RE: Kursk: Potential nuclear hazards

["Bauman, Rodney L. (84U) " <84u@BECHTELJACOBS.ORG>]

During operation, a PWR's pressurizer contains water covered by a steam

bubble - not pressurized noble gasses.  By either expanding (by electric

heaters) or collapsing (by water spray) the steam bubble, the pressurizer is

capable of regulating the reactor coolant system's (RCS) pressure.  This

steam bubble "goes away" during RCS cool-down/depressurization.  This is

what is commonly termed "going solid."



I do not know why the Kursk's reactors required pressurized gas that would

still be present after shutdown/cool-down.  Maybe it has something to do

with the control rod drive units.  Control rods entering a reactor core from

underneath normally utilize pressurized gas to drive rods during a reactor

scrams (however, I don't know if the pressurized gas is used for every

reactor scram or just those coincident with a loss of AC power). 



Rodney Bauman, CHP, RRPT

Bechtel Jacobs Company, LLC

Project Health Physicist

ETTP and Y-12 Waste Operations

Y-12 Plant Bldg. 9624, MS 8222

Voice: 865.241.5344

Pager: 865.417.0561

Fax: 865.576.3946

84u@bechteljacobs.org



> -----Original Message-----

> From:	BERNARD L COHEN [SMTP:blc+@PITT.EDU]

> Sent:	Wednesday, September 05, 2001 12:45 PM

> To:	Bjorn Cedervall

> Cc:	internet RADSAFE

> Subject:	Re: Kursk: Potential nuclear hazards

> 

> 

> On Tue, 4 Sep 2001, Bjorn Cedervall wrote:

> >

> > Now, on page 15 it says that the reactor is pressurized by gas (argon or

> > nitrogen). -Reserve gas? I don't understand how this gas comes into the

> > picture. Can anyone explain?

> 

> 	--In a PWR, the pressure is regulated by the pressurizer which has

> water from the reactor in the bottom and gas in the top. The interface is

> kept in sight so one knows that the water pressure is equal to the gas

> pressure which is easily measured and regulated. The pressurizer gained

> notoriety in the TMI accident because it was filled with water and no

> interface was visible. The operators interpreted this as meaning that

> there was too much water in the reactor and hence they throttled back

> (almost shut down) the emergency cooling water. But the reason the

> pressurizer was filled with water was that the exit valve was stuck open

> so water was pouring out thru the pressurizer. Thus the water was lost and

> not replaced.

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