Safety of Nuclear Power Plants

[Kuroi Hadou]

Originally Posted by Solace

Peak Oil isn't just about how much oil exists but how much we consume, and the energy it takes to get more. For example Canadian Tar Sands are a source of oil however the energy spent to refine it is dubious at best.

In order for oil production to be worth it, or any new energy source gathering, we have to overcome the net energy loss or it won't be worth getting in the first place. This is the reason why Peak Oil is an important concept to determine, and unfortunately trying to get clearer numbers for oil and other natural resource estimates from around the world is about as likely as waltzing into the Federal Reserve and peeking into their vaults.

I'm aware. And as the "easy to reach" oil dries up, the oil that is more difficult to obtain is all that's left, and so it becomes more and more economically justifiable to go for it and to develop methods that increase the energy spent/energy gained efficiency ratio. There's also the fact that natural gas is starting to supplant oil in terms of most dominant energy source, but this isn't the thread for such a topic.

Most energy estimates are based on current consumption, which is a misleading figure. Every time growth doubles, it takes more than all you used in all of the prior growth.

Now as we know growth isn't constant, but note that it happens unless there is something catastrophic that stops or reverses that growth. So while there are factors such as say....price, or weather, that slow demand for energy, we're still using it, and demand will increase exponentially.

To get us back on topic: That exponentially increasing demand is where alternative energy sources come in, and why we're not relying 100% on oil; in fact it makes up less than 50% of the United States' energy consumption. As we know from basic economics, particularly energy economics: Variety of supply = security of demand. There isn't a single nation on the planet that would base their entire economy on a single form of energy. Renewable energy sources are still in development, and nuclear is an excellent alternative for large scale generation of energy. Granted, you've got the problem of waste, but that's easy enough to deal with and you're going to have issues no matter what form of energy you're using.

As mentioned: The big problem with nuclear energy is the stigma that's been attached to it. Chernobyl, the major cause of said stigma it seems, was a disaster of epic proportions, but it was one that was literally by design. First of all corner's were cut to even build it, so there weren't nearly as many safety measures in place even for the time period it was built. Then, when the geniuses running the test decided to remove what little safety measures were in place, Murphy's law took effect and the rest is history.

Japan's current situation is similar: I've heard from reputable sources (including CNN and CNBC) that the company responsible for building the Fukushima reactor is actually known for cutting corners in the past, including the falsification of nuclear plant safety reports.

The lack of understanding the concept of exponential growth and its effects is a dangerous thing.

You sound like one of my professors in college. Seriously, that whole post is almost ver batim what he lectured in a seminar once.

[Solace]

Originally Posted by Kuroi Hadou

I'm aware. And as the "easy to reach" oil dries up, the oil that is more difficult to obtain is all that's left, and so it becomes more and more economically justifiable to go for it and to develop methods that increase the energy spent/energy gained efficiency ratio. There's also the fact that natural gas is starting to supplant oil in terms of most dominant energy source, but this isn't the thread for such a topic.

Indeed. It seems we're on the same level of understanding so let's not derail it with a broader discussion about energy.

nuclear is an excellent alternative for large scale generation of energy. Granted, you've got the problem of waste, but that's easy enough to deal with and you're going to have issues no matter what form of energy you're using.

I agree here as well. Nuclear reactors are expensive to create but offer incredible energy potential. Waste is always an issue, and shouldn't be trivialized, but that should be a problem to solve head on, not to avoid.

As mentioned: The big problem with nuclear energy is the stigma that's been attached to it.

Pretty much anything nuclear scares people. I can't say that it isn't for good reason, and those terrible events should be warnings and lessons, but fear shouldn't prevent us from working toward making technology work for us. Unfortunately misinformation, fear, ignorance, and cultural stigmas are large hurdles to overcome.

Cutting corners is a problem, and I'm not surprised to hear that it might be the case in Japan. On the other hand, it's difficult to predict the power of nature. I just hope it is contained before things get worse.

You sound like one of my professors in college. Seriously, that whole post is almost ver batim what he lectured in a seminar once.

I'd have loved to have sat in that seminar to hear him speak. I bet it was riveting.

[Kitsune]

Nuclears are a need nowadays and there are no any other options for large-scale constant supply of energy.

Anyways, as a student of geology one question came acress to my mind when looking at the news this weekend.

Why the hell were nuclear power plants in the eastern side of Japan when it was OBVIOUS that soon or late a great "tsunami" would crush into them?

That was not a matter it could happen, it was just a queston of when would that happen...

Spoiler for Map of japanese nuclear power plants:

http://vielmetti.typepad.com/.a/6a00...1bf9970c-500wi

[Tsuyoshi]

Originally Posted by Kitsune

Nuclears are a need nowadays and there are no any other options for large-scale constant supply of energy.

Anyways, as a student of geology one question came acress to my mind when looking at the news this weekend.

Why the hell were nuclear power plants in the eastern side of Japan when it was OBVIOUS that soon or late a great "tsunami" would crush into them?

That was not a matter it could happen, it was just a queston of when would that happen...

Spoiler for Map of japanese nuclear power plants:

http://vielmetti.typepad.com/.a/6a00...1bf9970c-500wi

Tri-ring pointed out various times already that the tsunami and the earthquake of such magnitude is a once in a 1000 years occurrance. The plants were already designed to withstand earthquakes but nobody was expecting it to be this devastating simply because it never happened before since nuclear plants were created in Japan at the very least. I doubt such a Tsunami was in the mind of the people who put the plants there decades ago.

[UtsukushiiOto]

http://www.youtube.com/watch?v=lVCWGc173ic

[Vallen Chaos Valiant]

Originally Posted by Kitsune

Nuclears are a need nowadays and there are no any other options for large-scale constant supply of energy.

Anyways, as a student of geology one question came acress to my mind when looking at the news this weekend.

Why the hell were nuclear power plants in the eastern side of Japan when it was OBVIOUS that soon or late a great "tsunami" would crush into them?

Nuclear powerplants are built near the ocean to obtain a source of coolant. And in general you built them wherever you CAN build them, not where you would like to build them. Politics ensure you can't just put them anywhere you like.

[Ithekro]

When was the last nuclear power plant built in the United States? I'm assuming the last one was around the time of the Three Mile Island incident which was over 30 years ago. Doesn't that mean the ones in operation might be getting old to the point one should consider replacing them...or have they be continually refitted and rebuilt like oil refineries?

[synaesthetic]

And this is why we can't have nice things.

Seriously, nuclear plants will not make a tentacle grow out of your ass. People watch too much goddamned TV and don't learn enough real science.

[Jinto]

This is going to be an extensive posting about boiling water reactors (BWR), their typical fail safe mechanisms and an analysis of what had happened in Fukushima 1 block 1.

Boiling Water Reactor,

A BWR is a so called light water reactor. Some readers might have heard of heavy water D2O and semi heavy water HDO. The D stands for deuterium, a special isotope of hydrogen (the deuterium is twice as heavy as normal hydrogen because it contains a neutron and a proton in its core instead of just one proton). Heavy water can be used to refine material (D2 or even T2) for fusion bombs, and is radioactive.

In contrast light water is what we know as normal water. Normal water can contain some traces of deuterium and tritium, but in general is simple H2O. Since light water can contain traces of deuterium and tritium, it can be called light water, even when there is a higher than normal dosis of deuterium and tritium in it. So, just because something is called light water doesn't mean it cannot be radioactive to a certain degree.

Now light water reactors, use light water as a moderator to allow for an efficient fission reaction of fission material. A moderator is a substance that slows down neutrons that are set free in a fission reaction of nuclear fuel. Nuclear fuel contains of heavy elements. The atomic cores of these heavy elements tend to break and set free radiation energy in the process.

The radiation energy can be classified like this:

alpha radiation - a particle ray of helium isotopes
neutron radiation - a particle ray of neutrons
proton radiation - a particle ray of protons
beta radiation - a particle ray of electrons or positrons
gamma radiation - a form of high energy electromagnetic waves


A wavelength based classification from very long wave length to short wave length:

radio waves => heat/infra red light => light => ultraviolet/x-ray radiation => gamma/cosmic radiation

When a heavy isotope like Uranium-235 breaks up into smaller elements it will release various types of energy. If you are interested in the whole decay chain of Uranium-235 you can read it up on Wikipedia: http://en.wikipedia.org/wiki/Decay_c...ctinium_series

I will not go much into the details of decay chains. But when you want to know what types of energy are set free by a radioactive isotope you have to look at those decay chain charts. Lets concentrate on the first decay step of Uranium-235 instead. In the first step it releases alpha radiation and becomes TH231 in the process. So when it decays it sets free 2 neutrons and 2 protons. These neutrons and protons have a lot of energy, kinetic energy. Or in laymans terms: the faster an alpha particle moves the more energy it has. The neutrons and protons are very fast and do not interact very much with other U235 isotopes for that matter.

This what can be called natural decay, the natural decay is really slow for U235, the half life is 7x10^8 years (700,000,000 years).

The nuclear fuel in BWRs typically contains only as little as 4% U235 which has a very meager natural fission rate. Actually its uranium dioxide UO2, where 96% of the uranium atoms are U238 and 4% are U235. The uranium dioxide is pressed into pellets and arranged in fuel rods with an outer casing of zirconium alloy (most common). The zirconium alloy's advantage is, that it is corrosion resistant and has a low absorbtion rate for thermal neutrons.

Now the natural decay rate is so slow, that it could not heat a cup of coffee. That is where the moderator comes into play. The moderator slows down the fast neutrons of the natural decay. When they slow down they become thermal neutrons. Now when such a thermal neutron hits a U235 isotope it will spontanously decay into several neutrons and two smaller isotopes, here some examples:

U-235 + n ===> Ba-144 + Kr-90 + 2n + energy
U-235 + n ===> Ba-141 + Kr-92 + 3n + energy
U-235 + n ===> Zr-94 + Te-139 + 3n + energy

The moderator also slows down the newly created neutrons, so that they can decay even more U235 now. As you can see, this can develop into a chain reaction that is like a snowball effect (releasing ever more energy). This is why there is only 4% U235 in the fuel, because its supposed to be a power plant not a fission bomb. The U238 will catch fast neutrons before they can become thermal neutrons, this will absolutely naturally prevent an out of control chain reaction (a passive safety mechanism).

Now the ratio of U235 in the fuel is not the only measure to keep the fission rate under control. For example the UO2 is pressed into pellets that are arranged in fuel rods so that the U235 does not conentrate locally. Furthermore when the light water is exposed to a higher amount of fast neutrons it will turn into semi-heavy and heavy water. Now semi-heavy and heavy water do not moderate as well as light water. However this effect has its limits. There is something else, that works even better. A very bad moderator is water vapor, its density is very low and hence its moderation effect is very low too. By varying the stream of light water (and thus the development of water vapor bubbles in it) through a BWR, it is possible (in theory) to control its maximum power output down to 30% of the maximum capacity. Of course this is not going to be sufficient to actually stop a BWR, so the most important control element are the control rods.
These rods typically contain boron. Boron catches thermal neutrons, its basically the thermal neutron equivalent to the U238 for fast neutrons. Now control rods are placed in between fuel rods to reach a maximum absorbtion efficiency. The control rods can be extracted from the reactor to start it up and retracted to shut the reactor down.

In theory the control rods could be used to micro manage the output of the reactor, but that means that the fuel rods cannot burn their fuel equally, because part of the fuel rod is basically inactive. Hence the reactor contains exactly so many fuel rods that it can heat the amount of water that is needed to run the power plant at approximately 100% power output. The prefered method to micromanage the output is the control of the light water stream.

In a BWR the light water is not only the moderator but also the coolant and the material that drives the steam turbines that drive the power generators. The following graphic from Wikipedia illustrates the basic concept of a BWR power plant:



1. Reactor pressure vessel (RPV)
2. Nuclear fuel element
3. Control rods
4. Circulation pumps
5. Engine control rods
6. Steam
7. Feedwater
8. High pressure turbine (HPT)
9. Low pressure turbine

10. Generator
11. Exciter
12. Condenser
13. Coolant (external)
14. Pre-heater
15. Feedwater pump
16. Cold water pump
17. Concrete enclosure
18. Mains connection

(source Wikipedia)

BWRs have the unique arrangement that the coolant of the core directly drives the turbine. For example in Pressurized Water Reactors (another type of light water reactor), the coolant has its own separate/closed circulation system using a heat exchange system to heat the water/steam that drives the turbines.

In the BWR, the direct use of the coolant to drive the turbine is more economic. But it also comes with the disadvantage that the turbines are exposed to radioactivity in the light water, so the turbines must be shielded during normal operation.

What cannot be seen in the graphic, is that the turbine can be bypassed in the cooling cycle. For example when the reactor is shutting down. This allows for higher pressures in the BWR cooling cycle that were otherwise impossible because of the rather weak pressure resistance of the turbine.

you can also read up the BWR basics in Wikipedia:

http://en.wikipedia.org/wiki/Boiling_water_reactor

Typical fail safe mechanisms:

I will order the typical fail safe mechanisms first according to their place in the power plant, and then I will further differentiate between passive and active fail safe mechanisms. In general the passive ones are considered to be less accident-sensitive. A fail safe mechanism is a mechanism that returns into a safe state when it fails. It does not mean that it cannot fail. Let me add a personal remark: Since fail safe mechanisms are man made they do not always return into a safe state when they fail.

Reactor and primary containment

passive safety mechanisms:

(1) The structure and composition of the fuel rods. The typical BWR fuel rods contain up to 4% U235 and 96% U238 in uranium dioxide (UO2). The U235 and U238 are mixed homogenously, so that U235 does not concentrate locally in the UO2. The U235 does emit fast neutrons which are absorbed by the U238. Hence, the ratio of U235 is not enough (even when moderated) to start a snowball effect chain reaction like in a fission bomb. At the worst the fuel becomes extremely hot, so that the fuel rods might be destroyed, but there is no risk of a nuclear explosion. Some plants use a slightly different fuel which contains Mixed Oxide fuel (MOX - the X stands for a number like for example 2 in UOX => UO2). Such fuels contain other radioactive oxides besides UOX (UO2), for example plutonium oxides or depleted uranium oxides. The positive economic effect of MOX is, that it rebreeds parts of its own fuel when in operation. The plutonium which is a waste product of fast breeder power plants and the depleeted uranium which is a waste product of burned down UO2 fuel can be conveniently reused this way. However, this fuel is considered to be more dangerous because it contains plutonium.

(2) The BWR is a light water reactor, so light water is used as a moderator. When the reactor overheats, because of higher radiation levels the light water will turn into heavy water. Heavy water is not as good a moderator as light water. So, the more radiation is set free by the fuel, the less effective becomes the moderator.

(3) The BWR is a light water reactor that boils water at low pressure. This will cause the generation of steam (vapor bubbles in the water). Now steam is a bad moderator because of its low density. So, with higher temperatures more steam will be created which makes the moderator less effective.

(4) Some BWRs have a so called core catcher. Typically a ceramic bowl that catches the molten core after a meltdown.

active safety mechanisms:

(5) The BWR has control rods filled with boron. Boron catches thermal neutrons, and thus stops the fission process. These control rods are situated below the reactor pressure vessel and can be electrically moved upwards into the core of the reactor. Should the electrical system fail, then a hydraulic backup system will take over. This backup system is designed fail safe, in that it has a pressured storage for the hydraulic fluid. When the electrical system fails, the valves that electrically hold the fluid back in the storage tank fail, this however releases the hydraulic fluid which then presses the control rods inside the reactor chamber.

(6) The reactor can be vented to release pressure. This might be necessary to guarantee the structural integrity of the reactor. Venting the light water can be a delicate matter, because the light water is radioactive to a certain degree and venting also means to lose coolant in the primary cooling cycle.

(7) Below the reactor pressure vessel can be a so called suppression pool. This suppression pool is meant to be able to suppress the shock wave of a rapidly depressurizing reactor pressure vessel. The primary containment must be able to take all the coolant and pressure that is inside the reactor vessel. The idea works like this, when the reactor vessel leaks its high pressurized coolant will be redirected to flow through the suppression pool before it can further expand into the primary containment. When it flows through the suppression pool two things will happen.
First the high pressurized coolant cools down in the pools water, this raises the coolants density and the pressure will be lowered in the process.
Second the radioactive coolant must pass through the suppression pool which will catch some of the heavier isotopes.


secondary containment

The secondary containment encapsulates the primary containment and the steam turbine, heat exchangers and primary cooling cycle pumps.

passive safety mechanisms:

(8) In some BWRs catalytic recombinators are used to recombine hydrogen and oxygen to water in a catalytic way. This is meant to prevent the two agents to form oxyhydrogen a highly explosive gas. Catalytic recombinators are installed at various places in the primary cooling cycle.

active safety mechanisms:

(9) The primary cooling cycle is meant to cool down the reactor. This requires a working external cooling cycle though (the heat exchangers must be cooled, otherwise the primary cooling cycle will not cool down).

(10) The secondary containment can take a full load of pressurized coolant from the primary containment. This however makes working in the area of the secondary containment impossible. Unless the coolant is vented into the outer containment.

active safety mechanisms:

(11) In an emergency boron can be induced in the primary cooling cycle. However, this will damage parts in the primary cooling cycle, so that the normal operation cannot be resumed without costly maintenance.

Outer containment

It has no passive safety mechanisms that I know (maybe catalytic recombinators in some BWRs).

active safety mechanisms:

(12) Parts of the control an power plant management electronics are housed in the area. The electronics do some of the open/closed looped controlling of the reactor and the other components and are therefore programmed with certain safety protocols, that allow for faster than humanly possible reaction to safety relevant events.

(13) In a case where coolant must be vented from the primary containment/reactor pressure vessel, the coolant will be caught inside the outer containment. This allows in theory, to clean the released gases before they are released into the environment.

Redundancy principle: Many of the active safety mechanisms are redundant. That means they exist several times. So that when one mechanism fails another can take over.

Diversity principle: The redundant safety mechanisms are usually diverse in that use completely different technology or methodolgy to reach safety. This helps to minimize the risk even further, because it likely prevents that the ecaxt same failure in the safety mechanism is triggered in all of the back up systems too.

(I hope I did mention all important safety mechanism now)


The following data is a direct translation of information presented at the german department for environment, environmental protection and nuclear safety (BMU)

Situation

Fukushima I

The blocks 1-3 where in state of power operation at the time when the incident occured. The blocks 4-6 where shut down at this time. The on-site emergency power generator failed because of a tsunami. Mobile emergency power generators where brought to the power plant.

Because of high radiation, the plant was fully evacuated at 10:45 03.16.2011. It is only entered to execute important tasks and to gather measuring data (press conference government at 12:00). The ambient dose rate at the gate is in between 2.5 - 6.5 mSv/h. In the meantime parts of the crew returned to the plant area because dosis levels were falling.

NISA reported, that TEPCO plans to access the power grid by connecting to high voltage power line in the area. The power supply will be granted by Tohoku Electric Power. It is planned to finish these activities at the afternoon of 03.17.2011.

According to NHK it is planned that the auxiliary service water pumps are to repaired in the meantime. According to TEPCO (citation by ASAHI) it cannot yet be guaranteed that the emergency cooling systems will work when the power is restored at the site.

Block 1

According to press information, the pressure in the containment of Block 1 increased in the course of the 03.12.2011. A filtered venting of the containment did happen beginning at 14:30 03.12.2011. An oxyhydrogen explosion occured at 15:36 03.12.2011 in the block but outside of the containment (remark: when they talk about containment, the primary and secondary containment is meant). Bornoized water was pumped into the reactor pressure vessel (it is not clear if the primary containment was flooded as well) starting at 20:20 03.12.2011.

According to press agency Kyodo the nuclear agency assumed that there is a leak in block 1 at 11:13 03.13.2011. Government spokesman Edano said, that there might have been a melt down. According to TBS approximately 70% of the fuel rods could be damaged. According IAEA information the electrical power supply is guaranteed by mobile emergency power generators. Sea water was injected.

According to information from the german Department for Foreign Affairs (03.16.2011), the number of damaged fuel rods climbed from 43% to 70%.

According to other sources the fuel rods are exposed at 1.8m length (17:00).

According to TEPCO a fire engine + water pump is assigned to help cooling the reactor (03.16.2011)

According to JAIF no information is available for the fuel rod integrity of possible fuel rods that may reside in the spent fuel pool of block 1 (09:00 03.17.2011).

The pressure in the reactor pressure vessel has increased:

Measure point 1:

03.17.2011, 12:00: 0.173 MPa
03.18.2011, 02:50: 0.265 MPa
03.19.2011, 03:30: 0.306 MPa

Measure point 2:

03.17.2011, 12:00: 0.144 MPa
03.18.2011, 02:50: 0.243 MPa
03.19.2011, 03:30, 0.256 MPa

(personal remark, while increased pressure might cause another emergency venting, it indicates that the pressure vessel is not leaking and hence is a basically a good sign)

INES classification:

For the time being the department classified the event that happened at block 1 as INES 4, because of the released radioactivity outside the plant. The INES classification was done at 03.12.2011 and has been updated to INES 5 on 03.18.2011.

Block 2

The coolant level of the reactor pressure vessel of block 2 remained below normal operation levels until 03.14.2011. Coolant injection was done by an emergency cooling system. NISA reported that the electrical power supply necessary for the emergency cooling of the reactor was guaranteed by mobile emergency power generators (11:55 03.13.2011).

However, the emergency cooling failed at 06:20 03.14.2011. Intermittendly the cooling with sea water was possible. At times the fuel rods were not covered with water (exposed). The pressure in the reactor pressure vessel reached 4.15 bar (approximately design pressure) at 20:00 03.14.2011. Emergency venting of the pressure vessel started at 20:37. According to TEPCO the reactor housing of the block (outer containment) was opened to avoid an oxyhydrogen explosion that would damage the reactor housing.

An explosion occured at 06:20 03.15.2011 in block 2. According to IAEA radiation of 400mSv/h was meassured on-site. JAIF reports 30mSv between block 2 and 3, 400mSv next to block 3 and 100 mSv next to block 4. According to press information the immense loss of pressure in the reactor pressure vessel indicates that the condensation chamber might have been damaged.

According to Kyodo, TEPCO said approximately 33% of the fuel rods are damaged. NISA assumes, that the high radiation at 10:00 originates from block 2. However, it is also possible that the high radiation is linked to the steam coming from block 3.

TBS says, the pressure levels in the primary containment and the reactor pressure vessel are falling. The coolant level seems to remain constant despite the injection of water. The fuel rods are exposed at 1.4m in the reactor pressure vessel.

According to JAIF (Japan Atomic Industrial Forum) no information is available for the fuel rod integrity of possible fuel rods that may reside in the spent fuel pool of block 2 (09:00 03.17.2011).

According to NISA (03.18.2011, 06:30), the injection of sea water in the reactor by the fire extuingishing system will be continued. White steam is coming from the reactor housing.

The pressure in the reactor pressure vessel increased:

Measure point 1:
03.17.2011, 12:00: 0.029 MPa
03.18.2011, 02.50: 0.085 MPa
03.19.2011, 03:30: 0.096 MPa

Measure point 2:
03.17.2011, 12:00: 0.047 MPa
03.18.2011, 02.50: 0.069 MPa
03.19.2011, 03:30: 0.083 MPa

The coolant levels in the reactor pressure vessel:
03.17.11 11:30 1.8m exposed
03.18.11 02:50 1.4m exposed
03.19.11 03:30 1.4m exposed

(personal remark: things seem to stabilize at block 2)

INES classification:

The events at block 2 were classified INES 3 at the 03.12.2011 and updated to INES 5 at 03.18.2011

Block 3

The emergency cooling system in block 3 failed at 05:30 03.13.2011. An emergency venting of the reactor pressure vessel into the primary containment and the injection of boronized water was initiated at 03.13.2011, 13:12. Fire engine pumps injected of sea water. An emergency venting of the primary containment was necessary.

An oxyhydrogen explosion occured at 03.14.2011, 11:00. According to IAEA information the primary and secondary containment remained structurally intact. According to TEPCO the pressure inside the reactor pressure vessel is stable.
According to NHK, there is steam cloud over block 3 since 03.16.2011, 08:30. NISA assumes the containment is structurally not intact.

There was an attempt to induce water into the spent fuel pool from a helicopter, it was aborted because of the radiation levels being too high (03.16.2011). The fuel rods are exposed at 2.3m length (03.16.2011).

According to JAIF (03.16.2011) water evaporates in the spent fuel pool.

Personel from the shared control room that is responsible for the reactors in block 3 and 4 has been evacuated, because concerns about a possible leak in the reactor pressure vessel (03.16.2011, 10:45). The operators returned at 11:30 to resume the injection of water.

According to JAIF the coolant level in the spent fuel pool of block 3 is low (03.17.2011, 09:00).

Televised media reports show helicopters dropping water over the reactor housing in 20 minute cycles (03.17.2011, 09:48). This was affirmed at a later point by the gevernment spokesman and NISA. According to the Japanese Police department 44t of water were dropped from helicopters.

According to NHK, an attempt to refill the spent fuel pool by using water cannons of the police was not accomplished due to high radiation levels at the site. The water levels in the spent fuel pool are falling (TEPCO 18:00). At 19:35 (NHK) the military began to refill the spent fuel pool using 5 water cannons. According to NHK, 30t of water were injected into the spent fuel pool by the water cannons of the military (03.17.2011).

NISA reparts at 03.18.2011, 06:30, that the inection of sea water into the reactor pressure vessel using fire exstuingishing systems is resumed.

According to NISA 50t of water were injected from 6 military water cannons into the reactor housing of block 3 (03.18.2011, 14:00). A US-Army water cannon was used until 14:45. Because of the visible steam it was assumed that the injected water must have reached the spent fuel pool.

The pressure levels in the reactor were:

Measure point 1:
03.17.2011, 12:00: 0.014 MPa
03.18.2011, 02:50: 0.096 MPa
03.19.2011, 06:10: 0.146 MPa

Measure point 2:
03.17.2011, 12:00: 0.023 MPa
03.18.2011, 02:50: 0.115 MPa
03.19.2011, 06:10: 0.106 MPa

The coolant levels in the reactor pressur vessel:
03.17.11 11:10: 1.95m (chanel B: 2.3m (defect?)) exposed
03.18.11 02:50: 2.00m (chanel B: 2.3m (defect?)) exposed
03.19.11 06:10: 1.20m (chanel B: 2.3m (defect?)) exposed

personal remark: it is a good sign that the pressure and coolant levels are increasing again in the reactor pressure vessel.

INES classification:

The event at block 3 was classified INES 5 at 03.18.2011.

Block 4

A fire and an explosion occured at 03.15.2011, 06:00 in the area of the spent fuel pool (inside the secondary containment). According to IAEA the fire was extinguished at 11:14. The fire/explosion cause two 8m² sized holes in the reactor housing. According to press information the psent fuel pool could not be refilled yet. There are attempts to refill it via helicopter or water cannons.

According to TEPCO and NISA another fire broke out close to the spent fuel pool (03.16.2011, 05:45). This severly damaged the roof of the reactor housing. NHK reports, that attempts to extiungish the fire were sucessfull. According to press information 2 employees are missing since when the fire broke out.

Kyodo reports, that it is planned to inject boronized water into the spent fuel pools to reduce the criticality. TEPCO said the reactor core of block 4 was completely unloaded and remains now in the spent fuel pool.

Its assumed that the fuel rods are damaged. According to JAIF (12:30) it is planned to inject water into spent fuel pool using fire engines.

According to press information (03.16.2011) the water is boiling in the spent fuel pool, a water cannon of the police department arrived but was unable to start operation because of debris in the area.

According to NISA the water injection was stopped at 03.16.2011, 14:00. There is no temperature data available for the coolant of the spent fuel fuel pool since (last report 03.15.2011, 19:00).

IAEA data for the water temperature inside the spent fuel pool:

03.14.2011, 19:08: 84 °C
03.15.2011, 19:00: 84 °C
03.16.2011, 14:00: no data
03.19.2011, 10:00: no data

According to JAIF the coolant levels in the spent fuel pool are low (03.17.2011, 09:00). According to Jiji, TEPCO says the fuel rods are partly exposed in the spent fuel pool.

INES classification:

The event in block 4 was classified INES 3 at 03.18.2011

Block 5 and 6

Nothing too important to report here. But they prepare the reactor housings for venting to decrease the possibilty of a hydrogen explosion.

IAEA data for water temperatures in the spent fuel pool in Block 5 (standard < 25 °C):
03.14.2011, 19:08: 59.7°C
03.15.2011, 19:00: 60.4°C
03.16.2011, 14:00: 62.7°C
03.17.2011, 03:00: 64.2°C
03.17.2011, 18:00: 65.5°C
03.19.2011, 06:00: 68.8°C

IAEA data for water temperatures in the spent fuel pool in Block 6 (standard < 25 °C):
03.14.2011, 19:08: 58.0°C
03.15.2011, 19:00: 58.5°C
03.16.2011, 14:00: 60.0°C
03.17.2011, 03:00: 62.5°C
03.17.2011, 18:00: 62.0°C
03.19.2011, 06:00: 66.5°C

personal remark: the situation in these blocks seems to be rather uncritical.

Fukushima II Daini

Because of several smaller incident in the power plant there the following INES classifications:

An event in Block 1 was classified INES 3 at 03.12.2011.

An event in Block 2 was classified INES 3 at 03.18.2011.

An event in Block 4 was classified INES 3 at 03.18.2011.
_________________________________________________

Spent fuel rods

In contrast to fresh fuel rods, spent fuel rods are filled with lots of naturally, fast decaying isotopes. Since the isotopes decay naturally, there is no moderator needed. These isotopes are by-products of the U235 fission. A spent fuel rod is taken to the spent fuel pool inside the secondary containment, and has to cool down there for several weeks. After that period of time, it can be brought to an external spent fuel pool outside the reactor building.

The problem with that procedure is, that the secondary containment is not as save as the primary containment where the reactor pressure vessel resides. One could assume a potentially higher risk stemming from fresh spent fuel rods in a case of emergency, when the cooling of the spent fuel pool fails.

[Asuras]

Fusion reactors and an inter-moon mass-helium transport system baby.

[Ithekro]

That would be expensive as all getout to start up and maintain. It would depend entirely on if the power generation provided would outstrip the cost of building the things in the long term...or even if it didn't, if it would provide stable power for when the fossil fuels "run out" verses other methods of power generation verses demand for energy.

[Kenn]

Originally Posted by KyuuA4

How about:

Spoiler:

Gundams on giant hamster wheels, which power turbines

Tis a shame that Gundams themselves are nuclear powered...most of them at least.

[Jaden]

More nuclear power will inevitably be used, the knowledge is widespread and all it takes is investment. There are fuels other than Uranium available too, the Thorium fuel cycle is being optimized and that stuff is plentiful enough to maintain our current power output for a millenium or so. And in that time someone will probably manage to find a new source, maybe even make those fusion donuts work.

And there will inevitably be more accidents, hopefully they will be learned from so that safety will increase along with the increased number of reactors.

[Kuroi Hadou]

Originally Posted by Jaden

More nuclear power will inevitably be used, the knowledge is widespread and all it takes is investment. There are fuels other than Uranium available too, the Thorium fuel cycle is being optimized and that stuff is plentiful enough to maintain our current power output for a millenium or so. And in that time someone will probably manage to find a new source, maybe even make those fusion donuts work.

Thorium is currently only considered viable in liquid core and molten salt reactors, and of those only a single one of the former is online, so there's not really conclusive evidence yet. There's also the issue mentioned above of energy spent for energy gained. The thorium cycle is bred into uranium via sintering, which requires a lot of heat. Furthermore, there's the time period that has to pass between thorium breeding into uranium 233, along with the radiation issues associated with the presence of uranium 232 that shows up from decay.

And there will inevitably be more accidents, hopefully they will be learned from so that safety will increase along with the increased number of reactors.

Well, at the very least history has taught us to not take chances with nuclear power.

[Dist]

I'm not familiar with nuclear power plants and this whole thing that is going on so could someone explain to me what is this '' worst case scenario '' people are speculating that may happen at Fukushima, and what does it exactly mean for the people in Japan .. Will it affect Tokyo and other cities and how ?

[Kuroi Hadou]

Originally Posted by Dist

I'm not familiar with nuclear power plants and this whole thing that is going on so could someone explain to me what is this '' worst case scenario '' people are speculating that may happen at Fukushima, and what does it exactly mean for the people in Japan .. Will it affect Tokyo and other cities and how ?

The "wost case scenario" is a meltdown, which is when the reactor core becomes so hot that the uranium in the fuel rods actually melts; this occurs at roughly 4,000 Fahrenheit. Once the uranium melts, the radiation within the core starts to leak out thought the channels made by the uranium burning through. The radiation escapes into the surrounding environment, which is what happened in Chernobyl. However, Chernobyl didn't have a radiation shield in place to block at least some of the radiation, which Fukushima does. But that won't do much good if the steam explosions open up holes in it.

As for what it means for the people of Japan: Complete disaster. The area around the reactor will be irradiated for potentially hundreds of miles, making the area uninhabitable for years. All of the people previously living there will have to find new homes, but Japan's available real estate is severely limited; there's literally nowhere they could go given the population densities combined with so little real estate potential. The rest you can probably figure out on you're own.

[Asuras]

Quite sad really, considering the state they're already in.

[Kuroi Hadou]

Originally Posted by Asuras

Quite sad really, considering the state they're already in.

It really is. It makes me want to floor the people whose first thought to this whole situation was whether their mangaka/seiyuu/whatever was safe.

[Asuras]

Well, quite honestly, the first thing I thought of was Tokyo Magnitude 8.0, but I don't really care much about the state of anime at this point. The horrors are just too brutal to care much about anything else than their future.

I'm sure they'll pull through alright though.

[Dist]

That sounds really awful .. I hope it won't go that far but from what I've read, it doesn't look too good.

Where exactly is the plant located at, though ? If the worst case scenario happened, would it also affect Tokyo ? Being the capital and all, that means ALOT of people .. :x