Nuclear power reconsidered

After decades of failure to slow the rising global consumption of coal, oil and gas, influential public figures such as Bill Gates and Elon Musk have concluded that the world needs to reconsider nuclear power in order to lower the demand for fossil fuels. Wind and solar power alone, without large-scale storage for these intermittent sources, are unlikely to meet the world's needs for reliable energy. See Figures 1 and 2 on the magnitude of the world energy challenge.

Nuclear power plants that use nuclear reactors to create electricity could provide the abundant, zero-carbon, dispatchable energy needed for a low-carbon future, but not by simply building more of what we already have. New innovative designs for nuclear reactors are needed to avoid the problems of the past.

(CC) Image: Geoff Russell
Fig.1 Electricity consumption may soon double, mostly from coal-fired power plants in the developing world.

© Image: Lawrence Livermore Lab
Fig.2 Electricity is only a third of the CO₂ problem. Other big needs include low-cost high-temperature process heat for industry and fuels for the transportation sector.

Issues Confronting the Nuclear Industry

New reactor designers have sought to address issues that have prevented the acceptance of nuclear power, including safety, waste management, weapons proliferation, and cost. This article will summarize the questions that have been raised and the criteria that have been established for evaluating these designs. Answers to these questions will be provided by the designers of these reactors in the articles on their designs. Further debate will be provided in the Discussion and the Debate Guide pages of those articles.

Safety

Fig.3 Historical record on safety and CO2 emissions.

Nuclear accidents have been compared to airplane crashes - in the public mind, far more horrible than the numbers actually warrant. Figure 3 shows how many deaths worldwide are resulting from the use of fossil fuels and other energy sources. Nuclear power over the last 50 years, when measured by objective criteria like number of deaths per terawatt hour of energy produced, has been safer than even natural gas (the safest of the fossil fuels), and comparable to wind and solar. In spite of this record on safety, the fears remain. Widespread deployment of nuclear reactors will require that the new designs address not only the fears that have arisen from accidents in the past, but also what might be conceivable in the future, including natural disasters, sabotage, and cyber attacks.

Because even a harmless malfunction can influence public opinion and set back deployment of nuclear power for decades, some proponents of the new designs are calling them "walk away safe" - that is, they are designed with the ability to shut down safely even if the operators just walk away and do nothing to prevent an accident. Let us call this level of safety S-1.

Beyond that, regulators could require safety level S-2 - that is, no way the operators (or terrorists) can cause a radiation leak by overriding the normal controls.

Finally, regulators could require safety level S-3, the highest level of safety - that is, no way, even using explosives, that terrorists could cause a disaster. S-3 may be impossible to achieve. In that case, reactor designers must consider possible scenarios and what the response would need to be.

Scenario Sab-1: Terrorists arrive with cable cutters, a hacksaw, and a memory stick with some malware from North Korea. The operators are expelled, except one, whose daughter is held hostage, and will be killed if anything goes wrong with the terrorist plan.

Scenario Sab-2: The terrorists have heavy equipment to drill through concrete, and a pump truck with some brown liquid.

Scenario Sab-3: The terrorists have hired El Chapo's tunneling team to come at the reactor from underground.

There may be dozens of scenarios to consider, including tsunamis, hijacked airplanes, and even a meteorite strike. The public should be encouraged, perhaps even rewarded for submitting scenarios worthy of consideration. The Fukushima disaster could have been avoided, if someone had thought to keep pump trucks on a nearby hill.

See also Radiation_Hazards and Fear of radiation.

Waste Management

Fig.4 Radioactivity over time of each major nuclide in spent fuel from a nuclear reactor. The dangerous nuclides decay quickly. Most longer-lived nuclides are less radioactive than natural uranium.

How much waste is produced compared to other sources of energy? How will it be contained, and what are the dangers to people and the environment? Like questions on safety, public perception of the dangers of nuclear waste is much worse than historical data shows. The volume of waste per terawatt-hour is 100,000 times less than coal. Even if only looking at radioactivity released to the environment, watt-for-watt nuclear power is 100 times less than coal.

Much of the worry about nuclear waste centers around the long life of some low-level isotopes in the waste (See Fig.4). There is concern about leakage into the environment decades or even centuries from now. Billion-dollar efforts to bury the waste deep under a mountain have only heightened public fears. Dry-cask storage at the power plants has proven to be a safe but temporary solution. This interim storage has the advantage of being able to recover the "waste" and burn it in newer reactors that can use the remaining 97% of available energy.

Transportation of spent fuel from reactors to disposal or reprocessing sites must be done safely. Reprocessing should be done at secure locations to avoid diversion of dangerous materials. Leakage into groundwater and ocean water near shore is a special concern. New reactor designs must address these concerns, even though they go beyond the design of the reactor itself. Will the waste be solid or liquid? Will it require special casks, or even special vehicles for transportation on public roads? (See Fig.5)

© Photo: Nuclear Fuel Transport Ltd.
Fig.5 Transport of Nuclear Fuel in Japan.

Other worries include the possibility of sabotage or theft of waste material that might be useful in a "dirty bomb". Again, regulators should evaluate specific plans by considering likely scenarios. Is the storage facility away from any population center and not a target for an airplane crash, a truck bomb, or even a short-range missile? Is there a secure perimeter with intrusion detectors? If there is an intrusion, is cutting through the concrete and steel difficult enough that there will be plenty of time for a response from local law enforcement, or even a nearby military base? (See Fig.6)

© Image: Holtec International
Fig.6 Dry underground storage in the desert, safe but still recoverable.

It is important to make a distinction between spent fuel from nuclear power, and the waste from bomb production, which was often done in a rush with little concern for pollution. Spent fuel rods can be stored safely. Weapons waste poses a much bigger problem due to the large variety and sometimes unexpected characteristics of the material to be buried. In evaluating a new reactor design, regulators must look at the complete fuel cycle, not just the waste from the reactor itself. Are there any problems with the mining, processing, or transportation of the fuel, or with the reprocessing of spent fuel?

See also Nuclear_waste_management.

Weapons Proliferation

Will deployment of reactors to untrusted countries, or countries that might be taken over by rogue actors, increase the risk of proliferation, either by theft of materials in the reactor, or by modification of the reactor to produce weapons-grade materials? Will fuel processing or other activities connected with nuclear power provide cover for a weapons program or a basis for a quick sprint to bomb making? Will knowledge of the new reactor designs or process technologies lead to easier ways to make bombs?

There are three nuclides with potential for making a bomb: U-233, U-235, and Pu-239. Every reactor design has a characteristic isotopic composition in its fuel, which evolves over time as the fuel is consumed. Some uranium reactors have a brief period in their fuel cycle where weapons-grade Pu-239 can be extracted from the partially used fuel. Some thorium reactors with on-site fuel processing may be vulnerable to skimming of a small fraction of U-233 from the process loop. Some molten salt reactors start with uranium enriched to 20% U-235, and that might provide a head-start to a country wanting to enrich all the way to bomb-grade.

Considerations like these favor designs in which all fuel processing is done at secure locations, and there is never any weapons grade material easily extracted from an operating reactor. The requirement should not be perfection, but simply that a new reactor should not allow an easier route to bomb making than currently available centrifuges.

See also Nuclear_proliferation

Cost

How will the cost compare to existing power sources including wind and solar? Existing nuclear plants have been very expensive, due to the inherent risks in Pressurized Water Reactors (PWR's) and the need for expensive structures and burdensome regulations to deal with that risk. Newer designs promise to be simpler, safer, and manufactured on an assembly line as replaceable parts, rather than site built. Elimination of water at high pressure and temperature avoids the risk of steam explosions. Reactor vessels with non-destructive "meltdown" behavior avoid the risk of another Fukushima.

Plants with replaceable parts can operate indefinitely, but if a plant is decommissioned, the process is little more than pulling out but not replacing all the parts. Cost is a lesser worry than the other issues, because the risk can be born by private companies promising to deliver reactors at an agreed price. See Cost_of_nuclear_power for further discussion.

One remaining worry is future costs if fuel or some essential material becomes scarce. Some PWR's require hafnium in their control rods, and there was worry about the world supply of hafnium if thousands of these reactors were to be deployed in the coming decades. As for the supply of fuel, the World Nuclear Association says it is essentially unlimited. Some of the new reactors can burn all the uranium, not just the 0.7% now burned by PWRs, and they can even burn thorium, which is three times more abundant than uranium.

See also Cost_of_nuclear_power.

New Reactor Designs

Here is a brief summary of several reactor types and representative examples of each type. See the specific reactor designs for responses to the issues raised in this article.

Small Modular Reactors

Small Modular Reactors (SMRs) include any type of reactor that is smaller than a conventional reactor, can be built as modules on an assembly line, delivered to the site where power is needed, and returned for recycling or disposal. The first SMR to be licensed in the United States was the NuScale SMR, a smaller version of a standard Pressurized Water Reactor (PWR) with additional safety features. NuScale has unfortunately failed to meet its promise of low cost.

Molten Salt Reactor

Molten Salt Reactors (MSRs) provide higher temperature and better thermal efficiency than PWRs, while avoiding the risk of meltdown and high-pressure steam explosions inherent in PWRs. The ThorCon nuclear reactor is an MSR based on proven technology, intended for a short-term solution (decades) while more advanced designs are perfected.

Fast Neutron Reactor

Fast Neutron Reactors (FNRs) are capable of burning spent nuclear fuel, old bomb cores, depleted uranium, and thorium. FNRs can breed more fissile material than they consume, making them the current best bet for long-term energy sustainability. This technology is not speculative, as are fusion and new breakthroughs in storage. The Integral Fast Reactor is a metal-fueled, sodium-cooled, pool-type FNR.

High Temperature Gas-cooled Reactor

Fig.7 Zero-carbon, very high-temperature process heat will be needed for some industries.

High Temperature Gas-cooled Reactors (HTGRs) use inert helium gas as a coolant and can provide temperatures even higher than MSRs. These reactors may prove useful for industries needing zero-carbon, high-temperature process heat, like the production of hydrogen from water and the refining of steel. See Figure 7.

Further Reading

• Electrifying Our World Dr.Robert Hargraves' excellent overview of energy, the growth human civilization, and possible solutions to the problems of energy poverty and global warming.
  
• What is Nuclear Energy Dr. Nick Touran's easy introduction to nuclear energy by a group of nuclear engineers.
  
• World Nuclear Information Library a comprehensive, authoritative collection of information on nuclear energy.
  
• Our World in Data has a section on Energy and Environment with nice interactive graphics.
  

Notes and References

Authors [about]: David MacQuigg CZ is an open collaboration. Please join in to develop this article!