United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-03: Calibration of Liquid Level Instruments

                                                            SSINS No.: 6835 
                                                            IN 83-03       

                                UNITED STATES
                            WASHINGTON, DC 20555 
                              January 28, 1983



All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 


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 

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. 


                                                          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

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