Heat wave: decrease in nuclear production

[jean.caissepas]

Yes of course but with 10 times less cooling needs eh ...

The 2nd article says that the power plant only needs 6 m3 / s to be cooled properly and that the flow is 20 m3 / s there ... there is therefore a safety factor of 3.

For information, EDF only has the right to raise the temperature of the river water by 1 degree, for the protection of flora and fauna (ATTENTION figure of 1990, which may have changed).

This explains why they must stop producing if the threshold should be exceeded (too much?).

[sicetaitsimple]

Even if indeed, it seems to me to remember that inside, these towers "drip" - probably because you are pumping excessively. And this heated water must return to the river ...

Not sure if I understood you correctly ... That it "drips" inside, it is the principle, a direct exchange of heat between the descending hot water sprayed as best as possible as in a waterfall and a current of ascending air.

On the other hand indeed, it is necessary to bring water to compensate on the one hand the evaporated flow, and on the other hand to make a purge of deconcentration of the circuit which due to the evaporation concentrates the contents of various salts contained in the make-up water.
Really with a ladle and without having checked, it is necessary to bring about as much water for evaporation as for the deconcentration purge, this also of course depending on the more or less scaling composition of the make-up water.
For a slice of 1450MW as at Chooz, we must be (really order of magnitude!) Of the order of 2m3 / s taken, 1m3 / s which will be evaporated and 1m3 / s which will return to the river as a de-concentration purge . I accept more precise figures, it's just to explain!

[izentrop]

We find numbers here

.
.. withdrawals are around 50 m3 / s for nuclear reactors from 900 to 1 MWe, and the water is fully returned to the source;
... air-cooling tower; part of the water evaporates into the atmosphere (water vapor plume); the other part returns to the condenser, a water make-up of about 2 m3 / s for a nuclear unit of 1 MWe, ..
https://fr.m.wikipedia.org/wiki/Eau_de_ ... thermiques

[Christophe]

Bin here it agrees with the 6 m3 / s announced for Chooz (50% margin) ...

When we do it together and we do not enter into trollism we find and we move forward ...

[sicetaitsimple]

Bin here it agrees with the 6 m3 / s announced for Chooz (50% margin) ...

Uh ... No, not really, but it's not a big deal.
The 6m3 / s is the flow required when the 2 units are stopped!
To operate systems in permanent operation (ventilation, cooling of pumps, compressors, etc.) but above all to remove residual power from the reactor, whether in normal or possibly accidental situation. There it's open circuit, it's pumped into the river and it goes back to the river, no evaporative cooling.

[Christophe]

This is explained in the second source cited by Christophe:
https://www.leprogres.fr/environnement/ ... oz-arretee

Well we must not have the same reading of this passage:

In terms of nuclear safety, the flow of the Meuse necessary to guarantee the cooling of the installations is of the order of 6m3 / second.

For me this sentence speaks of "normal" operation of only 6 m3 / s are necessary!

In terms of dissipated energy, this represents 13.5 GW assuming that 100% of this flow is evaporated ... therefore enough to largely dissipate the approximately 6 GW of thermal losses from a 3 GW plant ...

No actually it's not very serious (but always contradicting others ... it's just exhausting ...)

[sicetaitsimple]

No, you did not understand ... and it is not a will to contradict, just to explain.

The rather well-done article speaks of the flow required for "nuclear safety". When there is a need for "nuclear safety", it is because the plant does not produce any more electricity and that the residual power of the heart must be evacuated by systems designed for. In normal operation (electricity production), this contributes to the production of electricity, the energy released by the fission products comes in addition to the energy released by the fission itself.

These cooling systems do not work by evaporation, but by cooling with direct rejection.
The flow rate withdrawn (and therefore immediately rejected) can therefore be greater when stationary than the flow rate withdrawn in normal operation at full load.

[Christophe]

Proper cooling of a power station in normal operation is also nuclear safety ...

These 6 m3 / s correspond to more than double the energy to be dissipated by evaporation in normal operation ... which seems consistent (50% evaporation ...)

the energy given off by the fission products comes in addition to the energy given off by the fission itself.

??

[sicetaitsimple]

the energy given off by the fission products comes in addition to the energy given off by the fission itself.

??

The "comes in addition" was a bad expression, the correct term would have been "contributes".

In order of magnitude, in a full load PWR reactor, about 95% or even slightly more of the thermal power comes from the fission of the uranium235 and Plutonium 239 atoms, and 5% from the subsequent decay of their products of fission (for some within a few seconds of their appearance).

In short, if you stop a reactor from full load, you stop the 95% U235 / Pu 239 fission, but you still have 5% to evacuate in the next few seconds, then a significant power thereafter. .

To illustrate:
https://fr.wikipedia.org/wiki/Puissance_r%C3%A9siduelle

[Christophe]

Can't you speak French the first time?

I knew the notion of residual power but I thought it was more important than that ...

Well, let's do the table corner calculations ...

1% after 1 hour is a few tens of MW to dissipate ...
0.7% after 24 hours ...
0.25% after 10 days ...

1% or 1500/100 * 3 = 45 MW ...

PER REACTOR, therefore, a flow of water in simple exchange without evaporation is required with an authorized delta of + 1 ° C of: 45 / 000 = 4.18 m10.7 / s ... suddenly the 3 m6 / s are insufficient eh for 3 hours first hours ... especially since there are 24 reactors ...

So it would have taken 22 m3 / s to ensure cooling within the standards at + 1 ° C delta. 22 m3 / s was precisely the flow of the Meuse before the stop of the 1st chooz on Friday ... proof that they were at the limit - limit! And suddenly, nothing to do with Belgium! After + 1 ° C it's not much either, eh ...

Ok I understood the lesson!