The pitiful, inexorable slide of the Japanese nuclear station @ Kurushima continues as radioactive steam is reporting to be leaking from unit 3 along with leaks from unit 2.

Unit 3 was damaged by a massive explosion earlier this week that blew the roof off the facility. Steam can be seen flowing from the top of the reactor containment. Operators are unsure whether this steam is the result of a containment leak or from a spent fuel storage tank that is boiling.

 

In this satellite photo (via Reuters/Digital Globe) steam is visible rising from the roof area of unit three and a hole in the shed surrounding unit two. Note the steam flowing from the hole in the side of unit two. This hole appears to be lower in the structure in the containment rather than in the attic space directly above the containment.

The skeleton crew that had been withdrawn last night for safety reasons was returned later and increased from 50 to 100. This crew continues to pump seawater into the three cores. Presumably, the cores are vented periodically to reduce steam pressure. Unit four does not have fuel in the core and managers are deciding how to add water to the spent fuel storage tanks located at the top of the containment.

There are several problems with the spent fuel pools at the tops of these reactors.

• The explosions created so much damage the pools are unreachable under layers of radioactive debris.

• The areas in question are too radioactive to enter for more than a few minutes at a time, insufficient time for workers carrying hoses to pick away debris and get to the pools. 

• The airspace above the reactors is too radioactive for helicopter approach. 

As can be seen in photos, damage to the loft or attic area of unit four is severe. Management has suggested that the damage is the result of a lubricant fire but such a fire would not cause an explosion. Overheated zirconium cladding on fuel rods exposed to steam in a drying storage tank would generate hydrogen and the flammable zirconium would trigger the hydrogen explosion. Heat for the process would come from the exposed fuel itself.

The latest management plan is to bulldoze a path through the debris so a fire truck can pull up to the unit 4 building and spray sea water through the hole in the wall. Hopefully, some of the water would reach the spent fuel ponds.

NOTE: in addition to the ponds on top of each reactor, there is a larger pond on site with additional hundreds of tons of spent nuclear fuel. This pond is @ ground level and was flooded by the tsunami. It is possible some of the low level radiation at the reactor is from this pond.

If radiation within the facility can remain @ tolerable levels the crew may be able to find a routine that can cool the cores of the three reactors. By itself, this is a massive challenge.

Because of core damage the issue is no longer decay heat of the core which is the radioactive decay of daughter fission products in the fuel rods. The uranium fuel itself is now adding more and more heat as the control rods lose their ability to poison the nuclear reaction. Control rods work properly only when they are in precise alignment with the fuel rods.

Damage to the cores makes them more difficult to cool and each cycle of steam venting increases the risk of more core damage, greater criticality and more heat.
The operators are racing against time. The flooding/boiling/venting process has to bring the core temperatures down or cumulative core- and containment damage renders the flooding cycle ineffective.

If one reactor core has a catastrophic failure, stabilization efforts at the other cores will have to be abandoned as they were last night even if these cores are nearing stability. Everything would depend on radiation levels around a destroyed reactor.

When the Chernobyl reactor Number Four exploded in 1986, the other three reactors @ the site were relatively unaffected. These units continued to operate and produce power until 1999. These other Chernobyl units were not damaged and leaking radiation, however.

It is possible that operators have stabilized the core temperatures in unit one. No news here is good news.

If seawater is flowing through the cores into the suppression ponds and into the reactor basement there will be more cooling than would be the case if the flooding/boiling/venting cycle allows. The bottom of containment would be the cores’ heat sink. Leaking containment means core water levels may not be high enough to prevent fuel rods from melting with the fuel falling to the bottom of the pressure vessel. If this fuel can be covered with water it will not melt further.

A meltdown will only occur if there is water boils or leaks out of a pressure vessel. In this case the entire fuel load will overheat and collapse to the bottom of the vessel. It is possible for the fuel to burn through the bottom of the vessel and escape into the containment. It is also possible the fuel load will spread out over the bottom of the pressure vessel and not gain sufficient concentrated mass so as to be able to burn through. There may be enough control rod and other debris to poison the reactions taking place.

It is possible but unlikely units would suffer a steam explosion within the pressure vessels as operators would vent steam rather than allowing an explosion.

This vented steam is radioactive, of course.

Venting of pressure vessels would take place if the station became too radioactive to occupy and a permanent evacuation required. A steam leak is preferable to a steam explosion.

Since the containment is already open in unit 2 and likely in unit 3, the event of breakthrough meltdowns would release radiation outdoors. If there is water at the bottoms of the containments there will be flash steam explosions. An explosion could be small or it could be powerful enough to blow the containment apart. It is unknown how much if any water is @ the lowest levels of the containment structures.

What happens over the next 24 hours is likely to be critical. If there are more leaks or another fire the plant radiation levels will rise and control rooms will be evacuated again.

No word from any authorities about a cleanup plan.

UPDATE: The tendency of the current Japan Inc. management to run around like headless chickens — and to be equally effective — has caught the attention of the New York Times:

… in one of a series of rapid and at times confusing pronouncements on the crisis, the authorities insisted that damage to the containment vessel at the No. 3 reactor — the main focus of concern earlier on Wednesday — was unlikely to be severe.

Yukio Edano, the chief cabinet secretary, said the possibility that the No. 3 reactor had “suffered severe damage to its containment vessel is low.” Earlier he said only that the vessel might have been damaged; columns of steam were seen rising from it in live television coverage.

Also in the Times:

Flaws in Japan’s Leadership Deepen Sense of Crisis

Never has postwar Japan needed strong, assertive leadership more — and never has its weak, rudderless system of governing been so clearly exposed or mattered so much.

Japan faces its biggest challenge since World War II, after an earthquake, a tsunami and a deepening nuclear crisis struck in rapid, bewildering succession. The disasters require nationwide mobilization for search, rescue and resettlement, and a scramble for jury-rigged solutions in uncharted nuclear territory, with crises at multiple reactors posing a daunting array of problems. Japan’s leaders need to draw on skills they are woefully untrained for: improvisation; clear, timely and reassuring public communication; and cooperation with multiple powerful bureaucracies.

Blah, blah, blah.

It is hard to see that any big, strategic steps are being taken to cool the cores and spent fuel tanks. Where are the thousands of workers attempting to start the auxiliary cooling systems, to fix the diesel generators and to get the big pumps working? Japan Inc. is picking around the problems rather than making a full- court press.

Another note garbling is the difficulty of to make the media for making itself clear somewhat.

Right?

People have problems understanding what’s going on when the media message is garbled as is this by the Washington Post:

Tuesday’s blast at unit 2 was not outwardly visible, but was potentially more dangerous than some of the earlier explosions, because it may have created an escape route for radioactive material bottled up inside the thick steel-and-concrete reactor vessel.

Radiation-laced steam is probably building between the reactor vessel and the building that houses it, experts said, creating pressure that could blow apart the structure, emitting radiation from the core.

“They’re putting water into the core and generating steam, and that steam has to go somewhere. It has to be carrying radiation,” said nuclear engineer Arnie Gundersen, who has 40 years of experience overseeing the Vermont Yankee nuclear facility, whose reactors are of the same vintage and design as those at the Fukushima Daiichi plant.

Since steam can be seen venting from the building and managers admit the containment is damaged it is hard to see how pressure could build up inside it. Pressure is building periodically in the pressure vessel but this is vented by operators.

The pressure vessel is inside the containment.

If pressure cannot be vented from the pressure vessel it will explode and probably do severe damage to the containment as well. In unit 2 the pressure vessel’s suppression pool is damaged. The containment is also damaged because steam is escaping from it..

UPDATE: The establishment is getting better informed (Washington Post):

Jaczko, testifying before the House Energy and Commerce Committee on what his agency has been told about the crisis, said the plant’s unit 4 reactor appeared to have suffered a hydrogen explosion.

The reactor at unit 4 was shut down at the time of the earthquake last Friday, meaning that crews had transferred all of the radioactive fuel from the reactor’s core to the pool. The building housing the pool was damaged when two nearby reactor buildings exploded Saturday and Monday.

“It’s unprecedented,” said David Helwig, a retired nuclear engineer who spent 40 years working on boiling water nuclear reactors of the same design as those at Fukushima Daiichi. “That’s never happened before.”

Left exposed to the air, the fuel rods will start to decay and release radioactivity into the air.

Severe structural damage is the only way the fuel pool could be emptied, Helwig said. The 50-foot-deep pools have no outlets at the bottom, thus preventing them from draining in case of an accident.


The spent-fuel pool at another reactor, unit 3, also appeared compromised, Jaczko said. 

In other words, the pools are leaking water into the containments which was the story here, earlier.

• Reactor 4 is contaminated with radiation from the spent fuel pool and may be too ‘hot’ to enter.
• Reactor 3 is also hot and the compromised containment isn’t helping matters. Radioactivity carried by the water is a real problem. Reports are that radioactivity on the grounds is too dangerous for workers to enter or leave the reactors.
• The dangerous radioactivity is probably coming from these spent fuel pools.

The problems’ solutions slip out of reach. It is hard to see how this is going to be fixed. Water must be gotten to the pools so that the fuel rods can be cooled off and the radiation levels dropped. Then a non- leaking pool found, hopefully in the same reactor and the rods shifted. All this must be done in a high- radiation environment.

UPDATE: No news is good news. The plant operator seems to be ignoring the radiation hazard of the spent fuel rods to concentrate on cooling the cores. A power line is being run to provide power and perhaps get some pumps running:

Japanese officials raised hopes of easing the crisis, saying early Thursday that they were close to completing a new power line that could restore the reactors’ cooling systems.

Naoki Tsunoda, a spokesman for Tokyo Electric Power Co., or TEPCO, said the new power line to the Fukushima Daiichi plant was almost finished and that officials planned to try it “as soon as possible,” but he could not say exactly when.

The new line could revive electric-powered pumps, allowing the company to maintain a steady water supply to troubled reactors and spent fuel storage ponds, keeping them cool. The company is also trying to repair its existing disabled power line.

Late Wednesday, government officials said they’d asked special police units to bring in water cannons — normally used to quell rioters — to spray water onto the spent fuel storage pool at Unit 4.

The cannons are thought to be strong enough to allow emergency workers to remain a safe distance from the complex while still able to get water into the pool, said Minoru Ogoda of Japan’s nuclear safety agency.

The best news is that the Japanese are trying everything. If the complex can get though the next 72 hours with the cooling they have there is a good chance the crisis will end and the cleanup can begin.