Yet another new battery breakthrough

Where did you come up with that idea, a Tom Clancy novel perhaps? If the control rods in a conventional power reactor are not used for adjusting criticality above unity to ramp up power levels, how do you think they do it? How do you think they adjust criticality below unity to ramp down power levels during a normal shutdown, if not with the control rods?

Try "Elements of Nuclear Reactor Engineering" by L Wang Lau, Tennessee Valley Authority, for an explanation of how control rods work.

Sub-megawatt systems are just what we need, especially since our national power grids are so pathetic or not even existing in enough places.

- Brad Guth

There's a price tag in there. 200kw X 40 years X $.05 = three point five million dollars? Plus the cost of distribution and investor profit and they should be able to supply power for about $ 0.12/KWH . . .

Toshiba was supposed to be bidding on a small reactor in Gelena Alaska that was supposed to produce 10 megawatts of power at a cost of 5-12 cents a KWH - TO OPERATE . . . isn't automatic

Different system with a liquid sodium and underground bunker, and fairly large building.

It does.

They use control rods for control, constantly.

And a reactor can be designed to be under-moderated, where neutron-slowing (but not neutron absorbing) control rods or equivalent cooling fluid enhance the reaction rate. A boiling-water reactor is moderated by the water itself, so if ever the water is lost the main fission reaction stops. (A moderator is necessary to slow down neutrons to thermal velocities. Fast neutrons zip through and are lost.)

One of the problems in the Chernobyl disaster was that the ends of the absorbing rods acted as moderators, so actually made things worse.

John

How could that reactor be safe? It would have a critical mass of uranium, and produce the standard cocktail of incredibly nasty hot isotopes. And it would kill any person or cat who hung out in the vicinity for very long. At least you wouldn't need to mow the grass nearby. Hey, store the apartment complex's garbage next to the reactor, so it will stay fresh and odorless.

John

Sounds like something everyone in San Francisco should have... along with their overly taxed caffeinated soft drinks ;-)

...Jim Thompson

John Larkin wrote in news: snipped-for-privacy@4ax.com:

Clueless.

What country do you live in?

Supplying it with enough pure Li6 would in itself be excruciatingly expensive. It sounds more like a research reactor design intended to produce thermal neutron beams for experimental physics and a bit of electricity on the side rather than the new must have geek toy.

I expect it was formally launched on 1st April too. No mention of it at all on Toshibas own Japanese nuclear engineering site and they are genuine nuclear reactor builders with about 34% of the Japanese installed base, Designs which are intrinsically failsafe are now possible.

They are principally selling their new ABWR designs at present for which 1GW is their idea of a small design. Features list in English version includes "entranced (sic) reliability". I rather like that one....

Put enough shielding around it and prayer. In about equal measure.

Regards, Martin Brown

We have a lot of rooftop solar here, which makes about as much sense.

John

Glen Walpert hath wroth:

I like Tom Clancy military books because they inspire the imagination.

Correct. Todays reactors use control rods for shutdown, not for fine turning and regulating power levels. They certainly are not used to "initiate" the reaction, which the article suggests. Frankly, I don't see how one could safely build even a tiny reactor without control rods, as the article also suggests.

Ah, the voice of authority. See: DOE FUNDAMENTALS HANDBOOK. NUCLEAR PHYSICS AND REACTOR THEORY

section on Control Rods and section on Soluable Poisons in volume 2.

See:

which offers:

Additional means of reactivity regulation

Usually there are also other means of controlling reactivity: In the PWR design a soluble neutron absorber (boric acid) is added to the reactor coolant allowing the complete extraction of the control rods during stationary power operation ensuring an even power and flux distribution over the entire core. This chemical shim, along with the use of burnable neutron poisons within the fuel pellets, is used to assist regulation of the long term reactivity of the core,[5] while the control rods are used for rapid changes to the reactor power (e.g. shutdown and start up). Operators of BWRs use the coolant flow through the core to control reactivity by varying the speed of the reactor recirculation pumps (an increase in coolant flow through the core improves the removal of steam bubbles, thus increasing the density of the coolant/moderator with the result of increasing power).

In other words, the control rods are used for emergency shut down, while a soluable nuclear poison (chemical shim) is used for power control in pressurized water reactors. Control is by changing the concentration of boron in the cooling water, which is rather a slow process more suitable for control, not for an emergency shutdown. (Despite the lack of speed, some SCRAM procedures dump nuclear poisons into the cooling water for additional safety.) A chemical shim is also useful for long term compensation for nuclear poison buildup and fuel depletion. Since the proposed Toshiba reactor has an alleged lifetime of 40 years, presumeably without replenishing the fuel, such long term fine compensation will be a necessity.

Richard Henry hath wroth:

Ye of little imagination. Let's make the assumption that you wanted to design a radioactive decay assisted domestic water heater for the purpose of disposing of hot reactor byproducts and waste. Three obvious problems appear immediately.

1. Pollutants in the water may be become radioactive.
2. Shielding is necessary to avoid exposure.
3. Heat build up must be regulated and controlled.

The first (hot dirt) can be solved by filtration. Considering the junk found in domestic water, this might be a good idea even without nuclear heating. Incidentally, nuclear heated water will be essentially sterilized.

Shielding can best be accomplished by burying the water heater. This is the method that Toshiba proposes for their domestic reactor. It's also a common paradigm, where anything dangerous is made safe by burying it. Polyethylene foam should work well for both shielding and thermal insulation. The water in the heater will also provide substantial shielding.

Heat build up is a big problem. Unlike with a chain reaction, there is no easy way to regulate nuclear decay. It will decay, and therefore generate heat, continuously and without much variation. Left to itself, the water will simply get hotter and hotter, until it boils away. Some method of removing the waste heat will be necessary and can be done with conventional thermodynamic methods such as radiators and heat pumps.

There are plenty of other technical problems that will need to be solved. I'm sure they can be dealt with as they appear.

If the US embarks on a program to bury moderate half-life reactor and fuel processing byproducts in domestic water heaters, there will surely be a substantial reduction in domestic energy requirements, nuclear waste disposal, and water borne pathogen problems. We have successfully deployed fundamentally dangerous substances, such as propane, natural gas, and fuel oil, gasoline, electric power, etc in the home. We can surely do the same with nuclear power. After all, it is energy and should not go to waste.

On a sunny day (Wed, 19 Dec 2007 12:01:19 -0800) it happened Jeff Liebermann wrote in :

It would work, but the risk of Osama & Co ordering one, taking it apart, and making a dirty bomb, is too big.

I proposed in a letter to the local utility some years ago that they dispose of their radioactive waste by delivering small quantities of it to all their stockholders.

That would solve the decommissioning problem, would'nt it?

martin

Some are entertaining, but facts are not his big strong point. I only mentioned him because I read some serious reactor misinformation in one of his books, similar to your apparent misconceptions.

OK, then tell us how they start the reaction, if not with the control rods.

(I agree that they are not used to trim full power level in some reactor designs, but disagree that this is even slightly similar to "not used for control" or "only used for emergency shutdown".)

I did, but it provides absolutely no support for your stated position.

These documents are management overviews of basic reactor theory, completely lacking in detail. The reactor engineering textbook I mentioned gets into the actual design methodology in much more detail, being written for engineers not managers.

But the control rods are still the primary means of control.

--------------------------------------------^^^^^^^^^^^^^^^^^^^^^

Which part of "shutdown and startup" do you not consider to be control?

Indeed, control rod position is not the only means of adjusting criticality. Just the only one that has fast response, and the only one used for *normal* startup and shutdown in the current generation of PWRs and BWRs. Fine shimming of full power with other means in some reactor designs does not make the function of the *control* rods something other than control.

and normal shutdown, and normal startup, and normal large adjustments in power level if any - all control except for slow fine adjustment of full power levels in some reactor designs. Most definitely not *only* used for emergency shutdown.

Wasn't it the greenies and their anti-lead crusade that gave us MTBE?

Thanks, Rich

Why not email Toshiba and ask them about these things?

Good Luck! Rich