Sunday, March 25, 2007
Blood in the Bathtub: A Better LLNL RRW?
Debate rages over bathtub shape
--Ian Hoffman, Staff Writer, Inside Bay Area, 03/25/2007
For Gen. James Cartwright, the military commander over U.S. nuclear forces, the first hydrogen bomb to come out of an American nuclear design lab in 20 years doesn't look very new.
The warhead is launched by the same submarines on the same missiles at the same targets and produces the same blast as the warhead it replaces.
"This is far from being a new warhead because it still has the same form, fit and function as the existing warhead," agrees Steve Henry, deputy assistant defense secretary for nuclear affairs.
But Sen. Dianne Feinstein figures by putting more sophisticated warheads on the same missile "you are essentially creating a new nuclear weapon."
Weapons experts themselves are sharply divided.
In designing a hardier replacement for the warhead atop the Navy's Trident missiles, Lawrence Livermore Lab scientists poured more muscle and a few added features into an early 1980s-vintage warhead.
The new/not-new distinction is more than semantic: A truly new bomb probably would need explosive testing, something U.S. presidents have forsworn since 1992, partly to block other nations from testing new designs.
What everyone can agree on is that Livermore's latest bomb the first in a planned series of "reliable, replacement warheads," or RRWs never has been manufactured. That means it is vulnerable to the kinds of flaws and breakdowns that afflict every complex object, from trains to automobiles to computers and even living things. The same is true for newly made nuclear bombs, with thousands of parts.
"What you know from bringing in these bright, new, shining systems is they can bring in all these new defects," said Raymond Jeanloz, a physicist at the University of California, Berkeley, who sits on several advisory committees on nuclear weapons matters. "The nature of the glitches have always been very small, detailed things. These are very sophisticated systems, and it's just really hard to be sure that every detail has been shaken down. That doesn't necessarily mean it will have to be the same in the future, but in the past, really diligent people were part of the design and development cycles, and there were glitches."
Scientists, engineers, factory workers and nature itself build unforeseen flaws into the things they make. That's why products are recalled, women miscarry and consumers repair a larger universe of unacknowledged mistakes in the things they buy. It's why Windows users still are downloading security fixes and "updates" after the nth service pack.
On the other side of the equation from these "birth defects" is aging. In time, more and more critical parts break down in any organism or product until it reaches the end of its service life or dies.
Engineers depict these facts of birth, life and death as a curve that looks like a bathtub. After a number of early design- and manufacturing-related failures, the surviving units stumble through a smaller, constant number of random defects and then begin to fail in larger and larger numbers as age takes its toll.
It is tempting to think the most horrendously lethal weapons ever devised by humanity are immune to these facts of engineering and manufacture. They're not.
Numerous studies have found the weapons to be remarkably defect-free, especially as scientists learned to seal moisture out of the most sensitive components. But flaws have been found and when deemed necessary, fixed in every kind of bomb and warhead in the current U.S. nuclear arsenal, according to a 1995 study by scientists at all three U.S. nuclear weapons design labs.
That study suggested the wholesale failure of one or more bombs or warheads could come somewhere around the 28th year after a weapon is manufactured.
The deadly right-hand side of the bathtub curve, in other words, was imminent.
Yet subsequent studies showed that conclusion was statistically infirm, based on too small of a sample of examined weapons. Twelve years later, with many weapons aging past that mark and an average arsenal age of about 23 years, weapons scientists acknowledge there is no evidence yet for an age-related meltdown. It is partly fear of such a meltdown that has driven a plan by the weapons labs and the Bush administration to design replacements for every U.S. nuclear explosive.
"What is true is I think there has not been an upturn in the frequency of age-related findings that would create a sense of dramatic urgency in the sense we need to do something in the next year or two years or three years," said former Lawrence Livermore director Bruce Tarter, chairman of a committee studying the replacement warhead program for the American Association for the Advancement of Science.
U.S. nuclear bombs and warheads then rest somewhere in the stable bottom of the bathtub, past most of their birth defects and adolescence.
"I don't know where the right side of the bathtub shows up, but it is measured in hundreds of years," said Bob Peurifoy, a retired Sandia National Laboratories weapons executive.
A newly manufactured bomb such as Livermore's latest will slip into the bathtub at the left side, before possible defects in design and manufacture are discovered. The lab's RRW-1 is based heavily on a well-tested warhead from the early 1980s but will never be tested in its final manufactured state, and the probability of defects is unclear.
Livermore designers say they learn from mistakes, just as any automaker does.
"Just like Toyota, you have many fewer birth defects today than on a Toyota that you bought in 1985," said designer Bruce Goodwin, head of the lab's weapons program. "But at the end of the day a lot of the lessons learned from the last 25 years come down to simplicity of design. If you could look at RRW, you'd see many fewer parts, you'll see things that come together simply and come apart simply."
If the lab's designers make mistakes that, as in the current arsenal, don't show up for a decade or two, the RRW-1 is designed so that its first explosive stage produces at least four times the energy necessary to drive the rest of the bomb.
"You do have a very, very large margin in the system and so you can absorb defects, you can absorb insults or things that make it work less well," Goodwin said.
Without the proof of a nuclear test, skeptics such as Peurifoy aren't convinced.
"When you do something new, it's the left side of the bathtub, and if you look at automobiles, flashlight batteries, I don't care, you'll find that statistically, you make mistakes that you only discover after you put something into inventory," he said. "I go with the tried and true. I go with the stockpile that has been surveilled and maintained and, when necessary, fixed, and that's what we have today."