pwr incore instrumentation

[wlrun3@aol.com]

  ...are all pwr incore detectors uranium fission chambers...

[Motown homey]

No - CE uses Rhodium wire incores.  Not really sure how they work, but I changed out a few in my time as a road tech.

[wlrun3@aol.com]

   ...thankyou...

   ...are pressurized ion chambers used for incore instrumentation in either design...

[alphadude]

as i recall -PICs are too complex to deal with in such a harsh environment-think about it. they are used as excore detectors. In PICs as pressure increases from temp change the response curve will shift.

Activation wires were used like at Big Rock, fission chambers which generate current are most common or bi metalics which generate current. if my memory is right all are chunks of magic metal-no chambers

[thenuttyneutron]

No - CE uses Rhodium wire incores.  Not really sure how they work, but I changed out a few in my time as a road tech.

The Rhodium 103 incores are self powered neutron detectors.  The Rhodium gets activated and the Rhodium 104 will decay to Pd 104 via beta decay.  There are 2 decay schemes.   The beta decay scheme is more common and it has a 43 second halflife.  It takes about 6 minutes at my plant for the plant computer to update the incore power level.  This corresponds to about 5 half lives inorder to get an equilibrium rate of creation to decay.  Because these decay via Beta, they make their own power in a way.  You just connect it to ground and measure the current flow leaving the wire to ground.

Rhodium 103 is what the incores at my plant are made of.  There are a total of 9 instruments in each incore.  There is one background gamma detector, an incore thermo couple at the top, and 7 separate wires of Rhodium 103 that each measures a small axial section.  The incores are very accurate, but take a long time to update.  This is why they are not used in any safety functions at my plant.  These detectors are also self powered detectors.  We just connect them to a ground and measure the current flowing from the ground to the rhodium wires.

The excores at my plant consist of two fission chamber detectors, two source range, two intermediate range and 4 power range detectors.
We use the fission chamber detectors in refueling as an audible source range detector for refueling and for post accident monitoring.  The accident range detectors read out in counts per second (CPS).  The two Source Range Ion chamber detectors operate in the Ionization region and read out in CPS.  The two intermediate range detectors are Compensated Ion Chamber detectors that operate in the proportional region.  The intermediate range detectors read in amps (1x10^-3 for about 100% power).  For power ops we use four Ion chamber detectors that operate in the Ion region.  These power range detectors are actually a 2 in 1 detector.  There is a top and bottom that range between 0 and 62.5%.  These power range detectors measure their respective part of the core and can give you imbalance and power level.

The Excores are used for safety systems (RPS), an analog computer system that controls the plant called ICS ( god I love this system!), and a few other minor inputs.  The most important thing about these excores is calibration for accurate power indication.  The plant I work at is very different than most units.  We have a ramped Tave till about 28.5% power and it is constant after that at 582 F.  The Thot and Tcold diverge from 28.5% to 100% to keep Tave constant.  The Tcold actually decreases as the power level increases above 28.5%.  This changes the neutron leakage out of the core.  It can affect it in ways that can get you in trouble.  Your indicated power as you are coming down will read higher than actual power.  When you get below that 28.5% Power and Tave&Tcold start to decrease, it will cause you to have a power indication that lower than actual power.

[wlrun3@aol.com]

   ...how does the background gamma detector and the thermocouple in the incore detector string work...



   

[wlrun3@aol.com]

as i recall -PICs are too complex to deal with in such a harsh environment-think about it. they are used as excore detectors. In PICs as pressure increases from temp change the response curve will shift.

Activation wires were used like at Big Rock, fission chambers which generate current are most common or bi metalics which generate current. if my memory is right all are chunks of magic metal-no chambers

   ...are all light water reactor incore detectors either fission chambers or activation product detectors like the rhodium in the CE design...