nuclear weapons – Helian Unbound

No, We Don’t Need to Resume Nuclear Testing

According to an article entitled In Alarming New Study, Nuclear Lab Scientists Question U.S. Weapons’ Performance that recently appeared in Investor’s Business Daily, a couple of Los Alamos scientists have released a report questioning the reliability of the U.S. nuclear arsenal, and calling for a resumption of nuclear testing. It would be a bad idea. Let me explain why.

The two scientists claim that the reliability of the aging weapons in our arsenal will become increasingly questionable as the number of years since their “best if used by” date increases. They base their argument largely on uncertainties about whether computer codes will be able to accurately predict the performance of these aging weapons. It’s true that computer codes have not always been perfectly accurate in predicting the outcome of complex physical processes. However, the significance of that fact must be weighed in the context of how it affects all the nuclear powers, not just the United States. In the absence of nuclear testing, we all have the same problem. The relevant question, then, is not whether the problem exists, but how severely it impacts us compared to the other nuclear states. We have conducted more nuclear tests than any other country, and therefore have a much larger database than our competitors with which to compare code predictions. When it comes to computer codes, that gives us a very significant advantage as long as the moratorium on testing continues. That advantage will become a great deal less significant if testing is resumed.

However, computer codes are not the only means we have of assessing the reliability of the weapons in our arsenal. The U.S. also has an unmatched advantage in terms of experimental facilities that are able to access physical conditions relevant to those that occur in nuclear weapons. For example, these include the Z machine at Sandia National Laboratories, which is capable of producing a far more powerful burst of x-rays in the laboratory than any competitor, and the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, which can dump a huge amount of energy in a tiny target in a very short time. Such facilities can access extreme material densities and temperatures, enabling a host of experiments in weapon physics and weapon effects that are currently beyond the capabilities of any other country. If we resume testing we will be throwing this advantage out the window as well. In short, we may have our problems when it comes to assessing the reliability of the weapons in our arsenal, but the problems faced by our potential competitors are even worse. Under the circumstances, it makes little sense to do something as destabilizing as rocking the nuclear boat.

If we are really worried about the reliability of our arsenal, we should seriously consider adding another experimental facility to go along with Z, NIF, and the rest. I refer to what is known as an Advanced Hydrodynamic Facility, or AHF. We seriously considered building such a facility back in the late 90’s, but have pretty much forgotten about it since then. Basically, the AHF would be a very powerful particle accelerator, capable of delivering beams of energy so penetrating that they could image the critical, high-explosive driven implosion process in nuclear weapons in its entirety in three dimensions. Obviously, it would be necessary to replace the nuclear materials used in real weapons with suitable surrogates, but this would introduce very little uncertainly in the experimental results. An AHF would not only add to our existing advantage over other nuclear states as long as the test moratorium continues, but would effectively lay to rest any remaining uncertainties not resolved by the computer codes and experimental facilities we already have.

I can understand the eagerness of weapon scientists to resume nuclear testing. It would make their lives a lot more interesting. However, it would hardly be to the advantage of the rest of us. I suggest that, instead of unilaterally taking such a foolhardy step, we maintain and expand the advantage we already have and will continue to enjoy as long as the test moratorium continues.

The Bomb and the Nuclear Posture Review

A Nuclear Posture Review (NPR) is a legislatively mandated review, typically conducted every five to ten years. It assesses such things as the role, safety and reliability of the weapons in the U.S. nuclear stockpile, the status of facilities in the nuclear weapons complex, and nuclear weapons policy in areas such as nonproliferation and arms control. The last one was conducted in 2010. The Trump Administration directed that another one be conducted this year, and the review is already in its initial stages. It should be finished by the end of the year. There is reason for concern about what the final product might look like.

Trump has made statements to the effect that the U.S. should “expand its nuclear capability,” and that, “We have nuclear arsenals that are in very terrible shape. They don’t even know if they work.” Such statements have typically been qualified by his aides. It’s hard to tell whether they reflect serious policy commitments, or just vague impressions based on a few minutes of conversation with some Pentagon wonk. In fact, there are deep differences of opinion about these matters within the nuclear establishment. That’s why the eventual content of the NPR might be problematic. There have always been people within the nuclear establishment, whether at the National Nuclear Security Administration (NNSA), the agency within the Department of Energy responsible for maintaining the stockpile, or in the military, who are champing at the bit to resume nuclear testing. Occasionally they will bluntly question the reliability of the weapons in our stockpile, even though by that very act they diminish the credibility of our nuclear deterrent. If Trump’s comments are to be taken seriously, the next NPR may reflect the fact that they have gained the upper hand. That would be unfortunate.

Is it really true that the weapons in our arsenal are “in very terrible shape,” and we “don’t even know if they work?” I doubt it. In the first place, the law requires that both the Department of Energy and the Department of Defense sign off on an annual assessment that certifies the safety and reliability of the stockpile. They have never failed to submit that certification. Beyond that, the weapons in our stockpile are the final product of more than 1000 nuclear tests. They are both safe and robust. Any credible challenge to their safety and reliability must cite some plausible reason why they might fail. I know of no such reason.

For the sake of argument, let’s consider what might go wrong. Modern weapons typically consist of a primary and a secondary. The primary consists of a hollow “pit” of highly enriched uranium or plutonium surrounded by high explosive. Often it is filled with a “boost” gas consisting of a mixture of deuterium and tritium, two heavy isotopes of hydrogen. When the weapon is used, the high explosive implodes the pit, causing it to form a dense mass that is highly supercritical. At the same time, nuclear fusion takes place in the boost gas, producing highly energetic neutrons that enhance the yield of the primary. At the right moment an “initiator” sends a burst of neutrons into the imploded pit, setting off a chain reaction that results in a nuclear explosion. Some of the tremendous energy released in this explosion in the form of x-rays then implodes the secondary, causing it, too, to explode, adding to the yield of the weapon.

What could go wrong? Of course, explosives are volatile. Those used to implode the primary might deteriorate over time. However, these explosives are carefully monitored to detect any such deterioration. Other than that, the tritium in the boost gas is radioactive, and has a half life of only a little over 12 years. It will gradually decay into helium, reducing the effectiveness of boosting. This, too, however is a well understood process, and one which is carefully monitored and compensated for by timely replacement of the tritium. Corrosion of key parts might occur, but this too, is carefully checked, and the potential sources are well understood. All these potential sources of uncertainty affect the primary. However, much of the uncertainty about their effects can be eliminated experimentally. Of course, the experiments can’t include actual nuclear explosions, but surrogate materials can be substituted for the uranium and plutonium in the pit with similar properties. The implosion process can then be observed using powerful x-ray or proton beams. Unfortunately, our experimental capabilities in this area are limited. We cannot observe the implosion process all the way from the initial explosion to the point at which maximum density is achieved in three dimensions taking “snapshots” at optimally short intervals. To do that, we would need what has been referred to as an Advanced Hydrodynamic Facility, or AHF.

We currently have an unmatched suite of above ground experimental facilities for studying the effects of aging on the weapons in our stockpile, including the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, the Z Machine at Sandia National Laboratories, and the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT) at Los Alamos. These give us a very significant leg up on the international competition when it comes to maintaining our stockpile. That is a major reason why it would be foolish for us to resume nuclear testing. We would be throwing away this advantage. Unfortunately, while we once seriously considered building an AHF, basically an extremely powerful accelerator, we never got around to doing so. It was a serious mistake. If we had such a facility, it would effectively pull the rug out from under the feet of those who want to resume testing. It would render all arguments to the effect that “we don’t even know if they work” moot. We could demonstrate with a very high level of confidence that they will indeed work.

But that’s water under the bridge. We must hope that cooler heads prevail, and the NPR doesn’t turn out to be a polemic challenging the credibility of the stockpile and advising a resumption of testing. We’re likely to find out one way or the other before the end of the year. Keep your fingers crossed.

3+2: More Tinkering with the Nuclear Arsenal

It really seems as if the weapon designers at the nation’s three nuclear weapons laboratories, Los Alamos, Livermore, and Sandia, never really believed that nuclear testing would ever end. If so, they were singularly blind to the consequences. Instead of taking the approach apparently adopted by the Russians of designing and testing robust warheads that could simply be scrapped and replaced with newly manufactured ones at the end of their service life, they decided to depend on a constant process of refurbishing old warheads, eliminating the ability to make new ones in the process. When our weapons got too old, they would be repeatedly patched up in so-called Life Extension Programs, or LEPs. Apparently it began to occur to an increasing number of people in the weapons community that maintaining the safety and reliability of the stockpile indefinitely using that approach might be a bit problematic.

The first “solution” to the problem proposed by the National Nuclear Security Administration (NNSA), the semi-autonomous agency within the Department of Energy (DOE) responsible for maintaining the nuclear stockpile, was the Reliable Replacement Warhead (RRW). It was to be robust, easy to manufacture, and easy to maintain. It was also a new, untested design. As such, it would have violated the spirit, if not the letter, of Article VI of the Non-proliferation Treaty (NPT). If it had been built, it would also very likely have forced violation of the Comprehensive Nuclear Test Ban Treaty (CTBT), which the U.S. has signed, but never ratified. It was claimed that the RRW could be built and certified without testing. This was very probably nonsense. There have always been more or less influential voices within NNSA, the Department of Defense (DoD), and the weapons labs, in favor of a return to nuclear testing. That would not have been a good thing then, and I doubt that it will be a good thing at any foreseeable time in the future. In general, I think we should do our best to keep the nuclear genie bottled up as long as possible. Fortunately, Congress agreed and killed the RRW Program.

That didn’t stop the weaponeers. They just tried a new gambit. It’s called the “3+2 Strategy.” There are currently four types of ballistic missile warheads, two bombs, and a cruise missile warhead in the U.S. arsenal. The basic idea of 3+2 would be to reduce this to three “interoperable” ballistic missile warheads and two air delivered weapons (a bomb and a cruise missile), explaining the “3+2.” In the process, the conventional chemical explosives that drive the implosion of the “atomic bomb” stage of the weapons would be replaced by insensitive high explosives (IHE). The result would supposedly be a safer, more secure stockpile that would be easier to maintain. The price tag, in round numbers, would be $60 billion.

I can only hope Congress will be as quick to deep six 3+2 as it was with the RRW. The 3+2 will require tinkering not only with the bits surrounding the nuclear explosive package (NEP), but with the NEP itself. In other words, its just as much a violation of the spirit of Article VI of the NPT as was the RRW. The predictable result of any such changes will be the “sudden realization” by the weapons labs somewhere down the line that they can’t certify the new designs without a return to nuclear testing. There’s a better and, in the long run, probably cheaper way to maintain the stockpile.

In the first place, we need to stop relying on LEPs, and return to manufacturing replacement weapons. The common argument against this is that we have lost the ability to manufacture critical parts of our weapons since the end of testing, and in some cases the facilities and companies that supplied the parts no longer exist. Nonsense! The idea that a country responsible for a quarter of the entire world’s GDP has lost the ability to reproduce the weapons it was once able to design, build and test in a few years is ridiculous. We are told that subtle changes in materials might somehow severely degrade the performance of remanufactured weapons. I doubt it. Regardless, DOE has always known there was a solution to that problem. It’s called the Advanced Hydrodynamic Facility, or AHF.

Basically, the AHF would be a giant accelerator facility capable of producing beams that would be able to image an imploding nuclear weapon pit in three dimensions and at several times during the implosion. Serious studies of such a facility were done as long ago as the mid-90’s, and there is no doubt that it is feasible. In actual experiments, of course, highly enriched uranium and plutonium would be replaced by surrogate materials such as tungsten, but they would still determine with a high degree of confidence whether a given remanufactured primary would work or not. The primary, or “atomic bomb” part of a weapon supplies the energy that sets off the secondary, or thermonuclear part. If the primary, of a weapon works, then there can be little doubt that the secondary will work as well. The AHF would be expensive, which is probably the reason it still hasn’t been built. Given the $60 billion cost of 3+2, that decision may well prove to be penny-wise and pound-foolish.

The whole point of having a nuclear arsenal is its ability to deter enemies from attacking us. Every time people who are supposed to be the experts about such things question the reliability of our stockpile, they detract from its ability to deter. I think a remanufacturing capability along with the AHF is the best way to shut them up, preventing a very bad decision to resume nuclear testing in the process. I suggest we get on with it.

Do We Really Need New Nukes?

If an article that just appeared in the LA Times is any indication, the agitation for jump-starting the nuclear weapons program at the Department of Energy (DOE) and the three nuclear weapons laboratories (Lawrence Livermore, Los Alamos, and Sandia National Laboratories) continues unabated. Entitled “New nuclear weapons needed, many experts say, pointing to aged arsenal,” it cites all the usual talking points of the weaponeers. For example,

Warheads in the nation’s stockpile are an average of 27 years old, which raises serious concerns about their reliability, they say. Provocative nuclear threats by Russian President Vladimir Putin have added to the pressure to not only design new weapons but conduct underground tests for the first time since 1992.

“It seems like common sense to me if you’re trying to keep an aging machine alive that’s well past its design life, then you’re treading on thin ice,” said Rep. Mac Thornberry (R-Texas), chairman-elect of the House Armed Services Committee. “Not to mention, we’re spending more and more to keep these things going.”

Thornbury also offered support for renewed testing, saying, “You don’t know how a car performs unless you turn the key over. Why would we accept anything less from a weapon that provides the foundation for which all our national security is based on?”

Such comments are entirely typical. They would make a lot of sense if the U.S. nuclear weapons program existed in a vacuum. However, it doesn’t. It exists in a world with several other major nuclear powers, and they all have the same problems. Under the circumstances, the fact that such problems exist and are shared by all the nuclear powers is less significant than the question of which nuclear power is best equipped to deal with them. The question of who will benefit by the building of new weapons and a resumption of nuclear testing depends on the answer to that question. If one country has a significant advantage over its rivals in dealing with a common problem as long as the status quo is maintained, then it would be very ill-advised to initiate a change to the status quo that would allow them to catch up. At the moment, the United States is the country with an advantage. As noted in the article,

The U.S. has by far the greatest archive of test data, having conducted 1,032 nuclear tests. Russia conducted 715 and China only 45.

Beyond that, we have the ability to conduct tests with conventional explosives that mimic what goes on in the initial stages of a nuclear explosion, and superb diagnostics to extract a maximum of data from those tests. Perhaps more importantly, we have an unrivaled above ground experimental, or AGEX, capability. I refer to machines like Z at Sandia National Laboratories, or the NIF at Livermore, which are far more capable and powerful than similar facilities anywhere else in the world. Those who say they can’t access physical conditions relevant to those that occur in exploding nuclear weapons, or that they are useless for weapon effects or weapon physics experiments, either don’t know what they’re talking about or are attempting to deceive.

As far as the NIF is concerned, it is quite true that it has so far failed to achieve its fusion ignition milestone, but that by no means rules out the possibility that it ever will. More importantly, the NIF will remain a highly useful AGEX facility whether it achieves ignition or not. Indeed, before it was built, many of the weapons designers showed little interest in ignition. It would merely “muddy the waters,” making it more difficult for the diagnostics to precisely record the results of an experiment. The NIF could access weapons-relevant conditions without it. In fact, in spite of its failure to achieve ignition to date, the NIF has been a spectacular success as far as achieving its specifications are concerned. It is more than an order of magnitude more powerful than any previously existing laser system, its 192 laser beams are highly accurate, and its diagnostic suite is superb.

Another problem with the resumption of testing is that it will lead to the development of weapons that are much more likely to be used. Once the nuclear genie is out of the bottle, it will likely prove very difficult to put it back in. For example, again quoting the article,

John S. Foster Jr., former director of Lawrence Livermore National Laboratory and chief of Pentagon research during the Cold War, said the labs should design, develop and build prototype weapons that may be needed by the military in the future, including a very low-yield nuclear weapon that could be used with precision delivery systems, an electromagnetic pulse weapon that could destroy an enemy’s communications systems and a penetrating weapon to destroy deeply buried targets.

The commonly heard narrative at DOE goes something like this: “We need to develop small, precise, penetrating nuclear weapons because they will be a much better deterrent than the existing ones. Potential enemies are unlikely to believe that we would ever use one of the high yield weapons that are all that remain in the current arsenal. They would be far more likely to believe that we might use a small bunker buster that would minimize the possibility of significant collateral damage.” The problem with that narrative is that it’s true. We would be far more likely to use such a weapon than the ones in the current arsenal, and there would be no lack of voices within DOE and DoD calling for its use if an appropriate opportunity ever arose.

I can understand the agitation for a resumption of testing. It’s a lot sexier to make things that go boom than to serve as custodians for an aging pile of existing nukes. Unfortunately, the latter course is the wiser one. By resuming nuclear testing we would really be unilaterally surrendering a huge advantage, playing into the hands of our enemies and destabilizing the nuclear landscape at the same time.