Michael Portillo visits Hunterson B reactor

[Andrew]

On now, on BBC2, "Great Coastal railway Journeys"

[Brian Gaff (Sofa]

I wonder if powering a train with a nuclear reactor might be possible. It would certainly be heavy enough to not suffer from leaves on the lines!

Brian

[newshound]

There was certainly an illustration of one in the Eagle back in the 50's or early 60's. Just a concept of course, I don't recall whether there were car and plane versions.

Certainly technically feasible with an open cycle secondary circuit; might be more difficult with electric or mechanical drive from a steam turbine.

[The Natural Philosopher]

Trains are already powered by nuclear reactors.

No need to put them on the train when you have overhead cables.

Fixed reactor with plenty of access to cooling water is a far more efficient reactor than one stuck in a loco.

[Chris Hogg]

Fireball - a molten salt reactor only 1.4 metres in diameter, designed for aircraft to obviate the need for landing to refuel. Never got beyond the development stage because it was superceded by in-flight refuelling for conventional aircraft. IIRC although a reactor was installed in a plane, it was never actually used to power that plane, and the shielding needed to protect the crew was significant.

[Steve Walker]

Probably not possible within the loading gauge. However, what is the point, when it is simple enough to have fixed generators and overhead line?

[newshound]

Good point!

[newshound]

Not easy to provide the usual amount of shielding, certainly. DFR designed back in the 1950's produced 14MWe from a core the size of a dustbin. Some of the Soviet satellite reactors produced > 100kW thermal power from units with dimensions < 1 metre weighing a few hundred kg.

So I'd still say it was technically feasible. Not that I'd argue it was a good idea. Ball-park calc for something with a metre of lead for shielding would weigh ~ 200 tons (cylinder 3m long and 2.5m dia), but at least that would fit into a locomotive sized envelope.

[Andrew]

Connecting the nuke output to the rails would turn them into electric oven elements and burn off the leaves etc :-)

Andrew

[Andrew]

Adding overhead lines to existing track is very expensive and a visual eyesore in many pretty parts of the UK. Southern region had the right idea back in the ?1930's. De-icing is a nuisance but that can be done by the same trains used to blast leaves off the line.

[Theo]

Third rail is more expensive than overhead lines, because third rail is 750V DC and so needs a lot more amps compared with 25kV AC. That means you need to have substations - and associated grid feeds - every few miles, versus many tens of miles with AC. It is also harder to regenerate with DC because you can only feed regen into another train in section, whereas with AC you just backfeed into the grid[1]. You may need banks of resistors at the substation to absord regen power if there's nowhere else for it to go.

Also, Southern Region third rail is now banned for new systems because it has an exposed live conductor. Increases risks for staff and others who stray onto the railway (eg passengers on broken down trains). Modern DC systems have a shrouded conductor to reduce this risk.

Theo

[1] In theory it could, like a solar battery+inverter, but I'm not sure any of them do that. Probably there are not 750V multi-kA inverters easily available.

[Tim Streater]

A third rail system I took from New York some years ago had the rail, and the shoe, inverted. Instead of the show pressing down on the rail, it pressed up on the rail wwhich was a foot or so above ground. This helped protect it from show, of which they have much in those parts.

I have to say I'm not impressed by the exposed conductor argument. And there's no way you could change it now.

[newshound]

When I was a lad, my alternative route to school involved a footpath crossing the commuter line from Leatherhead to Waterloo. There were stiles or small gates either side, wooden sleepers providing a level walkway across the main lines (like there used to be on level crossings) and the third rails terminated about 15 feet clear of the crossing on each side. I don't recall *any* stories of electrocution anywhere on those lines when I was a kid. Brave souls (not me) would occasionally go up and kick the live line, without apparent effect. Of course they would have been standing on ballast at that point, I don't recall anyone trying it while standing on the main rail. And certainly never heard of anyone chucking a piece of wire to bridge between these rails. The most destructive thing anyone did was place a copper coin on the main rail, and hope to retrieve it after passage of the train. I always did wonder what you would have to get a shock.

Now, every year or so you seem to hear of a kid getting fried by accessing overhead wires from a bridge.

[charles]

I believe overhead lines carry a much higher voltage than 3rd rail.

[Tim Streater]

Sure but thass not the point.

[williamwright]

He must have been mentally ill.

Bill

[Chris Green]

It is to quite a significant extent, The third/fourth rail electrics are around 600 volts if my memory serves me correctly, the overhead wires are 11kv. Any sort of touch of the overhead wires is likely to be fatal if you're one the ground. Touching the live rail isn't a very clever idea but isn't necessarily instantly fatal, it would depend very much on how good a route to earth you provided.

[NY]

25 kV. The crucial thing with that sort of voltage is that you don't have to touch the wire: you can get a spark jump across a gap (especially in damp weather) when you are close to it.

[Theo]

It is often staff at greatest risk, because they're on the railway every day. This kind of thing:

Many bridges have protection so it's not possible to come within arcing distance of the 25kV. It's not perfect, but stops many accidents. Further, being on a 25kV electrified track is generally safe (apart from the risk of being hit by a train, of course)

On the other hand, on third rail it doesn't need much to have this happen:

Theo

[Chris Green]

It's not universal though it is becoming standard, there's apparently still a lot of 15kv 16.666Hz in Europe.