"So in the US we now have some 35,000 tons of used fuel sitting in close-packed spent fuel pools, waiting for something bad to happen and cause a major release. Why? In order to put off spending 0.1 cents per kWh for a few years." - Question - Once the used fuel is put in spent fuel pools, is it too late to transfer them to dry storage casks? Or can it still be done?
All spent fuel goes to the pools initially, and then is transferred out after 4 or more years of cooling. The difference between open-racking and close-packing is that to open-rack you must transfer the fuel to dry casks sooner. By close-packing, you can put off the cost of the dry-cask for as much as 12 years.
Quote is attributed to Wolfgang Pauli (no relation to Wolfman Jack). BTW, Bohr was Danish and escaped from Nazi-controlled Denmark to neutral Sweden thence on to England. Other than that ...
The NRC Commissioners erred terribly when they rejected the recommendation of the NRC staff's Fukushima Near-Term Taskforce to phase out high-density pool storage of spent fuel by accelerating the deployment of dry casks. As I see it, two major misrepresentations in the staff's analysis supporting that decision led to both the frequency and consequences of pool draining events being grossly understated.
1. Pool Draining Events
First, and as noted by others, was the NRC staff’s seemingly disingenuous selection of an extremely rare beyond design basis earthquake as the so-called "prototype event" for assessing the risks of pool draining leading to zirconium fires. There are obviously other credible events that could lead to pool boil-off or draining. These would include insider sabotage or missile attacks by domestic or foreign terrorists.
Relevant events would further include extended regional grid blackouts resulting from electromagnetic pulses (EMPs) as induced by either Carrington-scale solar storms or high-altitude thermonuclear blasts by an adversary. Note that the frequency of Carrington-scale solar storms has been estimated at 12% per decade. Such intense EMPs could fry large transformers that would take months to fix or replace. The result would be vast regionwide grid blackouts lasting several months or longer.
In the ensuing dystopian chaos, it is far from clear that mitigative actions could reliably be taken. Traffic chaos could make it extremely difficult for trained responders to reach affected reactor sites. And communication infrastructure failures could prevent responders from learning of the affected sites. Moreover, responders might understandably tend to prioritize defending home and family over all else. Such EMPs could thus result in unmitigated crises at all reactor sites in the blackout affected regions.
2. Pool Draining Event Progression and Consequences
As likewise noted in part by others, the NRC staff's analysis failed in two ways to adequately model the progression and consequences of pool draining events. First, the intensity of spent fuel burning was greatly underestimated due to MELCOR code's acknowledged inability to model exothermic zirconium nitriding reactions in air.
Second, no consideration was given to the likelihood and consequences of potential criticality excursions that could occur during pool draining or boil-off or while refilling an extensively drained or boiled-off pool. Almost all high-density pool racks use aluminum based neutron absorber plate materials (i.e., Boral, Metamic, Carborundum, and others) that, when no longer submerged, could readily disintegrate and/or melt from overheating by spent fuel nuclear decay and eventual zirconium burning. The absence of effective absorber plates could then give rise to pool criticality excursions.
Because the pools at pressurized water reactors (PWRs) are heavily borated, criticality-induced local pool boiling would produce strongly positive feedback and, thus, highly destructive energetic excursions akin to the one that destroyed Chernobyl.
Given that high-density spent fuel storage pools generally contain many core inventories of cesium and strontium and are located outside containment, it is clear to me that such events have far larger potential consequences than any conceivable reactor events.
So as I understand it, the bottleneck is getting the bundles into dry storage. The cost should be negligible, if this were done sensibly. Why do even need expensive casks? Why not just have underground silos, lined with concrete pipe sections, and a heavy lid to discourage kids from messing with it? Would that require fans and reliable power, or is passive air circulation enough?
There is no bottleneck. It's simply that dense packing saves a few present valued dollars by putting off the cost of dry cask storage while the spent fuel pool fills up. The casks can be underground but must be close enough to the surface they can be cooled by natural circulation. Google Holtec HiStore. Several countries use vaults rather than individual casks.
These too are cooled by natural circulation using large chimneys. Cooling is only a real problem for deep geologic respositories . Generally, the fuel must be dry casked for about 50 years before it can be buried, and even then the heat load determines how much SNF you can put into a given repository.
Even better than drilling silos, how about arch pipe? Are those Holtec casks really $800,000 each? That is absurd. How much decay heat are we talking about? Will a 20 foot chimney be enough to avoid the cost of a fan?
Very interesting and informative.
"So in the US we now have some 35,000 tons of used fuel sitting in close-packed spent fuel pools, waiting for something bad to happen and cause a major release. Why? In order to put off spending 0.1 cents per kWh for a few years." - Question - Once the used fuel is put in spent fuel pools, is it too late to transfer them to dry storage casks? Or can it still be done?
Al,
All spent fuel goes to the pools initially, and then is transferred out after 4 or more years of cooling. The difference between open-racking and close-packing is that to open-rack you must transfer the fuel to dry casks sooner. By close-packing, you can put off the cost of the dry-cask for as much as 12 years.
Got it. thanks.
This analysis is "so bad it is not even wrong..."
Adrian,
Could you be more specific?
Yes, the comment is arributed to Niels Bohr, a few years before he left Austria to escape Hitler's irrational and catastrophic hatred of Jews.
He made it to a student who had made a basic error in attribution.
Essentially the same facism that bans safe nuclear power with lies and deceit. Austria was still a democracy at that moment.
Quote is attributed to Wolfgang Pauli (no relation to Wolfman Jack). BTW, Bohr was Danish and escaped from Nazi-controlled Denmark to neutral Sweden thence on to England. Other than that ...
OK but how does that apply here?
if the water drains completely, then convective cooling is adequate to cool the fuel.
I totally agree, however ,that reprocessing fuel is the best and safest option if not the most economical.
Adding my two cents:
The NRC Commissioners erred terribly when they rejected the recommendation of the NRC staff's Fukushima Near-Term Taskforce to phase out high-density pool storage of spent fuel by accelerating the deployment of dry casks. As I see it, two major misrepresentations in the staff's analysis supporting that decision led to both the frequency and consequences of pool draining events being grossly understated.
1. Pool Draining Events
First, and as noted by others, was the NRC staff’s seemingly disingenuous selection of an extremely rare beyond design basis earthquake as the so-called "prototype event" for assessing the risks of pool draining leading to zirconium fires. There are obviously other credible events that could lead to pool boil-off or draining. These would include insider sabotage or missile attacks by domestic or foreign terrorists.
Relevant events would further include extended regional grid blackouts resulting from electromagnetic pulses (EMPs) as induced by either Carrington-scale solar storms or high-altitude thermonuclear blasts by an adversary. Note that the frequency of Carrington-scale solar storms has been estimated at 12% per decade. Such intense EMPs could fry large transformers that would take months to fix or replace. The result would be vast regionwide grid blackouts lasting several months or longer.
In the ensuing dystopian chaos, it is far from clear that mitigative actions could reliably be taken. Traffic chaos could make it extremely difficult for trained responders to reach affected reactor sites. And communication infrastructure failures could prevent responders from learning of the affected sites. Moreover, responders might understandably tend to prioritize defending home and family over all else. Such EMPs could thus result in unmitigated crises at all reactor sites in the blackout affected regions.
2. Pool Draining Event Progression and Consequences
As likewise noted in part by others, the NRC staff's analysis failed in two ways to adequately model the progression and consequences of pool draining events. First, the intensity of spent fuel burning was greatly underestimated due to MELCOR code's acknowledged inability to model exothermic zirconium nitriding reactions in air.
Second, no consideration was given to the likelihood and consequences of potential criticality excursions that could occur during pool draining or boil-off or while refilling an extensively drained or boiled-off pool. Almost all high-density pool racks use aluminum based neutron absorber plate materials (i.e., Boral, Metamic, Carborundum, and others) that, when no longer submerged, could readily disintegrate and/or melt from overheating by spent fuel nuclear decay and eventual zirconium burning. The absence of effective absorber plates could then give rise to pool criticality excursions.
Because the pools at pressurized water reactors (PWRs) are heavily borated, criticality-induced local pool boiling would produce strongly positive feedback and, thus, highly destructive energetic excursions akin to the one that destroyed Chernobyl.
Given that high-density spent fuel storage pools generally contain many core inventories of cesium and strontium and are located outside containment, it is clear to me that such events have far larger potential consequences than any conceivable reactor events.
Those were my two cents. Any questions?
Donald E. Carlson, PhD
Retired nuclear engineer and regulator
505-490-9137
So as I understand it, the bottleneck is getting the bundles into dry storage. The cost should be negligible, if this were done sensibly. Why do even need expensive casks? Why not just have underground silos, lined with concrete pipe sections, and a heavy lid to discourage kids from messing with it? Would that require fans and reliable power, or is passive air circulation enough?
There is no bottleneck. It's simply that dense packing saves a few present valued dollars by putting off the cost of dry cask storage while the spent fuel pool fills up. The casks can be underground but must be close enough to the surface they can be cooled by natural circulation. Google Holtec HiStore. Several countries use vaults rather than individual casks.
These too are cooled by natural circulation using large chimneys. Cooling is only a real problem for deep geologic respositories . Generally, the fuel must be dry casked for about 50 years before it can be buried, and even then the heat load determines how much SNF you can put into a given repository.
Even better than drilling silos, how about arch pipe? Are those Holtec casks really $800,000 each? That is absurd. How much decay heat are we talking about? Will a 20 foot chimney be enough to avoid the cost of a fan?
https://cemcast.com/reinforced-concrete-pipe/arch-pipe/