»Safe Nuclear Power and Green Hydrogen Fuel

Danger aside, what makes nuclear power attractive?
~ it’s competitive or cheaper than other forms of power generation
~ it’s easy to build compact plants that generate hundreds if not thousands of megawatts
~ – something wind and solar can never hope to match
~ compared with coal, still used to produce 50% of the US electricity needs, nuclear is clean
~ it creates no greenhouse gases
~ its waste, although highly toxic, is compact and when handled correctly, safe
~ uranium, the fuel reactors use, is widely available in the continental US and Canada, Australia has the largest known reserves
~ this makes it unlikely rouge states can affect supply
~ stable supply means lower long-term costs – especially when compared with oil and gas fired plants which are producing about 20% of US electricity
~ Reactor designs such as the Canadian CANDU can be very safe and less expensive to build than most reactors in use today
~ one drawback to this design, unfortunately, is its ability to produce weapons grade plutonium as a byproduct
~ on the plus side, it can use unenriched uranium – about .07% uranium 235, regular plants require between 2% and 7% uranium 235 in reactor fuel to run properly

PRBs
~ physicists and engineers at Beijing's Tsinghua University building a new nuclear power facility: a pebble-bed reactor (PBR)
~ – sometimes also known as a Pebble Bed Modular Reactor (PBMR)
~ is small enough to be assembled from mass-produced parts and cheap enough for emerging economies
~ its safety is a matter of physics, not operator skill or reinforced concrete
~ this reactor is meltdown-proof
What makes it so safe is the fuel:
~ instead of conventional fuel rods made of enriched uranium, PBRs use small, pyrolytic graphite coated pebbles with uranium cores
~ as a PBR reactor gets hotter, the rapid motion of atoms in the fuel decreases probability of neutron capture by U-235 atoms
~ this effect is known as Doppler Broadening
~ nuclei of heated uranium move more rapidly in random directions generating a wider range of neutron speeds
~ U-238, the isotope which makes up most of the uranium in the reactor, is much more likely to absorb the faster moving neutrons
~ this reduces the number of neutrons available to spark U-235 fission
~ this, in turn, lowers heat output
~ this built-in negative feedback places a temperature limit on the fuel without operator intervention
~ PBRs use high-pressure helium gas, not water, for cooling
~ reactors have been “run dry” – without cooling gas
~ result: they simply stabilize at a given temperature – lower than the pebbles’ shell melting point
~ no meltdown can occur

PBR from PBMR, South Africa
~ South Africa may have the most modern PBR on the drawing board
~ with the help of German scientists – acknowledged leaders in the field - planned to build several reactors within the next five years
~ the reactor core is a bin of uranium fuel pebbles
~ each tennis ball-sized pebble is rotated and/or checked for reactivity by removing them from the bottom of the funnel shaped reactor core
~ spent pebbles are replaced by adding new ones at the top of the stack
~ used ones that are still reactive also go to the top of the bin
~ the reactor can be re-fueled without stopping power production
~ – not possible in conventional rod reactors which requires a full shut down
~ pebbles, because of their round nature, allow the cooling gas to be introduced at the bottom and pass freely through the stack
~ the heated gas is removed to perform work like spinning a turbine to generate electricity then recycled in a closed loop back to the reactor core
~ PBRs use helium, which has high thermal conductivity and inertness (read: fireproof and noncorrosive) for cooling
~ this makes them more efficient at capturing heat energy from nuclear reactions than standard reactor designs
~ the ratio of electrical output to thermal output is about 50%

The high-temperature gas design also has a silver lining – it can produce hydrogen
~ generation of hydrogen has been the biggest stumbling block to it adoption as a clean fuel
~ hydrogen, found primarily in water, is expensive to extract as a gas
~ while the technical problems of handling, storage and use as fuel are largely solved,
~ the high energy cost to produce hydrogen has made it an energy transport medium, not a source
~ these new reactors run at high temperatures which are perfect for cracking abundant water or helium gas into hydrogen
~ PBRs could produce cheap hydrogen that could be piped to areas of need or used in the local communities
~ plant sites are much smaller than traditional nuclear power plants
~ their modular design allows for smaller plants that can grow with needs
~ a single PBR reactor would consist of one main building covering an area of about 1,300 square meters – less than half a football field
~ it would be about 42m high (6 stories), some of it below ground level
~ billion dollar steel reinforced concrete containment vessels are not required –
~ any coolant leak would be in the form of nonradioactive helium gas which would quickly disperse with out causing any ill effects