Information Notice 2009-09, Improper Flow Controller Settings Renders Injection Systems Inoperable and Surveillance Did Not Identify
| ML091050027 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 06/19/2009 |
| From: | Mcginty T Division of Policy and Rulemaking |
| To: | |
| Pong Chung, NRR/DE/EICB 415-2473 | |
| References | |
| IN-09-009 | |
| Download: ML091050027 (4) | |
ML091050027 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001
June 19, 2009
NRC INFORMATION NOTICE 2009-09:
IMPROPER FLOW CONTROLLER SETTINGS
RENDERS INJECTION SYSTEMS INOPERABLE
AND SURVEILLANCE DID NOT IDENTIFY
ADDRESSEES
All holders of operating licenses for boiling-water nuclear power reactors, except those who
have permanently ceased operations and who have certified that fuel has been permanently
removed from the reactor vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert
addressees that improper flow controller settings in the high-pressure core spray (HPCS)
system, high-pressure coolant injection (HPCI) system, and/or reactor core isolation cooling
(RCIC) system injection systems at several boiling-water reactors resulted in system flow
oscillations that rendered the systems inoperable. Testing failed to identify the inoperable
systems because the system alignment during the surveillance differed from the system
alignment when the systems are called upon to perform their safety functions. The NRC
expects that recipients will review the information for applicability to their facilities and will
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
Perry Nuclear Power Plant, Unit 1
As discussed in NRC IN 2008-13, Main Feedwater System Issues and Related 2007 Reactor
Trip Data, on November 28, 2007, an unplanned automatic reactor trip occurred at Perry
Nuclear Power Plant, Unit 1, that stemmed from a failure of the digital feedwater control system.
As the reactor vessel water level decreased, the RCIC pump automatically started but tripped
after 11 seconds on low RCIC pump suction pressure because the RCIC flow controller was
tuned incorrectly in 2006. At the time of the RCIC pump trip, RCIC was aligned to take suction
from the suppression pool instead of the normal path from the condensate storage tank (CST)
because of an inoperable CST level indicator. While using HPCS to maintain the water level in
the reactor vessel, the operating crew attempted to recover RCIC by first realigning the RCIC
pump suction from the suppression pool to the CST. With the RCIC flow controller in automatic, operators started and ran the RCIC pump and then attempted to feed water into the reactor. At
that point, the operator noted large injection flow oscillations and RCIC again tripped on low
suction pressure. Operators successfully recovered RCIC by starting the RCIC pump with the
flow controller in manual, and supplied water to the reactor vessel without large flow oscillations or RCIC tripping. It was later determined that the RCIC flow controller gain, reset and rate
settings had been altered from the settings used to successfully inject to the reactor vessel
during plant startup testing. These changes resulted in an overly responsive flow control loop.
Limerick Generating Station, Unit 2
On April 24, 2007, the Limerick Generating Station, Unit 2, was at 100-percent power when the
redundant reactivity control system inadvertently initiated a reduction in total feedwater flow to
the reactor vessel. Subsequently, the rapid decrease of the water level in the reactor vessel
caused an automatic scram. As the water level of the reactor vessel continued to decrease
during the event, the HPCI and RCIC systems automatically started at -38 inches, as designed.
Following initiation, the HPCI and RCIC systems experienced abnormal system flow oscillations
from no-flow to full-flow (5,600 gallons per minute for the HPCI system and 600 gallons per
minute for the RCIC system) for 3.4 seconds and 1.2 seconds, respectively. Additionally, the
common suction source for both systems unexpectedly swapped from the CST to the
suppression pool due to pressure oscillations in the common suction piping. Approximately
2 minutes following the scram, the operators placed both HPCI and RCIC flow controllers into
manual control and continued to restore reactor water level. Both systems responded to
manual control as expected, and the flow oscillations ceased. The licensee subsequently
determined it had incorrectly adjusted the flow controller gain and reset settings to the values
outside the expected range by a factor of 10. Additional information is available in Limerick
Licensee Event Report 50-353/2007-003, dated June 22, 2007 (which can be found on the
NRCs public Web site in the Agencywide Documents Access and Management System
(ADAMS) under Accession No. ML071730270).
Root Cause
In each of the above examples, one of the causes of the flow oscillations was improper flow
controller tuning of the HPCS, HPCI, and RCIC systems. Licensee test programs and
surveillance procedures did not identify this deficiency. Surveillance testing of HPCS, HPCI,
and RCIC pumps is performed while at power with the systems drawing water from the CST and
discharging through a full-flow test return line back to the CST, also known as a CST-to-CST
alignment. However, when these systems are called upon to perform their safety function, these systems draw water from the CST and inject into the reactor vessel. Industry operating
experience has demonstrated that HPCS, HPCI and RCIC system response is slower when
operating in a CST-to-CST alignment compared to actual injection operation. Therefore, these
systems need to be tuned and maintained appropriately to account for the difference in
response during actual vessel injection. General Electric/Hitachi Report 0000-0079-1103, Revision 1, delineates that RCIC operability of the flow control loop can be assured by
maintaining RCIC flow controller tuning settings used during successful reactor pressure vessel
injections.
DISCUSSION
The HPCS, HPCI, and RCIC systems are required to be operable as specified in plant technical
specifications. As illustrated above, failure to establish adequate procedures to properly tune
system flow controllers as required by Title 10 of the Code of Federal Regulations (10 CFR)
Part 50, Appendix B, Criterion V, Instructions, Procedures, and Drawings can result in these systems being rendered inoperable. In addition, surveillance testing did not reveal that systems
were inoperable and could not perform their safety function to inject water to the reactor vessel, which is contrary to 10 CFR Part 50, Appendix B, Criterion XI, Test Control.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below or to the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by TQuay for/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Pong Chung, NRR
301-415-2473 E-mail: Pong.Chung@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections. systems being rendered inoperable. In addition, surveillance testing did not reveal that systems
were inoperable and could not perform their safety function to inject to the reactor vessel, which
is contrary to 10 CFR Part 50, Appendix B, Criterion XI, Test Control.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by TQuay for/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Pong Chung, NRR
301-415-2473 E-mail: Pong.Chung@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ADAMS Accession Number: ML091050027
TAC No.: ME0622 OFFICE
EICB:DE
TECH EDITOR
BC:EICB:DE
D:DE
PGCB:DPR
PGCB:DPR
NAME
PChung
KAzariah-Kribbs
WKemper
PHiland
DBeaulieu
CHawes
DATE
5/12/09
4/15/09 email
5/26/09
5/28/09
6/3/09
6/3/09 OFFICE
BC:PGCB:DPR
D:DPR
NAME
MMurphy
TMcGinty
DATE
6/16/09
6/19/09
OFFICIAL RECORD COPY