Nuclear reactors in a war zone: A new type of weapon?

What are the vulnerabilities of a nuclear reactor in a war zone? Clearly, a nuclear reactor is not a nuclear bomb—reactors are designed to avoid runaway chain reactions. However, there are three vulnerabilities that can have serious consequences. First, an assault on an operating reactor can disrupt critical operations, such as the pumps that drive the coolant through the reactor. Loss of coolant, from an electrical grid shutdown, for example, can lead to meltdowns, chemical explosions, and the release of radioactivity, such as at Fukushima Daiichi. Second, a breach of containment structures and structural barriers can expose the nuclear fuel, leading to fires, explosions, meltdown, and the release of radioactivity, as happened at Chernobyl. Finally, used fuel is often stored on site in pools and dry casks. If these storage facilities are breached or the storage pools drained, then fires can lead to the release of radioactivity. This is the most probable mechanism for the release of radioactivity, as spent fuel remains highly radioactive for many decades after removal from a reactor core, but the storage facilities, particularly pools, are not well hardened against attack.

To understand how serious these three scenarios are, one must realize the size of the highly radioactive fission product inventory in nuclear fuels. On one hand, the inventory is small relative to the amount of fuel, only about 4 to 5 percent in irradiated fuel; however, a typical reactor will contain 100 tons of fuel, so the absolute amounts are significant. Importantly, the small inventory of fission products results in a nearly million-fold increase in the level of radioactivity (as compared with the activity prior to irradiation). At one meter distance, a person exposed to a spent fuel assembly (one year after removal from the reactor) will receive a lethal dose in less than a minute. Spent fuel assemblies or even small spent fuel fragments are an immediate threat to people and a very long-term threat to the environment—requiring exclusion zones on the scale of thousands of square miles.