Bulletin 79-21: Temperature Effects on Level Measurements
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
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
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
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
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.
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
Enclosure: Memo Westinghouse Electric Corp.
to Victor Stello dated June 22, 1979
Page Last Reviewed/Updated Friday, May 22, 2015