[Power] Aug 21 solar eclipse will reduce US energy generation by 9MW

[The Natural Philosopher]

Its not hard.

Just switch the solar off anyway.

Oh. It's on peoples rooves. hahahahaha.

[dennis]

Depends on the thermal mass in the core.

IIRC the AGR reactors we had(have?) can take days to warm up and presumably as long to cool down.

Boiling water reactors are somewhat quicker to respond.

[Chris Hogg]

It's here

[Mike Tomlinson]

En el artículo , Chris Hogg escribió:

Thank you. The Taggespiegel link in the first para is the one I saw (auf deutsch).

[newshound]

Going back to Privatisation and the original Pool system, it was accepted that it was better for plant longevity not to load follow with UK gas cooled reactors, and they had the happy concession of allowing to stay on the grid once they had been scheduled. They couldn't be "forced off" other than in exceptional circumstances. The old Pool system meant they could always "bid zero", so as the cheapest plant they were always scheduled on.

I believe it has all changed under NETA, but that is far too difficult for this bear of little brain.

Load following leads to temperature cycling of fuel and all sorts of other plant, giving thermal stress cycles and hence burning up the fatigue life.

There are also some subtleties in the nuclear physics if the power cycles are large.

My understanding is that the French pressurised water reactors are load cycled somewhat, although of course they manage national demand variations a lot by exporting surplus.

In fact the British AGRs do load cycle to some extent, because they have to reduce power during "on-load" refuelling.

[newshound]

It's a bit simplistic, but there is some truth to it.

Back when Fast Reactors were still under active consideration, there was some perception that these might be nasty and difficult to control, compared to the more lumbering thermal reactors.

One of the top management guys (I forget who) used to cover this in talks to the "informed" public.

His analogy was that people thought of thermal and fast reactors as being a bit like lorries and racing cars, and that this was, in fact, correct. In those days, as long as they were not actually being driven at racing speeds, racing cars were relatively well-behaved and easy to control. Articulated lorries were not as it was all too easy to jack-knife. This phenomenon can be described by engineers as a "spatial instability". And in fact physically large thermal reactors like the old Magnox plant do have thermal instabilities. You get temperature oscillations across the diameter (timescale tens of seconds) where one half rises while the other cools, and then this reverses. It's rather like some of the vibration modes in a drum-skin. If you think of the core as having four quadrants (N-S-E-W) you get oscillations where the temperature of N and S rises while E and W falls, and so forth.

This sort of thing is a pain in the neck for operators, because obviously you want the outlet gas to be as hot as possible, but there is an upper temperature limit set by materials. If temperatures are oscillating and you don't breach the maximum temperature limit, then your *average* temperature is below the optimum.

However, these oscillations don't run out of control in UK reactors because other intrinsic factors take over. The reactors have a negative temperature coefficient of reactivity, for various reasons a rise in temperature automatically has the same effect as slightly inserting the control rods.

[newshound]

It's not so much the thermal mass of the core, it is that the power is deliberately raised gradually to allow things to heat up uniformly, thus limiting the thermal stresses. It's the thermal diffusivity that matters, not the specific heat.

It's (sort of) the same reason that if you are towing a dead car, you edge forward until the tow rope is tight, and then pull off gently. Not bothering to do this and accelerating hard with a slack tow-rope leads to unintended consequences.

[Mike Tomlinson]

En el artículo , dennis@home escribió:

We still have them. Hinkley B has just auto-tripped due to a gas pump failure.

[Mike Tomlinson]

En el artículo , newshound escribió:

Presumably this is less of an issue in modern reactors because the materials science is better understood?

I seem to remember that the RBMK reactor at Chernobyl had a positive CoR, and this was one of the major factors that contributed to the accident.

That was a fascinating post, thank you.