Information Notice 2012-25, Performance Issues with Seismic Instrumentation and Associated Systems for Operating Reactors
| ML121590444 | |
| Person / Time | |
|---|---|
| Issue date: | 02/01/2013 |
| From: | Laura Dudes, Mary Muessle Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Alexion T W, NRR/DPR, 415-1326 | |
| References | |
| IN-12-025 | |
| Download: ML121590444 (6) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001 February 1, 2013 NRC INFORMATION NOTICE 2012-25: PERFORMANCE ISSUES WITH SEISMIC
INSTRUMENTATION AND ASSOCIATED
SYSTEMS FOR OPERATING REACTORS
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor or
non-power (research or test) reactor under Title 10 of the Code of Federal Regulations
(10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities, except those
that have permanently ceased operations and have certified that fuel has been permanently
removed from the reactor vessel.
All holders of and applicants for a power reactor early site permit, combined license, standard
design certification, standard design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of an occurrence where seismic instrumentation and associated monitoring and
alarm systems did not provide reliable indications or alarms. Thus, plant operators were unable
to promptly determine if the ground motion levels exceeded the Operating Basis Earthquake
(OBE) ground motion levels. It is expected that recipients will review the information for
applicability to their facilities and consider actions, as appropriate, to avoid similar problems.
However, suggestions contained in this IN are not NRC requirements; therefore, no specific
action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
Mineral, Virginia Earthquake on August 23, 2011, and its impact to nuclear power plants
On August 23, 2011, a magnitude (Mw) 5.8 earthquake occurred near Mineral, Virginia. The
ground motion resulting from the earthquake was felt strongly by the local community and was
also felt in most of the eastern United States. The nuclear power plant closest to the epicenter, North Anna Power Station (NAPS), declared an Alert because of the significant earthquake
vibrations felt on site, and both units experienced automatic reactor trips from 100 percent
power, initiated by the Power Range Nuclear Instrument High Negative Flux Rate Reactor Trip.
All safety system functions were maintained throughout the event. After a detailed inspection of
the plant, the licensee identified no significant damage to the safety-related structures, systems, and components (SSCs) of the plant. Shortly after the earthquake, the NRC dispatched an
Augmented Inspection Team (AIT) to NAPS to gather additional information and conduct a
review of the event. The AIT report identified potential generic issues related to the
performance and operability of seismic instrumentation for nuclear power plants.
Several licensees of other nuclear power plants, including the Surry Nuclear Power Station
(SNPS), declared Notifications of Unusual Events for seismic vibration felt by station personnel, during the August 23, 2011, seismic event. Although no damage to safety-related SSCs was
identified, issues were noted with the functioning of seismic instrumentation at SNPS.
Additional information appears in NRC AIT Inspection Report 05000338/2011011,
05000339/2011011, 07200016/2011001, and 07200056/2011002, dated October 31, 2011, on
the NRCs public Web site within Agencywide Documents Access and Management System
(ADAMS) Accession Number ML113040031.
BACKGROUND
For licensees whose construction permit was issued prior to January 10, 1997, Appendix A to
10 CFR Part 100, Seismic and Geological Siting Criteria for Nuclear Power Plants,Section VI,
Application to Engineering Design, Paragraph (a)(3), Required Seismic Instrumentation, states that Suitable instrumentation shall be provided so that the seismic response of nuclear
power plant features important to safety can be determined promptly to permit comparison of
such response with that used as the design basis. Such a comparison is needed to decide
whether the plant can continue to be operated safely and to permit such timely action as may be
appropriate. Regulatory Guide (RG) 1.12, Revision 1 (April 1974), Instrumentation for
Earthquakes, describes an acceptable approach to using seismic instrumentation to satisfy the
requirements of Appendix A to 10 CFR Part 100.
For applicants for a construction permit or operating license under 10 CFR Part 50, or a design
certification, combined license, design approval or manufacturing license under 10 CFR Part 52, on or after January 10, 1997, Appendix S to 10 CFR Part 50, Earthquake Engineering Criteria
for Nuclear Power Plants, Paragraph IV(a)(4), Required Seismic Instrumentation, states that
Suitable instrumentation must be provided so that the seismic response of nuclear power plant
features important to safety can be evaluated promptly after an earthquake. Paragraph
IV(a)(3), Required Plant Shutdown, requires shutdown of the nuclear power plant if the OBE is
exceeded. RG 1.12, Revision 2 (March 1997), Nuclear Power Plant Instrumentation for
Earthquakes, describes an acceptable approach to using seismic instrumentation to satisfy the
requirements of Appendix S to 10 CFR Part 50.
Part B, Discussion, of Revision 2 to RG 1.12 states, Instrumentation is provided in the free- field and at foundation level and at elevation in Seismic Category I structures. Free-field
instrumentation data will be used to compare measured response to the engineering
evaluations used to determine the design input motion to the structures and to determine
whether the OBE has been exceeded. The instruments located at the foundation level and at
elevationwill be used in long-term evaluations. The seismic instrumentation at a number of
operating reactor plants is installed consistent with RG 1.12, Revision 1, which does not
specifically require seismic instrumentation to be installed on the free surface in the free field.
DISCUSSION
When an earthquake occurs, data recorded by the seismic instrumentation is used by the
operators to make a rapid determination of the degree of severity of the event, including the
need to shutdown the plant when the OBE is exceeded. The data, coupled with plant
walkdowns, is used to make the initial determinations of whether the plant must be shutdown, if
it has not already been shut down by the plant operators or the perturbations resulting from the
seismic event.
At NAPS, portions of the seismic instrumentation panel inside the main control room were not
connected to an uninterruptible power supply and therefore were not functioning during the
momentary power outage (approximately 8 seconds) of the emergency busses while the
emergency diesel generators started and loaded following the loss of offsite power. This
resulted in an inability of the plant operators to promptly determine if the ground motion levels
exceeded the OBE or Safe Shutdown Earthquake (SSE, also referred to as Design Basis
Earthquake) levels, since the 3.1 seconds of strong ground motion portions of the earthquake in
each of the three orientations occurred during the 8 second power outage. Although the
seismic event resulted in an automatic shutdown (initiated by a power range nuclear instrument
high negative flux rate) of both operating units at NAPS, the licensee could not immediately
confirm conclusively that the plant had its OBE or SSE levels exceeded until the Kinemetrics tri- axial seismic time history accelerograph recording was analyzed. The Kinemetrics tri-axial
seismic time history accelerograph recorder had been powered via a battery-backed power
supply.
An additional consequence of the momentary loss of power to the seismic instrumentation panel
in the control room was that the site could not use the seismic response entry criteria to enter
the Emergency Action Level (EAL) matrix for a seismic event. The entry criteria for the Seismic
Response EAL required that the Engdahl strong motion accelerograph peak shock annunciator
illuminate, which would indicate a seismic event greater than OBE. Since there was a
momentary loss of power, this annunciator did not illuminate. It is important to note that the lack
of control panel alarm from the seismic monitoring panel did not delay an Alert declaration. The
Shift Manager used a different EAL matrix entry criteria, (i.e., Shift Manager judgement), and
appropriately declared an Alert.
NAPS, which had instrumentation conforming to RG 1.12, Revision 1, had no seismic
monitoring instrumentation located on the free surface in the free field. Free field
instrumentation data can generally be compared more accurately to the original design input
motion to validate the seismic engineering design for the structures, systems and components
at the site. The recordings from instrumentation located at the containment basemat, because
of influence of the structure itself as well as interaction with the surrounding materials and
structures, are typically not as accurate for determining input ground motion data from the
The data recorded by the Engdahl (scratch-plate) style seismometers was not as complete as
the data recorded by the Kinemetrics (accelerometer-based) equipment for the instruments
located on the basemat of Unit 1. The recorded data indicated significant differences in the
amplitude of the motion recorded at various frequencies between the scratch-plate style seismometers and the accelerometer based seismic instrumentation. Further, no data was
recorded for two frequencies of interest on the scratch-plate instruments, while the
accelerometer based instruments indicated seismic motion was occurring and recorded data for
those frequencies.
One other site discovered a seismic instrumentation issue as a result of the Mineral, VA
earthquake. At SNPS, subsequent to the earthquake, the United States Geological Survey
(USGS) provided seismic data which indicated that ground motion accelerations (nominally
0.04 to 0.05g, where g is the acceleration due to gravity) were of sufficient magnitude to trigger
the seismic monitors, which have a setpoint of 0.01 g. However, the Kinemetrics SMA-3 seismic monitors at the site did not trigger during the event, leading the licensee to declare the
seismic monitors inoperable. The USGS data confirmed that the Surry site did not exceed the
OBE ground motion. Additional information appears in NRC Integrated Inspection Report 05000280/2012002, 05000281/2012002, dated May 10, 2012, on the NRCs public Web site
within ADAMS Accession Number ML12131A564.
SNPS troubleshooting efforts revealed that all three sensor masses for the Kinemetrics
triggering unit were misaligned. The masses were locked on their stops in all three orthogonal
directions and could not trigger at the 0.01g setpoint. The triggering units calibration is done in
the Instrumentation and Control shop and then returned to the field location for re-installation. It
is likely that the sensor masses became misaligned sometime between shop calibration and
triggering unit re-installation. Post installation testing consisted of mechanically agitating the
trigger unit, which did not detect the misalignment. The vendor recommends a technique of
gently blowing on the trigger sensor to verify that the masses will respond to ground motion.
The masses were subsequently re-centered, and each trigger sensor and response was
functionally tested to verify proper operation.
CONCLUSION
Plant operators rely upon the proper calibration and functioning of seismic instrumentation and
the associated seismic alarm system to enable them to make timely decisions about whether a
plant may continue to operate and whether it fully conforms with its licensing basis during and
following an earthquake. In addition, the examples in this IN illustrate the importance of
licensees understanding the design, operation and performance of their seismic
instrumentation. By evaluating the performance of seismic instrumentation and associated
alarm systems and considering the appropriate actions, licensees can assure more accurate
earthquake ground motion recording and better information for plant operators during any
seismic activity at their plant sites.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) or Office of New Reactors project manager.
/RA/ /RA/ by JLuehman
Mary C. Muessle, Acting Director Laura A. Dudes, Director
Division of Policy and Rulemaking Division of Construction Inspection
Office of Nuclear Reactor Regulation and Operational Programs
Office of New Reactors
Technical Contacts: Yong Li, NRR Gursharan Singh, NRR
301-415-4141 301-415- 2962 E-mail: Yong.Li@nrc.gov E-Mail: Gursharan.Singh@nrc.gov
301-415-2621 E-mail: Robert.Bernardo@nrc.gov
Note: NRC generic communications may be found on the NRCs public Web site, http://www.nrc.gov, under NRC Library.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) or Office of New Reactors project manager.
/RA/ /RA/ by JLuehman
Mary C. Muessle, Acting Director Laura A. Dudes, Director
Division of Policy and Rulemaking Division of Construction Inspection
Office of Nuclear Reactor Regulation and Operational Programs
Office of New Reactors
Technical Contacts: Yong Li, NRR Gursharan Singh, NRR
301-415-4141 301-415- 2962 E-mail: Yong.Li@nrc.gov E-Mail: Gursharan.Singh@nrc.gov
301-415-2621 E-mail: Robert.Bernardo@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
ADAMS Accession Number: ML121590444 *via e-mail TAC ME8473 OFFICE NRR/DIRS/IOEB NRR/DE/EMCB NRR/DE/EICB Tech Editor BC:NRR/DE/EICB
NAME RBernardo YLi GSingh (DRahn for*) JDougherty* JThorp*
DATE 7/18/2012 8/1/2012 8/1/2012 6/1/2012 8/23/2012 OFFICE BC:NRR/DIRS/IOEB BC:NRR/DE/EMCB BC:NRR/DPR/PRLB BC:NRR/DPR/PROB BC:RII/DRP/RPB5 NAME HChernoff (EThomas MMurphy* JQuichocho (LTran GBowman* GMcCoy*
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DATE 11/15/2012 8/23/2012 8/24/2012 8/15/2012 8/22/2012 OFFICE D/NRR/DE D:RES/DE LA:NRR/DPR/PGCB PM:NRR/DPR/PGCB BC:NRR/DPR/PGCB
NAME PHiland MCase* CHawes* TAlexion DPelton
DATE 11/16/2012 12/20/2012 12/28/2012 01/16/2013 01/23/13 OFFICE D:NRO/DCIP D:NRR/(A)DPR
NAME LDudes (JLuehman MMuessle
for)
DATE 01/28/13 2/1/2013 OFFICIAL RECORD COPY