Chinese leaders are rational actors, most of whom would not encourage escalation where risk of nuclear conflict exists. But it would take only one bold leader willing to run greater risks than his predecessors—who believed, as Soviet boss Leonid Brezhnev did, that the “correlation of forces” is shifting decisively in his country’s favor—to focus China’s immense energies on triumph in the western Pacific. The Soviet leadership had often been cautious, wary of the immense power of the United States. Yet Leonid Brezhnev was opportunistically tempted in 1973 to take a chance in the Mideast, even with the memory of Nikita Khrushchev’s failed 1962 gamble over Cuba—which Khrushchev, unlike Brezhnev, had planned in advance. Conceivably a Chinese leader might be similarly tempted.
Consider the warning that Lieutenant General Xiong Guang issued to the Clinton administration during the 1996 crisis in the Taiwan Strait, after the U.S. sent the Seventh Fleet into the strait to warn against Chinese military action. The Chinese were trying to intimidate Taiwan during its presidential election campaign, during which the question of seeking permanent independence from the mainland took center stage. The general expressed doubt that America would trade Los Angeles to avenge a Chinese nuclear strike against Taipei.
Herman Kahn warned that strategic gambles by national leaders have been frequent in history: “We tend to forget that throughout history many decision-makers were delighted to accept ‘double or nothing’ tactics if the odds looked sufficiently favorable.” Shifts in the nuclear balance can matter, if—as proved the case in 1973—they change how leaders behave during a crisis. Perceived vulnerability, whether in force structure, force deployment, or will to prevail, can tempt an adversary to take a reckless, potentially catastrophic gamble. U.S. policy, particularly regarding its nuclear arsenal, must focus on making sure China always considers the odds of such a gamble hugely unfavorable.
At the root of miscalculation in a Yom Kippur type of confrontation is the seductive trap of mirror imaging: believing an adversary assesses the nuclear balance the same way, and regards nuclear arsenals as only for last-ditch deterrence purposes. We can avoid such mistakes if we keep in mind that assessments of the nuclear balance are not intellectual exercises in philosophical pure reason. They turn rather on prosaic everyday factors—specifically, what adversaries think, which can be quite different from what America thinks.
This is especially true as to revolutionary and rogue powers, but also can apply to rivals. It forms the basis for the Fifth Lesson of nuclear-age history: THE NUCLEAR BALANCE MATTERS IF ANY PARTY TO A CONFLICT THINKS IT MATTERS, AND THUS ALTERS ITS BEHAVIOR.
Interlude: A Thin Line between Peaceful and Military Nuclear Capability
THE SEPTEMBER 11 attacks brought to global public consciousness the fear that rogue nations might use or transfer nuclear weapons to terrorist groups, and that terrorist groups could themselves make a nuclear bomb. The first fear has far more foundation than does the second.
The good news is that it is very hard to make bombs; the bad news is that it is not impossible. Let’s look at uranium and plutonium and see why this is so.
All uranium atoms have 92 positively charged protons at their nucleus (with 92 almost weightless negatively charged electrons orbiting that nucleus). But all uranium atoms are not the same. Though there is no way to tell one from another chemically, different isotopes of uranium have different numbers of neutrons, the proton’s neutrally-charged companion. Most atoms in a vein of natural uranium ore have 146 neutrons (for a total mass, protons plus neutrons, of 238). But a very few of them—less than 1 percent—have three fewer neutrons, and this “U-235” is extremely important for our story.
U-238 is fissionable, but not readily so. U-235, on the other hand, is fissile—its nucleus is easily split, creating two smaller nuclei, but more importantly, releasing energy plus two or three free neutrons. In a small enough space, those neutrons can each enter other uranium nuclei, splitting them to release more energy and neutrons, and so on, in a chain reaction. A critical mass of uranium-235—roughly 100–115 pounds in metal form and smaller than a soccer ball—will start a self-sustaining chain reaction on its own. If the same object is sufficiently compressed, it can become supercritical, dangerously increasing the rate of the chain reaction.
But the vast majority of uranium ore is U-238 and cannot emit neutrons rapidly enough to support a chain reaction. The solution for anyone seeking that reaction is for high-speed centrifuges to spin uranium that has been processed from ore to a powdered form called yellowcake, so that the marginally heavier U-238 molecules move to the bottom of the spinning cylinder, separating out from the precious, infinitesimally lighter U-235 that stays on top of the centrifuge. This process—of removing U-238 from U-235—is called uranium enrichment.
In order to generate an uncontrolled, supercritical chain reaction in uranium (a nuclear explosion), a would-be bomb maker must: 1. sufficiently enrich the uranium, 2. compress it ultra-rapidly into a supercritical mass, and 3. set it in an explosion-friendly physical shape.
For example, the Hiroshima bomb used uranium enriched to 80 percent U-235. Within the bomb, half the uranium was fired—by a miniature version of a World War II warship’s naval gun—into the other half, causing a supercritical mass to form and detonate in microseconds (millionths of a second).
Supercritical chain reactions in uranium typically at least double with each fission. Think of the parable about the king who offers a peasant serial doublings of wheat stalks on a chessboard—one stalk of wheat on square one, two on square two, etc. Before reaching 64 doublings the kingdom goes broke; the final squares are never covered, as there is no wheat left with which to do so. The difference in the nuclear case is that doublings go past the 64th square—to the 84th. Exponential progressions look like the famed “hockey stick” curve, one that accelerates at an ever-increasing rate with each doubling.
In the 84-doubling sequence not uncommon in a fission weapon, after 70 doublings only 1 percent of the energy will have been released. After 80 doublings only 5 percent will have been released, and after 83 doublings only 50 percent. North Korea’s early tests fell far short of the Hiroshima bomb in yield. A primitive weapon releases far less energy than a well-engineered one.
Commercial fuel is not sufficiently enriched to attain supercriticality, but failure to control the reaction or a failure in the cooling system can lead to an uncontrolled chain reaction and a “meltdown” in which the reactor fuel in the core overheats and melts into the floor. This is a highly radioactive event, and highly dangerous to those exposed to the intense doses of radiation (few in number, if the containment vessel protecting the reactor remains intact). A runaway chain reaction cannot generate a nuclear explosion but in water-cooled designs can cause a hydrogen explosion from the reaction of steam with core-surrounding cladding, as happened in the 1986 Chernobyl nuclear accident in Ukraine and at several reactors in the March 2011 nuclear meltdowns in Japan.
At first glance it seems a huge leap for a nuclear proliferator state to get from 3.5 percent, low-enriched, commercial uranium fuel for a power reactor all the way up to 93 percent, highly enriched, weapons-grade uranium fuel for a bomb. But simple arithmetic gives a counterintuitive result: commercial-grade fuel is perilously close to weapons-grade fuel.