Joined: Sep 30, 2010
Posts: 1
Location: New Jersey
Status: Offline
Posted:
Sep 30, 2010 - 10:54 AM
Post subject: Forecasting transmitter drift
My goal is to monitor primary process element performance and increase the interval between sensor calibrations.
The primary devices used are mostly Roesmount pressure/dp transmitters with analog outputs. These devices are supporting dedicated hard wired control loops. There is no distributed control system or networked data system for these devices.
My question is how to assemble device performance and evaluate thedata in order to justify increasing the interval between calibrations. The interval is currently dictated by the plants operating license through the Nuclear Regulatory Commission.
Carl_E
ICE Student
Joined: May 30, 2010
Posts: 11
Location: Illinois, USA
Status: Offline
Posted:
Oct 03, 2010 - 03:43 PM
As someone who lives 40 miles downwind of a nuke generating plant, I truly hope your inquiry is more consistent with compliance than a mere query of random internet sources for something as critical as increasing calibration intervals.
TO: ALL HOLDERS OF OPERATING LICENSES OR CONSTRUCTION PERMITS FOR NUCLEAR POWER REACTORS
SUBJECT: CHANGES IN TECHNICAL SPECIFICATION SURVEILLANCE INTERVALS TO ACCOMMODATE A 24-MONTH FUEL CYCLE (Generic Letter 91-04)
<snip>
Licensees must address instrument drift when proposing an increase in the surveillance interval for calibrating instruments that perform safety
functions including providing the capability for safe shutdown. The effect
of the increased calibration interval on instrument errors must be addressed because instrument errors caused by drift were considered when determining safety system setpoints and when performing safety analyses.
Enclosure 2 describes information required to address the effect that instrument drift caused by an increased calibration interval can have on safety.
<snip>
Generic Letter 91-04 Enclosure 2
GUIDANCE FOR ADDRESSING THE EFFECT OF INCREASED
SURVEILLANCE INTERVALS ON INSTRUMENT DRIFT
AND SAFETY ANALYSIS ASSUMPTIONS
Discussion
The U.S. Nuclear Regulatory Commission (NRC) staff determined that licensees should address the issue of instrumentation errors caused by drift in order to justify an increase in surveillance intervals to accommodate a 24-month fuel cycle. Licensees must evaluate the effects of an increased calibration interval on instrument errors in order to confirm that drift will not result in instrument errors that exceed the assumptions of the safety analysis.
Instrument drift affects the capability of a system to perform its safety
function and is a consideration for determining safety system setpoints.
The amount of instrument drift that occurs over a long interval between
calibrations may not be readily available from the instrument vendor.
However, operating experience and available vendor data can provide insights on the increase in instrument errors that could occur with an increased calibration interval. These insights, with a program to monitor and assess the long-term effects of instrument drift, can provide the basis for increasing the refueling outage related calibration intervals for
instruments that perform safety functions.
Justification for Increased Calibration Intervals
Licensees should address a number of issues to provide an acceptable basis for increasing the calibration interval for instruments that are used to perform safety functions. The NRC staff has identified a specific action
that licensees should address for each of these issues in order to justify a
proposed increase in the calibration interval. A summary of the applicable issue is provided after each of the following actions.
1. Confirm that instrument drift as determined by as-found and as-left calibration data from surveillance and maintenance records has not, except on rare occasions, exceeded acceptable limits for a calibration interval.
The surveillance and maintenance history for instrument channels should
demonstrate that most problems affecting instrument operability are found as a result of surveillance tests other than the instrument calibration. If the calibration data show that instrument drift is beyond acceptable limits on other than rare occasions, the calibration interval should not be increased because instrument drift would pose a greater safety problem in the future.
2. Confirm that the values of drift for each instrument type (make,
model, and range) and application have been determined with a high
probability and a high degree of confidence. Provide a summary of the methodology and assumptions used to determine the rate of instrument
drift with time based upon historical plant calibration data.
The licensee should have a body of as-found and as-left calibration data
that permits the determination of the rate of instrument drift with time
over the calibration interval. This data should allow the determination of
instrument drift for those instruments that perform safety functions.
Generic Letter 91-04 - 2 - Enclosure 2
3. Confirm that the magnitude of instrument drift has been determined
with a high probability and a high degree of confidence for a bounding
calibration interval of 30 months for each instrument type (make, model
number, and range) and application that performs a safety function.
Provide a list of the channels by TS section that identifies these instrument applications.
The magnitude of the instrument drift error that occurs over a longer
interval is an important consideration to justify an extension of the
calibration interval for instruments that perform safety functions.
Licensees need to identify the applications where the calibration interval
for these instruments depends upon the length of the fuel cycle and could be as long as 30 months (the extension limit for this calibration interval).
Licensees should determine the projected value of the instrument drift error that could occur over a 30-month interval for each of these applications.
4. Confirm that a comparison of the projected instrument drift errors
has been made with the values of drift used in the setpoint analysis.
If this results in revised setpoints to accommodate larger drift
errors, provide proposed TS changes to update trip setpoints. If the
drift errors result in a revised safety analysis to support existing
setpoints, provide a summary of the updated analysis conclusions to
confirm that safety limits and safety analysis assumptions are not
exceeded.
Licensees should ensure that the projected value of instrument drift for an increased calibration interval is consistent with the values of drift errors used in determining safety system setpoints. These setpoints ensure that the consequences of accidents and anticipated transients are bounded within the assumptions of the safety analysis. If the allowance for instrument drift that was used to establish trip setpoints for safety systems would be exceeded, licensees should establish new trip setpoints for safety systems. Instrument Society of America (ISA) Standard, ISA-A67.04-1982, "Setpoints for Nuclear Safety-Related Instrumentation Used in Nuclear Power Plants," provides a methodology for evaluating instrument drift. The NRC endorsed this standard in Regulatory Guide 1.105, "Instrument Setpoints for Safety-Related Systems." If a new setpoint must be used to ensure that safety actions will be initiated consistent with the assumptions of the safety analysis, this will require a TS revision to reflect a new trip setpoint value. If the combination of instrument drift errors and current trip setpoints is not consistent with existing safety analysis assumptions, licensees should perform a new safety analysis to confirm that safety limits will not be exceeded with the increased drift associated with longer calibration intervals.
5. Confirm that the projected instrument errors caused by drift are
acceptable for control of plant parameters to effect a safe shutdown with the associated instrumentation.
Licensees should determine the effect of instrument errors on control
systems used to effect a safe shutdown. Licensees must confirm that the
instrument errors caused by drift will not affect the capability to achieve
a safe plant shutdown.
Generic Letter 91-04 - 3 - Enclosure 2
6. Confirm that all conditions and assumptions of the setpoint and
safety analyses have been checked and are appropriately reflected in
the acceptance criteria of plant surveillance procedures for channel
checks, channel functional tests, and channel calibrations.
Licensees should take care to avoid errors or oversights when establishing acceptance criteria for plant surveillance procedures that are derived from the assumptions of the safety analysis and the results of the methodology for determining setpoints. The NRC staff experience is that licensees have encountered problems when asked to confirm that instrument drift and other errors and assumptions of the safety and setpoint analyses are consistent with the acceptance criteria included in plant surveillance procedures.
This review should include channel checks, channel functional tests, and the calibration of channels for which surveillance intervals are being
increased.
7. Provide a summary description of the program for monitoring and
assessing the effects of increased calibration surveillance intervals
on instrument drift and its effect on safety.
Finally, licensees should have a program to monitor calibration results and the effect on instrument drift that will accompany the increase in
calibration intervals. The program should ensure that existing procedures
provide data for evaluating the effects of increased calibration intervals.
The data should confirm that the estimated errors for instrument drift with
increased calibration intervals are within the limits projected.
In summary, licensees can provide a justification for increased surveillance intervals for instrument channel calibration by addressing each of the items noted herein.
Carl_E
ICE Student
Joined: May 30, 2010
Posts: 11
Location: Illinois, USA
Status: Offline
Posted:
Oct 05, 2010 - 10:18 AM
ISA offers training:
Transducer/Transmitter Installation for Nuclear Safety Applications Using ANSI/ISA-67.01.01
The ANSI spec might cover the topic you queried about
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