Boron Issues

[jamesr]

I would expect the B10 to be dissolved in the water sheilding as boric acid. So any neutrons produced are slowed down (or moderated in nuclear terminology) to thermal speeds. They then, while bouncing around in the water get captured by a B10. The resulting lithium will not travel very far in water, as it is charged and slow down within a 10-100 nm. Heating up the water a little in the process (similarly for the helium). The lithium will react with the water producing lithium hydroxide. The boric acid and lithium hydroxide can then react, as any acid and base do leaving a salt, lithium borate in this case. If the concentration of the salt gets too high it can precipitate out – taking some of the boron out of the bulk of the water and reducing the chance of neutron capture slightly.

However, given the low levels of neutrons produced, I wouldn’t expect the shielding water to have to be filtered & topped up with fresh boron for at least 5 years if not the life of a reactor.

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.

[Brian H]

jamesr wrote: I would expect the B10 to be dissolved in the water sheilding as boric acid. So any neutrons produced are slowed down (or moderated in nuclear terminology) to thermal speeds. They then, while bouncing around in the water get captured by a B10. The resulting lithium will not travel very far in water, as it is charged and slow down within a 10-100 nm. Heating up the water a little in the process (similarly for the helium). The lithium will react with the water producing lithium hydroxide. The boric acid and lithium hydroxide can then react, as any acid and base do leaving a salt, lithium borate in this case. If the concentration of the salt gets too high it can precipitate out – taking some of the boron out of the bulk of the water and reducing the chance of neutron capture slightly.

However, given the low levels of neutrons produced, I wouldn’t expect the shielding water to have to be filtered & topped up with fresh boron for at least 5 years if not the life of a reactor.

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.

Since LPP would be purchasing decaborane, I assume it would be B11 from the source. The B10 would be acquired separately.

What is the penetration and intensity overall of the gamma radiation? Assuming the B10 to be an external shell around the water, would it be a danger in the surrounding service space? Since the =<12s decay time you give for the B10 is so brief, I would assume that the gamma would be produced only while the core was active, and a short period afterwards (a few minutes to subside to insignificant levels).

P.S. I didn’t mean to imply that the shell in contact with the water was B10; actually, I believe it’s exterior to the water container — a shell around the shell, as it were. But don’t quote me. 😉 :cheese:

[jamesr]

Brian H wrote:
What is the penetration of the gamma? Assuming the B10 to be an external shell around the water, would it be a danger in the surrounding service space? Since the =>12s decay time you give for the B10 is so brief, I would assume that the gamma would be produced only while the core was active, and a short period afterwards (a few minutes to subside to insignificant levels).

The B10 would normally dissolved in the water as boric acid not as a shell An alternative to water could be borated polyethene sheets, as they wouldn’t need to be as thick to slow down the neutrons. The decay time is 1ps not 12s ie. pretty instantaneous.
The low energy gammas do need some additional shielding, but a steel water tank plus a few inches of lead, or a foot of high density concrete should be sufficient.

[Brian H]

jamesr wrote:

What is the penetration of the gamma? Assuming the B10 to be an external shell around the water, would it be a danger in the surrounding service space? Since the =>12s decay time you give for the B10 is so brief, I would assume that the gamma would be produced only while the core was active, and a short period afterwards (a few minutes to subside to insignificant levels).

The B10 would normally dissolved in the water as boric acid not as a shell An alternative to water could be borated polyethene sheets, as they wouldn’t need to be as thick to slow down the neutrons. The decay time is 1ps not 12s ie. pretty instantaneous.
The low energy gammas do need some additional shielding, but a steel water tank plus a few inches of lead, or a foot of high density concrete should be sufficient.
I can no longer locate the source posting, but I distinctly recall something (I think from Eric) indicating that the B10 was external, not dissolved. Something like 1″ or so thickness.

[Brian H]

jamesr wrote:
… The decay time is 1ps not 12s ie. pretty instantaneous.
The low energy gammas do need some additional shielding, but a steel water tank plus a few inches of lead, or a foot of high density concrete should be sufficient.

Oops, missed the caret^ in your original statement! :red:
Yeah, I’d say picoseconds are “pretty instantaneous”! :cheese:

[Aeronaut]

Brian H wrote:
I can no longer locate the source posting, but I distinctly recall something (I think from Eric) indicating that the B10 was external, not dissolved. Something like 1″ or so thickness.

That was my understanding- a metal or plastic water tank containing a 1m (distilled?)water shield, covered by 10cm of boron (type unspecified), covered by 2cm of lead or boronated polyethylene. We discussed this with Eric and Rematog around March of ’09 iirc. Searching the site for boronated polyethylene may bring up the thread.

[jamesr]

Aeronaut wrote:
That was my understanding- a metal or plastic water tank containing a 1m (distilled?)water shield, covered by 10cm of boron (type unspecified), covered by 2cm of lead or boronated polyethylene. We discussed this with Eric and Rematog around March of ’09 iirc. Searching the site for boronated polyethylene may bring up the thread.

Sounds familiar… I found this reference from Eric from way back in 2006 https://focusfusion.org/index.php/forums/viewthread/91/#346

[Brian H]

jamesr wrote:

That was my understanding- a metal or plastic water tank containing a 1m (distilled?)water shield, covered by 10cm of boron (type unspecified), covered by 2cm of lead or boronated polyethylene. We discussed this with Eric and Rematog around March of ’09 iirc. Searching the site for boronated polyethylene may bring up the thread.

Sounds familiar… I found this reference from Eric from way back in 2006 https://focusfusion.org/index.php/forums/viewthread/91/#346

Excellent find. Slightly edited for spelling, etc., here’s the relevant excerpt:

The main shielding is for the residual neutrons—about 80-100 cm of water and 20 cm of boron-10 with a small, few-cm layer of lead to absorb the gammas. None of the x-rays will get through that.
…
5) What are the approximate dimensions of the proposed reactor?

Reactor plus shielding is 2 meters across but the whole thing, including capacitor bank may be more like 3x2x2 meters.

[zapkitty]

Brian H wrote:
Excellent find. Slightly edited for spelling, etc., here’s the relevant excerpt:

The main shielding is for the residual neutrons—about 80-100 cm of water and 20 cm of boron-10 with a small, few-cm layer of lead to absorb the gammas. None of the x-rays will get through that.
…
5) What are the approximate dimensions of the proposed reactor?

Reactor plus shielding is 2 meters across but the whole thing, including capacitor bank may be more like 3x2x2 meters.

Which are the figures I’ve been working with for my notional first-gen application implementations… so an inline dual-core could be about 5x2x2?

core |caps| core } 2m
<—- 5m—->

… 10MW at the proposed initial 5MW/core settings… damn that’s small…

[QuantumDot]

for radiation shielding they should look at demron, which claims to be able to stop a certain amount of gamma rays.

especially for vehicles or mobile DPF for power, or neutron sources

http://www.radshield.com/

[Brian H]

zapkitty wrote:
…

Which are the figures I’ve been working with for my notional first-gen application implementations… so an inline dual-core could be about 5x2x2?

core |caps| core } 2m
<—- 5m—->

… 10MW at the proposed initial 5MW/core settings… damn that’s small…

Yeah, somewhere I did some simple calcs figgering out the volume/W ratios of different power sources. In your design, 20 m^3 for 10MW is .5MW/m^3, = 500,000W/1,000,000 cm^3 = 0.5W/cm^3. Which is a big number!

[Aeronaut]

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.

[psupine]

I was imagining something in a standard shipping container for quick install or swap out, and centralized construction, service and refueling. The dimensions discussed here, and the fast radiation decay to safe levels would make transport feasible.

Even if the energy recovery from excess heat ends up being a turbine housed in a separate container, (supercritical CO2?) the elements are small enough to be containerized. Although perhaps this portability makes the chance of outright theft somewhat harder to deal with.

[zapkitty]

Aeronaut 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?

[Rezwan]

jamesr 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?

[Author]

Posts