Tag: Nuclear power

A Day At The Beach

evenabrokenclock10Leave a comment

ocean flood

This is the fourth in a series of seven articles aimed at describing some of the threats that humanity faces in the coming years. It is the issue of global sea rise. There are many who dispute whether carbon dioxide and methane emissions from human civilization are the primary cause of global warming. But regardless of the source of the warming climate, it is becoming more and more clear that sea level is rising in response. That will have an incredible impact upon the population of the world, since there has always been a great desire to live at or very near to the sea shore. And the level of the sea has seldom been constant over geological time, since glaciers have expanded and contracted many times over the past million years, causing the sea level to vary hundreds of feet during these oscillations.

What is different this time, is that our current civilization was developed with the current sea levels. So all of the infrastructure associated with the great cities of the world, it is mainly at sea level. And for many of the people who live in poor countries, like Bangladesh, they exist on river estuaries which are extremely susceptible to sea level rise. So whether the current rise in sea levels is due to anthropogenic greenhouse gas emissions, or whether it is merely a continuation of the cycle of ice sheet expansions and contractions that preceded our species, it becomes necessary to develop a plan for dealing with ongoing sea level rise.

The best option would be to have a controlling thermostat knob on our climate that we could use to compensate for either natural effects on the climate, or for those that humanity has caused. At present, we do not have that. If the scientists who are convinced that human emissions of greenhouse gases are responsible for increasing the temperature, then one knob would be raising and lowering the CO2 concentration of the atmosphere. As seen by the political response to this in the US, there is extremely heavy opposition to this technique from those who are invested in the status quo of the energy industries. It also will require huge investment in both research and in physical facilities to enable renewable energy resources to supplant fossil fuel sources. There is no doubt that we do need to invest in both the research and the facilities, along with redesigning of the electrical grid to be more resilient and to accept the intermittent nature of renewable energy sources.

One option for a zero carbon energy source that is not being discussed is nuclear energy. No, not the energy created from the fission of U235 atoms used in every nuclear power plant in the world at present. Instead, what is needed is to develop reactors that use the thorium power cycle. At one time, nuclear energy research considered thorium as a viable source of electric power. There is one small problem with the thorium cycle, though. It is not capable of generating plutonium as a byproduct. Back when the nuclear power industry was being developed, there was a desire to have plutonium production so that spent uranium fuel rods could be processed to remove the plutonium for weapons production. The vast majority of the research for nuclear energy used enriched uranium U235 as the source for power generation, and thus research for thorium went by the wayside.

But the U235 power cycle also produces other long-lived radioactive isotopes that keep reactor rods fatally radioactive for hundreds of thousands of years. Thus humanity is tasked with trying to isolate wastes from power generation inside of geologically stable environments for many millennia longer than humanity has had a civilization. This is scarcely a realistic model to build a sustainable civilization upon. And U235 reactors are inherently unstable. Complex neutron absorption systems have to be maintained in order to keep the reaction at the sweet spot. Too much absorption, and the nuclear fire goes out and no electricity is generated. Just right, and you can remove the excess heat with water that flashes to steam and eventually turns electric generators. Too little neutron absorption, and the system is capable of melting down into a puddle of zirconium and uranium, that will eventually break through all known containment systems. At the same time, gases generated from the reaction will likely ignite, releasing a cloud of radioactive elements out of the containment system.

Thorium, on the other hand, is an inherently stable reaction system. The active isotope of thorium (Th232) is 99.98% of all thorium in nature. When it absorbs a neutron, it eventually reacts through subsequent beta particle decay into U233. This isotope of uranium is capable of sustaining nuclear fission, but unlike its cousin U235, it does not create longer-lived radioactive isotopes as byproducts. Instead, the fission products it produces are all lighter than the starting materials, and their radioactive half lives are mainly less than a hundred years. Thus it is conceivable that waste products could be maintained in an isolation facility for a reasonable period of time and then would not be a hazard to future generations in future millenia.

The thorium cycle has another advantage. It is impossible to get a runaway reaction using thorium. Since the proposed design for a thorium reactor involves a molten salt reactor, any loss of containment would result in a salt-thorium mixture solidifying on the ground, incapable of performing further fission. All of these advantages over the existing U235 nuclear cycle says that thorium fission should be investigated thoroughly and promptly brought to commercialization. Again, another problem (reducing CO2 generation while providing stable electrical power generation) that could be solved by the investment of the government into scientific research, and opportunities for employment of nuclear engineers and metallurgical engineers and mechanical engineers. Oh, and by the way, the main ores of thorium also contain rare earth metals and phosphates. Both of these are highly desirable materials. Also, thorium is four times more abundant in Earth’s crust as is uranium.

This was a detour from the immediate problem we are intending to address, which is sea level rise. What is needed is a way to do triage for the developed world in trying to determine what infrastructure is indefensible given a certain amount of sea rise, and what infrastructure can be salvaged if we begin to take action now. For example, London installed a barrier on the Thames back in the 1980’s that serves to protect London from abnormally high tides. Would such a barrier be feasible for the Hudson to protect the NY – NJ region from ongoing sea rise? What will the implications of ongoing sea rise be for cities such as Miami, where the tourist infrastructure is at risk. As much as those who believe in karma wish for Mar-A-Lago to suffer inundation, the entire southeastern coast of Florida is at risk. And areas like Newport News and Charleston South Carolina are already going through periods of rainless flooding caused by peak tides. This will only get worse over the next few decades. What is needed to enable these highly-populated metropolitan areas to still be functional? What if it is determined that it is not feasible? How do we deal with the displaced populations?

The issues of displaced populations becomes even more dire when you consider the underdeveloped nations most at risk from rising seas. In these areas, it would be necessary to develop lower-tech means to mitigate the risk. One partial solution is to reestablish mangrove barriers as initial surge suppressors. Mangroves have the ability to capture soil in the roots, thus allowing the ground level to rise as the water level rises. But it will be necessary to develop ways to prevent salt water intrusion, and it will be extremely beneficial if the techniques used to counteract sea level rise use the local farmers and laborers as the contractors to do the work to save their own land. That way, they receive a benefit in building and maintaining these facilities, presumably receiving an income, and they then have an incentive to make sure they work, since their farming livelihood depends upon the new systems functioning properly.

The issues concerning sea level rise are longer-term in their impact and solutions. But in order to effectively deal with them, we must plan now based on what we know will happen. Otherwise we will be caught off guard, like in 2018 when the warmer and less dense waters of the Gulf of Mexico caused the extremely rapid intensification of Hurricane Michael. For one of the consequences of global sea level rise is due to the decrease of density at higher temperatures. Seawater takes up about 1% more volume at 30ºC than it does at 20°C. And the higher water temperatures from a warming climate not only act directly on the water level, they also provide more fuel for the storms that feed upon their heat. We may have been caught off-guard by a hurricane much stronger than expected, but we should not be caught off-guard by physical effects we can predict decades in advance.

 

 

Nuclear Energy Doesn’t Have To Be Scary

evenabrokenclock10Leave a comment

nuclear-power-plant-837823_960_720

 

Quick – can someone tell me what potential source of energy could single-handedly provide all of the energy requirements of the US for the next 1000 years? And at the same time, foster independence in rare earth materials that are mainly sourced from China? And would not generate carbon dioxide as it is consumed?

No, it’s not coal. Coal can provide a significant portion of energy needs, and coal ash is a prospective source of rare earth metals that may be harvested, but it creates a huge amount of CO2 and has other detrimental effects, like the mountain top removal that is a blight in my home state of West Virginia. (Point of personal perspective – over 40 years ago, I had a part-time job as a chemist for a concrete company. There was a new coal fired power plant coming on line in Nebraska, and the concrete company was considering using coal ash as an extender for cement in making concrete. I performed wet chemical analysis of fly ash, going through most of the metals by reacting with reagents, then precipitating out various compounds and evaporating them to dryness in platinum crucibles. The reaction stream went all the way to sodium, which had to be precipitated with some uranium salt. I had fun doing that work, but the one thing I remember is that if you hit a fly with a stream of acetone used to dry dishware, you would cause the fly to drop out of the air instantly, and a dehydrated fly husk would be all that was left behind.)

Give up on the original question? It’s thorium, the radioactive material that has a 14 billion year half life. Thorium, along with uranium, was looked at by the US government when nuclear power and nuclear weaponry were uppermost in the minds of the government. But one factor weighing against thorium, turns out to be now a very beneficial factor. See, it is nigh unto impossible to obtain any nuclear weapon grade material out of the thorium fission reaction process. Uranium reactors will create plutonium as one of the natural byproducts of fission. If U238 (the most common uranium isotope in reactor fuel) absorbs a neutron, it becomes an extremely unstable isotope U239, which eventually transmutes into a plutonium isotope. Since U238 is the primary isotope in a pressurized water reactor, the spent fuel rods from a reactor will always contain plutonium. That is one reason why fuel rod security is required, since plutonium can be chemically separated from the toxic mix of radioactive stew found in a fuel rod.

Thorium, though, does not create plutonium. It does create the uranium isotope U233  which is the active fuel for a thorium reactor.  It also creates small quantities of another uranium isotope U232 which acts as a poison against creating a fission bomb out of U233 . So the issues of nuclear weapon proliferation by segregating out fissile material from thorium fuel are not of concern.

(Paragraph of translation. If you understand the concepts of isotopes, please skip over this paragraph.  Now, the last paragraph used a bit of physics jargon that is necessary to understand this post. I mentioned Uranium 232 (U232)  and Uranium 233 (U233).   Both of those refer to the element uranium, which has 92 protons. Where they differ is in the number of neutrons. Uranium 233 has one more neutron than does uranium 233. An element may have many different numbers of neutrons, and that is especially true in the heaviest (by atomic number) elements. These different isotopes have remarkably different characteristics, especially when dealing with nuclear reactions. This is important in the discussion below.

In order to appreciate the difference between a thorium reactor, and the current pressurized water reactors (PWR) using uranium, it is necessary to discuss PWR’s. The current nuclear power industry takes fuel rods and inserts them into the core of the reactor. A reactor contains control rods of neutron-absorbing materials. These control rods are raised and lowered in order to moderate the nuclear fission occurring in the fuel rods. If the control rods were raised totally out of the core, the fuel rods would not be able to hold the runaway nuclear reaction that would ensue. The zirconium cladding of the fuel rods would melt, and the contents of the fuel rods would pool at the bottom of the reactor. This event would not be good, putting it mildly.

When a PWR works properly, it heats water which is kept pressurized in the primary coolant loop. The water is circulated into a steam generator, where the steam is created which runs the electrical generators. Fuel rods in a PWR have a limited lifespan, and once they are no longer useful to generate electricity, these rods must be pulled out and stored in water to handle the immediate heat generated from nuclear reactions still continuing in the fuel rods. In some cases, the rods are held in water pools for 10-20 years. Then the rods must be kept secure and eventually stored somewhere where they will be able to stay segregated from the environment for geologically significant periods of time (hundreds of thousands of years). It is only after that much time has gone by before the spent fuel rods no longer pose a threat to health.

So, with uranium as the source fuel, you can generate enormous amounts of energy without CO2 generation, but with huge potential issues. You have extremely complex systems operating at incredible pressures and temperatures that must keep operating in order to prevent a runaway reaction. Then, if all works right, you have to take the fuel rods out after only a few percent of the potential energy is released, since the fission byproducts work to poison the reaction long before all of the uranium has fissioned.  And then you must isolate the fuel rods for hundreds of thousands of years, or else there is a risk of radioactive contamination of the environment. No wonder nuclear power is viewed with disfavor.

Thorium would be significantly different, though. Thorium reactors can use a molten salt as the liquid that would carry the thorium, the U233, and all fission products coming from the nuclear reactions. This means that the operating pressures of the system are far lower than in a PWR, reducing the potential for leakage or cracking of the containment system. And if the liquid salt does leak out, what would happen? It would freeze in place. Indeed, the possibility of a reactor core meltdown disappears with a thorium-fueled reactor.

It is essential to separate out the fission products and radioactive isotopes generated in this type of reactor. This can be done by taking a small side stream of the circulating salt solution, and using standard chemical separation techniques to return the unburned U233 to the salt solution. Other radioactive isotopes can be removed using this method. Because the fuel can be recycled indefinitely until it is burned, the remaining daughter fission products (the lighter elements remaining from a uranium nucleus that has fissioned) have a much shorter half life. Instead of hundreds of thousands of years for spent fuel rods to become harmless, it will only take a couple of hundred years for the fission byproducts from thorium to decay to a harmless state.

One thing that thorium has going for it is 4 times more plentiful in the earth’s crust than uranium. And it’s primary ore is one that includes rare earth metals and phosphate. So a commercial mining operation aimed at recovering thorium will also produce rare earth metals, and phosphate for fertilizer. All of these materials are essential for our modern economy.

Granted, any process involving radioactive materials has risks, and even though a thorium-fueled liquid salt reactor is simpler than a PWR, there are many challenges concerning the commercialization of this technology. But if we as a society are concerned with trying to develop energy sources that do not produce CO2 , and can serve as baseload power generators, certainly thorium reactors are a technology that should actively be researched. To think, we may have had the answer to our energy dilemmas in hand over 60 years ago, only to throw it away since thorium doesn’t lend itself to making good bombs (an oxymoron of the first degree).  Let’s try to rectify humanity’s mistake and work to investigate and commercialize this amazing resource we have been given from our earth.