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Information Notice No. 83-03: Calibration of Liquid Level Instruments
SSINS No.: 6835 IN 83-03 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, DC 20555 January 28, 1983 INFORMATION NOTICE NO. 83-03: CALIBRATION OF LIQUID LEVEL INSTRUMENTS Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided as a notification on calibration of liquid level instruments which may have safety significance. It is expected that recipients will review the information for applicability to their facilities. No specific action or response is required. Description of Circumstances: Several licensees have reported inaccurate liquid level indications from instruments on various tanks such as chemical addition tanks (CATs) or boric acid storage tanks (BASTs) which contain liquid chemicals or solutions with densities different than that of water. Those instruments that are not calibrated with density compensation will not measure the volume of liquid accurately. Although density compensation is a basic requirement for accurate level measurements, it is periodically overlooked. On past occasions, pure water at 60F was used as a reference to calibrate the differential pressure transmitters measuring the liquid level in the tanks, irrespective of the density difference from that of the solutions being measured. Density corrections must be made for those liquids other than water that are contained in the tanks. The corrections must also consider the temperature of the liquid. One licensee recently determined that measuring instruments on the 4,300-gallon CAT had not been density compensated correctly for the 17 percent (by weight) solution of the sodium hydroxide in the CAT. After the density correction was factored into the measuring system, it was found that the actual volume of solution in the tank was some 300 gallons below the minimum required by technical specifications. For tanks with boron concentration of less than 1,000 ppm, the liquid level indication will be relatively accurate because the density of the liquid compared to that of water will not differ significantly. However, there were several tanks which operate at an elevated temperature whose differential pressure instrumentation employed to measure the liquid level was not initially compensated for these, elevated operating conditions. Under these conditions, a heated tank could have overflowed when liquid level was indicating less than 100 percent full. Compensation for differences in density and/or temperature of liquid solutions should be included in the measuring system during calibration. 8212060361 . IN 83-03 January 28, 1983 Page 2 of 2 Some of the more important systems that may be affected by this problem are as follows: Refueling Water Storage Tank (Westinghouse) Borated Water Storage Tank (B&W) Chemical Addition Tanks (to containment spray systems) Safety Injection Accumulators Boric Acid Storage Tanks Standby Liquid Control Tanks (BWR) Volume Control Tanks It is suggested that holders of operating licenses or construction permits review this information for applicability to water-calibrated level instruments on tanks containing liquids other than water and other than at ambient temperatures. No written response to this notice is required. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Edward L. Jordan Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: V. D Thomas 301-492-4755 Attachment: List of Recently Issued Information Notices
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