Why Truman Dropped the Bomb

[Shapley]

Just a side note:

When fission occurs, the fission produces among the byproducts neutrons, and lesser elemental nuclei (elements with a lower atomic number than the original fuel). The neutrons produced as a direct result of the fission are "prompt" neutrons. Some of the lesser elemental nuclei decay shortly after their production, releasing neutrons known as "delayed neutrons".

If a reactor is taken to the point that supercriticality (an increasing rate of fission) is maintained by prompt neutrons alone, it is said to be "prompt critical". In such a case, control of the reactor is not possible, for the reasons Analog cites above.

V/R
Shapley

[Shapley]

Analog,

Thanks for the explanation. OT and I were both puzzled, because we do not use the term "dollar" in Naval Nuclear Power terminology, at least not that I've heard, and apparently not OT either. Void worth, as I understand it, is a term limited to boiling-water reactors (such as Chernobyl), which the Navy does not use. Boiling in the core is a no-no in a pressurized water reactor.

V/R
Shapley

[analog]

Sorry, guys - Dollar came from the old Glasstone textbook we used when I took reactor physics in 1967. It's so intuitive I never let go of it, though in commercial power we used "per cent millirho". I knew the Navy used something else.

Not knowing quite who was audience i tried to write the above like Asimov would've, developing just one real simple thought at a time. Hope nobody was offended. I have to think simple, or not at all.

Thanks for adding delayed neutrons. In terms of my simple multiplying engine, the delayed neutrons set the duration of my "Instant" to a few tenths of a second. So it multiplies a few times a second. Once you get prompt critical, there's no more delay in the arrival of fresh neutrons, so that duration drops to a fraction of a millisecond . Now the multiplying engine speeds up to thousands of multiplications a second and runs away. That speedup is a drastic change in behavior, to running on prompt neutrons alone, hence the term Prompt Critical.

The guys at Chernobyl were trying to get around an at power trip, ie hang onto reactor after a turbine trip from low power. The idea was cooked up by some electrical engineer types who apparently didn't fully appreciate reactor physics. No navy nuke I know would've allowed it.

<small>[ 08-26-2005, 03:31 PM: Message edited by: analog ]</small>

[Shapley]

Analog,

No problem. I didn't doubt your expertise, I just knew we were coming from different backgrounds on this.

I wouldn't have recognized the "Asimov approach", since I've not read his works.

The audience here is quite varied. You never know who's lurking in the background here. That's what makes it such a fun group.

V/R
Shapley

[analog]

Amen, and thanks.
Look for Asimov in your thrift shops - he has hundreds of fascinating paperbacks on every subject from Shakespeare to the Bible to Astronomy and Biochemistry. You'd probably love "The Neutrino".

[Selma in Sandy Eggo]

Thanks for the explanation, Analog. <<Q - is the name from the magazine? A favored indicator or test instrument?>> The Asimov approach always works well, and has since he used to write the occasional Analog column. I am forever indebted to him for explaining how to decipher chemical terms, in just such an article, when I was twelve or so.

Shapley, I'm appalled. No Asimov at all? Not even a little? If not the SF, how about the murder mysteries, the textbooks, the essays? Try it, you have such a treat in store!

[Shapley]

Selma,

I have his books on Physics sitting on the shelf at home, where they've been for years, begging to be read. Everytime I reach for them, some sailing book nearby will grab my attention, and I'm off on another adventure 'round the horn or into the mysterious South Pacific.

Maybe I need to rearrange the shelves....

V/R
Shapley

[Shapley]

Analog,

We used the term "delta rho", which we were supposed to pronounce "The change in reactivity levels over time", but we just said "delta rho". (Our instructors used to be very adamant that we not "speak in symbols", but we always did.

Of course, we oftentimes just said we were going to "give it a little shot of reactivity", which sounded like a Bob Dylan song to me:

Give me a little shot of that reactivity, baby.
Just a little touch from your fissile hand.
Oh, Give me a little shot of that reactivity, baby,
and you'll put my T[ave] back in the green band.

Baby, you've been gone so long from me,
my average coolant temperature is on the slide,
But, baby, just a smile, just a touch,
and you'll put my delta rho back on the positive side!

Give me a little shot of that reactivity, baby,
just let me feel the warmth of your hand,
give a little shot of that reactivity, baby,
and you'll but my T[ave] back in the Gree-een Bayand!

Of course, it just cries out for a verse about Xenon buildup and Macroscopic cross-sections for absorption, but I couldn't quite fit them in.

V/R
Shapley

[OperaTenor]

Hi Analog,

What Shap said, I wasn't familiar with the Dollar term, thanks for elucidating.
I always thought boiling water reactors were just a bad idea, but that might've been my Navy education prejudicing me. The process of boiling water has so much thermodynamic latitude(bless LHV), I would think it not a good band to rely on, since so much enregy transience can occur with no change in pressure or temperature(help me, Analog, if I'm way out to lunch here).

BTW, let's not forget those thermalized neutrons....



<small>[ 08-29-2005, 10:51 AM: Message edited by: OperaTenor ]</small>

[piqaboo]

originally posted by Shapley:
We used the term "delta rho", which we were supposed to pronounce "The change in reactivity levels over time",

Reminds me of my job description, which includes
"responsibility to follow up", which is pronounced "nag".

[BigJon@Work]

Originally posted by Shapley:
Give me a little shot of that reactivity, baby.
Just a little touch from your fissile hand.
Oh, Give me a little shot of that reactivity, baby,
and you'll put my T[ave] back in the green band.

Baby, you've been gone so long from me,
my average coolant temperature is on the slide,
But, baby, just a smile, just a touch,
and you'll put my delta rho back on the positive side!

Give me a little shot of that reactivity, baby,
just let me feel the warmth of your hand,
give a little shot of that reactivity, baby,
and you'll but my T[ave] back in the Gree-een Bayand!

Of course, it just cries out for a verse about Xenon buildup and Macroscopic cross-sections for absorption, but I couldn't quite fit them in.

Let's see if we can get bignag to write a tune for this . . .

[analog]

Originally posted by OperaTenor:
Hi Analog,

I always thought boiling water reactors were just a bad idea, but that might've been my Navy education prejudicing me.

BTW, let's not forget those thermalized neutrons....

OT, Shap

I gather Shap is navy also? Hats off to both of you.

I spent my years in a commercial PWR. The thinking at my utility was they didn't want a BWR on the coast because of how fast salt water wrecks demineralizers. They knew they'd someday wind up with irradiated salt in the reactor from condenser leaks. They wanted that extra barrier of steam generator tubes between the ocean and the reactor. I think they were wise. The Westinghouse PWR is pretty much a scaled up navy plant with chemical shim and only about 3% enrichment. We had a 2200 megawatt core, 1300 ft^3 pressurizer, and on a good day could make 746 megawatts (exactly a million horsepower)of electricity at about a fifth the cost of oil fired generation...


I liked the "Ode to reactivity."

One of our control room sayings, post chernobyl:
"I'm scared of the Dark,
...and I'm scared of Sharks,
....but mostly of graphite moderated reactors."

[analog]

<<Q - is the name from the magazine? A favored indicator or test instrument?>>

Selma --

It's sorta a laugh at myself - analog as opposed to logical.
Analog computers are considered relics, but i still love them especially for automatic controls. I like my slide rule, too.

(foolishness deleted)

<small>[ 09-06-2005, 06:55 AM: Message edited by: analog ]</small>

[OperaTenor]

Hi Analog,

Thank you.

Yes, but not only Shapley. Hal9000 was also a Navy nuc. Shap and I attended NPS the same year, but different classes(me - 8104, Shap - 8107), and Hal was in a bit later than we were. I seem to recall somewhere around 1990 for enlisting.

However, They were both surface EO's, and I was a submarine MO.

The boat I was on(USS Guardfish, SSN-612), was an SSN-593(4) class fast attack sub with an S5W reactor. It had a whopping 78MW core. 16,000 hp at the shaft.



<small>[ 09-05-2005, 03:07 AM: Message edited by: OperaTenor ]</small>

[annettehala]

Wish I had seen this earlier. I have been to Hiroshima more times than I can count. During my growing up years I was torn between allegiances. WWII confused me. The people of my race were destroying my homeland. I made the atomic bombing of Hiroshima and WWII in the Pacific my special project in high school. I wanted to study every detail and form my own opinions. I don't have time to give a detailed review now, (see my other post link ) but in summery I am glad we dropped that bomb and I don't believe it was any crueler than any other weapon of war.