Boron Issues

[Rezwan]

Also, note new decaborane handling posts and links.

Website posts:
Decaborane handling issues

Decaborane and the vacuum system

Forum posts:
https://focusfusion.org/index.php/forums/viewthread/585/
https://focusfusion.org/index.php/forums/viewthread/584/

[Aeronaut]

zapkitty wrote:

Inline dual-core designs double shielding size and weight, while unnecessarily shielding the cap bank. A tandem multi-core design does little to increase shielding size, yet keeps the caps and cores out where they’re fairly easy to replace during a service call. Reducing downtime is going to be a huge selling point, imo, figuring a quick swap on-site followed in the depot by a nearly complete tear-down to replace the electrodes.

Errr… nope… that was a block diagram, not a blueprint 🙂 The caps in my concept would be no more shielded than required. Actual shields would be in sections and removed as needed for DPF servicing.

As to placing two cores adjacent in the same shielded volume… how close can the cores be before interfering with each other via heat, EM fields, radiation etc ? How would your concept be laid out?

Not really sure about proximity calculations, my stronger suits are electronics and fabrication. If you design the cores as round cylinders they can be rapidly swapped similar to loading and unloading a torpedo tube. The shipping container is compact,stackable. and standardized. There’s a large pool of skilled techs. The cool down to background levels is slightly less than 13 hours- not sure what to expect for acceptable exposure limits or cool down times for maintenance pros and what types of protective gear could possibly decrease cool-down times, which would be the lion’s share of expensive downtime for periodic required servicing. As if we don’t have enough unknowns already :grrr:

The most cost-effective way I’ve found to build and shield a 320 or more core installation is to build a central water tank from 30′ by 4′ or wider plate steel cut for welding the core tubes, which would become a significant portion of the tank’s structure. Spacers from the tubes would help support the top deck which would be a great place to put communal machinery and cap banks. I think this can be done within 1 bank’s timing limitations and the entire system can make a serious bid for recycling a single priming pulse to greatly extend cap bank life.

What I really wanted in a recycling scheme was around 1,000 cores to optimize the timing, but as you can see, even 320 cores is going to have some serious cooling requirements. Rematog discussed the industry standard cooling tower if you’d like more details about cooling a centralized installation.

[jamesr]

Rezwan wrote:

Separating Boron into B-10 & B-11 is done on an industrial scale already for conventional nuclear plants. I’m not sure what the cost is but it shouldn’t be significant in the whole scheme of things.

Do you have any links on this? The process, cost and safety concerns?

I think normally it is done by ion exchange chromatography. Here are a few links
Musashi et al, Column chromatographic boron isotope separation at 5 and 17 MPa with diluted boric acid solution (2008)
Song et al, Advances in boron-10 isotope separation by chemical exchange distillation (2009)

If you can’t access the paper directly here’s an extract where he discusses the history of boron separation (I’m useless at chemistry so don’t ask me what it all means!):

The separation of B-10 was started during World War II. Aether was originally selected as the donor ([Palko and Drury, 1961a], [Palko and Drury, 1961b], [Palko and Drury, 1964] and [Saxena et al., 1961]) and the process condition was: a glass distillation column with a height of 4 m and a diameter of 19 mm, and packing Dixon ring of 1.6 mm × 1.6 mm were adopted. The operation temperature was 70 °C and the pressure was 2.7 kPa at the top and 4.0 kPa at the bottom. The operation cycle lasted 88 days and the yield of B-10 was 2 kg/year with a mass purity of 83%. However, due to the irreversible decomposition of (C2H5)2O·BF3, the decomposition rate of the feed was 12% per day. Higher temperature (70 °C) and high vacuum were required in this process, which consequently limited the production capacity.

Later, aether was replaced with ether and the industrial equipment which can yield 300 kg B-10 (95%) per year was built (Conn and Wolf, 1958). The process condition was as follows: 9 cascaded columns made of Monel steel were adopted. The diameters of the first 3, the second 3 and the final 3 columns were 457.2 mm, 304.8 mm and 152.4 mm respectively. The columns had an average height of 8.33 m and were packed with Stedman Packing. The operation pressures and temperatures were 20 kPa/90 °C at the top and 38.7 kPa/104 °C at the bottom. Compared with the former donor aether, although the irreversible decomposition still existed, the decomposition rate of the feed was only 1.2% per day and the vacuum was allowed to be ten times lower. Production yield increased obviously, yet a certain degree of vacuum was still necessary.

At present, anisole, instead of ether, is widely used in the production of B-10. Compared with ether, anisole has a higher single stage separation coefficient. The process condition is as follows: the whole apparatus consists of four parts: the exchange column, the decomposer column, the recombination device and the solvent purification tank. The copper exchange column is 81.3 m high and operates at 25 °C and normal pressure. The decomposition rate decreases remarkably to only 0.01% in every operation circle.

Katalnikov (Frank, 1995) explored the kinetics and thermodynamics in the separation of B isotopes by chemical exchange distillation using complex anisole, and demonstrated two ways to improve the process: (1) operate at a high pressure so that the capacity of the column would be increased and the kinetics would be improved and (2) apply ideal temperature gradient technology to optimize the separation process. In the past few years, Weijiang Zhang, et al. ([Jiang et al., 2007], [Han et al., 2007], [Han et al., 2006], [Wang et al., 2006] and Yu et al., 2005 J.Y. Yu et al., A Mathematical model in separation of boron isotopes by chemical exchange reaction method, J. Isotopes 18 (4) (2005), pp. 216–219 196.[Yu et al., 2005]) experimentally studied problems such as decomposition reaction and evaluation of donors in chemical exchange distillation. Modeling and simulation were also carried out by them to illustrate and optimize the separation process, which provide an effective way for further studies.

Here is a company that does it currently: Ceradyne Inc

[Brian H]

About the 320 units sharing cap banks: AFAIK, the positioning (connector length etc.) to each core from its caps is critical. That would seem to me to rule out any “sharing”. That is, I don’t think it’s going to be possible to “gang” operate multiple FF’s as though they were a single unit, all firing simultaneously. In clusters, each is going to have to be a stand-alone complete operating entity, sharing current output and possibly thermal waste handling capacity, but not much else. IMO.

[zapkitty]

Brian H wrote: About the 320 units sharing cap banks: AFAIK, the positioning (connector length etc.) to each core from its caps is critical. That would seem to me to rule out any “sharing”. That is, I don’t think it’s going to be possible to “gang” operate multiple FF’s as though they were a single unit, all firing simultaneously. In clusters, each is going to have to be a stand-alone complete operating entity, sharing current output and possibly thermal waste handling capacity, but not much else. IMO.

I don’t know if the lengths are that critical but if it turns out
that way at initial production then at least the dual inline core should still work… if a radial setup is still required then have the cap bank in a ring equidistant between the cores with the business ends of the caps facing inwards (or outwards depending on the engineering.)

That way both cores should see the same cap bank with the same connector environment… I think… 😉

[Brian H]

zapkitty wrote:

About the 320 units sharing cap banks: AFAIK, the positioning (connector length etc.) to each core from its caps is critical. That would seem to me to rule out any “sharing”. That is, I don’t think it’s going to be possible to “gang” operate multiple FF’s as though they were a single unit, all firing simultaneously. In clusters, each is going to have to be a stand-alone complete operating entity, sharing current output and possibly thermal waste handling capacity, but not much else. IMO.

I don’t know if the lengths are that critical but if it turns out
that way at initial production then at least the dual inline core should still work… if a radial setup is still required then have the cap bank in a ring equidistant between the cores with the business ends of the caps facing inwards (or outwards depending on the engineering.)

That way both cores should see the same cap bank with the same connector environment… I think… 😉
They’d still have to co-ordinate firing and recharging, etc. I think you just invoked an exponential nightmare.

[Aeronaut]

The inductance formulae make parallel branches our friend, as the Warsaw machine’s cap bank demonstrates. This idea also pre-supposes that the switching problems have been reasonably solved so it can re-direct the capacitive fraction (which would have been returned to the cap bank) and all outputs into firing the next stage while providing some useful output. Q would have to be >1.5, I’m guessing. But if we’re ever up against a cap lifetime issue, this may be a workaround to some degree.

[vansig]

strangely, i thought that chromatography could produce only small samples, and so was better for analytical use; whereas bulk samples needed something called a “vacuum arc centrifuge”.

http://ieeexplore.ieee.org/iel5/4915369/5080607/05080611.pdf?arnumber=5080611

[vansig]

Brian H wrote:
They’d still have to co-ordinate firing and recharging, etc. I think you just invoked an exponential nightmare.

Doubtful. It should be rather like the workings of a V8 engine, with elements carefully timed, and firing in the appropriate sequence.

[Alchemist32]

I just wanted to clarify a few points. Boric acid is not used in reactor water, this would create a major radiation problem from the production of approx 10^18 to 10^20 prompt gamma photons per second. It would also cause major problems regarding the conductivity of the water (causing corrosion). Instead, in some reactors, boric acid is added to the concrete surrounding the core. This boric acid is normal abundance boron since the 20% B-10 is more than sufficient for this purpose.

Unfortunately, the separation of B-10 and B-11 is not done on an industrial scale. It hypothetically could be, it just isn’t. The major use of isotopically enriched boron is in semiconductor doping, where B-11 is used to produce neutron-hardened ICs for the military. A secondary and much smaller use is for B-10 enriched boron compounds utilized in boron neutron capture therapy (BNCT) (I am a professor in this area). B-11 enriched decaborane would be exorbitantly expensive, ~ $10,000 per gram, although, this cost could be brought down to about $5k per gram.

[jamesr]

Alchemist32 wrote: I just wanted to clarify a few points. Boric acid is not used in reactor water, this would create a major radiation problem from the production of approx 10^18 to 10^20 prompt gamma photons per second. It would also cause major problems regarding the conductivity of the water (causing corrosion). Instead, in some reactors, boric acid is added to the concrete surrounding the core. This boric acid is normal abundance boron since the 20% B-10 is more than sufficient for this purpose.

Unfortunately, the separation of B-10 and B-11 is not done on an industrial scale. It hypothetically could be, it just isn’t. The major use of isotopically enriched boron is in semiconductor doping, where B-11 is used to produce neutron-hardened ICs for the military. A secondary and much smaller use is for B-10 enriched boron compounds utilized in boron neutron capture therapy (BNCT) (I am a professor in this area). B-11 enriched decaborane would be exorbitantly expensive, ~ $10,000 per gram, although, this cost could be brought down to about $5k per gram.

From my masters last year we had several lectures on PWR water chemistry and they went through a number of operating scenarios used in the past and how they have improved the corrosion rates by carefully adjusting the pH, and adding small amounts of things like zinc. But they all use boric acid. Initially all at natural isotopic ratios, but as it stays in there longer the proportion of B10 drops slightly as it is used up.

The pH condition is normally kept at ~7.4 (neutral pH at 300C is 5.71) but varies over the fuel cycle as the concentration of boron is reduced from ~1200ppm to 0 by diluting it as the fuel is used up over an 18month or so period, before refueling again. So it is overall basic, due in part to the lithium, which is carefully controlled and kept at around 2ppm concentration. The large change in boron concentration over a fuel cycle to maintain criticality means it cannot be built into the structure and has to able to be gradually reduced to compensate.

Advanced operating cycles are now using enriched boron of around 30% B10 in order to work with higher enrichment MOX fuels, and longer cycles to achieve higher burn-up rates. This has been done at Gosgen and other Seimens plants since 1999. The B-10 concentration again drops normally during a fuel cycle but is topped up with 98% B-10 solution.

At 1200ppm considering the many tonnes of water in the system this corresponds to several kg of boron in the primary circuit and CVCS (chemical & volume control system) at any one time. So I assumed if they are using kg quantities of B-10 enriched boron for some PWRs, then there must be the equivalent amount of B-11 by-product lying around somewhere.

I don’t doubt the price though – I’m sure they spend millions on the boron systems for PWRs

For BWRs the water chemistry is complicated further due to the concentrating effect of the boiling action. But the principle of the neutron absorption rate having to change over a fuel cycle is still the same.

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