Oh, you just can’t wait to figure out what the hell that means, can you?

I noticed a fun fact about plutonium pits while reading the AAAS report on the Reliable Replacement Warhead: During the Cold War workers at Rocky Flats worked plutonium (“wrought processing”) to make a spherical pit; today, TA-55 casts them in a furnace (image at right).

The AAAS panel noted the change, explaining that the decision was made in part due to the expense and difficulty of installing the necessary equipment for wrought processing at TA-55. (Haninah also mentioned this in passing in his excellent DefenseTech series on the RRW and included a link to Kautz et al, “The Pit Production Story” from Los Alamos Science Number 28, 2003.)

Anyway, the AAAS panel observed that a sufficient test pedigree exists for cast pits. Someone asked about the difference between wrought and cast pits at an ACA panel. Dick Garwin claimed the two methods result in pits that perform equivalently:

QUESTION: … You stated that if it turns out that there are serious problems with pits we can always remanufacture them to original specifications. At present I believe that’s not exactly true because the original specifications called for wrought plutonium pits and today we only have the capability to build the cast ones. … Do you believe that there is no difference, or are you supporting building a modern pit facility that will allow us to build wrought pits?

[snip]

GARWIN: This was an early question when people at Los Alamos started manufacturing pits there. They had them made at Rocky Flats, but Rocky Flats was shut down and Los Alamos was made to bite the bullet and build new pits at TA-55 for the W-88 nuclear weapon. I was on the visiting committee that looked at this. We have made certifiable pits. They are made by cast and machine process. The decision was made and people have judged that cast and wrought perform equivalently. One can find minor differences in strength, and the more we know about it, the more they are equivalent within the range that you need.

There is not a significant difference in primary yield and you don’t need to reopen that question. That decision has been made. Remanufacturing to original specification will allow the substitution of cast plutonium for wrought plutonium so long as the dimensions are correct.

[Emphasis Mine]

Turns out, Los Alamos performed a series of subcritical experiments “to investigate differences in material properties between cast and wrought plutonium driven by high explosives (HE).”

Los Alamos named the series … wait for it … Stallion, and the experiments … I am so not making this up … Mario, Rocco, and Armando.

Mario, Rocco and Armando. The Italian Stallians that prove cast Pu performs just as well as wrought.

Of course, casting pits is only the most significant of a number of changes that occurred when production moved to TA_55. Another significant difference is that Los Alamos developed a “dry machining” technique that avoids the use of lubricants that leave a toxic mess (think radioactive Santorum).

Okay, okay, that’s enough. I am sorry. Off to have a beer with John Park.

If you want to know more, just
read Kautz et al.