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December 04, 2009

Nano to Macro Scale Nuclear Technology Applications


Betavoltaics can store about one million times more energy than other battery like devices but currently cannot release it very quickly.

Nano-to-Macro Scale Engineering Applications of Nuclear Technology-An Overview by Rusi P. Taleyarkhan, School of Nuclear Engineering, Purdue University (7 page pdf)

Nuclear science and technology offers the capability for radical industrial innovations from the nano-to-macro scales and is a field that already impacts over $600B in annual worldwide activity. Areas impacted are as diverse as medicine, industrial process control, energy, explosives, materials processing, agriculture, food preservation, sterilization, non-destructive interrogation for the molecular structure of compounds to use as tracers for transport and the tracking of fluids. This paper focuses on novel nano-macro scale peaceful applications for the oil-gas industry, for the metals industries, for enabling fundamental advances in boiling heat transfer, for induction of super compression in imploding bubbles to then lead to thermonuclear fusion and energy amplifications of over x one million times compared to chemical sources, to generation of nanopores in materials that may see applications such as for high-efficiency membranes for use in batteries and for dialysis, to the development of a novel class of low cost, multidisciplinary, fundamental particle detection systems.


Nuclear safety studies have spinoffs that improve safety in other industries. It has helped to improve the understanding and safety for handling liquid natural gas and help prevent aluminum-water explosions.

The Science of Nuclear safety has also resulted in advancements with supercooled powders. Nano-micron scale supercooled powder production using spontaneous molten metal-water explosions (e.g., 10g Sn at ~1100 K dropped into water bath at ~310 K); Cooling rates estimated to be in range of 100,000 K/s to one million K/s.





Enhancement of boiling heat transfer and hydrophilicity via irradiation

Some of the most wide-ranging phenomena utilized in every-day life involves hydrophilicity and the boiling of water at hot surfaces. This aspect governs the safety limits and consequently, the power output of water-cooled nuclear reactors; for a 1,000 MWe plant, even 1% enhancement implies power generation availability for an additional 10,000 homes (based on per capita electricity consumption in the USA). Enhancement of boiling heat flux for a given system has enormous significance and implications on economics and safety of operations (including that of nuclear reactors). Radiation treatment of solid surfaces appears to provide such a means as has been noted lately in several nuclear safety-motivated studies (Honjo, 2008) wherein gamma radiation has been shown to improve surface hydrophilicity and enhancement of critical heat flux (CHF) by an impressive ~ 10%, as well as delaying the onset of the well-known Leidenfrost point of the boiling curve – thereby, fundamentally impacting quenching characteristics of hot metals.


Betavoltaics

The promise and potential of betavoltaics is immense. This primarily due to recent advances in a combination of areas related to:
(1) isotope production and potential availability at reasonable cost;
(2) significant advances in novel radiation-hard semi-conductor chips that can be micro-to-nano-fabricated; and,
(3) leap-ahead advances in intrinsic conversion efficiencies; as also from significant advances in photo-voltaic technology.

Unlike the ~ 1 eV energy level of visible photons used for photovoltaic cells, beta energies from isotopes are in the 100,000 – one milllion eV range, and thus can provide unsurpassed higher-energy densities for application in confined quarters.

The theoretical conversion efficiency of a betavoltaic increases sub-linearly with increasing semiconductor bandgap. The direct-conversion technology results in a number of advantages over conventional power sources: Long-lived power: Continuous current is produced during the entire decay period of the radioisotope source. The use of isotope sources with half-lives that range from years to decades allows continuous power production for similar periods. Examples include 204Tl ,85Kr , 90Sr, 147Pm and 3h with half-lives of 3.8y, 10.8y, 28.8y, 2.6y and 12.3y, respectively. Recent advances in efficiency of conversion to > 10% as well as materials degradation with 247Pm type isotopes and related studies using 3H at Purdue University will be discussed at the conference.

Comment from Regular Reader Goatguy

The betavoltaic concept is actually intriguing from a number of perspectives.

Let's go with the obvious gotchas first: it is not a 'public' technology no matter how packaged. It is absolutely impossible to imagine ordinary consumers having megacuries of isotopes either in their homes, vehicles or general workplaces. It also is only marginally a commercially-feasible concept: the same security issues exist, and it won't be placed into all but the most hardened secure locations. So ... "big business" is about it, with security forces, cards, cameras, fences, reconnaisance, etc. The military is an obvious (but again, strangely, compromised by the 'tight security' issue!) placement, as are utilities, police forces, municipal entities, heavy industry, mining & exploration, shipping and rail, and the like. Aerospace, yes - especially so.

So.

First, the diagram is wrong. The semiconductor would be on both sides of the isotope. (duh). The beta electrons aren't particularly inclined to to one way or the other.

Second, beta has an extremely short free path through solids. Therefore only the thinnest films of it (and the thinnest barriers through the semiconductor) allow for efficient tunneling and capture.

Third, The cells would most likely be chemical-vapor deposited so that thousands of layers per centimeter could be built up. there is a COST to that (though it is also readily mass-producible)

Fourth, using shorter half-lives, typically with higher beta energy, energies of 100Wh/kg (360kJ/kg) aren't out of the realm of the possible. Combined with conventional emerging super-caps and conventional Li-ion battery systems having a net power density of 200 kJ/kg and specific energies up to 1000+ W/kG are clearly achievable.

At the dozen-kilogram level, such power systems might be perfect for remote data loggers where photovoltaic is out of the question. Satellites wouldn't need the batteries, but could probably use the super-caps, to allow them to work in burst mode over long lifetimes.

At the megagram (ton) level:

100 watt, peak, practical cell
50% weight utilization
50.00 =W/kg
180.00 =kj/kg-hr
0.05 =kWh/kg
1000 kg (proposed)
50.00 =kWh/kg/h
1,200.00 =kWh/kg/day


producing over 1,000 kWh/day of electricity...

2,500 heat kWh
9,000,000,000 joules
9,000,000 BTU
375,000 BTU/hr

So, removing the 375,000 BTU with simple air-cooling would be satisfactory.

the biggest problem there would be having triplicate or quadruplicate cooling systems to keep the 'energy block' from melting down in the event of a coolant breakdown. Probably "different systems" - underground aquifer tap + air cooling + "city water" cooling as a backup.

There are quite a few businesses that could use such power densities, and autonomy from the grid. Computer facilities in particular come to mind, if for nothing but the "core-core" equipment and routers, telecommunications and robotic systems-control apparatus.

Another player might be municipalities - especially rapid-transit 'underground' type systems. Virtually all substations can be quite hardened (and secured, and surveillance watched), and the net availability of the baseline power (with capacitive storage) is ideal for running the nominal system without purchasing much grid power.

I don't think there is much of a need though for systems larger than a few tons, say 10 or so megawatt-hours/day. Reason is, the systems rapidly approach the size where compact natural-gas generation, or pebble-bed nuclear systems have much higher energy density for the weight and footprint.

Police stations could use the devices at the several-ton level to generate baseline electricity (and deliver it quickly by the capacitive discharge route) for fleets of flywheel cars, or fast-charge ionic battery systems. (Busses could use this too). Here, the only real metric is whether the cost per megajoule of the betavoltaic power is no more than a factor of 2 greater than grid power. Why 2? Because at a 2:1 parity, in the event of a long-term electrical failure, the fleet of cars wouldn't diminish by more than 25% or so to keep law and order.

Significantly: if the cost per kilowatt-hour of electricity is even reasonably close to the grid wholesale level, then the technology is an easy "must buy" - since with all likelihood, the plateauing production of oil combined with the necessarily increased demand for it by route of India, China and the whole Far East ... is going to cause baseline grid electricity to markedly increase in price in the not too far future.


FURTHER READING
Previous coverage of liquid nuclear betavoltaic batteries

In 2007, IEEE Spectrum reported that DARPA wanted GTI (one of the betavoltaic companies) to run full speed toward proving that a reactor of the 100- to 1000-kilowatt scale could be built.

A liquid nuclear diode could catch energetic alpha and beta particles, gamma rays, and even the new atoms left over from the fission of larger atoms, Tsang says. Fissile fragments could be a particularly good source of energy. In the fission of U-235, for example, the fragments carry 85 percent of the energy released. Because the fragments are heavy, as they plow through the semiconductor they ”make a shower of electron-hole pairs along the path,” he says.

Note: Alpha radiation (positively charged helium nuclei) and beta radiation (electrons).


MIT Technology Review reports on Widetronix's batteries are made up of a metal foil impregnated with tritium isotopes and a thin chip of the semiconductor silicon carbide, which can convert 30 percent of the beta particles that hit it into an electrical current. "Silicon carbide is very robust, and when we thin it down, it becomes flexible," says Widetronix CEO Jonathan Greene. "When we stack up chips and foils into a package a centimeter squared and two-tenths of a centimeter high, we have a one microwatt product." The prototype being tested by Lockheed Martin produces 25 nanowatts of power.

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