# Newb in nuclear

1. May 3, 2006

### Totam

I am new to nuclear.

you could answer me one question : why do people say "fission", I thank you

2. May 3, 2006

### Astronuc

Staff Emeritus
From Merriam-Webster's dictionary - Etymology: Latin fission-, fissio, from findere to split

1 : a splitting or breaking up into parts

3 : the splitting of an atomic nucleus resulting in the release of large amounts of energy

3. May 3, 2006

### Totam

thank you, please one more question, could tell me who first discovered atom splitting method ?

4. May 5, 2006

### Grogs

Hahn and Strassman were the first to observe nuclear fission in 1939. Fermi and Szilard built the first self-sustaining nuclear reactor in December 1942.

5. May 5, 2006

### Astronuc

Staff Emeritus
Let's not forget Lise Meitner's contribution to the discovery of fission.

Otto Hahn won the Nobel Prize in Chemistry in 1944 for "his discovery of fission of heavy nuclei". I think Meitner and Strassman should have shared the prize. :grumpy:

Sir James Chadwick had discovered the neutron in 1932. He won the 1935 Nobel Prize in Physics for the discovery.

6. May 5, 2006

### Kalouste

Lise Meitner was 60 years old and was stuck in Stocholm in 1938, although she was born in Austria. Lise Meitner was considered to be one of the most notable scientists in Germany: "Our Madame Curie", Einstein said. Otto Hahn and Meitner shared a laboratory in Berlin (Kaiser Wilhelm). Meitner completed a portion of the periodic table all by herself but insisted with the editor of Physikalische Zeitschrift to include Hahn's name, although he had done nothing to earn that right.

Anyway, in 1938 Germany invaded Austria and the permanency of Meitner in the Kaiser Wilhelm Institutes strongly depend on her colleagues' opinions. Meitner was jewish. Hahn asked Heinrich Horlein, the laboratory finances responsible, to get rid of Meitner.

Was only when Strassman and Hahn felt desioriented with experiment results that they needed again the "brain" of the team: well, all work developed by Hahn and Strassman was supervisioned by Meitner from Stocholm since her departure.

Near Christmas, Lise Meitner and her nephew Robert Frisch unveilled Hahn's experiment, which inferences I assume you know.

The name: fission

Frish recalled the bacteria division process and, when he was returning to Copenhaga, asked a american biologist from Bohr's Institute what was the correct term for describing such process: he answered "fission". Meanwhile, Hahn had already published the results in Berlin, with a minimal reference to Meitner's crucial contribution. Although Hahn's efforts (he even started a campaign for 15 years in which he had given all credits to himself) Lise Meitner was never forgotten and today we mention her.

Post Scriptum: Sorry for any grammar errors found. I'm still learning english.

Last edited: May 5, 2006
7. May 5, 2006

### Morbius

Astronuc,

Yes - Meitner was really the first to understand / explain what was happening.

Hann and Strassman were the first to fission U-235; but that's not what they were
trying to do. They were trying to transmute Uranium to the next higher element,
subsequently called Neptunium.

Instead, they got fission products - but didn't understand what was happening.

Meitner understood what was happening - but the hope was that Hahn, et al would
not realize what was happening - because it points the way toward developing
nuclear weapons. So Meitner wasn't going to announce her interpretation of the
Hahn experiment - it would just put Hitler's Germany on the right path to having
nuclear weapons.

Dr. Gregory Greenman
Physicist

8. May 5, 2006

### Astronuc

Staff Emeritus
So technically, Meitner discovered fission!

9. May 5, 2006

### Morbius

Astronuc,

Depends on your definition of "discovered" - but as I understand it, and as I
define "discovered" - then yes; Meitner discovered fission. She was the first
to actually understand the results of Hahn and Strassman.

Hahn and Strassman were the first to obtain the experimental indications of
fission - but for me - "discover" is explaining the result.

Hahn and Strassman later, independently; came to the same conclusion that
Meitner did. The indications that they had done so led Leo Szilard and members
of the Uranium Committee to press FDR to start the Manhattan Project. That's
when Szilard wrote the famouns "Einstein letter" that was sent to FDR over
Einstein's signature.

Edward Teller was always proud of the fact that he drove Szilard to his meeting
with Einstein, since Szilard didn't drive.

Dr. Gregory Greenman
Physicist

10. May 6, 2006

### Grogs

They had a great show on this recently. It was one of the 'Ten Days That Changed the World' on the History Channel. It started with Teller and Szilard driving to Einstein's house to ask if he'd sign the first letter, then progressed through the first and second letters, the CP-1 reactor, and all the way to the dropping of the first bomb on Hiroshima.

11. May 6, 2006

### Morbius

Grogs,

Yes - I also saw that program and recommend it highly.

The History Channel does some good stuff - however sometimes they really get it
wrong. Last night on the "Super Tools - Ships" segment of Modern Marvels, they
discussed how the plasma torch used for cutting steel plates for building aircraft
carriers employs Hafnium because of its high temperature characteristics.

They go on to say that the high temperature characteristics of Hafnium is also the
reason it is used in the control rods of some nuclear reactors.

WRONG WRONG WRONG, History Channel.

Hafnium is used in the control rods of nuclear reactors because it has a high
neutron capture cross-section - it gobbles up neutrons - which is what a control rod
has to do. The temperatures experienced by the control rods is only a few hundred
degrees. There are other materials in the control rods and drives and the associated
areas of the reactor that can't take the high temperatures that Hafnium can - but don't
need to - because the temperatures don't get that high.

Hafnium is used in control rods because it a neutron absorber. One can also use
Cadmium and Boron as control absorber - and they don't have the high temperature
characteristics that Hafnium has - characteristics that are not needed in control rods.

Dr. Gregory Greenman
Physicist

12. May 6, 2006

### Astronuc

Staff Emeritus
Boron is used in control rods in LWRs normally in the form of B4C, and it can be enriched from 20% B-10 to more like 55%. But the problem with B-10 is the (n, $\alpha$) reaction which produces He.

Also, PWRs use Ag-In-Cd, but Ag can be expensive and In and Cd are toxic. In addition, Ag-In-Cd swells and creeps.

Hf (in the recrystallized form) is attractive because it does not swell, it is relatively inexpensive as a by-product of the production of nuclear grade Zr, it has good high temperature properties, and it does not produce gas. One downside is that Hf absorbs hydrogen and it will swell if that happens. Hf was withdrawn from the commercial nuclear market because of hydrogen absorption and swelling problems in PWR control rods, however it is used in some modern BWR control blades.

The Russians have been using Dysprosium in the form of Dy2TiO5, and now the Indians are looking at it.
http://www.indian-nuclear-society.org.in/conf/2005/pdf_3/topic_06/T6_CP3_Amit_Sinha.pdf [Broken]

Last edited by a moderator: May 2, 2017
13. May 7, 2006

### Morbius

Astronuc,

As I recall, BWR control blades primarily use Boron as the neutron absorber, and
PWRs primarily use Cadmium in the pins of the control rods.

When I was a graduate student, one of my teachers, Prof. A.F. Henry; I recall stated
that the U.S. Navy bought up practically all the Hafnium for their propulsion reactors
since it is such a good absorber.

Dr. Gregory Greenman
Physicist

14. May 7, 2006

### Astronuc

Staff Emeritus
Morbius, traditionally BWRs used B4C encapsulated in SS304/SS308 tubing, and these were then contained in a perforated sheath. Since the 1990's Hf rods, plates and bars have been introduced into the high fluence zones of control blades in order to extend the life. Hf doesn't swell as much as B4C, nor does it have the depletion issue as a function of exposure.

In PWRs, the manufacturers traditionally used Ag-In-Cd, each element of which absorbs over different range of neutron energies, with Cd being the thermal neutron absorber and In and Ag absorbing higher thermal, epithermal and resonance energies. In one vendors fuel/core design, the control rods occupied the equivalent 4 fuel rod positions and they decided to use B4C with Ag-In-Cd tips because of mass issues.

Anyway on PWR vendor did use Hf in the control rods. Unfortunately, SS is rather porous to H, and the H from the coolant found its way to dry Hf, which sucked up the H and began to swell as a result of HfH2 formation. The control rods swelled and cracked - a big NO-NO! The Hf rod were withdrawn from service.

15. May 7, 2006

### Morbius

Astronuc,

As I recall from Professor Henry, who used to be the head of computational reactor
physics for Westinghouse's Bettis Lab - one of the two naval reactor design labs
[the other being GE's Knolls Atomic Power Lab aka. KAPL], the naval propulsion
reactors use Hafnium as control absorber.

The naval reactors are PWRs [ one doesn't want a free coolant surface as in a BWR
with a ship-board reactor that won't always be level ], then I assume the naval
reactors use something other than SS to clad the Hafnium control elements; or they
would have the same problem you explain above.

Do you know what the naval reactors use in place of SS to clad their control rods?
If one knows what the Navy uses - could that also be used in commercial PWRs?

Dr. Gregory Greenman
Physicist

16. May 7, 2006

### Astronuc

Staff Emeritus
One way to mitigate hydrogen absorbtion in Hf and for that matter Zr and Ti is to allow the surface to oxidize. I believe the naval control rods have a different geometry than commercial, since the fuel has a different geomentry. All that those details remain classified, even though the Russians (and possibly Chinese) apparently copied one or more of the designs. It's generally known that naval reactors contain Zr, U, Hf and water, and that's about it.

17. May 8, 2006

### Morbius

Astronuc,

Yes - I'm aware of the classified geometry of the naval reactors. One of my
co-workers is an ex-Navy nuclear engineer explained it - of course, we both have
security clearances.

Dr. Gregory Greenman
Physicist