On 17-Jun-16 9:49 AM, Chris Hogg wrote:
On Fri, 17 Jun 2016 09:09:09 +0100, Nightjar
wrote:

On 16-Jun-16 9:58 AM, Andy Burns wrote:
Nightjar wrote:

In the 1970s, the Soviet Union built a series of remote lighthouses
along their northern coast, which ran off individual subcritical
reactors.

Yes, but with enough juice for a light bulb ...

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Terrestrial


Isn't a light bulb basically all that a lighthouse needs?

Bulb wattages vary widely. Here's a big one of 3 kW
http://tinyurl.com/hdbxwl5 . But modern LED arrays probably use much
less. But in older lighthouses, you also needed to supply the power
for turning the huge (and technically and aesthetically rather
beautiful IMO*) Fresnel lens systems**. Although the bigger ones
typically weighed several tons, they floated on a bath of mercury so
actually required very little effort to turn them once the initial
inertia had been overcome***. In older, manned lighthouses, this was
manpower, literally. The lighthouse keepers would regularly (every few
hours) have to wind up a falling-weight system that rotated the lens
(think Grandfather clock), but later, on unmanned lighthouses the
power had to come from another source, usually electric, from diesel
generators and batteries IIRC.

* Images here http://tinyurl.com/z2kpsu8 The bigger and heavier ones
stand several feet high.

** A rotating lens system was essential, to give the appropriate
number of flashes per minute that identified the particular
lighthouse, rather than just switching the lamp on and off repeatedly,
which as we all know, shortens the life of the bulb dramatically. The
Fresnel lenses were very efficient at gathering the maximum amount of
light from the bulb and focusing it where needed. Ranges were
typically 20 miles or so, depending on lighthouse height, bulb power
and atmospheric conditions.

*** There used to be the national lighthouse museum run by Trinity
House in Penzance some years ago, and they had several in a range of
sizes. The biggest floated in a mercury bath and could be turned with
one finger. But Trinity House closed the museum in 2005 and I think
the collection was broken up and dispersed. An absolute tragedy and
disgrace!


Although they are described as lighthouses, the vast majority of the
Soviet nuclear powered lights were little more than navigation beacons.

There is one that often appears in photos, which does have all the
gubbins of a full blown lighthouse and that has radiation warnings, but
it also has diesel generators and large fuel tanks, so the reactor was
obviously not there to run the light. Perhaps it ran a backup system to
call for attention if the main power failed.

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Colin Bignell