The Future of Power Generation in Great Britain

[hidetheelephants]

phumy said:

When i was a mere lad and a reactor control engineer and our load was fluctuating one of our big concerns was the Xenon build up. If you can master the control of all the different extra systems required for "load following" and controlling the Xenon in a Nuke then it might happen, but not for 50 odd years yet.

I doubt it will take that long given the cash the chinese are directing at research; molten salt reactors self-purge xenon, add on a negative void coefficient and load-following is almost intrinsic.

[phumy]

hidetheelephants said:

phumy said:

When i was a mere lad and a reactor control engineer and our load was fluctuating one of our big concerns was the Xenon build up. If you can master the control of all the different extra systems required for "load following" and controlling the Xenon in a Nuke then it might happen, but not for 50 odd years yet.

I doubt it will take that long given the cash the chinese are directing at research; molten salt reactors self-purge xenon, add on a negative void coefficient and load-following is almost intrinsic.

Still reckon itll take 50 years, after R&D, Production, Testing then scaling it up to an acceptable output.

[Gary C]

hidetheelephants said:

I doubt it will take that long given the cash the chinese are directing at research; molten salt reactors self-purge xenon, add on a negative void coefficient and load-following is almost intrinsic.

I know I said I would never post here again but,

"Self purge Xenon", thats a new one on me, how does it do that ?

[hidetheelephants]

Gary C said:

hidetheelephants said:

I doubt it will take that long given the cash the chinese are directing at research; molten salt reactors self-purge xenon, add on a negative void coefficient and load-following is almost intrinsic.

I know I said I would never post here again but,

"Self purge Xenon", thats a new one on me, how does it do that ?

The action of the liquid flowing around the reactor tends to expel the xenon into the ullage space where it can either be extracted and stored or left to decay depending upon design specifics or regulatory requirement, although some MSR advocates think gas sparging with perhaps helium may be necessary to speed things up and maintain utmost neutron economy.

[WatchfulEye]

Hinkley Point C has achieved "J-0", marking the completion of the foundations for unit 1, and the commencement of above-ground civils for the reactor building.

[3.1416]

Gary C said:

I know I said I would never post here again but,

"Self purge Xenon", thats a new one on me, how does it do that ?

Please do.

Never say never again.

[Gary C]

hidetheelephants said:

Gary C said:

hidetheelephants said:

I doubt it will take that long given the cash the chinese are directing at research; molten salt reactors self-purge xenon, add on a negative void coefficient and load-following is almost intrinsic.

I know I said I would never post here again but,

"Self purge Xenon", thats a new one on me, how does it do that ?

The action of the liquid flowing around the reactor tends to expel the xenon into the ullage space where it can either be extracted and stored or left to decay depending upon design specifics or regulatory requirement, although some MSR advocates think gas sparging with perhaps helium may be necessary to speed things up and maintain utmost neutron economy.

How does it get out from the fuel ? Its formed from the fission product decay of Iodine in a uranium fueled reactor. Is a molten salt sufficiently atomically mobile to allow it to separate ? Certainly what I have just had a quick read seems to suggest it needs 'processing' rather than just bubbling out

A reactor without Xenon would be nice. Its 'exciting' to do a falling Xenon start on a power reactor.

[hidetheelephants]

The test reactor run by ORNL didn't throw up any great concerns about the mobility of the Xenon; being the 1960s they just vented it up a big chimney!

[phumy]

Gary C said:

hidetheelephants said:

Gary C said:

hidetheelephants said:

I doubt it will take that long given the cash the chinese are directing at research; molten salt reactors self-purge xenon, add on a negative void coefficient and load-following is almost intrinsic.

I know I said I would never post here again but,

"Self purge Xenon", thats a new one on me, how does it do that ?

The action of the liquid flowing around the reactor tends to expel the xenon into the ullage space where it can either be extracted and stored or left to decay depending upon design specifics or regulatory requirement, although some MSR advocates think gas sparging with perhaps helium may be necessary to speed things up and maintain utmost neutron economy.

How does it get out from the fuel ? Its formed from the fission product decay of Iodine in a uranium fueled reactor. Is a molten salt sufficiently atomically mobile to allow it to separate ? Certainly what I have just had a quick read seems to suggest it needs 'processing' rather than just bubbling out

A reactor without Xenon would be nice. Its 'exciting' to do a falling Xenon start on a power reactor.

You sound as though you have either been involved in or have witnessed a Xenon start up, I very much doubt you have but would be willing to hear of your experiences?

[Gary C]

phumy said:

You sound as though you have either been involved in or have witnessed a Xenon start up, I very much doubt you have but would be willing to hear of your experiences?

You doubt me ?

When one of our reactors trips from full power (approx 1600MW), a startup can be done quick enough that Xenon levels are high when rods are pulled.

We pull half of the black rods to 100% out, then all Grey rods to 50%, then begin to withdraw the remaining black rods until the reactor is critical. Normally this is at about 20%, but in a high Xenon start it can be ~70% (or even impossible while remaining compliant with max permitted rod withdrawl limits)

I did a few, took the reactor critical then initiated a power rise, normally, the doppler effect means you have to keep pulling the rods out marginally to maintain the power increase (rods are on manual at this point), however in a falling Xenon start, power tends to increase nicely by itself, while you wait for the power increase to begin its positive feedback effect on the Xenon. When it begins to speed up, you have to insert the rods to maintain the target doubling time qute promptly.

A startup without a high Xenon inventory is much easier.

[phumy]

Gary C said:

phumy said:

You sound as though you have either been involved in or have witnessed a Xenon start up, I very much doubt you have but would be willing to hear of your experiences?

You doubt me ?

When one of our reactors trips from full power (approx 1600MW), a startup can be done quick enough that Xenon levels are high when rods are pulled.

We pull half of the black rods to 100% out, then all Grey rods to 50%, then begin to withdraw the remaining black rods until the reactor is critical. Normally this is at about 20%, but in a high Xenon start it can be ~70% (or even impossible while remaining compliant with max permitted rod withdrawl limits)

I did a few, took the reactor critical then initiated a power rise, normally, the doppler effect means you have to keep pulling the rods out marginally to maintain the power increase (rods are on manual at this point), however in a falling Xenon start, power tends to increase nicely by itself, while you wait for the power increase to begin its positive feedback effect on the Xenon. When it begins to speed up, you have to insert the rods to maintain the target doubling time qute promptly.

A startup without a high Xenon inventory is much easier.

Thats really interesting, so i take it the regulatory authorities (NII & ONR) are aware of this and allow this kind of start up to happen, with the risks involved?

So, what would happen if you didnt or was not able (for what ever reason) to maintian or arrest the doubling time promptly?

[Gary C]

phumy said:

Thats really interesting, so i take it the regulatory authorities (NII & ONR) are aware of this and allow this kind of start up to happen, with the risks involved?

So, what would happen if you didnt or was not able (for what ever reason) to maintian or arrest the doubling time promptly?

its all within regulations certainly

We normally startup with a doubling time of around 150-200 seconds, so every ~180 seconds the power doubles. When the Xenon begins to fall under the influence of the increasing neutron flux, and thus tends to increase the flux, the doubling time can move towards 100 s requiring you to pull it back, if it gets to 30s the protection will automatically trip the reactor (which is a world away from a chernobyl style prompt critical style excursion).

Worth noting, while they are 'doubling times' the power at this point is in the order of 200kw in a reactor cabable of 1700MW so its not significant really, its just exciting because if you dont watch it, it can trip and at least 12 hours of work would be down the drain, probably more to get back to the same point in the startup.

Reactor startups are really 'fun', lots to do and normally takes us a couple of days of preparation and 12 hours to take from pulling rods to synchronising the generator.

[phumy]

Gary C said:

its all within regulations certainly

We normally startup with a doubling time of around 150-200 seconds, so every ~180 seconds the power doubles. When the Xenon begins to fall under the influence of the increasing neutron flux, and thus tends to increase the flux, the doubling time can move towards 100 s requiring you to pull it back, if it gets to 30s the protection will automatically trip the reactor (which is a world away from a chernobyl style prompt critical style excursion).

Worth noting, while they are 'doubling times' the power at this point is in the order of 200kw in a reactor cabable of 1700MW so its not significant really, its just exciting because if you dont watch it, it can trip and at least 12 hours of work would be down the drain, probably more to get back to the same point in the startup.

Reactor startups are really 'fun', lots to do and normally takes us a couple of days of preparation and 12 hours to take from pulling rods to synchronising the generator.

Gary, thats great im learning something here, how short a time after a trip could you re-start after Xenon buildup?

[Gary C]

phumy said:

Gary C said:

its all within regulations certainly

We normally startup with a doubling time of around 150-200 seconds, so every ~180 seconds the power doubles. When the Xenon begins to fall under the influence of the increasing neutron flux, and thus tends to increase the flux, the doubling time can move towards 100 s requiring you to pull it back, if it gets to 30s the protection will automatically trip the reactor (which is a world away from a chernobyl style prompt critical style excursion).

Worth noting, while they are 'doubling times' the power at this point is in the order of 200kw in a reactor cabable of 1700MW so its not significant really, its just exciting because if you dont watch it, it can trip and at least 12 hours of work would be down the drain, probably more to get back to the same point in the startup.

Reactor startups are really 'fun', lots to do and normally takes us a couple of days of preparation and 12 hours to take from pulling rods to synchronising the generator.

Gary, thats great im learning something here, how short a time after a trip could you re-start after Xenon buildup?

Very much depends on the power history and how long since its been refuelled, but practical limits of aligning the plant ready for startup means its really ~60 hours from trip to critical sp Xenon is always likley to be such that startup is possible (unless really late in the fuel cycle, but as we refuel on load, thats not normally a problem). Its a large complex plant and much of it needs 'turning around' from a trip to ensure its configured for startup. We also have to have a prediction of criticality done by the physicist to ensure we can start up and when to expect it.

[phumy]

Gary C said:

You doubt me ?

When one of our reactors trips from full power (approx 1600MW), a startup can be done quick enough that Xenon levels are high when rods are pulled.

We pull half of the black rods to 100% out, then all Grey rods to 50%, then begin to withdraw the remaining black rods until the reactor is critical. Normally this is at about 20%, but in a high Xenon start it can be ~70% (or even impossible while remaining compliant with max permitted rod withdrawl limits)

I did a few, took the reactor critical then initiated a power rise, normally, the doppler effect means you have to keep pulling the rods out marginally to maintain the power increase (rods are on manual at this point), however in a falling Xenon start, power tends to increase nicely by itself, while you wait for the power increase to begin its positive feedback effect on the Xenon. When it begins to speed up, you have to insert the rods to maintain the target doubling time qute promptly.

A startup without a high Xenon inventory is much easier.

See bold, i wouldnt say that 60hrs is a quick turn around and after that amount of time almost all the Xenon would have decayed anyway, so its not really a proper Xenon start up is it?

I would say its more of a normal restart, 60 hours after a trip.

[anonymous-user]

phumy said:

You sound as though you have either been involved in or have witnessed a Xenon start up, I very much doubt you have but would be willing to hear of your experiences?

Still doubting?

[phumy]

El stovey said:

Still doubting?

You explain all you know about Xenon start up then.

Am i not allowed to question on a subject that is close to me and yet i have never observed what Gary was saying, im interested.

[anonymous-user]

phumy said:

El stovey said:

Still doubting?

You explain all you know about Xenon start up then.

Am i not allowed to question on a subject that is close to me and yet i have never observed what Gary was saying, im interested.

Ok sorry missed the nuances. I though you were calling him a liar and he proved you wrong. My mistake.

[Gary C]

phumy said:

Gary C said:

You doubt me ?

When one of our reactors trips from full power (approx 1600MW), a startup can be done quick enough that Xenon levels are high when rods are pulled.

We pull half of the black rods to 100% out, then all Grey rods to 50%, then begin to withdraw the remaining black rods until the reactor is critical. Normally this is at about 20%, but in a high Xenon start it can be ~70% (or even impossible while remaining compliant with max permitted rod withdrawl limits)

I did a few, took the reactor critical then initiated a power rise, normally, the doppler effect means you have to keep pulling the rods out marginally to maintain the power increase (rods are on manual at this point), however in a falling Xenon start, power tends to increase nicely by itself, while you wait for the power increase to begin its positive feedback effect on the Xenon. When it begins to speed up, you have to insert the rods to maintain the target doubling time qute promptly.

A startup without a high Xenon inventory is much easier.

See bold, i wouldnt say that 60hrs is a quick turn around and after that amount of time almost all the Xenon would have decayed anyway, so its not really a proper Xenon start up is it?

I would say its more of a normal restart, 60 hours after a trip.

Maybe I used our terminology. We call a fast turn one that is done as soon as we have achieved shutdown. Its a good day when its done in ~60hrs but it can be faster (but often much slower as we have to fix what broke). If its fast enough, we catch the falling Xenon.

Certainly, its a falling Xenon that is the issue. At power a Xenon peak on a power reduction is hit about 7-10 hours. On a shutdown, its more about the very high level of Xenon produced and the amount remaining on restart, the peak has long past, but there is still a large inventory. A power reactor has very little Xenon override margin really.

. A normal quick turn around of our reactor is about 60 hrs, it is marginal if this is Xenon affected, but we do if we turn around as fast as we can, we hit a falling Xenon level that means criticality at around 60% on Bulk group 2 (or more) rather than the more normal 20%. As Xenon levels are falling fast, you get the positive feedback effect.

I have written an Excel based simulator of our reactor, (but I cant share it as its IP of the company), works on about 4 niles of reactivity with about 6 niles of negative reactivity, Xenon on a trip from full power can easily exceed much more than 4 niles (as I recall). We dont tend to keep the numbers in our heads, do dont sue me

Edited by Gary C on Saturday 29th June 22:15

[Talksteer]

phumy said:

I was talking about my times on a Magnox (Graphite Core) reactor, one that was designed probably in the `50`s.

You mention that its possible for large PWR`s to ramp at 5%/hour, thats hardly useful with todays dynamic grid, where half decent fluctuations of the frequency, especially during the winter occur`s in minutes or sometimes even seconds when a big thermal trips off the grid. In any case nukes in the Uk dont sit at partial load waiting to respond (at 5% per hour) to fluctuations, theyre always at baseload doing what they do best.

I used to work for a company in the Uk who can assist frequency stabilisation by running their plant from 0MW to 450MW, or any multiples inbetween, in around 4-6 mins, using gas. Not gas turbines, and not sat at spinning reserve, just straight start up from cold.

That was typo by me it should have read 5% per minute (not hour) between 60 and 100% output. Thus an EPR could add ~80MWe per minute to the grid or Hinckley Point C adding 1300MWe in 8 minutes.

This is only possible over 80% of the fuel cycle.

PWR are more able to dig themselves out of iodine pits simply because their moderator is their coolant. Thus if core temperature drops you can get some of the reactivity back you lost due to xenon.

PWR's original application was obviously one where the reactor had to be able to respond like an oil fired steam boiler.