4 ms·

Yes, demand response will play a huge role in the grids of the future. But when you say "current versions", which current operating nuclear plant achieves this

by _ph_ 6y ago

Yes, demand response will play a huge role in the grids of the future. But when you say "current versions", which current operating nuclear plant achieves this ramp speed? Also, it means you have to run your reactors regularly at below 100%, so you still can react on additional demand, which increases further the cost of a very expensive technology.

jabl 6y ago
> But when you say "current versions", which current operating nuclear plant achieves this ramp speed? IIRC that 5% figure I read was wrt EPR and AP1000, presumably older generation LWR's are slower, by how much I'm not sure. France has run older generation PWR's in load-following mode for decades, but I'm not sure which ramp speeds they achieve; fast enough in practice in any case it seems. CANDU reactors in Canada have steam bypass and can apparently ramp at >10%/min. In any case, my point is that ramp speed is in practice not a technical limitation. Of course you want to run a generator with high capital cost but very low marginal cost at 100% as much as possible, but if you now and then need to ramp (say, if the wholesale price goes negative) you can do it. > Also, it means you have to run your reactors regularly at below 100%, so you still can react on additional demand, which increases further the cost of a very expensive technology. To be clear, I'm not advocating a 100% nuclear grid. I'm just pointing out that the "nuclear can't ramp and is thus unsuited for the grid of the future" isn't correct. In particular, I think solar and a moderate amount of storage is very well suited to cover the daily variation in many parts of the world. I also think that dispatchable low-carbon sources (which could be hydro, or nuclear, or something else like geothermal where available, CCS where geological formations for storing CO2 are available, etc.) have a role to play in least-cost deep decarbonized grids. See e.g. https://doi.org/10.1016/j.joule.2018.08.006 https://doi.org/10.1016/j.joule.2018.08.006
- p_l 6y ago
  From my understanding some of the "delay" in ramping up is related to enrichment level of the nuclear fuel and thus how fast the speed of the reaction can change.
  - jabl 6y ago
    Kind of. When reducing power there's a buildup of a particular Xenon isotope, which is a powerful neutron adsorber. So until that isotope decays away sufficiently you might have problems starting the reactor back up again. Unless you have enough excess reactivity, such as by having fresher fuel loaded. AFAIU France primarily uses reactors which are earlier in their fuel cycle for load balancing, and ones which are near the end run with a flatter profile.
    - p_l 6y ago
      Makes sense! Didn't know about specific as it's not really my area, but would running a PWR with very high enrichment level (AFAIK some designs use 93% U-235) allow quick spin down and spin up?
      - jabl 6y ago
        > would running a PWR with very high enrichment level (AFAIK some designs use 93% U-235) allow quick spin down and spin up? Well.. there are a lot of factors in a reactor design affecting the ability to increase or decrease power quickly. Geometry, fuel/moderator ratio, fuel density, burnable poisons (for flattening the reactivity swing over the fuel cycle), amount of control rods etc etc. Fuel enrichment being only one thing, which in turn affects other things as well (e.g. reactors using highly enriched uranium tend to use different fuel designs than low enriched fuels). But yes, military reactors for navy ships obviously have very different demands on them than civilian power reactors, and are designed accordingly. And yes, while US navy reactors use 93% enriched fuel, it's not necessary, e.g. French and apparently Chinese submarines use low enriched fuel (7% for French).

by _ph_ 6y ago

jabl 6y ago

> But when you say "current versions", which current operating nuclear plant achieves this ramp speed? IIRC that 5% figure I read was wrt EPR and AP1000, presumably older generation LWR's are slower, by how much I'm not sure. France has run older generation PWR's in load-following mode for decades, but I'm not sure which ramp speeds they achieve; fast enough in practice in any case it seems. CANDU reactors in Canada have steam bypass and can apparently ramp at >10%/min. In any case, my point is that ramp speed is in practice not a technical limitation. Of course you want to run a generator with high capital cost but very low marginal cost at 100% as much as possible, but if you now and then need to ramp (say, if the wholesale price goes negative) you can do it. > Also, it means you have to run your reactors regularly at below 100%, so you still can react on additional demand, which increases further the cost of a very expensive technology. To be clear, I'm not advocating a 100% nuclear grid. I'm just pointing out that the "nuclear can't ramp and is thus unsuited for the grid of the future" isn't correct. In particular, I think solar and a moderate amount of storage is very well suited to cover the daily variation in many parts of the world. I also think that dispatchable low-carbon sources (which could be hydro, or nuclear, or something else like geothermal where available, CCS where geological formations for storing CO2 are available, etc.) have a role to play in least-cost deep decarbonized grids. See e.g. https://doi.org/10.1016/j.joule.2018.08.006 https://doi.org/10.1016/j.joule.2018.08.006

p_l 6y ago
From my understanding some of the "delay" in ramping up is related to enrichment level of the nuclear fuel and thus how fast the speed of the reaction can change.
- jabl 6y ago
  Kind of. When reducing power there's a buildup of a particular Xenon isotope, which is a powerful neutron adsorber. So until that isotope decays away sufficiently you might have problems starting the reactor back up again. Unless you have enough excess reactivity, such as by having fresher fuel loaded. AFAIU France primarily uses reactors which are earlier in their fuel cycle for load balancing, and ones which are near the end run with a flatter profile.
  - p_l 6y ago
    Makes sense! Didn't know about specific as it's not really my area, but would running a PWR with very high enrichment level (AFAIK some designs use 93% U-235) allow quick spin down and spin up?
    - jabl 6y ago
      > would running a PWR with very high enrichment level (AFAIK some designs use 93% U-235) allow quick spin down and spin up? Well.. there are a lot of factors in a reactor design affecting the ability to increase or decrease power quickly. Geometry, fuel/moderator ratio, fuel density, burnable poisons (for flattening the reactivity swing over the fuel cycle), amount of control rods etc etc. Fuel enrichment being only one thing, which in turn affects other things as well (e.g. reactors using highly enriched uranium tend to use different fuel designs than low enriched fuels). But yes, military reactors for navy ships obviously have very different demands on them than civilian power reactors, and are designed accordingly. And yes, while US navy reactors use 93% enriched fuel, it's not necessary, e.g. French and apparently Chinese submarines use low enriched fuel (7% for French).