Information Notice No. 84-75: Calibration Problems - Eberline Instrument Model 6112b Analog Teletectors

                                                          SSINS No.: 6835  
                                                          IN 84-75         

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                            WASHINGTON, DC 20555 

                              October 5, 1984 

Information Notice No. 84-75:   CALIBRATION PROBLEMS - EBERLINE 
                                   INSTRUMENT MODEL 6112B ANALOG TELETECTORS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP), research and test reactors, and fuel facilities. 

Purpose: 

To alert licensees to a problem in properly calibrating the Eberline 
Teletector with installed replacement detector tubes supplied by LND Inc. A 
simple two point calibration, still in use by some licensees, may not detect
this problem. Suggestions contained in this information notice do not 
constitute NRC requirements and, therefore, no specific action or written 
response is required. 

Description of Circumstances: 

GPU Nuclear has identified a problem with high range Geiger-Muller (GM) 
detector tubes obtained for use with the Eberline analog Teletector Model 
6112B. After installing the replacement tube (Model 71623), supplied by LND 
Inc. of Oceanside, New York, GPU experienced an inability to achieve an 
acceptable calibration on the 0-1000 R/hr scale. Although the response of 
the instrument remains linear on each scale, the potentiometer setting 
needed to calibrate the 0-50 R/hr scale makes it impossible to obtain a 
proper meter response on the 0-1000 R/hr scale. The result is that the 
instrument reads low on the upper scale. 

Unless an intense calibration source is used to check this upper scale, the 
calibration error will not be detected. In response to this situation, 
Eberline announced, by letter dated July 31, 1984, a change in the type of 
high range detection tube used in the 6112B Teletector. 

The calibration problem was traced to a reduced detector gas pressure in the
Model 71623 GM tube. This resulted in a lower tube sensitivity than that 
designed for the analog Teletectors. The design sensitivity for the high 
range GM tube is 20 +/- 20% cpm per mR/hr in a Cs-137 field with 600 volts 
applied to the tube. The sensitivity of the tubes supplied to GPU Nuclear 
was measured at 12 cpm per mR/hr. 

LND has stated that its Model 716 GM tubes can meet the design 
specifications. Suspect replacement tubes can be screened before placing 
them in service. 


8410030233  
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                                                          IN 84-75         
                                                          October 5, 1984  
                                                          Page 2 of 2      

No specific action or written response is required by this information 
notice. If you have any questions about 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 Contacts: R. L. Pedersen, IE 
                    (301) 492-9425 

                    J. E. Wigginton, IE 
                    (301) 492-4967 

Attachment: 
List of Recently Issued IE Information Notices