Kursk sub's risk of leaking radiation minimized by built-in protections, health physicist says

August 21, 2000

While the loss of human life in Russia's Kursk nuclear submarine is tragic, a radiation expert says the environment will likely be spared significant radioactive contamination. So far, measurements have indicated no breakdown in the substantial structural defenses that are designed to prevent a radiation leak from the submarine's nuclear reactors.

Andrew Karam, a health physicist and radiation safety officer at the University of Rochester who has done tours of duty on nuclear-powered submarines, says all such subs have several built-in lines of protection surrounding the nuclear reactor. He adds that, despite recently expressed concerns, these defenses should stay intact--even in sea water--for a long time.

First, the sub's uranium fuel is surrounded by cladding, a material which safely contains the fuel's byproducts, which include radioactive iodine, technetium, strontium, and cesium. The cladding is typically made of stainless steel or a zirconium alloy, which can absorb high levels of nuclear radiation without leaking or degrading.

The physical integrity of the sub's nuclear reactor and coolant system also protects against radiation leaks. The reactor's walls are typically made of very thick steel which resists corrosion and stays structurally stable amidst high temperatures. Karam points out that the protection of the reactor walls is even more robust after the sub sunk and its reactor shut down, since they no longer had to withstand high-temperature nuclear reactions.

The third line of defense is the sub's own hull, which shields the nuclear reactors, and the sub as a whole, from the outside world. Even though the hull was breached when the Kursk sank, there is a twisting path of hundreds of feet from the reactor area to the outer part of the ship. So while the Russian sub was breached at one of its ends, the reactor is better protected because it is in the center of the sub.

Another thing to keep in mind, Karam says, is that the various byproducts of the uranium fuel release radioactivity at a higher rate than the fuel itself. But the positive side is that most of these byproducts decay over a much shorter period of time (over a few years or decades), releasing most of their nuclear radiation in that amount of time rather than remaining a long-term risk.

It's presently unknown as to how and when the nuclear sub will be recovered, but Karam expects the radioactive byproducts of the fuel to stay safe inside the core of the sub in the meantime. In a news conference yesterday, however, former Russian navy captain and environmentalist Alexander Nikitin said he feared radioactive leakage from the Kursk within a month.

Karam disagrees, saying that if there is any leakage, "this is going to take a long time." He agrees with Nikitin that any contamination would be very localized because any radioactive particles that might emerge are likely to quickly bind with clay minerals abundant in the sea floor. Yet Karam suggests that leakage may never occur.

Karam notes that there has been no reported leakage from the other known nuclear subs that have sunk (including the "Thresher" and the "Scorpion") in the past few decades.

Andrew Karam
Radiation Safety Officer
University of Rochester
(716) 275-1473

American Institute of Physics

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