Re: [Phys-l] Japan situation : information, or lack thereof

[Bill Nettles <bnettles@uu.edu>]

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of Hugh Haskell
> Sent: Wednesday, May 04, 2011 9:51 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] Japan situation : information, or lack thereof
>
> Bill N. and Bill M.,
>
> Thanks for the information on the sea-based reactors. Are we still
> monitoring the Thresher/Scorpion reactors? I wonder if they will
> retain their integrity over long periods of time exposed to the sea
> water. I understand that Thresher hit the bottom at a pretty good
> rate of speed, so its reactor was probably subjected to a pretty good
> stress test, but unless the claims of those who assert that
> Scorpion's accident was caused by an exploding torpedo are right, my
> understanding so Scorpion's accident was due to a collision with an
> undersea mountain. Obviously not good for the ship or its crew, but
> not as potentially damaging as a high-speed impact with the ocean
> bottom.

[Bill Nettles] Yes, they still monitor the sites regularly. Probably not annually now, but did that often in the past. Data for integrity verification is important. Also, it provides a pretty good corrosion test for the zirconium clad.

> But I guess that my concern about the reactors would be as a result
> of battle damage, rather than simply from the sinking. If the reactor
> suffers a direct hit from a large explosive weapon, which
> subsequently sinks, will it retain its integrity, or could this
> spread the reactor "all over the sea bottom"?

[Bill Nettles] There aren't many conventional weapons that will directly breach the reactor vessel.  If a bunker buster did reach the power plant it would probably shear the main coolant pumps from the primary coolant pipes and toss the reactor vessel en toto a little bit. The RV's are very stout. I strongly believe the fuel elements will retain integrity.

> I think that the reactors being PWRs makes sense except that, it
> doesn't seem consistent with them not supporting superheaters for the
> propulsion steam. I know that in an oil-fired ship, the saturated
> steam is fed back into the burner in a separate heat exchanger which
> heats the saturated steam to the higher temperature. Maybe I don't
> understand the heat exchange process between the primary and
> secondary water systems, but it does seem that it should be possible
> to put the saturated steam back through the heat exchanger to
> superheat it even in a nuclear reactor. Can either of you tell me why
> this isn't done? My experience was in the weapons department and not
> engineering or reactor so I have to admit, I'm not expert on how the
> superheaters worked, but I do know that every steam engineer I knew
> during my navy career was a firm advocate of superheated steam as a
> reliable and highly versatile propulsion system.

[Bill Nettles] Superheaters would play havoc with the temperature balance between the high and low temp secondary system which would in turn affect the primary temps. The reactor has a negative temp coefficient (cold water coming in increases the reactivity) so the reactivity automatically increases when more steam is fed to the turbines (which causes the return secondary temp to drop which makes the primary return temp drop). This makes the power levels of the reactor respond automatically to steam demands with need for rod motion. Also, high temp water corrosion is a concern. Adding a superheater would add a bigger layer of maintenance and operational concern.  It might make the propulsion system more efficient overall, but it would increase operational complexity, not something you want to do in a nuclear ship or sub. KISS.  It took a loooonnnggg time to convince Rickover to allow any kind of digital electronic controls in the maneuvering spaces.

> Also, since you served on Enterprise after I did, Bill M., can you
> tell me what the lifetime of that refueling (the second, IIRC) was
> intended to be, and if, after the third refueling, is it scheduled
> for or has it gotten a fourth (and last) one?
>
> My understanding is that it is scheduled for decommissioning sometime
> around 2030--a very long lifetime for a modern man-o-war.
>
> And one last question that I didn't know enough to ask my reactor
> officer buddy at the time, is the fuel in these reactors a permanent
> installation, like in the submarines? My recollection is that the
> entire reactors were going to be pulled out and replaced with new
> ones during the 1970 refueling, so I assume that means that the fuel
> was an integral part of the reactor and when this fuel was depleted,
> the reactor and its depleted fuel would be scrapped. Is my
> recollection correct? I also know that the fuel in the SSNs is HEU.
> Is that also true of the fuel in the surface ships? I suspect it is,
> but I don't know for sure.
[Bill Nettles] You may have misunderstood what you heard. The entire fuel load of a reactor is replaced at refueling, not the reactor vessel itself. Sometimes pumps and steam generators are replaced, depending on tests. When commercial reactors refuel, it is only a portion of the core that is replaced. For NR, the whole core is replaced. Sometimes new control rods are used, sometimes old.  The control rod policy may have changed since I left NR.  I'll have to leave you with your suspicions regarding HEU, neither confirming nor denying. :)
Bill N.

> Hugh
> --