Nuclear Submarines

**Manuel I Komnenos** · October 10, 2010, 08:23 PM

During the past years, a number of nuclear submarines have been sunk like Thresher and Scorpion.
These submarines carried nuclear weapons and of course a nuclear reactor.
I've read that the US Navy conducts usual searches in order to find out about the radiation levels in the regions were the submarines were sunk. Do these submarines pose a real danger for the sea environment around them? How is it possible that the nuclear reactors have not released the nuclear fuel they carried or why haven't the nuclear weapons detonated?

**Nikos** · October 10, 2010, 08:33 PM

Not really a historical question, moved to the Athenaeum.

-Nikos

**Phier** · October 10, 2010, 08:39 PM

Well for the detonation question.

Because nuclear explosions are very complicated to set up. You don't really accidentally trigger one by soaking it in salt water. There is specialized compression of the nuclear material which must be precise, and at precise temperatures.

**Adar** · October 11, 2010, 04:08 AM

Originally Posted by Phier

Well for the detonation question.

Because nuclear explosions are very complicated to set up. You don't really accidentally trigger one by soaking it in salt water. There is specialized compression of the nuclear material which must be precise, and at precise temperatures.

Actually, submerging nuclear material in salt water may cause an explosion. The water acts as a moderator and reduce the speed of the neutrons so that they become thermal neutrons (slower neutrons are more likely to be absorbed by the nuclei of an atom than fast neutrons) . If nuclear warheads on submarines are configured in the "cannon set up" as implied by Nyxos (I am unsure about the english name but I mean the one where a smaller mass is shot into the larger mass to reach critical mass) then it doesn't really matter since any neutron slowed down would already have left the nuclear mass. But the way water affect neutrons did cause some serious problems at Oak Ridge during world war 2.

Contact between Los Alamos and Oak Ridge was kept to a minimum by the military. The result was that the engineers planning the enrichment process used a method were uranium was kept under water. But calculated the "safe amounts" based on data from Los Alamos concerning the critical mass of Uran-235/238 in a dry environment. Luckily the physicists at Los Alamos managed to convince the military that they could not guarantee the security at Oak Ridge unless they where given insight in the enrichment process. Needless to say, they became quite shocked when they found out about the enrichment procedure

(this is based on the book "Surely you must be joking Mr Feynman")

**Phier** · October 11, 2010, 08:23 AM

Originally Posted by Adar

Actually, submerging nuclear material in salt water may cause an explosion. The water acts as a moderator and reduce the speed of the neutrons so that they become thermal neutrons (slower neutrons are more likely to be absorbed by the nuclei of an atom than fast neutrons) . If nuclear warheads on submarines are configured in the "cannon set up" as implied by Nyxos (I am unsure about the english name but I mean the one where a smaller mass is shot into the larger mass to reach critical mass) then it doesn't really matter since any neutron slowed down would already have left the nuclear mass. But the way water affect neutrons did cause some serious problems at Oak Ridge during world war 2.

Contact between Los Alamos and Oak Ridge was kept to a minimum by the military. The result was that the engineers planning the enrichment process used a method were uranium was kept under water. But calculated the "safe amounts" based on data from Los Alamos concerning the critical mass of Uran-235/238 in a dry environment. Luckily the physicists at Los Alamos managed to convince the military that they could not guarantee the security at Oak Ridge unless they where given insight in the enrichment process. Needless to say, they became quite shocked when they found out about the enrichment procedure

(this is based on the book "Surely you must be joking Mr Feynman")

Well thats a bit different than a warhead spontaneously exploding

**Adar** · October 11, 2010, 08:53 AM

Originally Posted by Phier

Well thats a bit different than a warhead spontaneously exploding

I tried the phrase myself in such a way that it was clear that I it won't happen in the case described in this thread. But that soaking nuclear material in water actually may have unforseen consequences in other situations.

**Phier** · October 11, 2010, 09:04 AM

Originally Posted by Adar

I tried the phrase myself in such a way that it was clear that I it won't happen in the case described in this thread. But that soaking nuclear material in water actually may have unforseen consequences in other situations.

I know YOU don't think that but I felt it might confuse the non-science people to the danger.

**Nyxos** · October 11, 2010, 02:36 AM

You need critical mass to achieve a nuclear explosion, and the reactor will NEVER achieve it, because the amount of enriched uranium or whatever they are using in that specific reactor wouldn't be enough. You need 35 kilos of highly enriched (95+%) to get a chain reaction, and the nuclear warheads are separated in 2 parts, one of 30 kilos and one of 5 (well thats usually how its done), and you have a small amount of explosives to make the two parts connect which creates the explosion.

But you might have radioactive leaks if the sub has been underwater for some time, like it has happened in ex USSR when countries became independent and found themselves with a couple nuclear subs that they couldn't operate.

The danger for the environment is not negligible, especially that the fuel will stay active for centuries (or more)

**Hotspur** · October 11, 2010, 07:39 AM

Wait, a number of submarines like Thresher and Scorpion? Thresher and Scorpion represent the sum total of USN nuclear submarine losses. Thresher was lost in '63 and Scorpion in '68.

It's not like the sea floor is littered with the crushed hulls of US nuclear submarines.

Unlike the Russians....

**Adar** · October 11, 2010, 08:09 AM

This is the wikipedia description of the environmental impact caused by USS Scorpion
Environmental monitoring

The U.S. Navy has periodically monitored the environmental conditions of the site since the sinking and has reported the results in an annual public report on environmental monitoring for U.S. nuclear-powered ships and boats. The reports provide specifics on the environmental sampling of sediment, water, and marine life that is done to ascertain whether the submarine has significantly affected the deep-ocean environment. The reports also explain the methodology for conducting this deep sea monitoring from both surface vessels and submersibles. The monitoring data confirm that there has been no significant effect on the environment. The nuclear fuel aboard the submarine remains intact and no uranium in excess of levels expected from the fallout from past atmospheric testing of nuclear weapons has been detected by the Navy's inspections. In addition, Scorpion carried two nuclear-tipped Mark 45 anti-submarine torpedoes (ASTOR) when she was lost. The warheads of these torpedoes are part of the environmental concern. The most likely scenario is that the plutonium and uranium cores of these weapons corroded to a heavy, insoluble material soon after the sinking, and they remain at or close to their original location inside the torpedo room of the boat. If the corroded materials were released outside the submarine, their large specific gravity and insolubility would cause them to settle down into the sediment.