NUCLEAR, BIOLOGICAL AND CHEMICAL WEAPONS
June 3, 2023: The U.S. Air Force is updating its radiation surveillance aircraft fleet with three new three WC-135R aircraft. Two have already been completed and the third will soon be delivered. The $218 million WC-135R program involves installing radiation detection equipment on these three new C-135 aircraft to replace C-135s that had been used since the 1960s. Since then, fourteen aircraft have served as radiation detection aircraft. The WC-135R is basically a KC-135 aerial refueling aircraft converted to be a radiation detection aircraft. The original radiation monitoring aircraft were weather monitoring aircraft which, before the proliferation of weather satellites fifty years ago, were the main source of data on atmospheric conditions.
The WC-135Rs have been regularly used to detect North Korean nuclear weapons tests and collect enough data to determine if a nuke had been used and how successful the test was. The 2006 nuclear weapons test in northeast Korea, revived interest in such arcane subjects as "partially successful" nuclear weapons, faking a nuclear explosion and arcane detection methods. The North Korean test showed up on earthquake detectors (seismographs) as a small (4.2 magnitude) quake. A few quick calculations revealed that this indicated an explosion of less than one kiloton (equal to 1,000 tons of conventional explosives). Since the North Koreans were using plutonium for their bomb, and the smallest plutonium bomb is (for technical reasons) at least twenty kilotons, this set off alarms. This indicated that the North Koreans were either faking it (with conventional explosives), or had a poorly built bomb that only partially went off.
WC-135R was designed to collect enough evidence to determine a large explosion is real or fake. A nuclear explosion, even a "fizzle", a bomb that does not detonate all its nuclear material, will emit some unique chemicals into the atmosphere. This will happen even with an underground explosion, because the earth is full of cracks and crevices that allow some of the gasses to escape into the atmosphere. WC-135Rs flying off the coast of North Korea, did indeed pick up the presence of unusually high levels of argon 37 and xenon 133. These two elements are present naturally in very small quantities. One of the things American WC-135R recon aircraft do regularly is check the natural levels of these rare elements off the coasts of North Korea and Iran, the two nations most likely to carry out a nuclear test. These tests are conducted underground because that contains most of the radiation rather than spewing radiation over a lot of territory with an open air test. By treaty and general agreement, open air tests have been banned since the 1960s. Radiation detection aircraft are also called in to monitor the spread and levels of nuclear fallout from actual or suspected nuclear power plant accidents. The best example of this was the 1986 power plant disaster in Chernobyl Ukraine, then part of the Soviet Union. WC-135R are again flying near Ukraine because Russian invaded in early 2022 and seized a huge (the largest in Europe) power plant complex, Russian mismanagement of the complex threatens to create another Chernobyl. Before the Soviet Union collapsed in 1991, there had been several lesser (than Chernobyl) nuclear disasters in remote areas. American radiation detection aircraft monitored these as well.
There is always a detectable (by a WC-135R) amount of radiation after an underground test. With pre-test baseline samples collected by ground sensors or WC-135R, it's easy to see when a nuclear explosion has occurred nearby, because the normal levels of these two elements spike. Then there are industrialized nations that have nuclear material (from power plants) and could build nuclear weapons. This group includes South Korea. Japan, Canada, Germany, the Netherlands and Australia, with more to come.
Having instruments that can detect minute quantities of rare elements has made it impossible to fake a nuclear test, and there have been some very large conventional explosions. In 1985, some 4,500 tons of ammonium nitrate and fuel oil (a "fertilizer bomb) were detonated by American researchers to create an explosion similar to a nuclear one. Seismographs indicated that this explosion was similar to what would be expected for an eight kiloton nuclear bomb. There have been similarly large explosions before, but always accidental. In 1947, a ship carrying 8,500 tons of ammonium nitrate exploded in a Texas port, destroying the surrounding area, and killing over 500 people. These large conventional explosions create the mushroom shaped cloud we associate with nuclear explosions. Such clouds are typical of any large explosion, nuclear or not. But unless certain types of radiation are present, you know the explosion is non-nuclear.
Poor bomb design, or low quality components, have caused fizzles in the past. In 1998, several of Pakistan's nuclear weapons tests failed in a similar fashion to the current North Korean one. It may be that design that was sold to North Korea by the Pakistani nuclear scientists who, at that time, were running an illegal nuclear weapons sales business on the side. North Korea is currently the most active supplier of illegal nuclear weapons tech. This tech is very expensive and it is an important source of hard currency for North Korea.
No other country has atmospheric radiation detection aircraft but there is a lot of radiation detection equipment available commercially to constantly monitor land areas. Many armed forces also have such equipment installed in military vehicles for use during conflicts where there is a risk of atmospheric radiation.