Small modular reactor design could be a SUPERSTAR

R&D Magazine ^ | Feb 9 2012

[Pontiac]

Nope. Not nearly enough enrichment for "boom-making".

I think you are wrong about that. True the standard idea was that you needed 90% or more enrichment for bomb grade Uranium but I don’t believe that is true any more.

I believe that with modern tampers and a high out put neutron source initiator a talented nuclear engineer could produce a low yield bomb with enrichment at this level.

I personally would not want to take the chance that a terrorist group could not find such an engineer.

[Pontiac]

There was nothing wrong with the reactor design at Fukushima. The secondary side of the plant was the problem. That and the sea wall was insufficient (which they had been warned about).

[Blood of Tyrants]

There are several SMR designs out there. No one has built a working model yet.

[MCH]

The PBR has not lived up to its hype.

True that. I prefer Coors. But hey - it's pretty impressive that PBR can be used to generate nuclear power! Who knew?

[LomanBill]

>>What to do......what to do......

What NOT to do......

“In the Soviet-era program, which started in the 1970s but was abandoned, tractors fitted with containers of cesium 137 (and lead shielding to protect the driver) irradiated wheat seeds before sowing them, in an attempt to induce beneficial mutations in the crops. The radiation was also applied to grain after harvest, to prevent it from germinating. A total of ten of the containers have been recovered in Georgia, Moldova and Ukraine; no one knows how many more are unaccounted for....”
http://www.smithsonianmag.com/science-nature/hotstuff.html?c=y&page=5

“Oopski”

[Lx]

There was nothing wrong with the reactor design at Fukushima. The secondary side of the plant was the problem. That and the sea wall was insufficient (which they had been warned about).

It's all part of the same plant. Look at Fukishima's design and compare it to TMI's which was designed by Babcock and Wilcox.

TMI:

Fukishima:

Fukishima doesn't exactly have a great containment building. They store fuel rods outside the containment building. The suppression pool is outside the containment building, and 23 currently operating plants in the US have the suppression pool/Torus design. Plus, they don't use a heat exchanger so the steam from the reactor drives the turbine instead of it being a separate system. In TMI, the steam generator/heat exchanger is inside of the containment building. There are 23 plants in the US that use this design which is less than comforting.

GE scientists quit in protest over the Mark 1 design (Fukishima)

[Wonder Warthog]

"I think you are wrong about that. True the standard idea was that you needed 90% or more enrichment for bomb grade Uranium but I don’t believe that is true any more. I believe that with modern tampers and a high out put neutron source initiator a talented nuclear engineer could produce a low yield bomb with enrichment at this level."

Everything I'm finding on search says it's still 90% or greater needed.

[chimera]

And do you know why the BWR design has those features in contrast to those of a PWR? And no, I’m not talking about cost, I’m talking about the science behind the engineering.

[chimera]

I think Little Boy used 64 kg. of 80% enriched uranium. The trouble with lower enrichment is that more mass is needed, and more mass means more difficulty in assembling the material into a supercritical mass. The drive to higher enrichments in oralloy-based weapons was a result of the need to make the weapons smaller and more deliverable. Of course, the availability of plutonium-implosion makes the whole enrichment thing kind of moot.

[Pontiac]

GE scientists quit in protest over the Mark 1 design (Fukishima)

Mark 1 is the containment design not the reactor design.

Yes the Mark 1 containment failed as the GE engineer feared that it would. That does not invalidate the reactor design which would have weathered the earth quake safely had the stand by diesel generators not have been installed below grade or if the plant had an adequate sea wall.

TMI is at least a generation newer than Fukushima and is not a fair comparison. GE Mark 1 is quite old the newest GE plants in the US are Mark 6. By the way B&W are no longer in the reactor business (other than servicing the existing B&W plants).

All nuclear plants that I am aware of store the bulk of their spent fuel outside of their primary containment. Most plants store their spent fuel in a special building built for the purpose which is inside what is called secondary containment. In more modern plants this building is a reinforced concrete structure with special ventilation and redundant cooling water systems.

[SnuffaBolshevik]

"...use water both as a coolant and as a moderator to slow down neutrons created in the fuel as it fissions. Instead, fast reactors use materials that don't slow down neutrons—often a liquid metal, such as sodium or lead"

I'm obviously not a nuclear engineer or anything close but this part caught my eye. Since lead is far denser than water, wouldn't it slow down neutrons more efficiently?

Thanks in advance.

[Pontiac]

Thanks for the props on the enrichment.

[Lx]

Short answer, no.
I would assume it is due to the extremely high pressures the PWR system uses so it uses a heat exchanger to keep the high pressures where needed and the pressure to turn the turbine where it’s needed as well as keeping the water from the reactor inside the containment building. I assume they put the heat exchanger in the containment dome in case of a leak but I am not a nuclear expert, no where near one but I do understand mechanical systems. From what I read in Wiki, BWR’s have problems with the turbines being contaminated by the reactor’s byproducts over a period of years.
All the special alloys, their increased thickness needed to contain the pressure as well as the radiation no doubt adds a lot of money to the cost of a PWR but this is one place where pinching pennys is a bad idea.

I just read (WIKI) that a PWR’s shut down in a completely cold state requires from one to three years of water circulated cooling; if that fails, it’s still possible for a meltdown. I thought the control rods were able to stop the reaction and only residual temperature needed to be dealt with. This is an area of concern.

I don’t understand why in a BWR, they put the spent fuel outside the containment dome. I know that once the refueling takes place, they intern the old fuel in a cask that is stored on site. But from what I’ve seen and keep in mind I’m no expert, that the PWR’s have a pool inside the containment dome that they store all the spent fuel in until it’s ready to be entombed on site until the nuclear waste disposal site goes into operation which is probably never.

I’ve been on a tour of Rancho Seco when it was running and they took us as close to the airlock to get in the containment building. I’m assuming that there’s a bigger one since they have to get fuel and equipment in there so why not just store the spent fuel rods there until it’s time to deal with them?

Rancho Seco got shut down because a bunch of greenies put an initiative on the ballot to close it down, that’s why they were giving tours. The problems Rancho Seco had were with the Westinghouse turbine and I don’t remember any major problems with the nuclear part although I think any problem there is a major problem.

I think the worst problem with Fukishima was location. Even I can see the problem with that. The diesels were one of the most important safety systems and then they drown due to the seawater. Does it take a genius to envision a scenario where the site gets flooded? Besides the diesels, the electrical systems probably weren’t too happy being flooded with seawater which conducts electricity better than tap water.

[Pontiac]

Since lead is far denser than water, wouldn't it slow down neutrons more efficiently?

Actually no. Lead’s nucleus being very large will cause the neutron to simply bounce off in what is termed and elastic collision. In other words the neutron does not loose any energy in the collision.

When a neutron strikes water it is considered to strike the Hydrogen nucleus (for the purpose of the explanation). The hydrogen nucleus being composed of a single proton is nearly the same mass as the neutron has an inelastic collision; that is energy is transferred from the neutron to the hydrogen nucleus. Thus the neutron slows and becomes more likely to cause the fission of a Uranium atom.

[SnuffaBolshevik]

Thanks for the succinct explanation.

I learn something on Free Republic every day.

[chimera]

Yes, BWRs have lower operating pressure and slightly lower operating temperature. In simple terms, that means less stored energy, so any kind of credible accident will progress differently than a PWR accident. For example, in a large-break LOCA, the peak pressures are quite a bit lower than for a PWR LOCA. There are others as well. That is the reason for the differences in containment design.

The primary radiation hazard on the power extraction side of a BWR is 16N, produced by n-p reactions in the 16O in the coolant. This has a 7 second half-life, so it goes away very quickly. In fact, it is possible to walk right up to the turbine and condenser of a BWR a short time after shutdown (I have done it). 16N emits a 7 MeV gamma ray, so if it is around, shielding is problematic.

Reliability of backup diesel power will be the primary focus that will occupy both industry and regulators. I would not be surprised to see some regulatory guidance issued concerning redundancy of diesel backup during various outage scenarios. Specific compensatory measures will depend on plant site characteristics. I would not expect plants inland to have to do the same kinds of things as plants near the shoreline of oceans.

Do you know what SMUD did after they trashed Rancho Seco? Do you have data on how well those things are pulling the load? Give you a hint: it ain't good.

[chimera]

Actually, I was a little off. Little Boy had a blended uranium mass. It had 50 kg enriched to 88%, with the remaining 14 kg enriched to 50%. That seems to give a “weighted average of about 82.7% So it was mostly near-90% stuff. I guess the key is that 50 kg of 88% material. Get that fissioning and you get enough neutrons to set off a lot of the lower-enrichment material, kind of like the tampers in a staged weapon.

[Pontiac]

I find that I learn a lot on FR myself.

One reason I keep coming back.

[Wonder Warthog]

"Since lead is far denser than water, wouldn't it slow down neutrons more efficiently?"

Actually, no. Neutrons "slow down" by losing momentum in collisions with other matter. The most effective "slowing down" material is one that has a high percentage of hydrogen. If you think of the neutron as a billiard ball hitting 1) another billiard ball (i.e. hydrogen), or 2) a bowling ball (lead). With 1), the neutron transfers its momentum to the hydrogen nucleus (i.e. the neutron stops and the hydrogen nucleus goes flying off with the neutron's energy). With 2), the lead nucleus is so massive that the neutron just bounces off with its direction changed, but little energy lost.

What lead stops effectively is/are gamma rays (due to the large number of inner shell electrons that the gammas can "kick out" of their shells).

This is a fairly common misconception among "non-nuke" folks.

[Lx]

Thank you for the information, very fascinating.

Do you know what SMUD did after they trashed Rancho Seco? Do you have data on how well those things are pulling the load? Give you a hint: it ain't good.

This doesn't sound good, please enlighten me. I don't live in a SMUD area anymore, we have PG&E.