As the world grapples with the nuclear threat emanating from North Korea, it is not only bombs that should concern us. It is also the dozens of nuclear power plants in Japan and South Korea that are vulnerable to attack should war break out in the region. Commercial nuclear reactors were never designed to survive volleys of missiles that could breach reactor containment buildings, sever coolant lines, destroy the reactor core and spent fuel pools—all of which could cause a nuclear meltdown. Moreover, many of the reactors in Japan and South Korea were built in clusters, which means their destruction could lead to levels of contamination greater than in Chernobyl and Fukushima.

Historically, nations at war have tended to attack nonoperational reactors rather than live ones because of radiation concerns. When Israel bombed Iraq’s Osirak and Syria’s Al Kibar plants in 1981 and 2007, respectively, it was before the suspected weapons reactors had commenced operations. During the 1980s Iran–Iraq war, Iraq struck two Iranian nuclear power reactors that were still under construction. But this cautionary approach changed when the United States hit a small, live research reactor complex outside Baghdad at the start of the Persian Gulf War in 1991, even though the reactor’s core remained untouched. Then there were Saddam Hussein’s 1991 Scud attack and Hamas’ 2014 small rocket strikes on Israel’s Dimona reactor—but both failed.

In other instances, threats were present but never realized. During the Balkan Wars in the 1990s, Slovenia shut down its nuclear power plant in Krsko out of fears that Serbia’s air force would bomb it. Belgrade, too, felt that its large nuclear research reactor was vulnerable and sought international assurances that Washington would not hit the installation. Fortunately, no attacks took place in either country. In South Asia, where war and the threat of war has troubled the region for decades, both India and Pakistan have contemplated attacks on each other’s reactors, but reached an agreement in 1988 to refrain from doing so.

That there was no release of radioactive material in these cases is cold comfort. In a war, the United States would be unconstrained to halt North Korea’s nuclear weapons use, even if Washington’s 1994 Agreed Framework with Pyongyang scotched any thoughts of attacking the Yongbyon weapons reactor. This would open the door for retaliatory attacks on reactors (if it wasn’t already a part of North Korea’s general battle plan). Although Seoul has placed its plants in the southern part of the country, away from the border, the groupings of up to six reactors per location means a military strike would require relatively low effort, but would have a strong impact. In Japan, plants are also clustered together with up to seven per site.

The effects of such an attack would be significant, if not devastating. In both Chernobyl and Fukushima, the economic cost has been in the hundreds of billions of dollars. There were lost revenues from agriculture, fisheries, and commerce in Japan, in addition to the immense expense of containing the reactor releases, sealing the plants, disposing of radioactive debris, cleaning up the environment, switching to alternative energy sources, and relocating populations. The human impact would be less clear. The health effects of the Chernobyl accident still remain a matter of debate. There have been thousands of often treatable thyroid cancers, but the hundreds of thousands of cancer fatalities projected by some experts never appeared despite the exposure of much of Europe to increased albeit very low doses of radiation. In Fukushima, which released ten percent the amount at Chernobyl, offshore winds blew much of the radioactive release over the ocean, sparing local populations from more intense exposure. Psychological trauma among evacuees and others has been widely reported for years following both the Soviet and Japanese accidents.

Korea and Japan can, of course, establish missile defense around reactors. Taking the reactors offline would also reduce thermal generation and extend the melt point of the core. But none of these methods are fail proof. Missile defense is imperfect. What’s more, plants that have been operating for a long time contain very large inventories of highly radioactive spent fuel, which if cut from coolant, will release their toxic elements. And not all of these sites can be realistically shut down. In South Korea, nuclear plants produce about one-third of the country’s electricity. (Japan only runs a few of its 42 operable plants at the moment, but intends to bring more on line as the legacy of Fukushima fades.)

The presence of large numbers of operating and nonoperating reactors in the region requires the authorities to put in place plans to reduce public risks in the event of an attack. This includes distributing potassium iodide pills to block the intake of radioiodine to prevent thyroid cancer. The authorities should educate people regarding whether sheltering in a safe place or self-evacuation is the best strategy to reduce radiation exposure. Arrangements to remove large populations from zones projected to be heavily contaminated ought to be considered, as must measures to contain and halt emissions from damaged plants. Doing so in the midst of war, however, will be difficult.

Some might argue that the immediate consequences of an attack on nuclear power plants would pale in comparison with conventional bombardment from North Korea, which could result in hundreds of thousands of deaths. The death toll would also magnify dramatically if Pyongyang were to use nuclear weapons. But compromised reactors, even if they are not killing machines, remain weapons of mass disruption and terror. As Japan, South Korea, and the United States plan ahead, the vulnerability of nuclear plants to attacks must not be ignored.