Light Water Reactors

[wlrun3@aol.com]

Is the function of the Volume Control Tank in the Chemical Volume and Control System similar to that of the Pressurizer in the Reactor Coolant System?

[sovbob]

As an expansion volume, yes.  Sort of. 

Beyond that, no.  Not at all.

[Matthew B]

The VCT gas space is pressurized with H2 to keep an excess of H2 dissolved in the Rx coolant.  This ensures that oxygen produced by radiolsys is quickly recombined into water.

The VCT is also where chemistry adjustments to the Rx coolant are made.

[Fermi2]

Chemistry control is a secondary function.

It's used to accomodate volume changes in the RCS, and supply a source of makeup and supply the RCP Seals.
It also supplies a back pressure to ensure proper operation of seal leakoff from the RCP Seals.
AND it's the primary means of controlling reactivity for burnup and Xenon.

[HydroDave63]

AND it's the primary means of controlling reactivity for burnup and Xenon.

What is Xenon? I'm in DEP and my recruiter didn't mention anything called Xenon? Will I need a Xenon waiver?

[Fermi2]

Try the SEARCH function NUB!

[wlrun3@aol.com]

I see that an analogy comparing the pressurizer in the primary (rx bldg) with the vct in the cvcs (aux bldg) is a stretch.

[Sun Dog]

What is Xenon? I'm in DEP and my recruiter didn't mention anything called Xenon? Will I need a Xenon waiver?

Xenon was the third choice for the phonetic character of the 26th letter of the English alphabet.  Xenon lost out to Zihuatanejo (2nd place) and the final winner, Zulu.

[Gamecock]

Xenon was the third choice for the phonetic character of the 26th letter of the English alphabet.  Xenon lost out to Zihuatanejo (2nd place) and the final winner, Zulu.

No, no, no...

Remember Xenon...warroir princess on Fox  a few years ago 

[HydroDave63]

MMMmmm....notice how the hydrogenated material vinyl is used to cover the bones of the blood-forming regions, clearly some advanced rad protection technology of the Atlantean Era

[wlrun3@aol.com]

What is a BPRA. What does it do. What does it look like. How is it installed.
I am asking these questions to reinforce what I have already learned through exhaustive and profitable utilization of the formidable Nukeworker Search function.

[HydroDave63]

What is a BPRA. What does it do. What does it look like. How is it installed.
I am asking these questions to reinforce what I have already learned through exhaustive and profitable utilization of the formidable Nukeworker Search function.

Burnable Poison Rod Assembly

http://www.westinghousenuclear.com/Products_&_Services/docs/flysheets/NS-FS-0091.pdf

[wlrun3@aol.com]

Is the BPRA inserted into fuel assemblies like a RCCA by CRDM or does the burnable poison come already in special fuel assemblies...or both.

[Fermi2]

Looks just like an RCCA and loaded the same way.

[matthew.b]

AND it's the primary means of controlling reactivity for burnup and Xenon.

So would you call adjusting soluble boron "not adjusting chemistry?"

[Fermi2]

No because boron is not used for chemistry control, but it causes chemistry affects. So no.

[thenuttyneutron]

So would you call adjusting soluble boron "not adjusting chemistry?"

I call it a water add.  I use either a computer program, some RO Curves& a procedure, or a controlled copy document called the RO Guidance that is provided to me by the Reactor Engineers to come up with an amount to add.

Most times I just add water for inventory and rod index control.  Early in core life I have to make neutral batches instead of straight water to make up for inventory lost through the RCP seals because adding water alone would be too much from a reactivity standpoint.  On one occasion the day after a misaligned rod incident, I was adding tons of boric acid to the makeup tank (chemical volume tank I think it is called for you Westinghouse types) to maintain rod index, and power constant due to Xenon burnup.

Boron is used because it is cheap and effective.  I know chemistry is busy during startup adjusting Lithium concentrations and sampling because OPS is changing the Boron concentration a lot.  The Li control is important to maintain a near neutral or slightly alkaline RCS chemistry.  During normal plant operations, I will sometimes put a demin in service per chemistry request to remove lithium (made through boron activation).

As for the pressurizer, it is an important component in a PWR.  It is what pressurizes the RCS.  It is especially important during a transient because it acts like a surge volume and will dampen pressure swings caused by the transient.  It is the only place in the RCS that is at saturation conditions because it has heaters at the bottom.  It keeps the rest of the RCS sub-cooled.  For lack of a better term, it is like a spring and shock absorber for RCS pressure/inventory control.  There is a spray valve that will open and spray water through the steam bubble to lower pressure if it gets too high during a transient.    

During normal plant ops the Pressurizer level is controlled constant.  The heaters cycle on and off to maintain pressure and there is a small amount of spray at a constant rate around the spray valve through a bypass into the steam space.  The spray taps off the discharge of one of the RCPs and the bottom of the PZR taps into a hotleg.  The makeup pumps ( charger pumps I think is the Westinghouse term) are used to inject water into the RCP seals at a constant rate and into the RCS through a level control valve based on the PZR level.  The chemical volume tank is the supply for these Makeup Pumps.  RCS letdown and RCP seal return are aligned to go back to the chemical volume tank.  Between the 2 inputs and 2 outputs, there should be a near constant mass of water.  There is a small amount lost through the last RCP seal stage and this needs to be made up.  I can also divert the letdown to another tank and reduce my total inventory as needed.

Disclaimer: This is a basic overview for the B&W plant that I work at.  I have never been to a Westinghouse or CE plant.  I do not know how they are designed.  I am assuming that it is similar.

[Fermi2]

Very similar and an extremely good description.

I believe a major difference is the Charging Pumps (Make Up Pumps in a B+W Plant) are also the High Pressure ECCS Pumps capable of injecting at full RCS Pressure.
IIRC must B+W plants have a separate set of pumps for that and they aren't capable of full RCS Pressure injection. I'm not certain about Davis Besse as it's a Raised Loop plant.

[thenuttyneutron]

Very similar and an extremely good description.

I believe a major difference is the Charging Pumps (Make Up Pumps in a B+W Plant) are also the High Pressure ECCS Pumps capable of injecting at full RCS Pressure.
IIRC must B+W plants have a separate set of pumps for that and they aren't capable of full RCS Pressure injection. I'm not certain about Davis Besse as it's a Raised Loop plant.

There are two Makeup pumps that will inject at full RCS pressure.  There are two High Pressure injection pumps with discharge pressure of 1600 psig.  If I piggy back the High pressure pumps with Low Pressure Injection, I can get about 1800 psig out of a HPI Pump.  There are 2 LPIs with a 200 psig discharge pressure.

DB is a raised loop plant.

[Pman52]

DB is a raised loop plant.

Not to go too far off topic, but what are the operational differences between a raised and lowered loop B&W plant?  In other words, what are the benefits/drawbacks of a raised loop plant for an operator in the control room? 

[Fermi2]

They raised the loops to promote additional natural circulation post accident. Otherwise not much. The Raised loop was to be the next generation for B+W.
A relative of mine was one of the original DB SROs.


Are the Make Up Pumps ECCS?

[Matthew B]

Are the Make Up Pumps ECCS?

That's a sort of.

B&W didn't count on them for the design basis LOCA.  The idle pump(s) do auto start on a safety injection.  Tech Specs say that 2 must be available with independent power.

IIRC the suction doesn't auto-transfer from the make up tank to the RWST.  (Does B&W call it a RWST?  They use their own name for most everything.)

[thenuttyneutron]

That's a sort of.

B&W didn't count on them for the design basis LOCA.  The idle pump(s) do auto start on a safety injection.  Tech Specs say that 2 must be available with independent power.

IIRC the suction doesn't auto-transfer from the make up tank to the RWST.  (Does B&W call it a RWST?  They use their own name for most everything.)

*Disclaimer.  I can't check all the details now. This is all from memory.

The Makeup Pumps I operate have no auto start.  If there is a loss of power on the bus, the breaker will re-close after 2.5 seconds when the bus is re-powered.  This interlock is disabled after 100 seconds if the bus remains dead (no EDG start).  I can't check now, but the MU Pumps are not parts of ECCS in the Tech Specs.  It is part of the TRM however for a Boron Injection flow-path.

There is an auto swap between the BWST and MU tank that I can override to force the MU pump on to the BWST.  It is all driven on level.  If Level gets too high in the MU tank, suction goes to there.  If the Level gets too low, suction will transfer to the BWST.  The MU pump will trip if it gets stuff between the two to protect the pump.  It will also trip if there is a low low level in the MUT.

[Fermi2]

Do your Makeup pumps supply the Coolant Pump Seals?

[thenuttyneutron]

Do your Makeup pumps supply the Coolant Pump Seals?

Yes.

[Fermi2]

That's why they start after a LOP but do not necessarily line up after a LOCA