How weak interaction LENRs can take us out of the nuclear safety and economic black hole Lewis Larsen
Low Energy Nuclear Reactions (LENRs) based on weak interactions and their ultra low momentum (ULM) neutrons not only have the potential to be used for an entirely new source of green, clean energy (see [1] Low Energy Nuclear Reactions for Green Energy and [2] Widom-Larsen Theory Explains Low Energy Nuclear Reactions & Why They Are Safe and Green in SiS 41), they may also solve many serious public safety and environmental problems associated with current nuclear fission and fossil-fuel power generation technologies, and at the same time, dramatically reduce the risks of nuclear weapons proliferation and significantly improve long-term profitability for the global power generation industry.
LENRs have the potential to offer revolutionary business and environmental opportunities such as green low-cost, distributed power generation systems and/or large grid-connected power plants based solely on weak interactions and gamma-shielded neutron captures (see [3] Portable and Distributed Power Generation from LENRs SiS 41), as well as substantial savings on nuclear waste cleanup costs (see [4] LENRs for Nuclear Waste Disposal SiS 41). In this article we shall explore how LENRs could reduce costs and the time it takes for decommissioning old reactors; and the potential for retrofitting certain types of nuclear reactors with safer, cheaper LENR-based subcritical fission heat sources that can replace existing reactor cores. In the next and final article in this series, we shall discuss retrofitting existing coal-fired power generation plants with green LENR-based boilers, an attractive economic option for commercial power plant operators.
As discussed previously [4], compared with neutrons at thermal and higher energies, ULM neutrons generated by LENRs could be extraordinarily effective in triggering nuclear fission in fissile isotopes, and 3 – 4 orders of magnitude more efficient at releasing nuclear binding energy via neutron capture on various 1/v target fuels/isotopes. That is one way in which LENRs could help improve existing fission power technologies.
Strong interaction fission reactions produce extremely energetic products that are much more hazardous than ‘simple’ alpha decays or weak interaction beta decays. Nevertheless, LENR ULM neutron-triggered fission reactions do produce substantially larger total energy releases than the most energetic weak interactions. When 1/v fissile heavy elements [4] such as uranium and/or plutonium serve as target fuels for LENR ULM neutrons, asymmetric heavy element fission releases ~190 – 200 MeV per reaction.
Nuclear binding energy released from fissile target fuels is ~243 to 512 times breakeven energy cost for producing ULM neutrons, depending on whether protons or deuterons are the base fuel for making ULM neutrons. U-235 fission produces a much larger multiple of breakeven than the ~16 MeV released by the green LENR lithium-8 beta decay reaction [2]. Fission releases much more energy than energetic beta and/or alpha decays that occur in LENR systems; also more than ULM neutron captures that typically occur on various isotopes of ‘green’ target fuels such as nickel, titanium, calcium, or even dysprosium (such captures typically release binding energies of ~7–8 MeV [5]; any energetic gammas produced are converted directly into heat by nearby heavy electrons).
Spent fuel now stored in cooling ponds located at nuclear power stations is generally acknowledged to be a source of major hazards [6] Close-up on Nuclear Safety (SiS 40). Developing a technology for the cleanup of high-level nuclear wastes using LENR-based transmutation reactors [4] would remove the hazard of storing them locally and/or shipping them cross-country to secure storage sites such as Yucca Mountain in the US [7]. Nuclear weapons proliferation and environmental risks would be sharply reduced because fissile and/or highly radioactive isotopes would never have to leave commercial reactor sites.
Most existing commercial nuclear power plants are light-water reactors (LWRs), with pressurized-water (PWRs) [8, 9] or boiling-water (BWRs) [10, 11]. In PWRs and BWRs, a nuclear reactor core containing fuel rods and related assemblies is enclosed within a thick, solid steel-alloy reactor vessel inside a thick steel-reinforced concrete containment building. These massive structures contain the radiation and protect the physical integrity of the reactor.
Of 439 nuclear power plants currently operating worldwide, 264 of them are uranium-fueled PWRs, now the most common type in service; and 94 are uranium-fueled BWRs, the second most common type. Light water PWRs and BWRs comprise 82 percent of operating reactors and provide 88 percent of global nuclear power generation capacity [12].
Nuclear power plants cost much more to build than to operate over their entire 20 – 60 year lifetimes. Some 60 percent of total, fully-burdened power generation costs are actually initial capital investment costs [13], exclusive of upstream mining and enrichment or downstream decommissioning and cleanup. In other words, the greater part of the economic costs is required to design, construct, license all of the necessary physical facilities, load the first round of fuel assemblies, and connect to the electrical grid. A financier would say that nuclear power plant facilities have very front-loaded cost structures. By comparison, ongoing variable costs of operation (staff, nuclear fuel, maintenance, regulatory compliance, etc.) are modest. If the costs of upstream mining and enrichment processes are included, the reactor vessel itself and its contents only averages about 18 percent of the total capital cost or roughly 11 percent of the total fully-burdened power generation cost [13].
When present-day commercial nuclear fission reactors are finally retired from decades of service, they must be decommissioned in approved ways to minimize health and environmental hazards [14] (see [15] The Nuclear Black Hole, SiS 40). Worldwide, primarily three strategies are utilized for decommissioning nuclear plant facilities [14]. They are:
In decommissioning after permanent reactor shutdown ~99 percent of the radioactivity that is of greatest concern to human health and the environment is associated with fuel rods and fuel assemblies [14]. The remaining 1 percent of post-shutdown radioactivity comprises the following: water that may be contaminated with radioisotopes; ‘activation products’ mainly found in steel-alloy structural components that were heavily irradiated with neutrons during a reactor’s operating life, including iron-55, cobalt-60, nickel-63, and carbon-14; and trace amounts of radioactive gases that may still be present. Spent fuel removal and disposal is thus a major part of the cost in decommissioning reactors.
Reactor decommissioning costs can be very tricky to forecast. In the USA, many utilities now estimate average costs of US$325 million per reactor (1998 $). In France, decommissioning of the Brennilis Nuclear Power Plant, a fairly small 70 MW power plant, cost 480 millions euros so far (20x initially estimated costs), and cleanup is still ongoing after 20 years. Despite huge investments in ensuring safe dismantlement of the reactor, radioactive elements such as plutonium, cesium-137 and cobalt-60 accidentally leaked out into a surrounding lake, further increasing costs and time. In the UK, decommissioning of the Windscale Advanced Cooled Reactor (WAGR), a 32 MW power plant, cost 117 million euros. In Germany, decommissioning of Niederaichbach nuclear power plant, a 100MW power plant, cost about 90 million euros [18].
I have already mentioned that radioactive nuclear waste in spent reactor fuel rods and assemblies could potentially be processed onsite with LENR technology to transmute waste into complex arrays of non-radioactive stable elements and isotopes [4]. Exactly the same approach could be used to get rid of fuel remaining in nuclear reactors after permanent shutdown. In such cases, using LENRs for cleanup might significantly lower costs and time for decommissioning, and avoid using the ‘safe enclosure’ and entombment options.
Nuclear power’s unusually front-loaded cost structure opens up a potential future business opportunity for plant operators to retrofit and improve existing PW and BW reactors for substantially safer, much less costly subcritical LENR fission power generation that, furthermore, would not produce large quantities of highly radioactive waste. This could be done by replacing current reactor cores with new heat sources based on LENR ULM neutron-triggered nuclear fission.
In a capital-conserving strategy, the majority of the global power generation industry’s enormous financial investment in infrastructure for commercial fission reactors (land, licensing, containment buildings, reactor vessels, steam generators, electrical generators, monitoring and control systems, etc.) could be protected and redeployed with limited economic and technological disruption. Plant operators that took advantage of retrofitting existing reactors with LENR technology would be rewarded with more profitable businesses that have intrinsically lower liability risks; the public and the environment would be rewarded with much safer, less hazardous LENR-based fission power plants that could continue to supply low-cost electricity to regional grids that supply billions of people worldwide.
The production rates of ULM neutrons from LENR reactions, to be used for triggering nuclear fission, range from 1011 up to 1016/cm2/s [3]. Amazingly, these large fluxes were obtained from small, poorly optimized laboratory systems. Yet they are comparable to neutron fluxes that occur in commercial fission reactor cores, which typically range from 1012 to 1014/cm2/s [19].
A ‘subcritical’ fission process [20] is one in which the total flux of fission neutrons during reactor operation is deliberately controlled so as to be insufficient to maintain ‘criticality.’ Put another way, in the absence of another external source of neutrons, there simply aren’t enough fission neutrons produced locally to achieve and maintain self-sustaining fission chain reactions [21] inside the reactor. Importantly, a fission reactor that is running below ‘critical’ will automatically fizzle out within a relatively short period of time.
As ULM neutrons can be used to trigger fission, we have developed proprietary concepts for LENR-based subcritical fission reactors. If successfully developed, potentially retrofitable LENR-based ‘cores’ might provide safety and environmental advantages over existing types of uranium-based fission reactors, or even some concepts for advanced thorium-based reactors [22], all of which depend on criticality to sustain nuclear reactions.
As large fluxes of ULM neutron-triggered high-energy fission neutrons and significant fluxes of energetic gammas would be released during reactor operation, subcritical ULM neutron-triggered fission reactors would still require the same types of radiation shielding and related containment structures needed in today’s reactors. In relying on fission to produce heat, LENR-based subcritical reactors could never be as environmentally green and safe as ‘pure’ weak interaction LENR-based systems that create their heat using substantially less energetic, non-fissile/fertile target fuels that produce heat via a combination of beta/alpha decays and gamma-shielded neutron captures. Nonetheless, LENRs could still improve on existing fission technologies as well as leverage the power generation industry’s existing capital investments in plant infrastructure.
The idea of developing safer subcritical fission reactors for producing power and transmuting nuclear waste is not new; it has been theoretically discussed by physicists for years. Perhaps the first well-publicized subcritical concept was invented by Italian Nobel laureate Carlo Rubbia in 1994. It was called an “energy amplifier” [23, 24] and consisted of a proton cyclotron accelerator combined with a thorium-based nuclear reactor cooled with liquid lead.
Conceptually, subcritical fission reactors depend on a very tightly controlled external neutron source to provide additional neutrons that are absolutely required to keep fission reactions going continuously in reactor fuel. Similar to Rubbia’s earlier energy amplifier, current subcritical concepts [25-31] typically integrate fission reactors with some sort of external particle accelerator to speed up protons. Those protons are then directed at a special target that produces a flux of energetic neutrons via spallation reactions. The neutron flux created by the accelerator beam is then allowed to come into contact with the reactor fuel, adding to neutron fluxes produced by local fission reactions in the fuel. These subcritical reactor designs are called Accelerator-Driven Systems (ADS). No large scale ADS has ever been built, possibly because of the additional expense and complexity of developing and integrating a large, external high-current particle beam accelerator.
The overall rate of fission in an ADS subcritical reactor is controlled by simply altering the accelerator beam current, which in turn controls the required external supply of neutrons. Power generation in the reactor’s fuel goes up or down in tandem with changes in total neutron fluxes (which are the sum of locally produced fission neutrons and moderated neutrons derived from energetic spallation neutrons produced by the accelerator).
A key advantage of subcritical fission reactors is their inherent controllability and safety: if an accelerator producing spallation neutrons is simply turned-off, the rate of fission in reactor fuel slows down and stops reasonably quickly. Uncontrollable ‘runaway’ criticality accidents like the Chernobyl Reactor #4 in the Ukraine (1986) [32] or the Three Mile Island TMI-2 reactor in the US (1979) [33] are all but impossible with subcritical reactors. Importantly, extremely complex, expensive real-time monitoring, control systems, and operating procedures that are necessary for current nuclear reactors to help prevent criticality accidents, would be unnecessary with LENR-based subcritical reactors. This should reduce initial construction costs and ongoing operating and maintenance costs.
Subcritical fission reactors by themselves will not necessarily solve radioactive waste problems. However, LENR-based fission technologies that combine subcriticality with complete waste burnup could potentially solve both problems at once. Given dramatically improved safety and tremendously reduced quantities of ‘hot’ radioactive waste, LENR-based systems might have much lower intrinsic liability risks, reducing insurance costs.
Our proprietary concepts for LENR ULM-based subcritical fission reactors eliminate the cost and complexity of a large external, integrated particle accelerator, replacing it with a lower-cost, better method of ‘in-core’ neutron generation that produces large, highly controllable fluxes of ULM neutrons created in close proximity to target fuels and subsequent nuclear reaction products. This LENR-based approach also handles the post-shutdown residual ‘decay heat’ issue as an integral part of the subcritical reactor design.
While using mainly LENR ULM neutrons to trigger fission would not suppress emissions of high-energy MeV neutrons that normally occur during fission processes (massive radiation shielding and containment structures would still be needed), the approach could still help solve many of today’s nuclear waste remediation and proliferation problems.
Fluxes of LENR ULM neutrons, working together with concurrent fluxes of fission neutrons, would be used to essentially burn up every isotope in fissionable nuclear fuel that is capable of capturing neutrons, including fissile/fertile isotopes, radiologically ‘hot’ fission fragments, and transuranic elements. By carefully controlling and dynamically adjusting the ratio of ULM neutron fluxes to concurrent fluxes of much higher-energy neutrons generated by fission processes, as well as to the isotopic composition and current numbers of available target nuclei, there would be essentially no radioactive waste remaining after fuel burnup; nuclear waste remediation would then cease to be a costly problem for plant operators.
Achieving effectively 100 percent burnup down to stable isotopes could also solve most reactor decommissioning radioactivity issues, because storage and disposal of radiologically ‘cold’ spent fuel remaining in an LENR-based fission reactor after permanent plant shutdown would not pose any serious safety or environmental hazards.
In LENR-based fission reactors, time needed to burn new, nanoparticulate fuels down to stable isotopes would vary, depending on the target fuel, operational and design details of a given reactor, and anticipated power demand over some time interval. It would likely require less than a few weeks for complete fuel burnup; not months or years.
Another important distinction between our LENR-based fission concepts and present reactor technologies is the physical form of nuclear fuel. Instead of being fabricated in the form of macroscopically large, cylindrical fuel rods [34] or ‘pebbles’ [35] (see [36] Safe New Generation Nuclear Power?, SiS 29), LENR target fuels would be in the form of specially designed and fabricated nanoparticulates (dispersed in gases or liquids) that have extremely high surface-to-volume ratios. By employing nanotechnology, this new type of nuclear fuel could be mass-produced inexpensively and would enable very rapid, complete burnup of target fuels down to ‘cold’ spent fuel comprised of stable isotopes.
Nanoparticulate target fuels utilized in commercial versions of LENR-based subcritical fission reactors would be loaded into and stored in separate nearby, deeply buried, secure underground fuel repositories. Although nanoparticulate fuels and hydrogen isotopes stored in such repositories would be densely packed, their composition and placement would be designed such that even densely packed masses of fresh fuel would remain very far from criticality under any conceivable scenario.
Compared to macroscopically large fuel rods or ‘pebbles’, high surface-area nanoparticulate fuels and LENR ULM neutrons should be able to produce much more complete energy release from target fuel before being ‘spent.’ This would substantially increase heat production from a given quantity of fissile material (e.g., uranium-235), thus improving plant profitability. Essentially 100 percent burnup of fissiles in LENR-based reactors would also eliminate any need to reprocess spent fuel to recover and burn valuable fissile isotopes. That should ease nuclear proliferation risks, as significant quantities of weapons-usable fissile isotopes would not be present in LENR-based reactors’ spent fuel.
At any given time, today’s commercial fission reactors may contain anywhere from 1 to 3 years worth of unburned uranium-235 fuel, as well as substantial quantities of other fissile isotopes (e.g., plutonium-239) and dangerous nuclear wastes. By contrast, use of nanoparticulate fuels in LENR-based subcritical fission reactors could eliminate the need to have large quantities of unburned fissile fuel and ‘hot’ wastes present inside LENR fission reactors during normal operation; nanoparticulates create this new capability because they enable dynamic injection of fuel into reactors.
The ‘heart’ of an LENR-based fission reactor could be conceptualized as a ‘nuclear combustion chamber’ in which: large concurrent fluxes of LENR ULM, moderated, and ‘fast’ fission neutrons are produced; neutron captures occur, triggering nuclear fission and a broad array of different transmutation reactions; and raw heat is generated for transfer and conversion into electricity by a system’s integrated thermal generators.
Akin to a combustion chamber in an IC engine, LENR-based subcritical fission reactors would be able to dynamically inject intentionally limited quantities of nanoparticulate target fuels and hydrogen isotopes into the ‘working region’ of a reactor. Such periodic injections would deliver only the minimum amount of fuel necessary to meet anticipated power demand during a period of a few days to perhaps a week or two.
When additional nuclear fuel is required to continue to generate power, necessary quantities of target fuel would be very quickly and securely conveyed from undergoing repositories and injected into an LENR-based reactor’s ‘combustion chamber.’
Unlike today’s nuclear plants, long-term refueling of LENR reactors would not involve a significant plant shutdown; it could be accomplished simply by unloading nanoparticulate target fuels and hydrogen isotopes directly from transport containers into secure underground repositories located at reactor sites.
Current PWRs/BWRs and most future ‘Gen-4’ nuclear reactor concepts (likely deployment would be circa 2030) typically have years’ worth of unburned fuel and waste products present in a reactor at any given time. By contrast, LENR subcritical reactors’ separate secure underground storage of fresh nuclear fuel, dynamic 'on-demand' injection of just enough fuel into reactors to satisfy relatively ‘near-term’ power demands, and complete fuel burnup, are revolutionary features unattainable in today’s reactors.
Unlike comparatively inflexible fuel requirements of today’s nuclear reactors, commercial LENR-based power plants could be extraordinarily ‘fuel-flexible.’ They could be designed to be able to utilize and switch between nanoparticulate fissile and/or fertile target fuels comprised of uranium, uranium-plutonium mixtures (MOX), and/or thorium isotopes. Uranium at any level of enrichment could be burned. Using integrated mass spectrometers, real-time computer modeling of fuel burnup, and digital sensor systems to dynamically monitor and control fuel burnup processes, LENR-based power plants could safely burn a variety of target fuels and reaction products down to a complex array of stable isotopes [4].
Use of nanoparticulate target fuels and LENR ULM neutrons could provide nuclear fuel suppliers and plant operators with unprecedented economic flexibility to dynamically vary and blend least-cost fuel mixtures in response to energy-equivalent market prices of alternative fissile and even non-fissile ‘target fuels.’ Unlike today’s nuclear plants, LENR-based reactors could switch among a variety of competing fissile or non-fissile target fuels or reasonable combinations thereof. When burning non-fissile, non-fertile target fuels, large fluxes of energetic neutrons and hard gammas would not be produced in LENR-based nuclear reactors; in that situation, massive shielding and containment structures are superfluous. In that case, the plants’ operating safety margins would be even higher.
As world uranium supplies decrease over time, there may come a day when the energy-equivalent economic price of fissile uranium or MOX becomes substantially higher than the price of alternative, less energetic non-fissile target fuels. In that event, LENR-based subcritical fission reactors could switch to burning less expensive fuel to reduce costs; today, certain non-nuclear ‘multi-fuel’ power plants [37] can readily burn a variety of fossil fuels.
If LENR-based subcritical fission reactors were successfully developed and deployed, fissile and/or fertile nanoparticulate target fuels (uranium, thorium, or MOX mixtures) would be transported under guard in thick bomb-proof casks from limited numbers of secure, government-licensed nuclear fuel production facilities to commercial power plants. Target fuels would then be ‘burned’ down to ‘cold’ stable isotopes in plants’ reactors.
As recoverable fissile isotopes and high-level radioactive waste would not be present in spent fuel from LENR-based reactors, further transport of spent fuel to physically distant sites for subsequent reprocessing to recover fissile or fertile isotopes would be unnecessary.
Spent fuel waste products comprising almost entirely stable elements could be readily stored or buried locally in other types of secure repositories that prevent contamination of groundwater. Alternatively, ‘cold’ spent fuel could be shipped from commercial reactors out to other locations for processing and recovery of valuable transmutation products such as palladium, platinum, gold, silver, etc. or simply buried in government-certified landfills.
Terrorists could do little to compromise integrity of underground fuel repositories short of using gigantic explosions to open them up. Assuming that such an objective was even achievable, such acts would create little additional mayhem, as releases of unburned nanoparticulate reactor fuel from repositories would be comparatively benign events.
Today’s criticality-based fission reactors are potential terrorist targets because large quantities of ‘hot’ radioactive waste are almost always present in fissioning fuel rods during reactor operation and/or in spent fuel assemblies stored in onsite cooling ponds. In contrast, future LENR-based subcritical fission reactors would contain only comparatively limited quantities of unburned fuel and very little hazardous waste in their ‘combustion chambers’ or stored onsite (cooling ponds are unnecessary as final LENR-based fission waste is ‘cold’). This characteristic would drastically reduce health and environmental risks associated with successful acts of terrorism on LENR reactors.
In a worst case terrorist attack scenario (e.g., crashing a very large aircraft into key containment buildings or striking them from the air with a small tactical nuclear weapon or large conventional 'bunker buster' bomb), this unique characteristic of LENR subcritical fission reactors means that a well-designed system could be totally destroyed during operation, yet would still release only minuscule amounts of hard radiation and ‘hot,’ long-lived isotopes into the environment. Compared with today’s systems, LENR-based reactors could greatly reduce the likelihood and consequences of nuclear terrorism.
A number of different concepts for ‘Gen-4’ fission reactors have been promoted by advocates of nuclear power. Two popular Gen-4 reactor concepts are the Integral Fast Reactor (IFR) [38] developed at the US Department of Energy’s Idaho National Laboratory and the Liquid-Fluoride Thorium Reactor (LFTR) [39], which was explored in the US from the 1950s to 1970s.
Table 1 is adapted from a chart presented in a talk on LFTRs given by Dr. Joe Bonomettis at Google.org on 18 November 2008 [40]. The modified chart compares selected characteristics of a typical Gen-2 LWR with a Gen-4 thorium LFTR as well as our concept for a subcritical LENR-based fission reactor. Assuming that Lattice’s concepts can be successfully developed as envisioned, Table 1 reveals that LENR-based fission reactors could be very attractive:
Table 1. Comparing
Uranium (LW),Thorium (LFT), and LENR Fission Power Reactors
| Important Characteristics | Reactors utilize criticality to burn fuel | Subcritical | |
| Gen-2 U-235 LWR | Gen-4 Thorium LFTR (U-233, MOX) | LENR Subcritical | |
Need massive shielding/containment? | Yes | Yes | Yes |
Overall plant safety | Better Than Gen-1 | >> Better than Gen-2 | Best (subcritical) |
Burn existing nuclear waste? | Limited | Yes | Yes |
Radioactive waste volume (relative) | 1 | 1/30th of Gen-2 | Almost zero |
Waste storage requirements | 10 000+ years | ~200 - 300 years | ~0 years |
Produce large amounts of fissile isotopes? | Yes | No | No |
High value nuclear by-products? | Limited | Extensive | Even more extensive |
Operating pressures / op. temperatures | High / Lowest | Low / Higher | Low / Highest. |
Fuel type | Solid Rods | Liquid | Nanoparticulate solids dispersed in gases or liquids |
Fuel burning efficiency | <25% | >95% | ~98 -100% est. |
Can reactor burn non-fissile/fertile fuels? | No | No | Yes |
Fuel flexibility | Limited | Much Higher | ‘Omnivorous’ |
Fuel fabrication/qualification | Expensive/Long | Cheap/Short | Cheaper/Shorter |
Fuel mining waste volume (relative) | 1 000 | 1 | < 1 |
Fuel reserves - global (relative) | 1 | > 1 000 | > 1 000 000 est. |
Can reactor have dynamic fuel injection? | No | Yes | Yes |
Plant cost | 1 (high pressure) | <1 (low pressure) | <<1 (many reasons) |
Plant thermal efficiency | ~35% (low temp.) | ~50% (higher temp.) | >60% (highest temp.) |
Cooling requirements | Water | Water or Air | Water or Air |
Retrofit to existing nuclear power plants? | Not Applicable | Unclear | Yes – can design for it |
Terrorists totally destroy reactor | Nuclear Disaster | Lot Less Disastrous | Limited Local Effects |
Development status | Deployed | Demo’d. 1950-1970 | Concept Stage |
Adapted from chart in [40]; other data estimated or compiled by Lattice Energy LLC
The author declares his commercial interest as President and CEO of Lattice Energy LLC.
Article first published 26/01/09
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