Reactor plant chemistry questions

[ChopperBob]

     Hello all. I'm new to this site. I am a retired MMC(SS) LELT. Got out in 1986. Having been out of the business for 20 yrs, my memory is failing me somewhat.
     I have a few chemistry questions about a light water PWR.
     1. What is the typical nuclide make up of CRUD, (i.e. what percentage of crud is Co-60, etc.)
     2. Do nuke plants typically measure "CRUD" and Co-60 in the coolant?
     3. Do nuke plants typically measure for Sr-90 in coolant?

    Thanks
     Bob

[alphadude]

 i would assume that you mean wear products and not fission products?

its typical- mn54, co60, co58 etc (filterables?)

% depends on plant operational history and what they have done for crud burst and chemical cleaning

yes they measure crud and co60

sr-90 is measured

[ChopperBob]

     So, it would be safe to assume that plants are required to measure for Sr-90 along with other fission products. And they are required to measure crud levels, including Co-60.
     I'm trying to figure out why a plant says they didn't measure for any of the above for an entire year. Does the NRC still get involved with Rx plant chemistry. If not, then who regulates chemistry measurement requirements?
    Thanks
     Bob

[Fermi2]

No, you are not required by federal regulations to monitor for Crud or Strontium 90.

You are required to monitor

1: Oxygen
2: Florides
3: Chlorides
4: Conductivity in  BWR
5: PH in a BWR
6: Boron in a PWR
7: RCS and E Bar (Corrected Idione) which is to ensure if a SGTR happens you won't exceed 10CFR100 limits.

There are no requirements for Secondary Chemistry by the NRC.

So far as release you have to monitor all vent stacks and water pathways activity with Rad Monitors, usually some sort of scintiallation detector. Depending on the pathway Automatic Release might be required. This depends on the utilities analysis of the pathway. Whatever the required setpoints are will be in the ODCM (Off Site Dose Calculation Manual) the basis for these setpoints will be either to maintain releases within 10CFR20 (In normal ops) or to measure dose rates at pathways designed to operate post accident for Emergency Plan Purposes. What you specifically monitor for is not specified by Federal Regulations.

CRUD is not a requirement and most utilities don't monitor for it.

Mike

[alphadude]

utilities monitor radionuclides to determine source term.. so in reality you are required to monitor. i think the confusion is process monitoring vs dose to the public concerns.. broadzilla answered from a process monitoring view point.. my answer is from a dose to the public view.  Daily a gamma spect is performed on a primary sample to monitor for failed fuel events and crud burst potential. This monitoring ties into the effluents of the plant and this information is required by law. To dispose of the waste, you need a profile which comes from monitoring, and all nuclides mentioned are part of the analytical process. For process and equipment wear, you monitor for O2, solids etc. 

Chemistry monitoring does include vendor specifications, which is not required by law.  Sounds like you asked an operator the question.  Every plant I have worked in (10 so far) looks at those items daily (except Sr which is special analysis).

[Fermi2]

The monitoring is required by the ODCM. CRUD isn't required for any of this. It's a great indicator of whats in the coolant, but isn't legally required UNLESS you're gonna have some sort of liquid release. With so many different types of fuel you can't be reral specific.

Usually any other monitoring, particularly secondary (or BOP Side is a BWR) is due to EEI Guidelines. For instance my plant is HUGE on ensuring Sulfates stay at a certain value, they also are big in SG Oxygen and Chlorides. None is required by law. In fact the NRC Philosophy is you mininmize dose to public via potentially leaking SG Tubes by limiting the activity in the coolant (E Bar and Gross Activity), minimizing allowed leakage and requiring Tubes to be plugged at using certain criteria. How you maintain your chemistry in order to accomplish this is up to you. Mostly it's within EEI CRiteria.


Mike

[alphadude]

yep ... what he said

[delkinto]

Corrosion and wear products are HUGE considerations for both primary and secondary at a PWR.  Here's some non-radiological considerations.

On the primary side, especially in larger cores, for example, nickel ferrite tends to deposit on the core which in turn can cause boron precipitates to form in hot regions.  This eventually leads to uneven power production across the core axially (axial offset anomaly), and can cause power production in the top and the bottom of the core to become uncoupled when manuevering power (xenon).  These  have been controlled largely by having to redesign cores and change the chemistry at temperature pH and lithium concentrations.

Iron and copper deposition in the secondary wreak havoc on Alloy 600 tubes, and we'll see for new SG replacements for alloy 690.

While not in tech specs,  controls are usually specified by endorsement of EPRI guidance in the plant updated FSAR, which is controlled by the facility operating license.  So it is regulated.  The NRC doesn't pay a whole lot of attention to these unless you start having problems that you can't seem to fix.  INPO, on the other hand, spends a lot of time in the area and numbers are reported for their performance indicators.


Hope this helps.

[Fermi2]

Any guidance in the UFSAR is guidance only and not regulation. FSAR requirements have to be met. FSAR statements that refer to guidelines are simply statements only. So SG Chemistry and CRUD is not regulated in the least. Thats the way an FSAR works.


Provided you stay within Thermal Limits you can't get boron precipitation. If you operate in a regime where you are outside your thermal limits THEN you have far bigger problems than Boron precipitation. Since the amount of Boron on a per LBM basis is less in the Top of the core than the bottom Axial Offest is not likely due to chemistry. The UFSAR and Fuel Analysis don't even mention chemistry as a credible cause of Xenon or Axial Instabilities. Every known case througout the industry was due to either Operator Error, Poor Core Design, or a loss of feedwater heating.

Mike

[delkinto]

Most facilities do commit to industry guidance in their FSAR.  As such they form part of the licensing basis of the plant which is in turn required by the operating license.  It depends on the specific language in the FSAR. Good examples include QA program, design reg guides, ANSI standards, IEEE, ASME etc, etc.  The operative regulation would be 10CFR50. Our plant makes specific statements commiting us to EPRI primary and secondary water chemistry guidelines, so they in effect become rules, especially for control parameters. 

My info on AOA was probably dated and I hadn't kept up on it.

Thanks.

[Fermi2]

QA is required by law. I sort of simplified things. If you put it in the FSAR you'll do it. Some things you'll pay fines for.

One thing I can't find, it's probably in the ODCM someplace but I haven't read all the ODCM background info, where does the requirement to monitor TRITIUM come from??

Mike