Information Notice 2013-12, Improperly Sloped Instrument Sensing Lines
| ML13136A362 | |
| Person / Time | |
|---|---|
| Issue date: | 07/03/2013 |
| From: | Laura Dudes, Kokajko L Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Mensah T | |
| References | |
| IN-13-012 | |
| Download: ML13136A362 (5) | |
ML13136A362 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001
July 3, 2013
NRC INFORMATION NOTICE 2013-12:
IMPROPERLY SLOPED INSTRUMENT
SENSING LINES
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 that have permanently ceased operations
and have certified that fuel has been permanently removed from the reactor vessel.
All holders of an operating license for a non-power reactor (research reactor, test reactor, or
critical assembly) under 10 CFR Part 50, except those who have permanently ceased
operations.
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.
All contractors and vendors that supply basic components to U.S. Nuclear Regulatory
Commission (NRC) licensees under 10 CFR Part 50 or 10 CFR Part 52.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of recent operating experience regarding instrument sensing line sloping problems
caused by improper design or installation that have occurred at U.S. nuclear power plants. This
IN also emphasizes to the recipients the importance of applying related design and installation
criteria and providing adequate oversight. The NRC expects 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
Watts Bar Nuclear Unit 2 Construction Project
On April 29, 2013, Tennessee Valley Authority (TVA), the construction permit holder for Watts
Bar Nuclear Unit 2 (Watts Bar 2), issued an interim construction deficiency report in accordance
with 10 CFR 50.55(e), Conditions of Construction Permits, Early Site Permits, Combined
Licenses, and Manufacturing Licenses, regarding a condition that has the potential to be a significant programmatic breakdown in the instrument sensing line installation program. Watts
Bar 2 determined that a number of instrument sensing lines within multiple systems may not
have been inspected completely for proper slope. The apparent cause of this condition involves
a misinterpretation of the related construction procedure, which lacked proper detail to define
the boundary of the sensing line from the panel isolation valve to process connection, including
the root valve. The construction permit holders corrective actions included revising the
construction procedure, providing training on the revised construction procedure, and
completing the required walkdowns or evaluations to correct any identified deficiencies.
Additional information is available on the NRCs public Web site in the Agencywide Documents
Access and Management System (ADAMS) under Accession No. ML13121A427.
James A. FitzPatrick Nuclear Power Plant
On November 1, 2012, Entergy, the licensee for James A. FitzPatrick Nuclear Power Plant, submitted licensee event report (LER) 3332012003 (ADAMS Accession No. ML12307A075) in
accordance with 10 CFR 50.73, Licensee Event Report System. In this LER, the licensee
reported that on September 2, 2012, with the plant running at 100 percent power, the high- pressure coolant injection (HPCI) system was declared inoperable. This condition was caused
by air in the instrument sensing line for the HPCI main pump discharge flow element, which
caused a false flow indication while HPCI was in standby. An apparent cause evaluation
determined that a portion of the sensing line was improperly sloped. The licensee took
immediate corrective actions to fill and vent the instrument lines using a revised procedure that
provided instructions to perform a pressurized back flush. Additional information is available in
ADAMS under Accession No. ML12307A075.
Browns Ferry Nuclear Plant Unit 1
On November 15, 2010, TVA, the licensee for Browns Ferry Nuclear Plant, Unit 1, submitted
LER 2592010002, which was later revised on May 20, 2011 (ADAMS Accession No.
ML11144A288). In this LER, the licensee reported that on September 16, 2010, it determined
that a condition initially identified on December 8, 2008, reflected the inoperability of a drywell
pressure channel for longer than allowed by technical specifications at its Browns Ferry Nuclear
Plant Unit 1. Subsequent review for extent of this condition identified that the inoperable
condition existed from October 2, 2008, until corrected on December 9, 2008. Additionally, a
subsequent occurrence of an inoperable drywell pressure channel between May 25, 2010, and
October 6, 2010, was discovered. The cause was improperly sloped instrument sensing lines
that allowed water to condense and collect in the sensing lines, resulting in nonconservatively
biased instrumentation output signals. The licensee took corrective actions that included
purging the instrument sensing lines of water to restore operability and implementing a design
change in the fall of 2010 to reconfigure the sensing lines to eliminate water traps. Additional
information is available in ADAMS under Accession No. ML11144A288.
BACKGROUND
The International Society of Automation (ISA), formerly known as the Instrument Society of
America, prepared standard ANSI/ISA-67.02.01-19991, Nuclear Safety-Related
Instrument-Sensing Line Piping and Tubing Standard for Use in Nuclear Power Plants, which
has been endorsed by NRC Regulatory Guide 1.151, Revision 1, Instrument Sensing Lines, with certain exceptions and clarifications, to provide design, physical protection, and installation
guidance for safety-related instrument sensing lines, and for sampling lines previously covered
by ANSI/ISA-S67.10, Sample-Line Piping and Tubing Standard for Use in Nuclear Power
Plants.
Related NRC Generic Communications
NRC IN 92-54, Level Instrumentation Inaccuracies Caused by Rapid Depressurization, dated
July 24, 1992, discusses inaccuracies in water level indication during and after rapid
depressurization events that may affect the indication of pressurizer level for pressurized-water
reactors and reactor vessel level for boiling-water reactors (ADAMS Accession
No. ML082340376).
NRC IN 84-45, Reversed Differential Pressure Instrument Sensing Lines, dated
June 11, 1984, discusses events that primarily occurred during construction and preoperational
testing that involved discovery of the high- and low-pressure sensing lines for safety-related
differential pressure instrumentation being reversed (ADAMS Accession No. ML082890902).
DISCUSSION
The provisions in 10 CFR Part 50, Appendix A, General Design Criteria for Nuclear Power
Plants, General Design Criterion 13 (Instrumentation and Control), require that
instrumentation be provided to monitor variables and systems to ensure adequate safety. Many
nuclear power plant safety-related instruments that use sensing lines are relied upon to perform
required safety functions, such as to initiate reactor trips, control flows, maintain proper fluid
levels, actuate emergency systems, and provide the operators information that is used as the
basis for actions to ensure adequate core cooling. For these instruments to function properly, their sensing lines need to be sloped adequately. Currently, ANSI/ISA-67.02.01-1999, which
has been endorsed by NRC Regulatory Guide 1.151, Revision 1, with certain exceptions and
clarifications, provides design, physical protection, and installation guidance for safety-related
instrument sensing lines, and for sampling lines previously covered by ANSI/ISA-S67.10. This
includes sloping guidance for instrument sensing lines.
The standard states that sensing lines for liquid measurements are to slope continuously
downward from the process connection to the instrument to help prevent air entrapment in the
lines that could impact the function of the instrument and lead to false indications. Conversely, it states that sensing lines for gas measurements are to slope continuously upward from the
process connection to the instrument to ensure water entrained in the gas does not impair the
function of the instrument. If slope requirements cannot be met, the addition of a high point vent
1 Copies of American National Standards (ANS) may be purchased from the American National Standards Institute (ANSI),
1819 L Street, NW., 6th floor, Washington, DC 20036 (phone: 202-293-8020). Purchase information is available through
the ANSI Web site at http://webstore.ansi.org/ansidocstore/. for liquid systems or a low point drain for gas systems may be necessary to ensure operability of
the instrument. This problem is typically caused by inadequate design or installation and can
result in false indication or improper instrument operation, which can hinder a safe response to
changing plant conditions. Since sensing line sloping problems often are caused by improper
design or installation, the most effective way to avoid them is by implementing a robust design
control process and by ensuring proper installation oversight at both initial construction and
during the implementation of design changes.
While Appendix A of 10 CFR 50 only applies to power reactor licensees, other licensees (e.g.,
non-power reactors) use similar instrumentation to that described in the above inspection
findings for important safety functions. Operability or functionality of these instruments could
also be affected by the issues described in those findings.
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 NRC project manager.
/RA/
/RA Sher Bahadur Acting for/
Laura A. Dudes, Director
Lawrence E. Kokajko, Director
Division of Construction Inspection
Division of Policy and Rulemaking
and Operational Programs
Office of Nuclear Reactor Regulation (NRR)
Office of New Reactors (NRO)
Technical Contacts:
301-415-5342
301-415-3177 E-mail: Alfred.Issa@nrc.gov
E-mail: Joseph.Ashcraft@nrc.gov
301-415-1315
E-mail: David.Rahn@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
- via e-mail
OFFICE
Technical Editor*
NRO/DCIP*
NRO/ICE2*
NRO/CAEB*
NRO/ICE2*
NRR/PROB*
NRR/EICB*
NAME
JDougherty
AIssa
JAshcraft
TFrye
IJung
GBowman
JThorp
DATE
5/23/13
06/12/13
06/14/13
06/14/13
06/14/13
06/17/13
06/18/13 OFFICE
NRR/PGCB*
NRR/PGCB
NRR/PGCB
NRO/DCIP
NRR/DPR
NRR/DPR
NAME
CHawes
TMensah
EBowman
(TAlexion for)
LDudes
SBahadur
LKokajiko
S. Bahadur
for
DATE
06/18/13
06/18/13
06/19 /13
06/ 24 /13
06/ 30 /13
07/ 3 /13