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We have several topics that include "fission" in the title, but there is none appropriate to the announcement that will be offered in post #3.
This topic is offered for NewMars members to report news of developments in the field of fission-only reactors, or to comment.
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This post is reserved for an index to posts that may be contributed by NewMars members over time.
Calliban: ADR Accelerator Driven Reactor
https://newmars.com/forums/viewtopic.ph … 04#p229404
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This post is about what appears to be encouraging news for a small reactor that may eventually qualify for use in populated areas:
https://interestingengineering.com/ener … 23_11_24_3
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The accelerator driven reactor (ADR) is an interesting concept.
https://en.m.wikipedia.org/wiki/Acceler … al_reactor
Carlo Rubio advocates what he calls an Energy Amplifier. This is a spallation driven nuclear reactor. A particle accelerator is used to accelerate a beam of protons to 1GeV. The protons collide with lead nuclei inside a nuclear reactor core. A collision at this energy will almost completely disintegrate a heavy nucleus, releasing a dozen or more neutrons. These neutrons are then absorbed by thorium nuclei in a fuel blanket surrounding the spallation source. The 232Th transmutes into 233U, which is fissile. When spallation neutrons impact 233U, energy is generated by fission. Fission releases even more neutrons, causing more fission and transmuting more 232Th into fissile 233U.
This type of reactor is useful, as in addition to generating power its discharged fuel would contain enough fissile 233U to fuel several downstream nuclear reactors of comparable power. On Mars we could use these devices to breed 239Pu and 233U from native or imported uranium and thorium. One interesting feature of spallation sources is that the number of neutrons produced by disintegration increases as the atomic weight of the target nuclei increases. This means that higher actinides in long-lived nuclear waste are even better targets than lead. Far from being waste, this material provides us with a useful source of neutrons. On Earth, this technology could allow the expansion of light water reactor fleets without concerns over uranium depletion. On Mars, the use of ADRs allows rapid expansion of nuclear power supply. It also allows 100% of the energy content of uranium and thorium to be extracted. This is important if uranium and thorium turn out to be rare on Mars or if we are importing these fuels from Earth.
On Mars, we would load an ADR with uranium or thorium metal fuel, clad with stainless steel. The reactor would be cooled with ducted sodium coolant channels or liquid lead. Fuel would be shuffled inward, with the innermost blankets discharged at perhaps 5% atom burnup. The resulting discharged fuel would be about 75% thorium, 5% fission products and 20% 233U. The metallic fuel would then be dissolved in nitric acid. Fission product nitrates would be extracted and vitrified as waste. The remaining mix of uranium and thorium nitrate would be blended down with additional thorium nitrate. This 5% 233U nitrate liquor is then used as fuel for unity breeding ratio aqueous homogenous reactors. The nitrate liquor from the ADR effectively provides a starter core for new reactors. This allows nuclear capacity to expand quickly to meet the energy needs of a rapidly growing Martian colony.
Last edited by Calliban (2025-01-28 10:05:29)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Additional: The Belgian government started construction of a lead-bismuth cooled spallation driven reactor last year.
https://www.myrrha.be/
Belgium is a country of 10 million people. Their ability to pursue this gives me confidence that it should also be possible for a Mars colony when population reaches a similar level. Early Mars reactors will most likely be modular light water reactors using fuel imported from Earth. But beyond a certain level of development, it makes sense to start using domestic resources and to extract as much energy from uranium and thorium as is physically possible.
An accelerator driven system can work in a number of different ways. A proton beam can directly transfer energy to a heavy nucleus causing it to break up into smaller pieces, including neutrons. These neutrons then cause fission and nuclear transmutation. Alternatively, a high energy proton beam can generate muons or anti-protons. Muons can catalyse fusion in a suitable target, releasing very fast neutrons. Anti-protons are a powerful spallation source. Upon impacting a heavy nucleus, they release almost 2GeV of energy, breaking the nucleus apart and releasing a great many neutrons. I am uncertain as to which neutron source is best. They all require high energy protons to work, so the best neutron source is the one that produces the most neutrons per MJ of energy input to the accelerator.
One substantial advantage that an ADR offers is safety. The reactor is subcritical, with additional neutrons provided by the electrically driven accelerator. Rapid reactor shutdown can be achieved by cutting power to the neutron source. This can be done more rapidly than mechanically inserting control rods. This design feature could be especially useful for certain types of nuclear reactor. The gas cooled fast reactor for example, has advantages of being an extremely compact direct cycle CO2 cooled reactor, with a hard neutron spectrum and high breeding ratio. A weakness with this reactor type is that a coolant leak removes moderation from the reactor, hardening the neutron spectrum, causing power to surge. An accelerator driven reactor could solve this problem, by tripping the accelerator if neutron count increases outside a pre-defined range.
Last edited by Calliban (2025-01-28 10:29:01)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Metallic nuclear fuels are now being considered for light water reactors.
https://www.neimagazine.com/advanced-re … -11283875/
This has a number of near term advantages. Metallic fuels have improved thermal conductivity and fissile density. This may ultimately allow higher power density reactors. Conversion ratio will also be slightly improved.
Another advantage that is less frequently discussed, is that metallic fuels are substantially easier to reprocess using pyroprocessing. The sent fuel pellets can be melted within a crucible and mixed with liquid cadmium. Fission products dissolve into the cadmium. The actinides are denser and remain seperate, allowing them to be cast into fresh fuel pellets.
This technology is especially interesting for the thorium fuel cycle. Fuel pellets can be made from uranium thorium zirconium alloy. Pryro fuel processing techniques are far more compact and suitable to automation than classic chemical plant reprocessing. This makes it realistic to consider onsite reprocessing within manual handling of fuel. It means that Martian based nuclear reactors can be based upon conventional light water designs and Martian thorium can be integrated into the fuel cycle relatively easily.
Last edited by Calliban (2025-02-14 07:19:40)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The article at the link below is about a design for small reactors to power data centers.
This are apparently smaller than SMR's.
https://interestingengineering.com/ener … oup=test_a
US firm unveils powerful nuclear reactor prototype to power data centers, AI
The Aalo Pod is designed to work in a grid-independent, fully dependent, or hybrid mode, giving users much-needed flexibility with nuclear and available grid power.Updated: Apr 09, 2025 06:58 AM EST
Photo of the Author Ameya Paleja
Ameya PalejaUS firm unveils powerful nuclear reactor prototype to power data centers, AI
Representative image of the Aalo X, the first nuclear reactor from Aalo Atomics.Aalo
Aalo Atomics, a Texas-based nuclear energy company, has unveiled the industry’s first fully modular reactor designed to meet the power demands of data centers.
Dubbed the Aalo Pod, the company says that the prototype belongs to the category of XMR, or an extra modular reactor with extra flexibility and modularity, according to a press release.
With the rise of demand for clean energy, nuclear power is poised for a major comeback as an energy source without any carbon emissions. Previous experiences in dealing with nuclear energy have faced issues such as project delays and cost overruns. Attempts are being made to avoid them using small modular reactor (SMR) designs.
According to Aalo Atomics, while SMRs are a feasible solution for nuclear power, they are not compatible with supplying energy for data centers. SMRs can take as long as a conventional nuclear power plant to build, but their power output is relatively small and cannot scale with the increasing demands of a data center.
“We believe that to address today’s massive data center market demand, another category of nuclear reactor is needed, one that blends the benefit of the factory manufacturing of microreactors, the power levels of SMRs, and the economic targets of a large reactor,” said Matt Loszak, the CEO of Aalo Atomics.
Aalo Pod, an XMR
The Aalo Pod is a 50MWe extra modular reactor, where the reactor and the plan are completely modular. The extra modularity of the design enables the reactor to be scaled easily from 10s of MW to 1,000s of MW as the demand for energy grows.
Compared to conventional nuclear power plants or modern-day renewable energy sources, the Aalo Pod has a small footprint of five acres for a 100 MW capacity. Each Aalo Pod consists of five Aalo-1 reactors that have been paired with a single power-generating turbine.
Unlike conventional nuclear power plants that need to go offline for refueling, a reactor in an Aalo Pod can be refueled anytime, while others contribute to energy production.
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This post is about NuScale having won approval for a second reactor design:
This first item is from the financial perspective.
https://www.msn.com/en-us/money/markets … elemetry=1
NuScale Power Corporation (NYSE:SMR) touched a new all-time high of $41.88 at intraday trading before slightly pulling back to end the day at $41.60.
The rally was likely boosted by the US Air Force’s milestone deal with another small modular reactor (SMR) provider, in line with the United States’ plan to ramp up the adoption of nuclear reactor technologies in the country.
It can be learned that President Donald Trump signed two executive orders last month to ramp up the development of nuclear technologies in the country. One of the orders includes the deployment of advanced nuclear reactor technologies for national security and to support the energy needs of Artificial Intelligence infrastructures such as data centers.
This next item is specifically about winning a second approval for their SMR design...
https://www.msn.com/en-us/money/savinga … ngNewsSerp
News about NuScale Power Doubles Number Of Approved
NuScale Power Doubles Number of Approved Small Modular Reactor DesignsThe Motley Fool
NuScale Power Doubles Number of Approved Small Modular Reactor Designs
"The uprate approval by the U.S. regulatory authority increases the power output per …NuScale Power Attracts Data Center Giants With Deployable SMR Technology
Seeking AlphaNuScale Power Attracts Data Center Giants With Deployable SMR Technology
NuScale Power: Tailwinds Are Here, But Elevated Costs Weigh
Seeking AlphaNuScale Power: Tailwinds Are Here, But Elevated Costs Weigh
NuScale’s SMR design approved
Nuclear Engineering InternationalNuScale’s SMR design approved
NuScale Power (SMR) Stock Surges 20% Following Second NRC Design ApprovalNuScale has received NRC design approval for an uprated 250 MWt NuScale Power Module that can put out more than 50% more power, the equivalent of 77 megawatts. This marks NuScale's second design approved by the United States' nuclear regulator12.
Learn more:
MWt vs MWe >>
The key difference between 250 MWt and 77 MWe lies in the type of power they represent:
MWt (Megawatts thermal): This refers to the thermal power generated by a system, representing the energy input. In the case of power plants, it measures the rate at which heat is produced from the energy source (e.g., nuclear fuel in a nuclear reactor or burning coal in a thermal plant).MWe (Megawatts electric): This refers to the electrical power output, representing the useful electricity generated and available for use.
Why the difference?Power plants, especially those that convert heat into electricity (like nuclear or thermal power plants), cannot convert 100% of the input thermal energy into electrical energy. This is due to inefficiencies inherent in the conversion process (e.g., steam cycle losses). The difference between the MWt and MWe values represents the amount of waste heat produced during electricity generation.
In the context of 250 MWt (77 MWe):
This indicates that a system is generating 250 MW of thermal power, but only 77 MW of that thermal power is being converted into useful electrical power. The remaining energy is lost as heat.This example highlights the efficiency of the power plant, which can be calculated by dividing the electrical output by the thermal input: 77 MWe / 250 MWt = 0.308 or 30.8% efficiency.
Megawatts thermal - Energy Education
Because of this, there are two values assigned to a powerplant: megawatts electric (MWe), and megawatts thermal (MWt). The former refers to the electricity outp...favicon
Energy EducationThermal power - Energy Education
In other contexts, it can be a measure of the output—such as the radiant heat given off by the Sun. For power plants, the thermal power input is measured in meg...favicon
Energy EducationMegawatts electric - Energy Education
The power input in a heat engine is measured as MWt, and the output power obtained as electricity is measured as MWe. Megawatts electric or MWe is one of the tw...
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This post is of a generic nature. I asked Google to refresh my memory of the characteristics of light water vs heavy water reactors.
The bottom line is that because Deuterium absorbs fewer neutrons than protium, reactors using Deuterium can operate with natural uranium.
These are results for Please refresh memory re light water reactor vs heavy water reactor does protium absorb more neutrons?
Search instead for Please refresh memory re light water reactor vs heavy water reactor does protium absorbe more neutrons?AI Overview
Here's a breakdown of the differences between light water reactors (LWRs) and heavy water reactors (HWRs), focusing on neutron absorption and moderation:Moderator and Neutron Absorption:
LWRs: Use ordinary water (H₂O) as both a coolant and a neutron moderator. However, protium (¹H), the most common isotope of hydrogen in ordinary water, has a relatively high tendency to absorb neutrons.
HWRs: Utilize heavy water (D₂O), which contains deuterium (²H), as a moderator. Deuterium absorbs significantly fewer neutrons than protium.
Consequences of Neutron Absorption:
LWRs: Due to the higher neutron absorption by light water, LWRs require enriched uranium fuel (a higher percentage of fissile uranium-235) to maintain a sustainable chain reaction.
HWRs: Because heavy water absorbs fewer neutrons, HWRs can operate using natural uranium fuel, which has a lower concentration of uranium-235.
Neutron Moderation:
Both light water and heavy water act as neutron moderators, slowing down fast neutrons released during fission to thermal energies, making them more likely to cause further fissions.Light water is generally better at slowing down neutrons due to the smaller mass of protium, allowing for more efficient energy transfer per collision.
Heavy water is a good moderator, but light water can be even better in terms of slowing down neutrons.
In summary, protium (in light water) absorbs significantly more neutrons than deuterium (in heavy water). This difference impacts the type of fuel required: LWRs with light water need enriched uranium, while HWRs with heavy water can use natural uranium.
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Heavy water moderated reactors have found a home in countries with limited uranium enrichment capability. The problems are: (1) Heavy water is energy intensive and expensive to produce; (2) The slowing down length in D20 is somewhat greater than in H2O. This makes the core bulkier, with greater distance between fuel assembles. That increases capital cost. The consensus within the industry is that using enriched uranium in a lightwater reactor is a better solution overall. But heavy water reactors have been shown to work.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The story at the link below is about research to manage micro-reactors in real time with computer control.
The story includes cautions about the risks of "load following" with details of failures in France where it is being done.
https://www.yahoo.com/tech/science/arti … 15912.html
The Cool Down
Researchers claim breakthrough in effort to pair micro nuclear reactors with AI management: 'Next, we aim to close the loop'
Rick Kazmer
Mon, July 28, 2025 at 6:45 AM EDTResearchers claim breakthrough in effort to pair micro nuclear reactors with AI management: 'Next, we aim to close the loop'
University of Michigan researchers are working on a way to put breakthrough nuclear microreactors on autopilot.
The plan would leverage machine learning, a branch of artificial intelligence, to allow the small nuclear chambers to adjust power output autonomously, according to a Wolverine news release.
This would reduce training time and improve performance in remote locations, in space, on ships, and even for grid support.
"This study is a step toward a forward digital twin where reinforcement learning drives system actions," assistant professor Majdi Radaideh, the study's senior author, said in the statement.
The team used advanced computing, giving reactors the know-how to adjust power demand on their own in a process known as load-following.
The idea behind the effort is to make the process more efficient and reduce training time while allowing for remote management, but Edwin Lyman, Director of Nuclear Power Safety at the Union of Concerned Scientists, expressed concerns about the research in an email to The Cool Down, saying that "this kind of theoretical study is getting way ahead of the actual state of these technologies."
"Putting aside the whole AI question, it isn't even clear if load following can be done safely with operating nuclear reactors, much less paper reactors that have not been built or tested," Lyman said. "It is not currently approved by the NRC for U.S. reactors, and in France, where load following is allowed, there is evidence that it is imposing stresses that may be responsible for the unusual cracking of pipes that is being seen in many reactors.
"I'm not aware of any testing that has been done yet on TRISO [tristructural isotropic] fuel under load-following conditions. And rapid changes in power level may have other safety implications that would likely require integral testing to understand. If there is no actual experimental data available for training AI models on real reactors, this effort is just garbage in, garbage out as far as I'm concerned."
The small reactors are a lower-cost alternative to larger ones used in the country's 54 nuclear plants, which generate nearly 20% of U.S. electricity, per the Energy Information Administration. They are being developed by companies such as Westinghouse.
The innovation would use eight rotating drums that center around the reactor core, the crucial place where atoms are split to make energy, as the University of Michigan detailed.
From there, it gets about as technical as you'd expect when dealing with atomic energy.
"One side of the control drum's circumference is lined with a neutron-absorbing material, boron carbide," the experts wrote. "When rotated inward, the drums absorb neutrons from the core, causing the neutron population and the power to decrease. Rotating the cores outward keeps more neutrons in the core, increasing power output."
The summary added that the real-time adjustments are superior to predictive models.
Neutrons are a key part of the fission reaction process, which is when atoms are split to create energy.
In a novel test, the researchers analyzed a setup that trained eight independent "agents to control a specific drum while sharing information about the core as a whole."
The drum-to-drum communication helped increase learning while reducing time.
It all boils down to superior performance — a 150% lower cost control than industry-standard mechanisms, as the University of Michigan observed.
Nuclear energy is promising because it produces no planet-warming air pollution when making power. Those dirty fumes are contributing to worldwide overheating that NASA and other experts have linked to severe weather — such as heat waves that could make some places too hot for living.
The downside is expense, slow development, and long-lasting nuclear waste. Fusion, which forms new atoms instead of splitting them like common fission, is an alternative that doesn't produce harmful byproducts. While breakthroughs have been promising, the tech isn't ready to provide energy sustainably.
Nuclear proponents cite misconceptions about waste (it comes in small pellets, not ooze-filled drums), and the boon of unlimited cleaner energy. Watchdogs warn that calamity is a meltdown away, and Lyman and his UCS colleagues generally warn extra against rushing to unleash new, untested or lightly tested nuclear technologies.
Pennsylvania's Three Mile Island is a prime example of the risk-reward scenario. A portion of the plant, the location of a 1979 nuclear disaster that narrowly avoided being much worse, is being reopened by Microsoft to offset skyrocketing data center power demand.
It's important to stay educated on these projects. Nuclear is promising, especially fusion, but critics have valid fears, as evidenced by past accidents, and often point to the expense and time investments to get nuclear going versus cheaper and less dangerous alternatives such as solar, wind, and wave power.
At Michigan, the experts said more testing needs to be completed before autonomous reactors are stationed in remote locations.
"Next, we aim to close the loop with inverse calibration and high-fidelity simulations to enhance control accuracy," Radaideh said.
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All light water reactors are naturally load following. Increased load reduces turbine speed. This opens steam inlet valves on the turbine, resulting in a reduction of pressure in the boilers (PWR) or core (BWR). Reduced pressure increases the rate of boiling, but also lowers the temperature of the coolant water by removing energy from it. Water is also the moderator, so reducing its temperature also reduces the average speed on neutrons. This adds reactivity to the core, increasing power.
This is a useful characteristic in LWRs. But it becomes problematic during a loss of coolant accident. During a LOCA, there is a sudden loss of pressure in the primary circuit. This causes a power surge, because boiling reduces coolant water temperature. LWRs have trip settings that scram the reactor if neutron detectors see a sudden surge in population. Without out that, the power surge resulting from LOCA would cause fuel damage, because of the lag imposed by heat transfer into the coolant. Delayed neutrons and the use of fixed neutron sources are both used to increase the average lifetime of neutrons. This limits the gradient of a power surge, allowing active control systems time to respond.
Last edited by Calliban (2025-07-30 01:43:05)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The Trump administration is to fast track development of a lunar nuclear reactor.
https://www.zerohedge.com/geopolitical/ … actor-moon
This is expected to be a 100kWe system. This would also be useful in supporting Mars mission and allowing ISRU propellant production.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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With a nod to Calliban's post #13, the Trump Administration is reported to be involved (somehow) in an initiative to restart Uranium enrichment at a site in Kentucky.
https://www.theverge.com/ai-artificial- … lectricity
The economic justification for the restart is power demands for AI.
We were speaking of innovation with Spaniard in another topic today. The article about restarting enrichment included this interesting item:
That’s all driving up demand for uranium enrichment, now seen as a significant bottleneck in the nuclear energy supply chain. General Matter isn’t the only operation seeking to enrich uranium in Paducah. The DOE has had a deal with another company called Global Laser Enrichment (GLE) since 2016 to sell it leftover tails, depleted uranium, from years of enrichment for nuclear weapons and reactors at the site. GLE has been developing a new way to enrich uranium using lasers that’s supposed to be efficient enough to re-enrich uranium tails so that they can be used to make fuel again. General Matter similarly plans to re-enrich depleted uranium tails in Paducah, according to the DOE press release, although we still don’t know what kind of technology it will use to do so.
I'd not heard of using lasers to enrich Uranium before, so would welcome a post by someone who can find more about it.
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Surprise! A closed nuclear plant is coming back online. The article at the link below reports on the decision to restart a closed plant in the US. The costs of renovating an existing plant are so much less than building a new one, it appears that an investment group had decided to take the risks, and they have won approval for the project.
https://www.yahoo.com/news/articles/ene … 00672.html
The Cool Down
Energy company receives approval to revive dormant nuclear power plant: 'An unprecedented milestone in US'
Simon Sage
Wed, August 20, 2025 at 1:15 AM EDTEnergy company receives approval to revive dormant nuclear power plant: 'An unprecedented milestone in US'
Michigan's 800-megawatt Palisades Nuclear Plant may be coming out of retirement, according to Canary Media.
The U.S. Nuclear Regulatory Commission has granted a series of approvals that would give Holtec International the ability to reboot the Michigan power plant.
Palisades has been closed for three years. It would be the first in America to reopen — and only the second or third globally to return after closure. Once operational, Holtec expects Palisades to be able to power 800,000 households.
Nuclear power is seeing a resurgence in America, with both Microsoft and Google spinning up fresh projects to power data centers. New York has plans to build a new plant at a scale it hasn't seen in 15 years.
Despite high-profile historical meltdowns such as Fukushima and Chernobyl, nuclear power is quite safe. Some estimates say that nuclear power has caused fewer deaths than hydro and wind power. Nuclear waste management is also a concern, but much of it can be reused. In fact, France mandates it.
Displacing coal and gas power to reduce their significant pollution and navigating steep political opposition to renewables while meeting rising energy demands is a challenge. Nuclear power is somewhat unique in being able to thread that needle.
The biggest roadblock to nuclear power is the long construction timelines and associated costs. Using infrastructure that's already available helps to circumvent that bottleneck to provide large-scale zero-emission energy. Holtec hopes to have Palisades up and running again as soon as this month.
"This is a proud and historic moment for our team, for Michigan, and for the United States," Holtec International President Kelly Trice said. "The NRC's approval to transition Palisades back to an operating license represents an unprecedented milestone in U.S. nuclear energy. Our mission remains clear: to restart Palisades safely, securely, reliably, and in support of America's energy future — while supporting local jobs and economic growth for decades to come."
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