Posted on 04/10/2011 10:20:12 AM PDT by topher
IAEA Briefing on Fukushima Nuclear Accident (10 April 2011, 15:00 UTC)
Presentation Summary of Reactor Status
On Sunday, 10 April 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:
1. Current Situation
Earthquake of 7th April
External power has been restored at all sites affected by the 7th April earthquake. The 3 litres of water that were spilled at Onagawa NPP have been cleaned up.
Changes to Fukushima Daiichi Plant Status
Overall, the situation at the Fukushima Daiichi plant remains very serious but there are early signs of recovery in some functions such as electrical power and instrumentation.
In Units 1, 2 and 3, 60,000 tons of contaminated water need to be removed from the turbine buildings and trenches. This water will be transferred to the condensers of each unit and the Radioactive Waste Treatment facility. In addition, temporary storage tanks have been ordered to provide additional capacity for the water and will be located adjacent to the Radioactive Waste Treatment facility. In Unit 2 water transfer from the condenser to the condensate storage tank was completed on 9th April.
Nitrogen gas is being injected into the Unit 1 containment vessel to reduce the possibility of hydrogen combustion within the containment vessel. The pressure in this containment vessel is increasing due to the addition of nitrogen.
In Unit 1 fresh water is being continuously injected into the reactor pressure vessel through feed-water line at an indicated flow rate of 6 m3/h using a temporary electric pump with off-site power. In Units 2 and 3 fresh water is being continuously injected through the fire extinguisher lines at indicated rates of 7 m3/h and 7 m3/h respectively using temporary electric pumps with off-site power.
In Unit 1 the pressure in the RPV is increasing as indicated on both channels of instrumentation. NISA has indicated that some instruments in the reactor vessel may not be working properly. In Units 2 and 3 Reactor Pressure Vessel and Drywell pressures remain at atmospheric pressure.
RPV temperatures remain above cold shutdown conditions, typically less than 95°C. In Unit 1 temperature at the feed water nozzle of the RPV is 235°C and at the bottom of the RPV is 120°C. In Unit 2 the temperature at the feed water nozzle of the RPV is 145°C. The temperature at the bottom of the RPV was not reported. In Unit 3 the temperature at the feed water nozzle of the RPV is 97°C and at the bottom of the RPV is 109°C.
The concrete pump vehicle sprayed fresh water (90 T) to the spent fuel pool in Unit 4 on 9th April.
There has been no change in status in Units 4, 5 and 6 and the Common Spent Fuel Storage Facility
2. Radiation monitoring
On 9th April, deposition of both iodine-131 and cesium-137 was detected in 5 and 6 prefectures respectively. The values reported for iodine-131 ranged from 7.8 to 650 becquerel per square metre and for cesium-137 from 3.3 to 370 becquerel per square metre. The highest deposition was reported for both, iodine-131 and cesium-137, in the prefecture of Ibaraki.
Gamma dose rates are measured daily in all 47 prefectures, the values tend to decrease. Dose rates are also reported daily for the Eastern part of the Fukushima prefecture, these values are decreasing as well. As of 9th April, the gamma dose rates, reported for distances of more than 30 km to Fukushima-Daiichi, ranged from 0.2 to 26 μSv/h.
In an additional monitoring programme, set up by MEXT in cooperation with local universities, measurements are made in 27 cities in 14 prefectures. As of 9th April, in 19 cities, the gamma dose rates were below 0.1 μSv/h. In 7 cities, gamma dose rates range from 0.13 to 0.21 μSv/h. In Fukushima City, a value of 0.46 μSv/h was observed. Typical normal background levels are in the range of 0.05 to 0.10 μSv/hr.
As of 7th April, iodine-131 and cesium-137 was detectable in drinking water in a few prefectures at levels far below those that would trigger recommendations for restrictions of drinking water. As of 7th April, one restriction for infants related to I-131 (100 Bq/l) is in place as a precautionary measure in only one village of the Fukushima prefecture.
On 9th April, the IAEA Team made measurements at 8 different locations in the Fukushima area at distances of 32 to 62 km, North and North West from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.4 to 3.7 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 0.19 Megabecquerel per square metre.
3. Marine Monitoring
As reported in the brief of 8th April TEPCO is conducting a programme for seawater (surface sampling) at a number of near-shore and off-shore monitoring locations as illustrated in Map 1
Map 1: TEPCO Seawater Sampling Locations
Until 3rd April a general decreasing trend was observed at the sampling points TEPCO 1 to TEPCO 4. After the discharge of contaminated water on 4th April, a temporary increase has been reported. On 10th April new data (7th April sampling day) for all TEPCO sampling points have been reported. At the near-shore sampling points TEPCO 1, TEPCO 3 and TEPCO 4 a further decrease with respect to the results for the sampling day 5th April, in the concentration of I-131 and Cs-137 have been reported. At the sampling point TEPCO 2 a further increase in the concentration of I-131 (from about 40 kBq/l on 6 April to about 150 kBq/l) and Cs-137 (from about 25 kBq/l on 6th April to about 65 kBq/l) was observed.
For the six sampling points TEPCO 5 to TEPCO 10th on April 7th the following has been reported: as TEPCO 5, TEPCO6 and TEPCO10 a further decrease of the levels of I-131 below 0.2 kBq/l and of Cs-137 below 0.1 kBq/l were measured.
At TEPCO7 an increase of the level of I-131 has been recorded. At TEPCO8 and TEPCO9 an increase in the levels of both I-131 and Cs-137 has been measured. The reading at TEPCO 9 is from about 0.07 kBq/l (6th April) to about 0.37 kBq/l for I-131 and from about 0.05 kBq/l to about 0.21 kBq/l for Cs-137.
MEXT Off-shore Monitoring Programme
As reported in the brief of 8th April MEXT initiated the off-shore monitoring program on 23rd March and subsequently points 9 and 10 added to the off-shore sampling scheme. On 4th April, MEXT added two sampling points to the north and west of sampling point 1. These are referred to as points A and B on the map below.
Map 2: MEXT Seawater Sampling Locations
On 10th April new data have been reported (7th April sampling day) for the sampling points MEXT6 and MEXT10. At MEXT6 sampling point an increase in I-131 (from about 18 Bq/l on 3rd April to about 57Bq/l) and Cs-137 (from about 10Bq/l on 3rd April to about 20 Bq/l) has been measured. At MEXT10 the level of I-131 remains about 35 Bq/l as on the 3rd of April; Cs-137 is no longer detectable.
No new data for the other sampling points have been reported at the date of 10th April.
4. IAEA Activities
The team of three agency experts in BWR technology will conclude their mission on Monday with meetings with NISA, MOFA(Ministry of Foreign Affairs), MEXT, Atomic Energy Commission (AEC), and Nuclear Safety Commission (NSC).
In addition to those reported in previous briefs the following countries have submitted monitoring data and/or links to national websites where data is available: USA, Czech Republic and Latvia.
Where does one go for the most accurate, most reliable, and most up to date information on all ongoing nuclear waste cleanup projects, worldwide?
Some information might be classified by various governments...
bttt
That's what I concluded, too, since #1 PV shows pressure but #2 and #3 don't.
I hope that when they get the rubble cleared they'll be able to go in and view (remotely) the actual damage and ultimately remove all fuel from all reactors and storage pools. Only then will I consider the crisis to have ended.
Well, that took ten years in TMI.
No, #2,3 are depressurized and too cold for something interesting being happening in them.
What I found bizarre was #1 temperature increase during the last earthquake: something occured in it. Maybe some fuel rods collapsed into the water?
One thing we analyze quite extensively for PWR accidents is called large-break loss-of-coolant (LB LOCA). This generally involve, as a worst-case, a double guillotine-break of the main steam lines. You get rapid depressurization and coolant blowdown, but the vessel is generally okay after that if you get high-pressure ECCS injection, or, worst-case, core sprays from the sparger rings.
Maybe hot spots getting cooled off as debris that is inhibiting coolant flow gets shifted around. Every reactor has hot spots and these are normal during operation. Coolant flow channel design, flow rates, and fuel cladding design take those into account. Heat generation in a core is not uniform because of the physics of neutron transport. There is always a bit of a flux tilt no matter how finely you try to control it. Also, the shuffling of partially depleted fuel assemblies to achieve optimum burnup results in less power being produced in certain places, more in others. Again, all of this is normal and routine and taken into account by the fuel management group.
What is different here is the unknown geometry. If there are damaged or warped fuel assemblies, that can result in non-uniform coolant flow and the formation of hot spots in places other than normally expected. So as those receive coolant and remove heat, you can see what appear to be random spikes and fluctuations in outlet temperature.
Just my best guess (based on experience). Still, its speculation until we can get a visual check.
I lend towards damage in the piping for #3, but the loss of instrumentation at the bottom of #2 makes me think of leaking through the control rod ports. Reactor #2 suffered the most, as far as I can remember, six hours having the fuel rods uncovered.
At this moment all speculation, of course.
Very interesting. Thank you, chimera.
Now, they are not very big in terms of cross-sectional area, but there are a fair number of them. Certainly if you have damage to maybe a half-dozen of them, that would allow for some amount of depressurization, as well as a (relatively slow) coolant leak pathway, which seems to be what they are having. I am doubtful if any core material can get through those points, but certainly liquid such as light water can. We'll just have to wait for a visual inspection to have the definitive word.
I am not sure how distance from epicenter affects damage...
BWR REACTOR VESSEL BOTTOM HEAD FAILURE MODES pdf
BTW - They revised the Tsunami height that hit this plant. Incredible. One splash wave was higher then the reactor buildings.
The numbers seem overly pessimistic. The predicted time of vessel failure is about 8 hours. There is no evidence at this point that gross failure of the vessel has occurred, although smaller leakage paths like instrument tubes would certainly explain some of the things they have seen. That means that either the calculation is overly conservative, or the sequence of events that has occurred is not as severe as that predicted to cause vessel failure at 8 hours after shutdown.
The big trouble besides #4 loss of containment, is #2 which has at least had a minor loss of containment. There was at least one explosion, possibly two in the lower suppression ring. Not supposed to have explosions in that area. Obviously radioactive water is leaking from the inside of #2. This water is originally sourced from the fire engine hose connected to the reactor. That radioactive water has flooded the lower sections of numerous buildings included the large cold spent fuel storage facility, along with the lower sections of reactor #5. Ground water and seawater are also being contaminated.
One of the reasons we may not have arrived at the earliest possible vessel failure for all 3 reactors, is that the reactors were shutdown about 1/2 hour before that huge Tsunami wave buried the facility. So the initial condition was not the same.
Bump for later read...
Damage to the suppression torus is not known at this point and awaits visual inspection. Leakage of coolant does not indicate a loss of containment. As discussed above, damage in other areas of the pressure boundary can result in a leakage pathway.
The SFP is normally not considered part of "containment", so saying reactor 4 has "lost all containment" is technically not true. Fuel in the SFP lacks the stored energy an operating core has. The purpose of containment is to manage the energy release that might occur if there is a worst-case accident under normal operating conditions, when you likely have a maximum of stored energy both from operational conditions and fission product inventory. Once in the SFP, you probably lack both. You certainly have to manage decay heat, which, at the root cause, has been the whole issue here all along.
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