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Definition of Pressure Boundary

Definition of Pressure Boundary

Definition of Pressure Boundary

Good afternoon all. I've been searching for a good definition of what a pressure boundary is and I thought I'd open it up here to see what you have to say. I'm trying to get a "layman's terms" type definition but I'm not picky.

The only definition I've found so far is from S-99:

"A boundary of any pressure-retaining vessel, system or component of a nuclear or non-nuclear system, where the vessel, system or component is registered, or eligible for registration, under boiler or pressure vessel legislation."

I have also searched N285 and ASME Section III subsection NCA and NB without any luck.

Thanks in advance,

RE: Definition of Pressure Boundary

Here's the Nuclear Regulatory Commission definition from 10 CFR 50.2 (http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0002.html):

Reactor coolant pressure boundary means all those pressure- containing components of boiling and pressurized water-cooled nuclear power reactors, such as pressure vessels, piping, pumps, and valves, which are:

(1) Part of the reactor coolant system, or

(2) Connected to the reactor coolant system, up to and including any and all of the following:

(i) The outermost containment isolation valve in system piping which penetrates primary reactor containment,

(ii) The second of two valves normally closed during normal reactor operation in system piping which does not penetrate primary reactor containment,

(iii) The reactor coolant system safety and relief valves.

For nuclear power reactors of the direct cycle boiling water type, the reactor coolant system extends to and includes the outermost containment isolation valve in the main steam and feedwater piping.


Patricia Lougheed


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RE: Definition of Pressure Boundary

In layman's terms, I usually define it as any wall, (but usually a metallic wall,) that experiences a static pressure differential between the two sides. I say "static" to exclude things like wind, explosions, airfoils, and shallow troughs, and I squeeze in "metallic" just to prevent people from thinking of sheetrock and cubicle walls. But concrete counts.

Beyond that, we can argue as to whether a pressure boundary falls within the scope of this code or that regulation, but it's still technically a pressure boundary even if no codes or regulations apply.

RE: Definition of Pressure Boundary

In layman's terms the pressure boundary is the restraining surface that is in contact with a pressurized fluid.  It prevents the fluid from escaping it's container.

RE: Definition of Pressure Boundary


Thanks! I think that is what I'm looking for. I have to do presentations on this stuff to all levels of staff but I think I get too technical in my description sometimes and loose them.

RE: Definition of Pressure Boundary

If you're goal is to detail the limits of an ASME Sec III pressure boundary I wouldn't focus on being generic.  vpl's definition is the one to use.

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