Fallout yield from a nuclear accident at sea?

[xpell]

I was reading about the nuclear accidents in early Soviet submarines and got a couple of questions, hope this is the appropiate forum to ask them.

Let's assume that a submarine suffers both a hull and reactor vessel rupture (for example, as a result of an attack in wartime) while at periscope depth (to ignore high water pressure conditions). I was wondering:

-What substances would bubble into the air and which ones would stay in water?

And now let's imagine that the submarine is able to emerge and somehow the reactor is still working (maybe moderated by seawater and because they use HEU, sometimes around 97% enrichment) but out of control. What substances would we see then? (Or, in other words: what substances would a reactor emit if just opened?)

AFAIK, these reactors are usually light water moderated PWRs with HEU for fuel.

Thanks in advance!

 

[etudiant]

In wartime, the worst case would presumably be a nuclear strike that vaporizes the reactor. That would be somewhat similar to one of the early A-bomb tests, a massive bomb that achieved about 600 kiloton yield from a pure fission design.
Barring that, the worst you could expect is a nuclear fizzle, where the reactor self destroys in an abortive explosion that blows it apart with the beginnings of a nuclear runaway fission. Estimates are for about a 100 ton of TNT level explosion that would scatter reactor fragments for some hundreds or thousands of yards. Uranium in bulk is very dense and not usually pyrophoric ( DU ammunition can be, if it splats against armor), so the bits would sink to the ocean floor.
The problem in short would be relatively small, involving a reactor much less than 10 % of the size of the smallest Fukushima reactor.

 

[a.ua.]

Inventory and Source Term Evaluation of Russian
Nuclear Power Plants for Marine Applications
http://www.nks.org/download/pdf/NKS-Pub/NKS-139.pdf

Chazhma Bay, Russia
Nuclear submarine accident
http://www.breakingthenuclearchain.org/documents/129875579/130263921/ChazhmaBay.pdf

Nuclear submarine K-431 — On 10 August 1985 the refuelling work on the nuclear
submarine K-431 at a pier in the Navy Shipyard of Chazhma Bay (Russian Far East) a
prompt explosive criticality accident occurred in the reactor compartment. As a result,
radionuclides with an activity of about 185 TBq (mainly short-lived radionuclides)
were released into the atmosphere. A fraction of these radionuclides was deposited in
the waters of the Bay in an area of approximately 0.1 km2
. The total activity of 60Co in
bottom sediments of the radioactive contaminated part of the bay was estimated at 185
GBq [41, 59].

http://www-pub.iaea.org/MTCD/publications/PDF/te_1242_prn.pdf

 

[NUCENG]

In wartime, the worst case would presumably be a nuclear strike that vaporizes the reactor. That would be somewhat similar to one of the early A-bomb tests, a massive bomb that achieved about 600 kiloton yield from a pure fission design.
Barring that, the worst you could expect is a nuclear fizzle, where the reactor self destroys in an abortive explosion that blows it apart with the beginnings of a nuclear runaway fission. Estimates are for about a 100 ton of TNT level explosion that would scatter reactor fragments for some hundreds or thousands of yards. Uranium in bulk is very dense and not usually pyrophoric ( DU ammunition can be, if it splats against armor), so the bits would sink to the ocean floor.
The problem in short would be relatively small, involving a reactor much less than 10 % of the size of the smallest Fukushima reactor.

Do you have a source for those estimates?

 

[NUCENG]

Inventory and Source Term Evaluation of Russian
Nuclear Power Plants for Marine Applications
http://www.nks.org/download/pdf/NKS-Pub/NKS-139.pdf

Chazhma Bay, Russia
Nuclear submarine accident
http://www.breakingthenuclearchain.org/documents/129875579/130263921/ChazhmaBay.pdf


http://www-pub.iaea.org/MTCD/publications/PDF/te_1242_prn.pdf

Those were interesting references. However, I found several differences in the K-431 scenario versus the information requested by the OP.

1. K-431 was in port.
2. K-431 was in refueling mode so the reactor was already open.
3. Fresh fuel had been loaded but the reactor had not previously been critical so there was no significant fission product inventory prior to the accident.
4. The K-431 accident was a reactivity excursion resulting in a huge power spike several times maximum design and a team explosion.
5. The K-431 was a 1st generation Soviet nuclear design that operated with 20% enrichment.

The "Chazhama Bay, Russia Nuclear Submarine Accident" source has a glaring error on the cause of the K-431 accident. They claimed the wake of a passing torpedo boat rocked the sub and caused the rods to dislodge. NKS-139 "Inventory and Source Term Evaluation of Russian Nuclear Power Plants for Marine Applications" (that you provided) describes the event as trying to reset the reactor vessel head with the rods attached and lifting it too high. I checked a few other sources through Google, and even Wikipedia has the same information.

The really unbelievable thing is that the reactivity excursion while trying to reset the reactor head was idntical to an incedent in 1965 in another Soviet submarine refueling. That time they did it twice. So much for lessons learned.

 

[NUCENG]

I was reading about the nuclear accidents in early Soviet submarines and got a couple of questions, hope this is the appropiate forum to ask them.

Let's assume that a submarine suffers both a hull and reactor vessel rupture (for example, as a result of an attack in wartime) while at periscope depth (to ignore high water pressure conditions). I was wondering:

-What substances would bubble into the air and which ones would stay in water?

And now let's imagine that the submarine is able to emerge and somehow the reactor is still working (maybe moderated by seawater and because they use HEU, sometimes around 97% enrichment) but out of control. What substances would we see then? (Or, in other words: what substances would a reactor emit if just opened?)

AFAIK, these reactors are usually light water moderated PWRs with HEU for fuel.

Thanks in advance!

Using public sources (IAEA Tech Doc 1242 "Inventory of Accident Losses at Sea...") provided by a.ua. the best information I have been able to find so far comes from three submarine sinkungs that did not have reactor accidents. USS Thresher sank with a total inventory of 1.15 PBq of which about 0.04 GBq is estimated to have been released. USS Scorpion sank with a total inventory of about 1.3 PBq and again about 0.04 GBq is estyimated as the release. A Soviet submarine Komsomolets (NATO Designated Mike Class) K-278 sank with a source inventory of 3.59 PBq and there haves been an estimated release of up to 370 GBq. However doing some simple Google searching indicates that the release is at least partially from leakage from twwo nuclear armed torpedoes that were aboard. The Russians have sealed the hull to limit further leakage.

I think the closest actual event to your scenario in the so called "Widowmaker" or "Hiroshima" the Soviet submarine K-19 on 4 July 1961. They experienced a Loss of Cooling Accident (LOCA) and had sufficient damage to the fuel that 8 crewman died of acute radiation sickness. I have not found an estimate ofr the radiation released while the ship was towed back to the Kola Peninsula.

Finally, if you are interested in specific isotopes you should refer to the information in NKS-139 provided by a.ua.

 

[a.ua.]

NUCENG

That time they did it twice.

This was done three times.

18 January 1970 Sormovo, Gorky region, Russia, USSR.
radiation accident during construction of submarine nuclear reactor
An accident during construction of a submarine nuclear reactor resulted in the release of radioactive vapor. Three individuals died of radiation exposure and two were injured.
If you strongly interested. You can read through the interpreter.
http://archive.russia-today.ru/2004/no_08/08_me_1.htm
http://lito.ru/text/58076

and in your own language
Accidents in Nuclear Ships
http://www.risoe.dk/rispubl/NKS/NKS-96-RAK-2TR-C3.pdf

 

[NUCENG]

NUCENG
...

Thank you. More interesting reading. There is a certain amount of sick fascination with how that could happen repeatedly. One thing that could really be causal is the desperate competition between the Soviets and the West during the Cold War. Today, we seem to be moving back in that direction with China added into the mix.

 

[a.ua.]

The "Chazhama Bay, Russia Nuclear Submarine Accident" source has a glaring error on the cause of the K-431 accident.

You're right.
maybe it Bellona

Perhaps if I was a moderator, I would remove this reference