United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 79-21: Temperature Effects on Level Measurements

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                               August 13, 1979

                                                      IE Bulletin No. 79-21 

TEMPERATURE EFFECTS ON LEVEL MEASUREMENTS 

Description of Circumstances: 

On June 22, 1979, Westinghouse Electric Corporation reported, to NRC, a 
potential substantial safety hazard under 10 CFR 21. 

The report, Enclosure No. 1, addresses the effect of increased containment 
temperature on the reference leg water column and the resultant effect on 
the indicated steam generator water level. This effect would cause the 
indicated steam generator level to be higher than the actual level and could 
delay prevent protection signals and could, also, provide erroneous 
information during post-accident monitoring. Enclosure No. 1 addresses only 
a Westinghouse steam generator reference leg water column; however, safety 
related liquid level measuring systems utilized on other steam generators 
and reactor coolant systems could be affected in a similar manner. 

Actions To Be Taken By Licensees: 

For all pressurized water power reactor facilities with an operating 
license:* 

1.   Review the liquid level measuring systems within containment to 
     determine if the signals are used to initiate safety actions or are 
     used to provide post-accident monitoring information. Provide a 
     description of systems that are so employed; a description of the type 
     of reference leg shall be included, i.e., open column or sealed 
     reference leg. 

2.   On those systems described in Item 1 above, evaluate the effect of 
     post-accident ambient temperatures on the indicated water level to 
     determine any change in indicated level relative to actual water level.
     This evaluation must include other sources of error including the 
     effects of varying fluid pressure and flashing of reference leg to 
     steam on the water level measurements. The results of this evaluation 
     should be presented in a tabular form similar to Tables 1 and 2 of 
     Enclosure 1. 

3.   Review all safety and control setpoints derived from level signals to 
     verify that the setpoints will initiate the action required by the 
     plant safety analyses throughout the range of ambient temperatures 
     encountered by the instrumentation, including accident temperatures. 
     Provide a listing of these setpoints. 


*    Boiling water reactors have been requested by a July generic letter 
     from the NRC to provide similar information. 
.

IE Bulletin No. 79-21                                          Page 2 of 2 
August 13, 1979 

If the above reviews and evaluations require a revision of setpoints to 
ensure safe operation, provide a description of the corrective action and 
the date the action was completed. If any corrective action is temporary, 
submit a description of the proposed final corrective action and a timetable 
for implementation. 

4.   Review and revise, as necessary, emergency procedures to include 
     specific information obtained from the review and evaluation of Items 
     1, 2 and 3 to ensure that the operators are instructed on the potential
     for and magnitude of erroneous level signals. All tables, curves, or 
     correction factors that would be applied to post-accident monitors 
     should be readily available to the operator. If revisions to procedures
     are required, provide a completion date for the revisions and a 
     completion date for operator training on the revisions. 


A report of the above actions shall be submitted within 30 days of the 
receipt of this Bulletin. 

Reports should be submitted to the Director of the appropriate NRC Regional 
Office and a copy should be forwarded to the NRC Office of Inspection and 
Enforcement, Division of Reactor Operations Inspection, Washington, D. C. 
20555. 

For boiling water reactors with an operating license and all power reactors 
with a construction permit, this Bulletin is for information purposes and no
written response is required. 

Approved by GAO, B180225 (R0072); clearance expires 7/31/80. Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

Enclosure: Memo Westinghouse Electric Corp.
to Victor Stello dated June 22, 1979 
Page Last Reviewed/Updated Tuesday, July 23, 2013