Methane on Mars. Does this mean Life?

So, the science and popular press was all in a huff in the last week or two about the possibility of life on Mars because of the confirmation (first reported in 2004 in many popular press reports) that there is methane (natural gas to you earthlings; CH4 to us nerds) being generated on Mars.

Now, part of the problem is that NASA's PR people think nobody cares if it's not instantly life-changing for everybody. And in part, they're right.

But, come on! Is this really appropriate?

NASA: Martian Methane Reveals the Red Planet is not a Dead Planet

Who besides a geologist is going to interpret that as anything other than meaning there's life on Mars?

So, here's the deal.

In 2004, Krasnopolsky et al. reported that they had discovered methane in the martian atmosphere. In 2009, Mumma et al. reported that they had seen methane appear, disappear, and reappear over several martian seasons. The methane appeared in the summer time. The amount of methane detected is in the parts per billion (ppb).

Methane has, at most a ~350 year half-life in the martian atmosphere. The amount detected should have disappeared long ago unless it is currently (as-in right this minute, not "currently" as-in geologically) being generated.

So, there are two ways to make methane: geologically and biologically.

Geologically:

1. Hydrothermal systems generate methane. We see no evidence for elevated temperatures or other features signifying a hydrothermal system.
2. Methane Clathrates can generate methane when heated.
3. Various volcanoes release methane.
4. Methane hydrates (clathrates are a form of hydrate).
5. I'm sure there are others that I don't know about

Biologically

1. Most (90%) of methane production on Earth is biogenic.
2. That's really all I know. I'm not a biologist... ;)

So, we know that on Earth there's life, and most of the methane we find comes from that life. So, obviously this means there's life on Mars, right? Of course not.

Each of the geologic origins of methane has problems on Mars, but extraordinary claims require extraordinary evidence, and I think a claim that methane on Mars proves the existence of life on Mars is extraordinary.

Would I be excited? Of course! But, there's no reason yet for President Obama to open a new cabinet position dedicated to intrasystem relations.

Here's another thing. That 350 year life of methane I quoted above is for photodisassociation due to photons (from the sun) striking methane and imparting enough energy to break the molecular bonds that hold the carbon atoms to the hydrogen atom...

So?

So, why is the methane disappearing so much more quickly than 350 years? That's the geologic question of interest to me. It's certainly not life destroying the methane. I don't know what it is. Perhaps there's a regular/periodic absorption and release of methane from clathrates or other hydrates? I'm not sure. I would love to know. Someone with more geochemistry background than I will answer this in the next few years. Whatever it is, Mars is becoming more interesting the more we study it... :)

In the meantime, rest assured that as soon as I hear anything about better evidence for life on Mars, I'll post it here.

Why do bubbles form in water

How and why do bubbles form in water?

Son and dad played with some water the other day. First, we blew into a glass of tap water with a straw. A few bubbles formed on the surface and quickly popped.

Why?

Surface tension.

Surface tension arises from the fact that a liquid is held together by cohesion. The molecules that make up the liquid are attracted to all adjacent molecules. Well, at the surface of a liquid, there are fewer adjacent molecules. This means the cohesive forces between the remaining adjacent molecules are enhanced. This is surface tension.

When you blow air through the water, the air displaces the water and we see buoyancy in effect. We also see surface tension take action (yes, even at the bottom of the glass of water). This is because there is a surface at the air-liquid interface, and the water molecules on that surface have fewer adjacent molecules; the forces are enhanced. The tension on the bubble would like to be minimized and the best way to do that is to maximize the surface area over which the force is distributed, giving you a roughly spherical shape to the air bubble.

So, due to surface tension a roughly spherical bubble forms. Due to buoyancy, that bubble moves upward through the water.

Why does a bubble form at the surface? Surface tension again. When the air moves through the top "layer" of water, the water tries to stick together and a bubble forms.

It pops so quickly because the surface tension of water is so great that the water is pulled back to itself quickly. Here's a poor-quality, high-speed-camera video of a soap bubble popping. If you squint and watch closely, you'll see that the bubble does not just collapse. It pulls back upon itself, like a retracting dome. This is due to the surface tension keeping the water together.




So, after that, we put a little dish soap into the water and again blew air through. This caused a lot more bubbles to form on the surface, and most of those bubbles lasted a long time.

Why?

Surface tension.

Dish soap is a detergent, which decreases surface tension. Because the surface tension is decreased, the bubbles on the surface of the water are able to stay together longer; the cohesive forces are not as strong now that the detergent has been mixed in and the water+soap doesn't pull itself back together as quickly. If the surface tension was 0, the liquid would be a gas...

Detergents are used specifically because they lower the surface tension of water, which stops its beading behavior and allows it to soak into clothing or better dissolve junk on dirty dishes. Also, higher temperatures decrease water's surface tension, allowing better cleaning behavior.

Why do the glass blocks at the Desert Botanical Gardens float on the water?

So, we went to the Desert Botanical Gardens in the Phoenix. They had a show exhibiting the art of Dale Chihuly. He's an artist who works with glass (blowing, shaping, etc.).

We saw this there and Sonny boy asked how does the glass float on the water.

Buoyancy, baby!

Basically, buoyancy works because of two properties of fluids:

1) In a fluid (water in this instance), pressure increases with depth.
2) Pressure, at any given depth, is exerted in all directions.

So, what this means is that for any real object that is submersed, the bottom of the object will experience a greater, upward-directed force than the downward-directed force on the top of the object. This results, after all the forces exerted by the fluid are summed, in an upward-directed force being applied to the object by the fluid.

So, why don't all objects float in water?

Well, there are other forces acting besides the buoyancy forces. Specifically, gravity.

Let's imagine two balls of equal size, one made of cork and one made of lead, say 1 m^3.

The density of cork is about 240 kg/m^3, so a 1 m^3 ball of cork has a mass of 240 kg, and will weigh 2352 newtons.
The density of lead is 11340 kg/m^3, so a 1m^3 ball of lead has a mass of 11340 kg and will weigh 111132 newtons.
The density of water is 1000 kg/m^3, so a 1m^3 ball of water has a mass of 1000 kg and will weigh 9800 newtons.

So, if you displace 1 m^3 of water with 1 m^3 of cork, you've replaced 9800 newtons of water with 2352 newtons of cork. Since the 1m^3 of water was sitting where it was, happily not moving (let's assume the water has a constant temperature throughout its depth), we can successfully argue that the water was feeling a buoyant force of 9800 newtons. That is, the weight of the water (mass * gravity) was perfectly balanced by the buoyant force of the water.

Now, let's put that 1m^3 of cork (2352 newtons) in place of the water. Suddenly, the buoyant, upward force of 9800 newtons is being opposed by only 2352 newtons of downward force. The water pressure pushes the cork up.

When we put the 1m^3 of lead in place of the water, the 9800 newtons of buoyant, upward force is met with 111132 newtons of downward force. The lead sinks.

Specific gravity is the term used to tell you if something will sink or float in water, but all it really is is a ratio of densities. Something less dense than water will float on the water; the volume of the water displaced times the density of the water times the gravitational acceleration tells you the weight of the water displaced and that tells you the buoyant force that must be met for an object to sink in water (or any fluid, once you know the fluid's density).

Now, hang on! The density of glass is higher than the density of water!

Ah, but the glass sculptures are filled with air, decreasing their bulk density to less than water. This is the same way boats float. The volume of the water they displace is very high, allowing a high weight of water displaced, which means a large buoyant force opposing a (relatively) small downward force due to gravitational acceleration; the boat/water bulb floats.

[aside] When I say "weigh" above, I mean it will produce a force of xxx newtons at the Earth's surface, at the equator. People often mix-and-match the concept of weight and mass. An object's mass is a fundamental quantity that defines how much material there is. An object with mass has weight when a gravitational acceleration is applied to it. Weight (w) is defined by:
w = m*g
where w is the weight, m is the mass, and g is the gravitational acceleration. You'll notice that weight has the units of force. That's because it is a force.
You can't (correctly) interchange your weight in pounds with mass in kilograms. It's often done, especially in popular literature, and even by many conversion tables. It's incorrect. A kilogram of lead on the Earth is the same as a kilogram on the moon, but it'll weigh about 1/6 on the moon.
[/aside]

Why the leap second?

So, at the new year celebration with friends, one friend, Trish, asked, "why do we have a leap second?" I gave a vague answer, mostly because I'd just downed the last of my DW's rum and coke; she wasn't there due to an unfortunate sledding accident recently discussed, and she wanted me to drink some "yummy" drinks for her. I know she likes rum and coke, so I had one. Ugh (the rum was pretty good, but the coke was horrid, as are all colas). I had to be goaded into finishing it; I did as I do with most alcoholic drinks...I downed it so I didn't have to taste it. So, I was a little flighty.

Let me more properly answer this question here...

First, we need to discuss how we keep time. One of the many ancient ways of keeping time was based on the position of the sun, which is dependent on the rotation of the earth. Everyone "knows" that a day is one full rotation of the earth and that the the length of a day is 24 hours. This is, in fact, how a day is defined by the National Institute of Standards: A day is exactly 86,400 seconds long (60 seconds/minute * 60 minutes/hour *24 hours/day).

A second is now thusly defined: The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

Interestingly, even this seemingly super-precise definition isn't quite good enough. According to Einstein's theory of general relativity, the length of time a second takes (huh?) depends on how far into a gravity well the clock is. So, a clock in Earth orbit will keep time at a slightly different rate from one at sea level (the orbital clock will, in about 10,000 years, gain a second on the sea level clock; relativity has been tested by GPS satellites, which need very precise time). So, whenever we talk of counting seconds, we are speaking of an ideal atomic clock at the geoid (just follow the link; there isn't enough space to explain everything).

So, we now have a day that is exactly 24 hours long. However, the earth itself doesn't care how we define a "day". Therefore, for science purposes, we define a "sidereal day" based on the position of the "fixed" stars. That is, we assume the earth's position does not change relative to very distant stars (obviously this is incorrect, but is pretty good). That is, there is rotation of the Earth, but not translation. We define the sidereal day as one full rotation of the earth such that the position of a star, say Alpha Centuari, is in the exact same position as it was the day before as viewed from the same point on the earth. This takes 23 hours, 56 minutes, and 4.090530833 seconds. For now.

Clearly our two precise definitions of time do not agree. Nor is the word "day" in every-day usage self-consistent. So?

Well, it gets even worse. Everyone "knows" that the length of a year is 365 days, except leap years, which are 366 days long. Also everyone knows that a year isn't exactly 365 days, which is why we need leap years (because otherwise our calendars would be wrong relative to our expectations). The amount of time it takes for the earth to complete one orbit around the sun is actually about 365.242 days. You'll notice that this is NOT 365.25 days, which is what you would expect given that a leap year happens every four years. Which is why a leap year does NOT happen every four years. If that were the case, three extra days would be added every 400 years. Therefore, any century year (1800, 1900, 2000, 2100, etc.) that is not divisible by 400 is not a leap year, even though it is divisible by 4. 2000 was a leap year, and 2400 will be a leap year. 1600 was the last leap year before 2000.

So, what does any of this have to do with leap seconds?

Well, it all points to the complication of using either observed, earthly phenomena (the position of the sun or stars in the sky) or precisely defined times (electron movement in a caesium atom) as a way to keep track of scientifically interesting stuff as well as day-to-day stuff with the same clocks. An atomic clock that uses the definition of the second as shown above will eventually tell you that it's noon when it has been dark for hours. That's obviously not useful.

And I haven't even spoken of the fact that the Earth's rotation is slowing due to tidal interactions with the moon, of the fact that Earth's axial tilt precesses with respect to the fixed stars. or...

Because the Earth's rotation rate is changing ever-so-slightly, we need a way to keep our clocks up-to-date. We wouldn't want to have the situation of having to suddenly add a 1/2 day to our calendars because we let our precise clocks get so out-of-sync with our perceived time; this would be much more distressing to the world than adding a second every few years. So, since 1972, we've been adding a leap second (so far, they've all been positive, but it's possible that at some time, we'll end up losing a second from our year. We'll probably get many protests when that happens). Since 1972, we've added 24 leap seconds to our clocks, sometimes in December, sometimes in June.

Note that leap seconds and leap years only share the name "leap" and the fact that our planet does not behave precisely according to our time keeping devices. A leap second can be added in any year whether it's a leap year or not, leap seconds are added irregularly while leap years are very predictable, and they account for different phenomena.

T6 Wedge fracture

What is a T6 wedge fracture?

The doctor's "education materials":

You have a compression fracture of one of the bones in your spine. This fracture occurs after minor injury (falling to the ground) in older persons with osteoporosis (thinning of the bones). It may also occur in young healthy persons after a severe trauma (car accident or fall from a height). This is a stable fracture and does not cause any injury to the spinal cord or nerves. This injury will take 4-6 weeks to heal and can be treated at home with bed rest and pain medicine.

In other words, a broken back. Linky, linky, linky...

This, my friends, is what happened to my DW this morning while sledding with our son.

There is this new, manufactured hill in town where the city has been doing construction to widen the roads, add a walk- and bike-path, and make it easier to cross town. We had driven past a few times and seen dozens of people out having fun. G has been asking if we could go. For Christmas, G received a sled on runners from his grandfather (GL); it was GL's when he was a boy. So, this morning, we decided to go and try out the hill with the "new" sled and a plastic sled we had purchased a week or so ago. We arrived and a big highway sign said, "No Parking, NOT a snowplay area." Yeah, right. Everyone was playing in the snow. Obviously this was a snowplay area.

So, we found a suitably steep slope, put G on the runners sled, and sent him off. He went all the way down, across the basin, and back up the other hill a bit. What fun! I came after him on the plastic sled. It was fast, and hard. I managed not to hurt myself. DW went next and she bounced along the slope. When we were all back at the top, DW said that we should find a more shallow slope. We did, G went down, and had fun. I went down, had fun. We came back up and went down again. G got tangled in his sled, hurt his knee a touch, but was fine. I went down on my stomache, without a sled. Slow, and fine. DW went next on the plastic sled, hit a jump (not purposely) at the bottom of the hill, and took flight. She landed on her back, compressing her T6 vertebra (not that we knew that at the time). A man nearby said he had probably broken a rib yesterday on this slope (but he was out again...). We went back up, G went down again, and then DW asked us to take her home. After some prodding by me, we went to the urgent care, and then to the ER (because UC doesn't do back x-rays). After a few hours at ER (very little wait in the lobby---we were triaged through pretty quickly), we got the above education.

The ER apparently receives about 22 sledding accident cases per day in winter. There were at least three sledding cases in there with us, one person was so bad off that he couldn't walk.

Apparently, the best way to go sledding is on your stomach, head first (with a bicycle helmet). Don't go on your bottom because you are very likely to get this kind of compression fracture in your back.

So, now DW is on hydrocodone, a mild, narcotic, semi-synthetic opiate. So, apparently she's a user. We're all keeping an eye on her. At least any cough she may have had will be relieved.

I don't have a scanner, so I can't show you her x-ray, but here are some good examples.

Be careful out there.

Next time, barring any other sudden cases of education, we'll be examining the potential dangers of nuclear energy w.r.t. accidents or sabotage.

Cons to nuclear power, part deux

So, I discussed waste and cost in the previous post. In this post I'll discuss proliferation.

3) Proliferation.
This basic argument against developing new nuclear energy technologies or power plants is based on the idea that somehow this nuclear technology can be used by rogues to develop nuclear weapons. The basic information on how to enrich uranium is already out there. I just discussed it in my previous posts. Gas diffusion is not difficult to accomplish. Centrifuge diffusion is not difficult to accomplish. Sure, it's expensive, but anyone who wants to and has the money can do it. So, why is the state department afraid of proliferation?

A) Nuclear enrichment abused; Iran as an example: Iran is a signatory of the Nuclear non-Proliferation Treaty (NPT), which basically says that only the P-5 (US, Russia, UK, France, and China), who have declared that they are nuclear weapons states, may produce or stockpile nuclear weapons. All signatories commit to collaborate on developing peaceful uses of nuclear energy. Iran is an NPT signatory. Russia has been helping Iran with nuclear fuel technologies, including enrichment. So far, that's all kosher according to the NPT... Enriching past the nuclear fuel to nuclear weapons grade uranium or plutonium basically just requires more diffusion cycles and more energy. Iran has more than enough oil and natural gas reserves to supply itself with energy for many many decades. Thus, the US is concerned that Iran is using the Russian technologies to build nuclear weapons rather than nuclear fuel. Considering Iran's wacked stance on some things, it's a valid concern, IMO.

Note that India and Pakistan, both of whom have had nuclear weapons since 1998 are not NPT signatories. North Korea is a signatory, as is South Africa.

So, we have several rogues who have or want to have nuclear weapons technologies. What does this have to do with nuclear power generation (specifically in the US)? Well, IMO, it has nothing to do with it. You cannot stop knowledge from proliferating. Just because Iran may be working toward having "The Bomb" doesn't mean we should necessarily hobble ourselves w.r.t. energy generation. Once a person or state has the knowledge of enrichment, they can go as far as they desire (and can afford) with that enrichment, so the only way we can stop them is to either destroy them or convince them it's not in their self-interest to build a bomb. The former isn't a reasoned option, so what can our state deptartment do to stop Iran from building a bomb? I dunno; I'm just a scientist, not a statesman, but I suspect our current path hasn't been working so well.

B) Redirection of already enriched nuclear fuel: This is theft or direct purchase of enriched fuel by a state or sub-state or group of wackos. Obviously the more states that have nuclear enrichment capabilities, the more opportunities to acquire enriched fuel that can then be made weapons-grade relatively easily. MIT estimates that there is enough enriched plutonium, produced from nuclear energy fuel generation, in Europe, Russia, and Japan to produce about 25,000 nuclear weapons, assuming 8kg/weapon. Obviously, only a few weapons are needed to greatly destabalize any given region.

Proliferation summary:
The means (knowledge and technology) of acquiring a nuclear weapon (via advanced enrichment) is not something we can easily control (see North Korea and Iran). The motive to acquire and use a nuclear weapon is something we (the US in particular) have not recently been very good at mitigating (see Iran). The opportunity to acquire a nuclear weapon or the fuel needed to make one is something we (the US) can stop within our borders and sphere of influence relatively easily. Stopping theft or purchase of Russian (for example) nuclear technology or fuel is not something we seem to have any hand in. The NPT has been fairly effective, but it only takes one state to feel threatened by another before it'll do what it feels it has to...

So, the expansion of today's nuclear power plants to non-nuclear (powered but not weaponed) states does pose some risks. Obviously the detonation of a nuclear weapon anywhere is cause for concern, and would likely be answered with a nuclear weapon. The cascade of responses could go all the way to WWIII. I do not know. I do not think it would take a nuclear weapon to start another world war, but I suspect the use of one would probably guarantee another large, if not world-wide war. This is obviously undesireable.

So, how can we mitigate the risks of nuclear weapons proliferation while still expanding nuclear power generation (or is it even possible)?

For one, the current fuel cycle is a pathway to weapons technology. There are other fuel cycles that do not lead to enriched, weapons-grade plutonium or uranium. These are not in wide-spread use, but they can be developed more aggressively and then spread to those countries that are looking to move to nuclear energy technologies.

For another, diffusing many of the tensions throughout the world is probably a good idea, regardless of the state of nuclear power proliferation. We do not need nuclear weapons to kill a lot of people...

Anyone who wants to can work out how to build a basic reactor. Such things are not difficult to do. The difficulty lies in ensuring that people don't want to move on to nuclear weapons...

I promised to say something about downblending in this topic's post. Downblending is the process of mixing weapons-grade and weapons-usable enriched fuels with depleted fuels to decrease the concentration of the fissible materials, in the process making nuclear power-grade fuels. This is a "new" way of more safely decreasing nuclear weapons stockpiles. In some ways this decreases proliferation risks by decreasing the ready availability of weapons-usable HEU that can be used in crude weapons, which can be made by relatively poor countries or groups (crude being similar in destructive scale to those used in WWII...).

Anyway, proliferation is a concern, but... The knowledge necessary for enriching materials to weapons-usable or weapons-grade form is easily obtainable, the technology isn't much more difficult to obtain, there is no need for nuclear weapons to kill many people or destabilize a region, and decreasing the desire to kill many people seems (to me) to be a more prudent approach than attempting to retroactively close Pandora's Box...

Cons to nuclear power

Okay. I'm a month or so late... So shoot me.

Why should we NOT increase our use of nuclear power?

There are a number of arguments against nuclear power. The list below is not in any particular order.

1) cost
2) waste
3) proliferation
4) accidents or sabatoge

1) Cost: This is---at best---an inane argument, IMO. We can spend the money now on new technologies or we can spend the money later on health care, global warming mitigation, etc. Saying "it's too expensive to build or develop new nuclear power plants," is just whining. Yes, I am perfectly happy to be dismissive of and condescending to anyone arguing against nuclear power on the basis of cost.

2) Waste: This is the best argument (IMO, of course) against nuclear power.

2A) To get the uranium ore, we must mine for it. This creates long-lived contamination around the mining site. The uranium tailings contain over a dozen radioactive species, including thorium-230, radium-226, radon-222, and polonium-210. These are all hazardous materials, of course. If, as in past practices, the radioactive sand is left on the surface, it could be blown about by the wind, washed away by rains, etc. There is not actually a high concentration (compared with other nuclear waste materials) of hazardous materials by mass, but there will always be a large mass of tailings from any given mine. The most serious and probable human health hazard associated with the tailings is lung cancer caused by inhaling these radioactive products.

Anti-arguments: Here's the thing, though... The most dangerous, common rock, in terms of radioactivity, is granite. Your granite tabletop (if you're so lucky) is continuously producing radon gas. It's not much, and it's certainly not a health concern. Your drywall plaster is probably made of calcined gypsum. That's releasing more ionizing radiation than your granite counter top, and it's in every room of your house. It's still not a health concern. All the portland cement you see and use (home foundations, sidewalks, some freeways, buildings, etc., etc., etc.) are emitting as much or more radon as fly ash from coal-fired power plants. The uranium tailings from old mines are certainly dangerous, but new techniques in dealing with the tailings are in place, and even better ones are being developed. That's a pretty hand-wavy argument that the waste from mining is "safe." It's not safe. Neither is burning coal. Here is a paper that argues that the radiation dosage from mine tailings isn't terribly dangerous. That's only one side of the story, of course. This paper estimates the dosage someone living around a coal-fired plant will be exposed to. This paper discusses the comparison between coal and portland cement sources of radon. We see more cancers from pollution and cement-derived radon in our homes than we do from mine tailings, and increased nuclear power generation will only decrease the overall number of cancers, even if we continued to use the worst methods of dealing with uranium tailings.


2B) To get fissionable material (U235) from the uranium ore (uranium oxide, "yellow cake"), it must go through enrichment. (Stolen from here): Natural uranium is composed of 0.72% U-235 (the fissionable isotope), 99.27% U-238, and a trace quantity 0.0055% U-234 . The 0.72% U-235 is not sufficient to produce a self-sustaining critical chain reaction in U.S. style light-water reactors, although it is used in Canadian CANDU reactors. For light-water reactors, the fuel must be enriched to 2.5-3.5% U-235. Uranium is found as uranium oxide which when purified has a rich yellow color and is called "yellowcake". After reduction, the uranium must go through an isotope enrichment process. Even with the necessity of enrichment, it still takes only about 3 kg of natural uranium to supply the energy needs of one American for a year.

The byproducts of enrichment are basically depleted uranium (DU, which is pretty much just U238) and uranium hexafluoride gas (UF6). U238 is relatively safe, with a half-life of about 4.5 billion years, via the path of alpha decay. Alpha particles are just helium nuclei. They can be dangerous when ingested or inhaled, but are pretty much harmless externally (alpha particles are stopped by a single layer of dead skin cells). That's not to say that alpha decay is harmless. Radon gas, polonium 210, etc. are implicated in cancers and other nasty deaths if inhaled (Pu210 is thought to have been the material used to poison Alexander Litvinenko). U238 is also chemically toxic, and can have seriously bad effects on the liver, once again if ingested. U238 is now being used in a process called "downblending." I'll discuss downblending in the proliferation discussion. UF6 is a different beast altogether. UF6 is an extremely unstable waste compound that's not easy to store or handle. Here you can find a 118 page PDF on safe handling procedures for UF6. I haven't read it. Let it suffice to say that UF6 is mostly bad because of its chemical (not nuclear) toxicity. The uranium part of UF6 is obviously radioactive. The depleted UF6 (with mostly U238, not U235) is stored as waste. Any amount of water mixed with UF6 will turn it into a rather nasty acid, so the storage of UF6 is a difficult task.

I cannot argue against the dangers of depleted UF6... It is as dangerous as any other toxic chemical used in other manufacturing processes. Since it also contains U238, it's scary to a lot of people. I'm not any more concerned about UF6 than any other toxic chemical (melamine?) that is moved around this country and others.

2A and 2B are the wastes from the processing and creation of nuclear fuel. There are wastes that come out the back end of the nuclear power generation process.

2C) Spent fuel rods contain fisson products that emit beta and gamma particles. They also contain actinides that emit alpha particles. These products include uranium-234, neptunium-237, plutonium-238 and americium-241, and even sometimes some neutron emitters such as californium (Cf). None of these are pleasant products. Some are so radioactively hot that they're thermally hot.

Many countries, the US excluded, reprocess these products to extract any left-over U235 for re-use as a nuclear fuel. This increases the concentration of the radioactive products in the waste. It also increases the concentration of the toxic chemicals used to process the materials. The US just stores the waste as-is, without reprocessing. One can argue either way about what to do with these products. Since we're in the US, I'll briefly mention Yucca Mountain.

Some geologists have certified that Yucca Mountain would be a safe place to store these waste products. Others have argued that it is not safe. I'm not sure who is correct. I'm not sure how dangerous these products are in the long term. I am sure that if we were to spend some money paying scientists and engineers, they could figure out a workable solution. It would not be ideal, it would not please everyone.

So, waste is the biggie. It's not solved, but it's not nearly as bad as many people think.

I think this post is long enough for now. I'll post arguments 3 and 4 later...