Exploring the Nazis' Use of Heavy Water

[kaos]

Heavy water ?

I ve read somewhere that the Nazis needed heavy water for their atom bomb. Isnt heavy water water with deuterium instead of hydrogen. So why is heavy water needed to make their project successful? Were they aiming for fusion instead??

 

[Astronuc]

Heavy water contains D rather than H. D (deuterium) has a low neutron absorption cross-section, and is used in heavy water reactors (e.g. CANDU) as it permits the use of low (or natural) enriched U.

The U-235 mostly fissions, but U-238 captures neutrons and becomes U-239, which then decays by beta emssion to Np-239, which then decays by beta emission to Pu-239. This is the common production method for producing Pu-239. Pu-239 was the basis of the "Fat man" atomic bomb dropped on Nagasaki, Aug 9, 1945.

from Wikipedia

In 1934, Norsk Hydro built the first commercial heavy water plant with a capacity of 12 tonnes per year at Vemork. During World War II, the allies decided to destroy the plant and its heavy water in order to inhibit the Nazi development of nuclear weapons. In late 1942, a raid by British paratroopers failed when the gliders crashed. All the raiders were killed in the crash or shot by German army troops. In February 1943, a group of 12 Norwegian infiltrators, trained in Britain by the Special Operations Executive and dropped by parachute into Norway, managed to disrupt production for two months by dynamiting the facilities. On November 16, 1943, the allied air forces dropped over 400 bombs on the site.

The allied air raid prompted the Nazi German government to move all available heavy water to Germany for safekeeping. However, on February 20, 1944, a Norwegian partisan was able to sink the ferry carrying the heavy water across Lake Tinnsjø at the cost of 14 Norwegian civilians.

cited by several sites discussing the Allied operation in the Telemark district.

 

[kaos]

Oh i see, its used to manufacture plutonium. Thanx for the info.I thoght that they got plans for fusionn or something.

 

[Astronuc]

They would have needed tritium, T = H³, for that, or they could have used LiD if they were knowledgeable - which I doubt.

Remember the US and Soviet Union did not have thermonuclear devices until the early 1950's.

The first thermonuclear weapon demonstration-- MIKE-- took place November 1, 1952, with a measured yield of about 11 megatons (11 MT), more than 500 times . . .

from www.fas.org

 

[mathman]

In order to detonate a fusion weapon, one needs a fission weapon as a trigger. Therefore it is necessary to develop a fission weapon before even thinking about a fusion weapon. The WWII German program, like the American and Russian programs, was aimed at fission weapons.

One problem the Germans had is that they had miscalculated the cross-section of Carbon, so they thought they had to use heavy water as a moderator. The US Pu production used graphite reactors (Hanford).

 

[Astronuc]

IIRC, the carbon used by the Germans had impurities which greatly increased the absorption of neutrons. The graphite used in the US was metallurgically pure - I believe from carbon black.

 

[Morbius]

IIRC, the carbon used by the Germans had impurities which greatly increased the absorption of neutrons. The graphite used in the US was metallurgically pure - I believe from carbon black.

The reason one wants heavy water is to produce Plutonium. In order to produce Plutonium,
you need a reactor - but you need a reactor that can be fueled by natural Uranium. One of
the reasons for going with Plutonium fuel is to avoid the need to develop enrichment
[ isotopic separation ] technology. You need enrichment technology to get the reactor to
run unless it can run on natural Uranium.

There are only two materials that can be used to moderate a natural Uranium reactor -
heavy water and graphite. The heavy water is a slam dunk - but the graphite is a bit
more iffy. A German scientist by the name of Walter Bothe measured the neutron
absorption properties of graphite and concluded it could NOT be used to moderate a
natural uranium reactor. Hence, the German program turned to heavy water.

Courtesy of the American Institute of Physics:

http://www.aip.org/pt/vol-53/iss-7/p34.html

In the USA, Enrico Fermi did the same experiment and got the same result - that
graphite could not be used. However, he thought that the neutron absorption properties
were measured higher than they should have been according to his theories. Fermi
investigated further - and discovered that graphite typically has trace amounts of
Boron - a potent neutron absorber - in it. Fermi obtained boron free graphite and
he remeasured its properties. The refined graphite COULD be used to moderate a
reactor that was fueled by natural Uranium. This led to thefamous exeriment of
Dec 2, 1942 in the squash court under the stands of the University of Chicago's
Stagg Field football stadium.

Dr. Gregory Greenman
Physicist