Where Those Reactors and Centrifuges Came From

[rodeodance]

March 10, 2007
Op-Ed Contributor
Where Those Reactors and Centrifuges Came From
By JEREMY BERNSTEIN

Aspen, Colo.

THE six-party agreement signed with North Korea last month should certainly be applauded as a necessary first step in improving relations with the United States. While a good deal of the North Korean program is shrouded in mystery — just this week the United States again urged the North Koreans to disclose any uranium-enrichment activities — there are some things we do know, including the nature and status of the country’s reactors.

North Korea’s one functioning reactor, at Yongbyon, uses natural uranium for fuel and graphite as its moderator (the substance that slows the neutrons and enhances the fission reaction). These are the same ingredients used in the first reactor ever designed, which was tested by Enrico Fermi at the University of Chicago in 1942. The best estimate is that Yongbyon has produced about 100 pounds of plutonium since it went into full operation in 1990. This is enough for six to eight nuclear bombs, depending on their design. (The North Koreans might have used about six kilograms in their Oct. 9 test.) The construction of the larger reactors North Korea was building was apparently already suspended, for various technical reasons, before the agreement.

The North Koreans have been fairly transparent about their reactor program but almost totally opaque about their program to make natural uranium suitable for nuclear weapons by using centrifuges. We know that there is such a program, but we do not know where it is or how much, if any, uranium it has enriched. Centrifuges are much easier to hide than reactors.

The provenance of the North Korean centrifuge program is a useful lesson in nuclear proliferation. One can trace it back to the spring of 1945, when the Russians were overrunning Germany. Along with the army came a cadre of atomic and nuclear physicists who were looking for both German physicists and metallic uranium. ..........

http://www.nytimes.com/2007/03/10/opinion/10bernstein.html?_r=1&th=&oref=slogin&emc=th&pagewanted=print

[Turbineguy]

1. Graphite moderated.

They can be tricky to operate as was found out at Windscale and Chernobyl.

I don't have my nuclear engineering books anymore but recall there is an isotope that builds up in the graphite reducing it's effectiveness as a moderator. The proper graphite properties are restored by periodically cooking out the reactor i.e. raising the core temperature to a point close to where the graphite itself burns for a period of time. Of course if it is done carefully and following proper procedure, everything goes fine.

After the Chernobyl disaster the Bulletin of the Atomic Scientists did a great writeup of what led to the events. It was interference by politicians into the reactor operation that caused the meltdown. With Bush posturing on nuclear power, lets hope these guys never get into the nuclear (nukular) business. With Bush's penchant for appointing incompetent political hacks to important posts, we'd be in the soup quick.

A nuclear engineer friend of mine described the Chernobyl meltdown as resulting from a "prompt critical excursion".

(Maybe one of the DU nuclear physics wizards can correct me if I am wrong here.)

On edit: Sorry, did not mean to hijack your thread.