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Maintinance requirements for a 100MW net power polywell

Posted: Fri Feb 15, 2013 4:33 am
by ANTIcarrot
What would scheduled and ongoing maintenance/monitoring look like for a small off-grid polywell?

Presumably they'd have to load high quality hydrogen and boron ever few months/years. Period shutdowns would also be desirable to visually inspect the insides. Vacuum pumps, fuses, filters may all need changing semi-regularly. If cooling requirements are at the high end, a small water electrolysis and hydrogen liquefaction plant may be required. On the other hand, the polywell itself is almost entirely solid state, and could probably run for long periods of time without human intervention.

So, say one person with their hand next to the scram switch, just for protocol's sake, and a small team looking after the support plumbing? With more if you pursue a policy of aggressive preventative maintenance?

Re: Maintinance requirements for a 100MW net power polywell

Posted: Fri Feb 15, 2013 6:53 am
by hanelyp
Related to maintenance, you might consider what could happen if something did malfunction.

About the biggest Bang I can see in a polywell is a failure and sudden discharge of a magnet, dumping the magnetic energy as heat + an EM pulse in the chamber. Destroys a sector of the magrid, but no danger outside the reactor. Sudden discharge of a direct conversion system could be similarly spectacular, but well contained. All together, no need for a dead man switch for general safety. And if something does need shutting down to prevent system damage, I doubt the dead man switch would be near as fast or reliable as an automatic shutdown.

A failure of the coolant supply would require an immediate shutdown of the reactor, but that can be provided for. Baring an external factor, pump failure should be preceded by bearing noise. Redundant pumps and a few valves would allow one pump to be replaced without needing to shut down the reactor. I figure filters could be inline with pumps.

Refilling fuel tanks won't require an interruption of the reactor.

A camera viewing inside might be arranged to watch the operating reactor in a mirror through a window.

Re: Maintinance requirements for a 100MW net power polywell

Posted: Sat Feb 16, 2013 7:45 pm
by D Tibbets
A Polywell, especially a P-B11 Polywell would not need much maintenance for the reactor itself. Fuel issues and shut down issues are trivial. Quenching of superconducting magnets are a concern but at least several orders of magnitude less compared to an ITER Tokamak type reactor (due to relative sizes). I would expect damage similar to the Large Hadron Collider when it had a quenching accident.

Various support equipment such as vacuum pumps need to be maintained and replaced periodically. Some redundancy , as mentioned, could be built in.

The cooling and steam plant (if employed) might be the biggest maintainance issue, just like it is in Coal fired plants.

If deuterium fusion is used concern about neutron heating of the magnets, and neutron degradation of the magnet and wall materials need to be concidered. With aneutronic fusion, these concerns are much less and possibly irrelevant over the expected lifetime of the reactor.

One issue that may be of importance is the handling of Boron compounds. Unlike hydrogen or Helium 3, it may deposit as a solid on surfaces. This might limit lifetimes of surfaces significantly, have effects on insulators, etc. Also, hydrogen embritalment may be an issue.

The hydrogen in a P-B11 plant would need to be isotopically purified to significantly reduce the deuterium content-this probably would not effect the reactor lifetime issues as the neutrons from D-D side reactions would be rare, but this could be a concern for personnel safety and shielding. Uncertain gamma ray output is also an issue. The Boron11 also would have to be separated from the more common Boron 10. But because of the tiny amounts of the isotropically purified hydrogen and Boron11 needed to make a unit of electricity I suspect the costs involved would be miner. It would be much easier and cheaper than enriching Uranium 235.

Safe storage of a decommissioned reactor or parts is a concern for D-T or D-D fired plants due to the neutron transmutations of materials into radioactive products. Storage up to several hundred years may be necessary (compared to several hundred thousand years for fission plant materials). An aneutronic fusion plant would have much less issues. A few years, or even a few weeks may be all that is needed. To make repairs in a Tokamak would require robotics. A short wait and an aneutronic reactor could be worked on in shirt sleeves. Note that aneutronic is a relative term. Generally less than 1 % of the energy coming from neutron producing reactions is the definition. D-He3 reactors can achieve this, but by a modest margin. A P-B11 reactor may improve on this by a factor of nearly a million. The neutron induced radioactivity varies proportionally. This compared to a D-T or D-D reaction where neutrons carry ~50% or more of the fusion energy.

Dan Tibbets