mitch McConnell, speaking on "Fox News Sunday," urged a cautious approach.
"I don't think right after a major environmental catastrophe is a very good time to be making American domestic policy. I think we ought to just concentrate on helping the Japanese in any way that we can," McConnell said.
Lieberman noted there are 104 nuclear power plants in the United States, and that about 23 of them are built according to designs similar to the nuclear power plants in Japan that are now the focus of the world's concern.
(Additional reporting by Deborah Zabarenko; Editing by Jackie Frank)
Monday, March 14, 2011
Performance of old nuclear plants in Japan demonstrates why much of current regulatory structure is overkill
by Rod Adams
My thoughts and prayers are with the people in Japan as they struggle to first survive and then to begin rebuilding their lives.
Not surprisingly, people who are professionally invested in actions to slow or kill nuclear energy developments are working at a feverish pitch to try to spin reality around. They have been working overtime during the weekend to make uninformed people forget that an enormous earthquake and tsunami have devastated much of nation of Japan. Instead, they want people to focus on a series of breathlessly reported stories about mysterious explosions at nuclear power stations and on the fact that the operators at the nuclear plants are struggling - like many of their countrymen - in the face of a broken infrastructure that cannot supply reliable power.
I want to keep it short this morning to give people more time to focus on more important things, like how to help people find enough clean drinking water and food and, longer term, how to help the Japanese economy recover. The activities at the nuclear plants will continue, the well-trained operators will continue to do their jobs admirably (not heroically, because they are in no personal danger either), and the anti-nuclear professionals will continue to hope for the worst and continue to be disappointed.
If you want to understand more about why nuclear reactors can experience brief hydrogen explosions, I highly recommend that you read a recent post at Brave New Climate titled Further technical information on Fukushima reactors.
Bill Tucker, the author of Terrestrial Energy, also has a piece worth reading in the Wall Street Journal titled Japan Does Not Face Another Chernobyl (I am tempted to add a subtitle to that - I think it would be accurate to put it this way "Japan Does Not Face Another Chernobyl: Much to the Disappointment of Professional Anti-nuclear Activists")
I have also been participating in interesting conversations at Can U.S. Nuclear Plants Handle a Major Natural Disaster? and Nuclear Experts Explain Worst-Case Scenario at Fukushima Power Plant - Aside: Can someone explain to me why Scientific American could not locate a more qualified nuclear operations expert than Peter Bradford? End Aside. It would be nice if some of you could come and join me to add a bit more perspective, information and sanity to the discussions.
I also think it is important to recognize the opportunity to explain to people why there will be no health consequences to the public from challenges at Japanese nuclear plants and why that prediction could confidently be made almost as soon as the earth stopped shaking, long before all of the details of the events began to unfold. This event should be understood and should certainly not lead to any additional uncertainty about whether or not it is a good idea to build as many new nuclear power stations as possible, even in places that occasionally shake, rattle and roll.
Because nuclear fuel is so energy dense, we can afford to wrap it up in numerous layers of engineered materials that protect the public even in the rare event of an earthquake that measures 9.0 on the Richter scale that is followed in close succession by a 30 foot high tsunami wave that wipes out emergency power supplies. We have known how to do that for a long time; even the 40 year old plants with 50-60 year old technology are coming through without harming the public. When nature throws all of that at you and the worst that happens is that you lose the services of a few industrial facilities for a while, you have a pretty darned resilient technology.
People who have been studying the lessons learned from the past have made some improvements in nuclear plant construction techniques. Newer plants in Japan are fairing better than older ones and the new plants that we will be building will be even more resilient. However, there is NO need for additional layers of regulation increased requirements that will simply add cost and make more dangerous natural gas more attractive for short term thinking energy executives.
Not that I want to gloat or anything, but can anyone tell me how the natural gas transmission and delivery infrastructure, the LNG reception infrastructure, and the oil refining infrastructure has weathered the natural disaster that occurred on March 11, 2011 in Japan? Has the fossil fuel industry managed to contain its hazardous and explosive material well enough so that it has not contaminated any areas outside of their gates and not hurt any member of the general public?
As you are watching all of the breathless tales about the unfolding nuclear plant issues that seem to be taking up about 50% of the coverage of the tragedy, notice how many times the stories are broken by advertisements from companies that sell natural gas, oil and coal. Think suspiciously about the flow of money that makes that inaccurate and emotionally charged coverage possible.
Labels: Japan earthquake
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POSTED BY ROD ADAMS AT 7:30:00 AM
Sunday, March 13, 2011
Information Sheet Regarding the Tohoku Earthquake from Federation of Electric Power Companies of Japan
by Rod Adams
I received this information sheet. It is important to disseminate the facts that it contains as widely as possible. In the interest of making sure that the information transfer is successful, I have not edited it.
Information Sheet Regarding the Tohoku Earthquake
The Federation of Electric Power Companies of Japan (FEPC) Washington DC Office
As of 4:30PM (EST), March 13, 2011
At 2:46PM (JST) on March 11, 2011, a 9.0-magnitude earthquake occurred near the Tohoku region of Northeast Japan. The epicenter of the earthquake lies 17 miles below the earth’s surface in the Pacific Ocean, 81 miles off the coast from Sendai City. Intense shaking could be felt from Tokyo to Kamaishi, an arc of roughly 360 miles.
The earthquake generated a tsunami with waves of more than 30 feet that caused widespread damage to a swath of the northeast Japan coastline. In addition to the significant destruction of buildings, infrastructure, and human property, two of Japan’s 17 nuclear power stations (sites)—Fukushima Daiichi and Fukushima Daini—suffered damage due to the tsunami. All three of the six operating reactors at Fukushima Daiichi Nuclear Power Station and all four reactors at Fukushima Daini Nuclear Power Station, both operated by Tokyo Electric Power Company (TEPCO), shut down automatically in response to the earthquake. TEPCO is one of ten member companies of The Federation of Electric Power Companies of Japan (FEPC).
A state of emergency was declared at Fukushima Daiichi at 7:03PM March 11. Unit 1 and 3 reactors at Fukushima Daiichi lost primary reactor cooling because of a loss of all electrical power. Emergency cooling systems were engaged to lower the core reactor temperature. In order to alleviate the buildup of pressure, slightly radioactive vapor, that posed no health threat, was passed through a filtration system and emitted outside via a ventilation stack from Unit 1 reactor vessel at 9:07AM on March 12 and Unit 3 reactor vessel at 9:20PM on March 13. At 3:36PM on March 12, an explosion occurred at Fukushima Daiichi Unit 1 reactor damaging the roof of the secondary containment building. The explosion—caused by the interaction of hydrogen and oxygen vapor between the primary containment vessel and secondary containment building—did not damage the primary containment vessel or the reactor core. Four workers who were injured by the explosion were transported to a nearby hospital.
In order to control the pressure of the reactor core, TEPCO began to inject seawater and boric acid into the primary containment vessels of Unit 1 (8:20PM, March 12) and Unit 3 (1:12PM, March 13). There is likely some damage to the fuel rods contained the reactor core of Unit 1 and 3 reactors. The water level in the reactor vessel of Unit 2 reactor is steady. Personnel from TEPCO are closely monitoring the status of Unit 1, 2, and 3 reactors. The highest recorded radiation level at the Fukushima Daiichi site was 1557 micro sievert (1:52PM, March 13). The most recent reported level at Fukushima Daiichi is 44 micro sievert (7:33PM, March 13).
While representatives of the Japanese government have acknowledged the potential for partial meltdowns at Fukushima Daiichi Unit 1 and 3 reactors, there is no danger for core explosion, as occurred at the nuclear power station at Chernobyl in 1986. Control rods have been successfully inserted at all of the reactors, thereby ending the chain reaction. The reactor cores at Fukushima Daiichi and Daini power stations are surrounded by steel and concrete containment vessels of 40 to 80 inches thick that are designed to contain radioactive materials.
Continued in next post
Two other plants in the Tohoku region, Onagawa Nuclear Power Station and Tokai Nuclear Power Station, were automatically shut down in response to the earthquake. The four reactors at these plants have functioning cooling systems and are being monitored by plant operators. The Rokkasho Reprocessing Plant and accompanying facilities, located far north of the tsunami zone in Rokkasho Town, is operating safely on backup power generation systems. Japan Nuclear Fuel Limited (JNFL), which operates the Rokkasho facilities, drained a 600-liter spill from the containment pool for spent fuel through a specialized wastewater treatment system. Two casks of low-level nuclear waste (LLW), which were being prepared for transport from Mutsu Ogawara Port when the earthquake occurred, have been successfully received at the Rokkasho facility.
Japanese nuclear facilities are built to exacting safety standards. They are designed to withstand powerful seismic events, such as earthquakes. In this earthquake—the strongest recorded over the past 100 years in Japan—the containment structures of Fukushima Daiichi maintained their structural integrity. These facilities were designed to withstand tsunamis within a range of assumed strength. In this event, however, the force of the tsunami exceeded the assumed range and flooded diesel generators at Fukushima Daiichi power station, thus precipitating the loss of power for the reactor cooling systems.
In order to minimize adverse health effects of any potential radioactive release, the Japanese government issued an evacuation order at 9:23PM on March 11 for a radius of 1.86 miles around Fukushima Daiichi. By 6:25PM on March 12, the evacuation area has been enlarged to cover the approximately 70,000 residents within 12.5 miles of Fukushima Daiichi and 6.2 miles of Fukushima Daini.
In addition to supporting the evacuations near Fukushima Daiichi and Daini nuclear power stations, TEPCO is collaborating with the Japanese government to ensure the safety of the all people in the affected region. Iodine tablets, to counteract the effects of radioactivity on the thyroid gland, have been distributed to people at the boundary of the evacuation zone. Sophisticated radiation screening equipment has been mobilized to measure radiation exposure for people close to the evacuation area. The Japanese Nuclear and Industrial Safety Agency said that as many as 160 people may have been exposed to radiation around the Fukushima Daiichi station. TEPCO and the Japanese government will continue to use their full professional and technological resources, as well as those offered by international organizations, to ensure the safety of those displaced by the earthquake and tsunami.
The automatic shutdown of the 11 operating reactors at the Onagawa Nuclear Power Station, Tokai Nuclear Power Station, Fukushima Daiichi and Daini, represents a loss of 3.5% of electric generation capacity for Japan. In addition, several thermal power stations were damaged in the earthquake and are currently under repairs. In order to compensate for this loss of electricity production, TEPCO has instituted rolling blackouts, information about which can be found on the TEPCO website. The Japanese government is also urging all residents in Japan to minimize their electricity use in order to support the relief and recovery effort in Tohoku.
FEPC, in cooperation with TEPCO and related organizations, will continue to work tirelessly to provide the public with the most accurate and timely information on the situation at the Fukushima Daiichi and Daini nuclear power stations.
End of quoted information sheet.
Labels: Japan earthquake
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POSTED BY ROD ADAMS AT 5:59:00 PM
Hope everyone can calm down a little now.....not as bad as the media portrays. Take a deep breath....
To be honest I'm not even sure what "alien" means. Alien to what? The universe is teeming with life.
'not as bad as the media portrays'
i think the media are MASSIVELY underplaying this. why no helicopter film of the reactor buildings from above?
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