From: jgd@dixie.com (John De Armond)
Subject: Re: Nuclear Power and Climate Change
Date: Thu, 07 Jan 93 10:32:57 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.

wcarroll@encore.com (William Carroll) writes:


>No, it was in a "hot shutdown". According to FPL, the reaction was being
>maintained, but no energy was being supplied to the grid. 

Hot shutdown has a specific meaning. That condition is when the reactor
is scrammed, the generator is tripped but reactor coolant temperature
is maintained by decay heat and/or reactor coolant pump heat input.

Hot standby is the condition where the turbine is tripped, the reactor
is making power and that power is being dumped to the condenser via
the bypass system.  Hot standby is not a normal condition since TMI
because the NRC now requires a turbine trip to cause a scram and because
reactor control is a bit touchy, particularly when coming down from
power and xenon is biting at your reactivity margin.  About the only
time hot standby is seen is during testing and if the operators think
the cause of the turbine or other trip will be remedied rapidly.
Remaining at power helps burn off xenon.

>It was my
>impression that this is what the NRC requires in that type of situation.
>After the storm, they were required to take it to a "cold-shutdown" until
>the emergency systems had been repaired and inspected. 

They were required by tech spec to proceed to cold shutdown, a process
that takes a few days, by the weather.  There was no damage to 
plant systems.  The only damage was to the off-site evacuation sirens,
a system required by the NRC for operation.

>on. Then the reaction had to be initiated again. I am certainly no nuke
>eng, but reading reports led me to believe that there is a _significant_
>difference in the startup times between the "hot shutdown" case and the
>"cold shutdown" case. Perhaps Mr. De Armond, or some other netter with
>industry experience, could clarify the difference for us.

There is a large difference in startup times due to limits on heat
rate.  The startup sequence is roughly, secure the residual heat
removal system and build primary system pressure while beginning
to establish water chemistry.  When the pressure reaches the 
reactor coolant pump (RCP) net positive suction head (NPSH), start the
RCPs.  The approximately 10 MW of energy input by the RCPs brings the
primary temperature up to operating temperature, about 557 degrees
for a Westinghouse.  This takes a day.  Meanwhile the Chemical and Volume 
Control System (CVCS) is reducing the concentration
of boric acid (neutron absorber) in primary coolant system from the 
shutdown concentration to the startup concentration.  A steam bubble
is established and level control initiated in the pressurizer as the RCS 
goes through 400 degrees.  At about this time feedwater from the steam
side is supplied to the steam generators and steaming commences.  Steam
is vented initially to the atmosphere and then to the turbine condenser.
This is hot standby.

After primary level, pressure and chemistry is established, the rods
are pulled according to the rod block sequence to put the reactor on
a 400 second period (power level doubles every 400 seconds.)  Power
level increases through about 12 decades until it reaches about 1% 
of full output.  The turbine is spun and the generator synced to the line.
The neutron monitoring system is in the control loop and rod withdrawal
is programmed to increase power as measured by the neutron monitoring
system at a rate of 5% a minute up to the demand setpoint.  Boric acid
is reduced by the CVCS so that the rods are fully withdrawn which gives
the maximum shutdown margin upon scram.

Going from cold shutdown to hot shutdown takes from 13 to 24 hours.
Going from hot shutdown to power operation takes typically an hour.

(This is from memory so sue me if I forgot something.)

>Well, since the emergency systems are part of the nuke plant, and required
>for its operation, I would say that, yes, the nuclear plant was damaged. No,
>the containment buildings were not damaged. Or at least not to a newsworthy
>level.

The siren system is NOT a part of the plant other than there is a trip
button on the control panel.  A county evacuation plan is not part of
the plant either but the plant cannot operate by law without there being
one in place.

>The damage that required the plant to shutdown was the emergency systems.
>That was certainly not the only damage to the site. My impression was that
>FPL's facilities at Turkey point did not sustain significantly more damage
>than any of a number of other properties in the South Dade area. The plant
>did survive relatively intact.

The plant "survived" intact.  Period.  

>So why should I believe Turkey Point is that much better designed than
>Homestead AFB?

Because we tell you it is.

John
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