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Posts Tagged ‘told you not to build nuclear power plants

Note:  When I published this post, three weeks ago, it was obvious that vast misrepresentation of the level of danger was underway at the highest levels.  It appears that the Fukishima catastrophe is far worse than Chernobyl.  The nuclear scientists have to increase the scale to over 9 in order to categorize the consequences of the danger of Fukushima.    So far, the ocean at over 400 miles deep is heavily contaminated; meaning any living form in the water is dead or soon to be dead.  It is like taking a swim in contaminated Lake Baikal, in Russia, and dying.  The water of Lake Baikal is clear and cobalt blue and terribly dead, as the water used to cool the nuclear reactor!  If also river water is contaminated, how would you feel living in Japan?

So far, the nuclear meltdown of Japan nuclear power plants are the third worst after Chernobyl (Ukraine) and Three Miles Island (USA); I don’t know:  With the successive aftershocks of about 6 on the Richter scale and the fourth plants acting up, consequences are not that encouraging for the foreseeable future. The collective intelligence of Japanese didn’t wait for their government to announce any warnings or reports:  They just fled; the furthest, the soonest, the quickest the best.  Every year, the Japanese mourn the victims of Hiroshima and Nagasaki nuclear bombs dropped by the USA in World War II.

The latest news are that this catastrophe has surpassed Three miles Island and the levels of radiation contamination has increased ten folds.  Only 50 professional operators have been working around the clock, and if no foreign specialized teams are flown in to replacing the over exhausted Japanese workers things might get out of hands.

I am wondering, if Japan invested on technologies to storing and transferring tsunami power, wouldn’t tsunami be a friendly event every year, like rain, sunshine, wind…?

It is understandable the main reasons for Japan’s decision to be dotted with nuclear power plants:  Japan has no oil or gas resources and has to import its needs in fuel and liquid gas by sea giant carriers.  Actually, Japan has been developing mini-transportable nuclear plants that are self maintained with a duration of five years and at a fraction of traditional plants https://adonis49.wordpress.com/2010/04/10/mini-nuclear-reactors-manufactured-in-series/.

France is already 60% sufficient in energy generated by nuclear sources and it has excess refined car fuel that it cannot find market for because France has shifted into efficient energy cars and substitute cleaner fuels.  France is about to be major market for performing electric cars.  Germany decided a couple of days ago on a 3-month moratorium for constructing nuclear power plants. The US was readying a program to re-launching a series of such plants:  Most probably, such a program will be revised.

The drawback is that Japan is an unstable island, geologically stuck smack on a major volcanic and seismic tectonic plate fault.  The earthquake that hit Japan, centered 150 miles in the deep ocean, was 7 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 7 times (not 0.7 times). So the first hooray for Japanese engineering, everything held up.

When the earthquake hit with 8.9 force, the nuclear reactors all went into automatic shutdown. Within seconds, after the earthquake started, the control rods had been inserted into the core and nuclear chain reaction of the uranium stopped.

The cooling system has to carry away the residual heat. The residual heat load is about 3% of the heat load under normal operating conditions.  The earthquake destroyed the external power supply lines of the nuclear reactor. A “plant black out” emergency sources receives a lot of attention when designing the backup systems.  Since the power plant had been shut down, it cannot produce any electricity by itself any more to keeping the coolant pumps working.

Things were going well for an hour. One set of multiple sets of emergency Diesel power generators kicked in and provided the electricity that was needed. Then the Tsunami hit, much bigger than people had expected when building the power plant . The tsunami took out all multiple sets of backup Diesel generators.

When the diesel generators were gone, the reactor operators switched to emergency battery power. The batteries were designed as one of the backups to the backups, to provide power for cooling the core for 8 hours. And they did.

Within the 8 hours, another power source had to be found and connected to the power plant. The power grid was down due to the earthquake. The diesel generators were destroyed by the tsunami. So mobile diesel generators were trucked in.

This is where things started to go seriously wrong. The external power generators could not be connected to the power plant (the plugs did not fit).  Another proof that you cannot design safe-proof dangerous systems. So after the batteries ran out, the residual heat could not be carried away any more.

At this point the plant operators begin to follow emergency procedures that are in place for a “loss of cooling event”. It is again a step along the “Depth of Defense” lines. The power to the cooling systems should never have failed completely, but it did, so they “retreat” to the next line of defense. All these procedures are part of the day-to-day training you go through as an operator, right through to managing a core meltdown.

It was at this stage that people started to talk about core meltdown:  If cooling cannot be restored, the core will eventually melt, and the last line of defense, the core catcher and third containment, would come handy for a little while.

But the goal at this stage was to manage the core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (pressure cooker) remain intact and operational for as long as possible, to give the engineers time to fix the cooling systems.

Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Which cooling system failed is not clear at this point in time.

The plants at Fukushima are of the Boiling Water Reactors  (BWR) types. They are similar to a pressure cooker:  The nuclear fuel heats water, the water boils and creates steam, the steam drives turbines that create the electricity.  The steam is cooled and condensed back to water.   The water is send back to be heated by the nuclear fuel. The pressure cooker operates at about 250 °C.

The nuclear fuel is uranium oxide manufactured is a small ceramic cylindrical pellet forms like Logo bricks, with a very high melting point of about 3000 °C.  The fuel pieces inserted into a long tube made of Zircaloy with a melting point of 2200 °C, and sealed tight. The assembly is called a fuel rod. These fuel rods are put together to form larger packages, and a number of these packages constitute the reactor or “the core”.

The Zircaloy casing is the first containment. It separates the radioactive Uranium fuel from the rest of the world.  The core is placed in the “pressure vessels” or the pressure cooker. The pressure vessels is the second containment. This is one sturdy piece of a pot, designed to safely contain the core for temperatures several hundred °C. That covers the scenarios where cooling can be restored at some point.

The entire “hardware” of the nuclear reactor – the pressure vessel and all pipes, pumps, coolant (water) reserves, are then encased in the third containment.

The third containment is a hermetically (air tight) sealed, a very thick bubble of the strongest steel. The third containment is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown. For that purpose, a large and thick concrete basin is cast under the pressure vessel, which is filled with graphite, all inside the third containment. This is the  “core catcher”. If the core melts and the pressure vessel bursts (and eventually melts), it will catch the molten fuel and everything else. It is arranged in such a way that the nuclear fuel will be spread out, so it can cool down faster.

This third containment is surrounded by the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. This is the part that was damaged in the explosion from the initial information

The uranium fuel generates heat by nuclear fission. Big uranium atoms, the biggest of atoms, are split into smaller atoms when hit by powerful neutrons. This fission generates heat plus neutrons . When the neutron hits another uranium atom, further splitting generate  “nuclear chain reactions”.

The nuclear fuel in a reactor can NEVER cause a nuclear explosion the type of nuclear bomb. In Chernobyl, the explosion was caused by excessive pressure buildup, hydrogen explosion and rupture of all containment, propelling molten core material into the environment or “dirty bomb”.

In order to control the nuclear chain reaction, the reactor operators use “control rods” that absorb the neutrons and kill the chain reaction instantaneously.  When operating normally, all the control rods are taken out. The coolant water carries away the heat at the same rate as the core produces, around the standard operating point of 250°C.

The challenge is that after inserting the rods and stopping the chain reaction, the core still keeps producing heat. The uranium “stopped” the chain reaction. But a number of intermediate radioactive elements (like Cesium and Iodine isotopes) are created by the uranium during its fission process.  Cesium and Iodine isotopes are radioactive versions of elements that will eventually split up into smaller atoms and cease to be radioactive anymore.

Those isotopes keep decaying and producing heat. But they are not regenerated any longer from the uranium they get less and less, and so the core cools down over a matter of days, until those intermediate radioactive elements are used up.  This residual heat is causing the headaches from the latest intelligence.

There is a second type of radioactive material created, outside the fuel rods, that have a very short half-life of seconds and split into non-radioactive materials.. So if these radioactive materials are released into the environment the released radioactivity is not dangerous, at all.  Those radioactive elements are N-16, the radioactive isotope of nitrogen (air) and a few noble gases such as Xenon: The neutrons are the cause of these short-lived radioactivity elements released in the environment.

So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200°C), as well as the second containment, the pressure cooker.

In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has 11 pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was about 550°C.

This is when the reports about “radiation leakage” starting coming in: Venting the steam is theoretically the same as releasing radiation into the environment.  The radioactive nitrogen as well as the noble gases do not pose a threat to human health because of their seconds of half-lives.

At some stage during this venting, the explosion occurred. The explosion took place outside of the third containment  “last line of defense” and the reactor building. The operators decided to vent the steam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in the steam more time to subside).

The problem is that at the high temperatures that the core had reached at this stage, water molecules can “disassociate” into oxygen and hydrogen – an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel that lead to the explosion of Chernobyl.

This scenario is believed never to be a risk at Fukushima. The problem of hydrogen-oxygen formation is one of the biggies when you design a power plant, so the reactor is build and operated in a way it cannot happen inside the containment. It happened outside, which was not intended but a possible scenario and OK, because it did not pose a risk for the containment.

So the pressure was under control, as steam was vented. Now, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts will reach the critical temperature of 2200 °C after about 45 minutes. This is when the first containment, the Zircaloy tube, would fail.

And this started to happen. The cooling could not be restored before there was some damage to the casing of some of the fuel. The nuclear material itself was still intact, but the surrounding Zircaloy shell had started melting.

What happened now is that some of the byproducts of the uranium decay – radioactive Cesium and Iodine – started to mix with the steam. The big problem, uranium, was still under control, because the uranium oxide rods were good until 3000 °C. It is confirmed that a very small amount of Cesium and Iodine was measured in the steam that was released into the atmosphere.

It seems this was the “go signal” for a major plan B. The small amounts of Cesium that were measured told the operators that the first containment on one of the rods was about to give. The Plan A had been to restore one of the regular cooling systems to the core. Why that failed is unclear. One plausible explanation is that the tsunami also took away or polluted all the clean water needed for the regular cooling systems.

The water used in the cooling system is very clean, like distilled water: Pure water does not get activated much and stays practically radioactive-free. Dirt or salt in the water will absorb the neutrons quicker, becoming more radioactive. This has no effect whatsoever on the core – it does not care what it is cooled by. But it makes life more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water.

But Plan A had failed – cooling systems down or additional clean water unavailable – so Plan B came into effect. This is what it looks like happened:

In order to prevent a core meltdown, the operators started to use sea water to cool the core.  The nuclear fuel has now been cooled down. Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced. The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure.

Boric acid has been added to the seawater. Boric acid is “liquid control rod”. Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core.

The plant came close to a core meltdown. Here is the worst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the water steam to avoid pressure buildup. The third containment would have been completely sealed to allow the core meltdown to happen without releasing radioactive material.

After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor, and all radioactive particles to settle on a surface inside the containment. The cooling system would have been restored eventually, and the molten core cooled to a manageable temperature. The containment would have been cleaned up on the inside. The messy job of removing the molten core from the containment would have begun, packing the (now solid again) fuel bit by bit into transportation containers to be shipped to processing plants.

Before the news of the failure in the fourth reactors we could surmise the damages will be contained and repaired within 5 years.  The reactor cores will be dismantled and transported to a processing facility, just like during a regular fuel change.  Fuel rods and the entire plant will be checked for potential damage.

The safety systems on all Japanese plants will be upgraded to withstand a 9.0 earthquake and tsunami (or worse), but the most significant problem will be a prolonged power shortage. About half of Japan’s nuclear reactors will probably have to be inspected, reducing the nation’s power generating capacity by 15%.  This will probably be covered by running gas power plants that are usually only used for peak loads to cover some of the base load as well. That will increase electricity bill and lead to potential power shortages during peak demand, in Japan.

The lesson learned so far: Japan suffered an earthquake and tsunami of unprecedented proportion that has caused unbelievable damage to every part of their infrastructure, and death of very large numbers of people. The media have chosen to report the damage to a nuclear plant which was, and still is, unlikely to harm anyone.

From the early morning Saturday nuclear activists were on TV labelling this ‘the third worst nuclear accident ever’. This was no accident (in the sense of man-made operating negligence of a fault in fundamental design according to the latest technologies), this was damage caused by truly one of the worst of earthquakes and tsunamis ever.

The second lesson is to the engineers: We all know that the water reactor has one principal characteristic when it shuts down that has to be looked after. It must have water to flow around the fuel rods and be able to inject it into the reactor if some is lost by a sticking relief valve or from any other cause – for this, it must have backup power to power the pumps and injection systems.

The designers apparently could not imagine a tsunami of these proportions and the backup power systems such as multiple outside power lines,  banks of diesels to produce backup power, and finally, banks of batteries to back that up, were all disabled one after another. There’s still a lot the operators can do, did and are doing. But reactors were damaged and may not have needed to be even by this unthinkable earthquake if they had designed the backup power systems to be impregnable, not an impossible thing for an engineer to do.

So we have damage that probably could have been avoided, and reporting of almost stunning inaccuracy and ignorance. Still, the odds are that no one will be hurt from radioactivity — a few workers from falling or in the hydrogen explosions, but tiny on the scale of the damage and killing around it.

A few arrogant nuclear States will voice their ignorance: “Of course our nuclear program is not going to be affected by an earthquake in Japan.” Beware of louder voices:  cataclysms will hit when nobody was ready and by devious unforeseeable ways.

Note 1:  In 1940, a German chemist accelerated a neutron on a uranium atom.  It was assumed that uranium core will absorb the neutron and increase in weight.  Uranium simply split into two other lighter atoms, releasing a neutron. Dr. Liz Meitner, another German physicist, calculated the energy released by the neutron and it fit with Einstein equation of mass of the neutron multiplied by the square of the speed of light.  A race for splitting nuclear chain reaction was on to creating the first atomic bomb.

Note 2:  Information on the construction of the Fukushima nuclear power plant and the consequences were extracted from articles published on wordpress.com


adonis49

adonis49

adonis49

May 2021
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