Information Notice 2012-16, Preconditioning of Pressure Switches Before Surveillance Testing
| ML120170120 | |
| Person / Time | |
|---|---|
| Issue date: | 08/29/2012 |
| From: | Laura Dudes, Mcginty T Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Beaulieu, D P, NRR/DPR, 415-3243 | |
| References | |
| IN-12-016 | |
| Download: ML120170120 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001 August 29, 2012 NRC INFORMATION NOTICE 2012-16: PRECONDITIONING OF PRESSURE SWITCHES
BEFORE SURVEILLANCE TESTING
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor under
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of
Production and Utilization Facilities, except those who 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 recent examples of technical specification-required surveillance testing using
procedures that unacceptably preconditioned pressure switches associated with various safety- related functions. The NRC expects that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar problems. Suggestions
contained in this IN are not NRC requirements; therefore, no specific action or written response
is required.
DESCRIPTION OF CIRCUMSTANCES
Monticello Nuclear Generating Plant
On July 7, 2008, at the Monticello Nuclear Generating Plant, NRC inspectors observed the
performance of a surveillance procedure for main steam line isolation instrumentation channel
functional tests and calibration, which includes pressure switches that trip on low main steam
line pressure. The NRC inspectors found that the surveillance procedure unacceptably
preconditioned the pressure switches by fully cycling them during test equipment installation, before obtaining the as-found trip setpoint. Given that the pressure switch instrumentation line
configuration at Monticello is designed with a test equipment connection point that consists of a
cap only, with no adjacent isolation valve, the surveillance procedure tested the pressure
switches as follows:
1. Isolate the pressure switch to be tested;
2. Uncap the test connection;
3. Connect the test equipment to the test connection;
4. Increase the pressure until the pressure switch resets and record the reset test data;
5. Bleed off the pressure until the pressure switch trips and record the as-found trip
setpoint;
6. Remove the test equipment and restore the pressure switch to operation.
This testing methodology caused the pressure switch and associated contacts to change their
state when the system pressure was relieved in step 2; again when pressure was applied to
reset the pressure switch in step 4; then a third time when the pressure was bled off to obtain
the as-found trip setpoint in step 5. Relieving system pressure to install test equipment results
in the maximum net actuating force on the pressure switch diaphragm which exercises the
pressure switch and potentially frees sticking contacts or mechanical binding. This calls into
question the subsequent measurement of the as-found trip setpoint and the ability of the
surveillance to verify the as-found operability. The licensee similarly tested approximately
30 pressure switches at Monticello that are relied upon to initiate technical specification-related
protective functions.
The NRC inspectors discussed this surveillance with the NRC Office of Nuclear Reactor
Regulation staff who issued Task Interface Agreement (TIA) 2009-006, Unacceptable
Preconditioning of Safety-Related Pressure Switches during Required Surveillance Testing at
Monticello. This TIA concluded that the licensees surveillance testing methodology constitutes
unacceptable preconditioning of the pressure switch and, absent an engineering evaluation, the
current surveillance testing methodology is unacceptable and must be changed so that the
applicable pressure switches are not cycled before obtaining as-found trip setpoint data.
Licensee corrective actions included developing an engineering evaluation of current
surveillance testing methodology to justify the preconditioning as acceptable.
Additional information is available in Monticello-NRC Integrated and Power Uprate Review
Inspection Report 05000263/2009004, dated October 26, 2009, and can be found on the NRCs
public Web site under Agencywide Documents Access and Management System (ADAMS)
Accession No. ML092990580, and in TIA 2009-006, dated September 30, 2009 (ADAMS
Accession No. ML092730349).
Waterford Steam Electric Station, Unit 3
During a 19-month period ending October 27, 2008, Waterford Steam Electric Station, Unit 3 experienced five differential pressure switch failures in the containment vacuum relief system, a
safety-related system that provides the means to prevent potential containment failures resulting
from a vacuum condition. The first failure occurred during functional testing when a differential
pressure switch failed to actuate on two attempts, and on the third attempt, it became unstuck
and responded normally to the applied pressure. After the first failure, the licensee identified
that under normal conditions, the differential pressure switches experienced differential
pressures that exceeded the calibration pressure of 150 percent of the design range.
The licensee determined that the root cause of the five differential pressure switch failures was
that design engineers did not perform a thorough evaluation of the operating conditions in 1987 as part of a technical specification change evaluation. The licensee suspected that
preconditioning before 2008 had masked potential sticking during prior functional tests. The
licensee assigned the human performance error related to preconditioning as a contributing
cause.
Additional information is available in Waterford Steam Electric Station, Unit 3 - NRC Problem
Identification and Resolution Inspection Report 05000382/2008007, dated December 11, 2008 (ADAMS Accession No. ML083500479).
BACKGROUND
Related NRC generic communications include the following:
- NRC IN 96-24, Preconditioning of Molded-Case Circuit Breakers before Surveillance
Testing, dated April 25, 1996 (ADAMS Accession No. ML031060110). This IN discusses
the detrimental effect that preconditioning of molded-case circuit breakers could have on the
diagnostic validity of surveillance tests.
- NRC IN 97-16, Preconditioning of Plant Structures, Systems, and Components before
American Society of Mechanical Engineers (ASME) Code Inservice Testing or Technical
Specification Surveillance Testing, dated April 4, 1997 (ADAMS Accession No.
ML031050353). This IN discusses the potential for maintenance activities performed before
surveillance testing (preconditioning or grooming) to adversely affect the validity of the
surveillance test results for structures, systems, and components (SSCs) or equipment.
DISCUSSION
Criterion XI, Test Control, of Appendix B, Quality Assurance Criteria for Nuclear Power
Plants, to 10 CFR Part 50 requires nuclear power plants to establish a test program to ensure
that all testing required to demonstrate that SSCs will perform satisfactorily in service is
performed. This IN discusses test procedures that did not ensure pressure switches would
operate satisfactorily in service because the test procedures unacceptably preconditioned the
pressure switches by fully cycling them before obtaining an as-found trip setpoint.
NRC Inspection Manual, Part 9900 Technical Guidance, Maintenance - Preconditioning of
Structures, Systems, and Components before Determining Operability, defines unacceptable
preconditioning as the alteration, variation, manipulation or adjustment of the physical condition
of SSCs before or during technical specification surveillance testing or ASME code testing that
will alter one or more of the SSCs operational parameters, which results in acceptable test
results. Such changes could mask the actual as-found condition of the SSC and possibly result
in an inability to verify the operability of the SSC. In addition, unacceptable preconditioning
could make it difficult to determine whether the SSC would perform its intended function during
an event in which the SSC might be needed. Preconditioning of pressure switches, as
described above, could potentially mask existing conditions, such as sticking contacts, mechanical binding, or setpoint drift. The pressure switch instrumentation line configuration at Monticello is designed with a test
equipment connection point that consists of a cap only, with no adjacent isolation valve.
Therefore, to install test equipment, upstream isolation valves must be closed, which also
isolates the pressure switch, causing it to depressurize when the cap is removed to connect the
test equipment. However, the Monticello engineering evaluation listed three plants that are able
to avoid pressure switch preconditioning because the plant is designed with a test equipment
connection point that consists of a cap, as well as an adjacent isolation valve, which allows
them to connect the test equipment and pressurize it to system pressure before opening the
isolation valve, thus maintaining system pressure at the pressure switch. These three plants
avoid pressure switch preconditioning by using an isolation valve (original or installed through
modification) at the test equipment connection point or by using an alternate connection point, such as a drain line that already had an installed isolation valve.
Criterion 21, Protection System Reliability and Testability, of Appendix A, General Design
Criteria for Nuclear Power Plants, to 10 CFR Part 50 states, The protection system shall be
designed for high functional reliability and inservice testability commensurate with the safety
functions to be performed. Preconditioning is a factor in inservice testability and, as such, requires consideration commensurate with the safety functions to be performed. However, there is no explicit regulatory requirement to modify the plant to add an isolation valve to avoid
preconditioning of pressure switches.
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 by JLuehman for/ /RA/
Laura A. Dudes, Director Timothy J. McGinty, Director
Division of Construction Inspection Division of Policy and Rulemaking
and Operational Programs Office of Nuclear Reactor Regulation
Office of New Reactors
Technical Contacts: Stephen Wyman, NRR Kenneth Riemer, Region III
301-415-3041 630-829-9628 E-mail: stephen.wyman@nrc.gov E-mail: kenneth.riemer@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
OFFICE DRP/RIII Tech Editor EICB/NRR BC:DRP/RIII
NAME CScott CHsu SWyman KRiemer
DATE 1/18/12 06/26/12 e-mail 7/27/12 e-mail 1/18/12 OFFICE BC:EICB/NRR D:DE/NRR LA:PGCB:NRR
NAME JThorp PHiland MCheok for CHawes
DATE 7/27/12 e-mail 8/6/12 8/7/12 OFFICE PM:PGCB:NRR BC:PGCB:NRR D:DCIP/NRO D:DPR:NRR
NAME DBeaulieu DPelton TAlexion for LDudes (JLuehman for) TMcGinty
OFFICE 8/6/12 08/14/12 8/23/12 8/29/12