IE Circular No. 81-03, Inoperable Seismic Monitoring Instrumentation

                                                          SSINS No.: 6830  
                                                          Accession No.:   
                                                          IEC 81-03        

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 
                               March 2, 1981  


Description of Circumstances: 

On November 8, 1980, an earthquake occurred off the coast near Eureka, 
California. The earthquake was reported to have a magnitude of 7.0 on the 
Richter Scale at the epicenter, approximately 25 to 75 miles from the 
Humboldt Bay Power Plant facility. There were 12 separate seismic events 
above a magnitude of 3.5 that occurred within 24 hours of the earthquake, 
the largest event measuring 5.2. Reported damage to structures included 
several houses that were moved off supporting posts, various chimneys that 
were knocked down, one highway overpass that collapsed, and unspecified 
damage that occurred at two pulp mills. There were three potentially 
different sources of plant response data: three sets of magnetic tape 
triaxial accelograph recorders; three sets of triaxial film recorders 
(passive device); and one set of triaxial response spectrum recorders 
(passive device). A review of the records from these instruments indicated 
the following: the magnetic tape triaxial recorders did not produce useful 
records due to a degraded low-voltage power supply in the recording system 
(previously scheduled for routine servicing one week after the earthquake); 
a buildup of dirt and dust appeared to make inoperable six of the nine film 
recorders (the readings from the other three are considered highly 
unreliable and were not obtained from the same set of triaxial recorders); 
the triaxial response spectrum recorder was the only instrument believed to 
produce reliable data. 

On January 24, 1980, an earthquake measuring 5.5 on the Richter Scale 
occurred about 10 miles north of Lawrence Livermore Laboratory (near San 
Francisco, California). Numerous aftershocks also occurred with one 
measuring 5.2 on January 26. The damage to civil structures was considered 
minor. Rancho Seco Nuclear Plant, located approximately 45 miles northeast 
of the earthquake area, reported no physical damage, although plant 
personnel felt slight building motion. 

Rancho Seco was shutdown for refueling during these earthquakes. During this
period, the electrical seismic instrumentation system was inoperable because
portions of the system were out for calibration. For the other instruments, 
power was not being supplied due to electrical cable problems. Whether the 
seismic instrumentation would have activated or not is unclear because the 
U.S. Geological Survey equipment close to the site did not trigger. Records 
from a passive recorder showed peak accelerations from 1 to 1.5 g and 0.1 g 

                                                           IEC 81-03      
                                                           March 2, 1981  
                                                           Page 2 of 3    

for the January 24 and 26 events respectively, which are in excess of values
which might be attributed to the seismic event. These indications are not 
believed to be accurate values since the recorder was in an area in which it
could be easily jarred by personnel. 

An earthquake measuring 3.6 to 4.1 on the Richter Scale occurred about 15 
miles from the Maine Yankee site on April 17, 1979. Personnel in the control
room felt the earthquake motion, but it was not felt by others inside the 
containment. An inspection of the strong-motion accelographs (Kinemetrics 
SMA-l) on April 19, 1979 revealed that one instrument was inoperable 
apparently because leakage of corrosive fumes from the rechargeable 
batteries destroyed the battery connection. Inspection of the seismic 
instruments on August 1, 1979 again revealed the corrosion problem as found 
before but occurring on both instruments. Based on this, a shorter 
inspection interval was initiated. Recent discussions with the 
manufacturer's representative indicate that the battery corrosion problem 
appears to be limited to the SMA-l units because the SMA-2 and SMA-3 units 
have not exhibited a corrosion problem. Those facilities that may have SMA-l 
units include Turkey Point Unit 3, Pilgrim, Maine Yankee, Vermont Yankee, 
Point Beach Unit 1, Fort St. Vrain, and Browns Ferry Unit 1. 

The experiences at the Humboldt Bay, Rancho Seco, and Maine Yankee 
facilities are of concern because, if a significant earthquake had occurred, 
important data relating to the plant response would not have been obtained. 
The experiences point out that (1) calibration or testing of the seismic 
instrumentation should not disable a major portion of the seismic 
instrumentation system for long periods of time; (2) the necessity for 
periodic surveillance and calibration of the entire seismic monitoring 
system; (3) the necessity to assess the adequacy of the 
surveillance/calibration interval; and (4) the necessity to detect those 
areas where accidental impact or high background vibrations may mask the 
actual seismic response. In addition, Licensee Event Reports (LERs) 
submitted to the NRC have revealed various problems relating to seismic 
instrumentation. The problems involve not only the electrical time-history 
instrumentation, but also the passive peak acceleration recorders. A 
description of the problems is enclosed. Note that the first problems 
identified in Attachment 1 could have prevented the recording of the plant 
seismic response if a significant earthquake had occurred. The remainder are
instances of less significant malfunctions. 

The requirements for seismic instrumentation are described in Appendix A to 
10 CFR Part 100 and Regulatory Guide 1.12. The instrumentation serves to 
enable a prompt review of the actual seismic response of plant features 
important to safety in comparison with that used as the design basis. This 
information can be used to determine whether a plant should be shutdown, or 
can continue to be safely operated, and to permit appropriate, timely 
action. If an earthquake were to occur near a nuclear facility, the most 
useful information of the plant's response would be from the onsite seismic 
instrumentation. Evaluation of the plant response due to a seismic event 

                                                           IEC 81-03      
                                                           March 2, 1981  
                                                           Page 3 of 3    

and evaluation of continued operation of the facility would be difficult 
without accurate and reliable data. Based on the above discussion, the 
following action is recommended. 

Recommended Action for Holders of Operating Licenses and Construction 

It is recommended that holders of operating licenses and construction 
permits review for applicability the specific items presented in the 
"Description of Circumstances" and the enclosure to the Circular. It is 
further recommended that the surveillance testing and calibration programs 
for the seismic instrumentation system be reviewed and revised as necessary 
to detect and prevent the malfunctions described herein and to limit the 
potential for having or making the entire seismic monitoring system (active 
and passive components) inoperable during all plant modes of operation. 

No written response to this Circular is required. If you require additional 
information regarding these matters, please contact the Director of the 
appropriate NRC Regional Office. 

1. Seismic Instrumentation Malfunctions 
2. Recently Issued IE Circulars  

                                                           Attachment 1   
                                                           IEC 81-03      
                                                           March 2, 1981  


PLANT                         LER NUMBER/              EVENT DESCRIPTION 

Beaver Valley Power           78-028                   Magnetic tape 
Station, Unit 1                                        recorder (Teledyne 
                                                       Geotech Model 
                                                       MTS-100), was 
                                                       found inoperable 
                                                       during surveillance 
                                                       test; replaced with 
                                                       new instrument 

D.C. Cook Nuclear Plant,      75-56                    One channel was found
Unit 1                                                 during surveillance 
                                                       testing to have a 
                                                       severe amplifier 
                                                       balance shift; the 
                                                       amplifier  board was 

                              76-19                    Movable masses on the 
                                                       peak recording 
                                                       accelerometers were 
                                                       against the stops; 
                                                       the units were 
                                                       replaced; initiated 
                                                       surveillance interval

                              76-50                    Cassette tape (Kine- 
                                                       metrics) on 
                                                       system was found 
                                                       sticking during 
                                                       surveillance testing; 
                                                       the sticking tape was 

Davis-Besse Nuclear           77-13                    Spurious activation 
Power Station                                          of seismic trigger; 
                                                       unit  was replaced 

                              79-111                   Excessive noise in 
                                                       recorded tape 
                                                       prevented reading of 
                                                       accelerometer traces 
                                                       during surveillance 
                                                       Model 37200); part of 
                                                       problem was due to 
                                                       one lead of AC input 
                                                       line on playback 
                                                       monitor was not 

                                                             IEC 81-03    
                                                             March 2, 1981 

                                  - 2 - 

PLANT                         LER NUMBER/              EVENT DESCRIPTION 

Hatch Nuclear Plant,          Letter from Georgia      One channel of the 
Unit 1                        Power to NRC dated       Triaxial Time-History
                              6/25/80                  Accelerometer 
                                                       (Kinemetrics) had 
                                                       shifted its sensiti- 
                                                       vity by 47% and 
                                                       natural frequency by 

Humboldt Bay                  NRC Reconnaissance       Magnetic tape time-
Power Plant                   Report dated 1/19/81     history 
                                                       (TERA Technology) 
                                                       were found inoperable 
                                                       due to a degraded low 
                                                       voltage power supply; 
                                                       6 of 9 film recorders 
                                                       (TERA Technology) 
                                                       were inoperable 
                                                       because of dirt and 
                                                       dust buildup 

Maine Yankee                  Inspection Report        Corrosion of connec-
Atomic Power                  50-309/79-11             tions to the 
Plant                                                  batteries 
                                                       on Kinemetrics
                                                       SMA-l units made the 
                                                       units inoperable; 
                                                       increased testing 
                                                       frequency initiated 

Rancho Seco Nuclear           Inspection Report        Seismic monitoring 
Generating Station            50-312/80-03             instrumentation was 
                                                       inoperable due to 
                                                       calibration and  
                                                       power supply problems  
                                                       with electrical 
                                                       cable; passive 
                                                       placed in area 
                                                       susceptible to 
                                                       impacts by passing 

                                                            IEC 81-03     
                                                            March 2, 1981 

                                  - 3 - 

PLANT                         LER-NUMBER/              EVENT DESCRIPTION 

Less Significant Occurrences - 

Beaver Valley Power           76-53                    Control room seismic 
Station                       78-040                   alarm indicated 
                                                       spuriously due to 
                                                       misaligned reed 
                                                       switches; the 
                                                       recording scribes on 
                                                       the Engdahl response 
                                                       spectrum recorders 
                                                       remained operable; 
                                                       the reed switches 
                                                       were adjusted 

Calvert Cliffs Nuclear        77-79                    The motor on the 
Plant, Unit 1                                          tape playback unit 
                                                       (Kinemetrics Model 
                                                       No. SMP-l) was found 
                                                       sticking; the motor 
                                                       was replaced 

North Anna Power              78-060                   Alarms from the 
Station, Unit 1               78-118                   (Engdahl) response 
                                                       spectrum recorders 
                                                       indicated spuriously 
                                                       on four separate 

Three Mile Island             78-002                   A defective recording
Nuclear Station,                                       plate was found in 
Unit 2                                                 the spectrum 
                                                       recorder; the 
                                                       plates were replaced 


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