Frequently Asked Questions

As a result of the issuance of the USNRC RIS, there appears to be some confusion on the impact of the USNRC  RIS to current CROSSFLOW clients as well as potentially new clients. Detailed discussion to the most frequently asked questions related to the impact of the issuance of the USNRC RIS is given in the FAQ section.


Has the US-NRC withdrawn permission for plants to use CROSSFLOW for Appendix K (MUR) and Power Recovery?

No they have not.
No plant has been required to take the CROSSFLOW system out of service and no plant has been required to down-power. Those plants already licensed for MUR uprate and those using the system for Power Recovery continue to do so, with the existing Topical Report providing the licensing basis.

What regulatory action is specified in the US-NRC RIS?

The US-NRC issued a Regulatory Issue Summary (RIS) 2007-24 to existing licensees and a Safety Evaluation (SE) to WEC/AMAG giving technical details for their justification of the suspension of the use of the Topical Report (TR) in future license applications. The US-NRC specified the following actions:

  •  Plants with existing CROSSFLOW systems must satisfy themselves that in using the CROSSFLOW system the US-NRC’s 5 concerns specified in the RIS are addressed with reasonable assurance.
  • The US-NRC has withdrawn their approval for the existing Topical Report TR CENPD-397-P, Revision-01-P. It may no longer be used as the technical basis for:
    • a NEW license application for a MUR or
    • implementing a NEW Power Recovery (which does not need US-NRC approval)

AMAG is preparing a new Topical Report for submission to the US-NRC.  In the meantime plants may apply to implement CROSSFLOW for
Power Recovery or MUR applications based upon plant-specific documentation (see next Question) which would have to address among
other things the issue of CROSSFLOW calibration for the specific conditions in which it is to be installed.

Can CROSSFLOW be used for any new flow measurement in the plant?

Yes, CROSSFLOW can be used in several ways:

  • An Appendix K - MUR license application can be submitted to the US-NRC provided that all the technical information to support the application is included. One of the main US-NRC issues is related to CROSSFLOW calibration, which is based on the extrapolation of laboratory results to plant conditions. This would have to be described in detail and would be evaluated by the US-NRC reviewers.
  • A Power Recovery application can be implemented. Although this does not have to be licensed by the US-NRC, technical work will have to be done and documented to satisfy the US-NRC Review.
  • In a Dual Mode Technology (UFM plus DP instrument measuring same flow), application where the CROSSFLOW system is used to monitor and correct drift in existing DP instrumentation.
  • Other applications, where a measurement uncertainty of 0.5% is not needed. This includes flow measurement of the Emergency Core Cooling System (ECCS), Cooling Water, etc.
  • Applications such as Primary Heat Transfer System (in CANDU reactors) flow measurement, where flow conditions can be reproduced in laboratory calibration.

What issues will the new Topical Report address and when will it be approved?

Five issues with the current Topical Report were identified by the US-NRC. These can be grouped as follows:

  • Concerns about acoustic noise
  • Calibration concerns
  • Traceability and statistical concerns
  • Concerns over adequacy of documentation (calibration procedure, installation procedure and procedures for using CROSSFLOW during operation)

A new topical report is currently being prepared which addresses each of these concerns. The status is as follows:

  • Several noise mitigation tools have been developed and are currently in use by CROSSFLOW users. AMAG believes that this issue has been adequately addressed and that the current system incorporates robust noise detection and correction tools.
  • AMAG is in the process of developing a new more robust meter design which will address the US-NRC’s issue relating to calibration (laboratory calibration with extrapolation to plant conditions) as well as the concern over traceability to a National Standard.
  • AMAG has revised the statistical approach used in calibration of CROSSFLOW. This follows the ISO recommendations and standard and will address the US-NRC concern in this area.
  • New documentation covering all aspects of calibration and installation and use of the CROSSFLOW system is being developed to provide a complete description meeting current standards.

An updated Topical Report is currently being written and is expected to be submitted to various
Regulatory Authorities for review in 2010.

There was a problem identified with the CROSSFLOW system at Byron/Braidwood. What happened?

The situation that developed at the Byron/Braidwood plants is fully documented in the INPO Significant Event Report (SER 3-04) dated 18 June 2004.

The error in the CROSSFLOW readings was determined to be due to correlated acoustic noise.
AMAG has since developed sophisticated on-line noise detection and correction tools that remove the effects of this correlated acoustic noise in real time.

Because of the manner in which the CROSSFLOW system was used at Byron/Braidwood the error was not detected for an extended time. The INPO recommendation is that a UFM should not be used for off-line periodic measurements as was the case a Byron/Braidwood.

What was the problem at Ft Calhoun?

At Ft Calhoun the CROSSFLOW system was used for Power Recovery. It became evident that acoustic noise was affecting the CROSSFLOW readings. As a consequence Ft Calhoun withdrew its Appendix K MUR license amendment application.

AMAG has since developed sophisticated on-line noise detection and correction tools that remove the effects of this correlated acoustic noise in real time.

Have other problems occurred at plants using the CROSSFLOW system?

No problems have occurred at other plants using the CROSSFLOW system. Analysis of the few problems that have occurred resulted in:

  • Implementation of the new noise detection and correction tools to address the problem caused by correlated acoustic noise.
  • Development of the new CROSSFLOW User Guidelines to provide plants with more guidance on the use of CROSSFLOW.

CROSSFLOW has proved its reliability and is in productive use by plants worldwide.

The US-NRC question laboratory calibration. How is this being addressed?

The issue with laboratory calibration is primarily an issue with the uncertainty associated with extrapolation from the laboratory to the plant conditions. In the past, laboratories could not reproduce the fluid dynamic conditions (velocity, temperature, etc) found in feedwater systems. A method of extrapolation is therefore required.

AMAG is actively working on establishing a traceable calibration method using current High Reynolds Number Laboratories to eliminate the extrapolation requirement.

How will the question of accurate plant modeling in the laboratory be addressed?

A new design of the CROSSFLOW transducer (multi-beam transducer) has been completed which has been shown to minimize or eliminate the effect of upstream geometry on the CROSSFLOW meter.

AMAG intends to more accurately model the upstream plant geometry, both by CFD analysis and also in the laboratory calibration.

The combination of using an accurate model in a laboratory that can achieve near plant operating conditions will reduce the uncertainty associated with the laboratory calibration.

The CROSSFLOW software associated with this new design has improved signal processing capabilities and improves the performance of the system as well as providing improved self-checking of meter performance.

How does the new system differ from the current system?

The original CROSSFLOW system used four ultrasonic probes arranged in pairs, one pair mounted upstream and the other downstream. Each pair consists of a transmitter and a receiver. In this configuration, two ultrasonic beams at the upstream and downstream pair results in a single time delay measurement.

The new meter design consists of up to 32 ultrasonic probes (16 ultrasonic beams) and up to 12 software channels.  It allows obtaining multiple time delay measurement and additional information on flow at the transducer location This additional information improves the accuracy of the measurement and allows characterization of the fluid dynamic conditions.

This characterization of the fluid dynamic conditions using (up to) 16 ultrasonic beams will allow the meter to determine whether the conditions at the transducer location in the plant is the same as those under which it was calibrated. Further it will allow the meter to determine whether the fluid dynamic conditions have changed to the extent that the calibration is no longer valid.

More advanced digital signal processing techniques reduce the sensitivity of the meter to the fluid dynamic conditions present at the installation location.

In addition the new system is able to detect and correct for situations where correlated acoustic noise is present.

The US-NRC questioned the quality of the statistical analysis supporting the laboratory calibration. How is this addressed?

AMAG intends to follow the ISO methodology as described in the Guide to the Expression of Uncertainties in Measurement (GUM). Work is currently being done to extend the guide to the field of feed water flow measurement by the National Metrological Institutes in Sweden (SP), Japan (AIST), Germany (PTB) and USA (NIST).

AMAG plans to work directly with SP to ensure that we meet the required rigor in our statistical analysis.

The US-NRC raised a concern regarding acoustic noise affecting the meter. How is this addressed?

Over the last 5 years AMAG has developed an in-depth understanding of the acoustic noise phenomena present in feedwater piping systems in Nuclear Power Plants specifically as it relates to the performance of the CROSSFLOW meter.

AMAG now has on-line, real-time noise detection and mitigation/correction capability in the current CROSSFLOW system.

Where does AMAG currently have Installations?

See Projects page for more information.