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Japan Nuke Watch, Sat Nite (JST): Power to Site, Radiation in Food

5:38 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It is Saturday morning here; Saturday night in Japan.

Some important developments that provide rays of hope and areas of concern. Concerns first.

First, some local produce has become contaminated with radiation. The New York Times reports authorities finding unacceptable levels of radiation in food in Fukushima:

The government said on Saturday that they had found levels of radioactive materials above safe limits in spinach and milk in Fukushima and Ibaraki prefectures, the first confirmation by officials that the nuclear catastrophe unfolding at power plants nearby has affected the nation’s food supply.

Yukio Edano, the chief cabinet secretary, said that the radioactivity contained in the average amount of spinach and milk consumed during an entire year would be equal to the amount received in a single CAT scan. Mr. Edano said that abnormal amounts of radioactivity were found only in these two products, though other foods were tested.

It was not known how much affected milk and spinach had already been shipped.

Subsequent reports indicate the government has banned the sale of produce grown in the Fukushima prefecture. They are still maintaining their 20 kilometer evacuation zone with warnings to stay indoors out to 30 km from the site.

[Update: Kyodo News reports findings of slightly higher levels of radioactive iodine in water samples in Tokyo and above legal limits in tap water at Fukushima prefecture.]

Second, they’re about to test the new electrical connection from the grid. TEPCO reports they have completed installing the new power connection from the grid to the site and then on to Units 1 and 2. They’re also working to extend to Units 3 and 4, though it’s unclear whether that implicates radiation levels near those two units.

As I suspected, not only did they need a new line from the grid; they needed to bypass much of the original interconnection points on the site that link to each of the Units and other buildings. These interconnection points were vulnerable to the tsunami and may be unusable. Recall that the back-up diesel generators used whenever grid power is lost were located in a low elevation building closer to the sea and were inundated by the tsunami.

Authorities say they now have power connections to the station, but have not tested the electrical components. They’ll need to make sure the interconnections to the individual Units are sound first, then carefully test connected electrical equipment, control panels and switching. Only then will we know whether the pumps and other critical cooling equipment that require electric power are still operable. Those tests are supposed to occur on Sunday.

Third, they’re bringing in the robots! If you watch the periodic reports on the NHK tv feed, they show an unmanned fire truck with water cannon shooting water into Unit 3. The truck is connected by a hose 800 meters long so they can constantly feed water into the unmanned truck-cannon, rather than expose workers with manned hoses. (Authories also report they are bringing in emergency fire crews from other regions to relieve those who have already reached their exposure limits.)

The remotely supplied water cannon allowed several hours (seven?) of continuous spraying on Saturday, and officials claim they sent 1260 tons of water aimed at Unit 3′s spent fuel storage pool. They also claim to have slightly lowered the temperature in the pool to below boiling, but it’s not clear whether they’ve confirmed this.

In addition, American and other western nations are sending in robots that can perform certain tasks in nuclear emergencies, including dragging fire hoses. From the NYT (h/t 4cdave):

At the request of the Japanese military, a Massachusetts company, iRobot, said it put four robots on a plane for Japan on Friday. Colin Angle, the chief executive, said it had sent two small robots that could measure radiation levels close to the reactors and two larger ones that could pull hoses to spray water on the fuel rods. He said Japanese soldiers could operate the robots from a protected vehicle.

Fourth, they’ve restarted another generator at Unit 5. This appears to be a generator on site, not power from the new power line extensions from the grid. The added generation has allowed them to resume more water pumping into Units 5 and 6 storage pools.

Both reactors were down form maintenance when the quake/tsunami struck, but they both have fuel in their reactor cores (per NYT Unit summaries) and more in their spent fuel storage pools. The generators can help keep the units cooled, so those units are now at significantly lower risk.

More: Could Unit 4 Storage Pool be leaking? US authorities have argued that the loss of cooling water in Unit 4′s spent fuel storage pool could be at least partially explained by a leak or damage to the storage pool walls or the “gate” that opens to allow transfer of fuel rod assemblies between the pool and the reactor vessel.

Union of Concerned Scientists has an explanation of one plausible reason for a leak in the “gate.” The gist is, the gate is normally sealed by an air pressurized seal driven by an electric air pump. The pump gets its power from the grid. Lose that and the air pump can’t seal the gate to ensure against leakage of water from the pool. As UCS notes, this scenario actually occurred at a US reactor, the Hatch facility in Georgia in 1986. It’s worth reading for the clear explanation, diagrams and actual pictures from other BWR plants.

More updates as we get them, and I want to thank our commentors who continue to bring in reports and updates. Thanks especially to 4cdave and others who maintained the late night vigils.

Japan Nuke Watch Wed Nite (JST): Frantic Efforts to Cool Reactors and Fuel Pools

7:04 am in Uncategorized by Scarecrow

Reactor Containment & Fuel Storage from UCS; (h/t commenter lobster)

It’s Wednesday evening in Japan, mid-morning in US east coast. [Evening (US) Update below.]

First, many thanks to commenter lobster, for the annotated diagram. In particular note the various levels of containment and the location of the fuel storage ponds on the fourth floor. The orange crane above is used to move fuel assemblies into and out of the reactor building, and to transfer them between the reactor vessel and the fuel storage pond.

— There is a storage pond on the fourth floor of each of the reactors, and all units had an inventory of fuel rods at varying degrees of “spent.” Only a small percentage is actually “spent” in this type of reactor, so there is still substantial energy/heat potential in so-called “spent” fuel rods. In addition to the storage pond in each reactor building, there is also a larger common spent fuel pond in another building that is used by all reactors at the Fukushima Daiichi station.

–The fuel is contained in zircaloy tubes, sometimes called “cladding.” When the reactor is shutdown, as occurred as soon as the plant detected the first earthquake, control rods rise into the core between the fuel rods to stop most of the fission reactions by absording neutrons. That happened at Units 1, 2, and 3; Units 4, 5, and 6 were already shut down for maintenance. As far as we know, control rods were fully inserted into Units 1-3 reactors as soon as the quake occurred. However, as cooling systems failed and melting of fuel occurs inside the reactor, that control protection is becoming less and less important.

– The reactor vessel holds the core — the fuel — and is a critical containment system. If the fuel melts from loss of continuous water cooling, it may eventually damage and melt through the reactor vessel.

– The reactor vessel is surrounded by another steel and concrete containment structure. This is the next line of containment if the reactor vessel is breached.

– At the bottom is a large doughnut-shaped “suppression” pool structure with tons of water to be used for emergency cooling. We’re beyond that stage in some units. But the idea is that if the core is overheating, and there is too much steam pressure building up inside the reactor, emergency valves open to allow steam to escape into the “suppression” pool, as water is reinjected into the vessel The released steam is slightly (relatively) radioactive, and hydrogen gas is created, so maintaining the integrity of the suppression pool and structure is important to avoid possible explosions. Officials believe the suppression pool structure in Unit 2 was damaged in conjunction with the explosion there, but we haven’t yet seen steam coming from here.

– Finally, there is the outer building housing all of the above and more. Units 1, 3, and 4 have already experienced hydrogen explosions that have severely damaged the walls and/or roofs of these reactor buildings. The explosion at Unit 2 has left most of the building intact, but it reportedly damaged the critical suppression pool.

Update as of Wednesday night 11:00 p.m. JST; mid-morning US EDT:

Frantic efforts continue to get cooling water into all six units at Fukushima Daiichi Nuclear Generation Station. At units 1-3, they are attempting to inject sea water into or around the reactor vessel. Authorities say the core in Units 1 and 2 were [twice] fully uncovered in the last 48 hours and may still be partially uncovered, suggesting that fuel and cladding melting may be continuing.
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