Information Notice 1997-62, Unrecognized Reactivity Addition During Plant Shutdown
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
August 6, 1997
UNRECOGNIZED REACTIVITY ADDITION DURING
PLANT SHUTDOWN
Addressees
All holders of operating licenses or construction permits for nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert
addressees to a recent incident in which a licensed reactor operator continuously inserted
control rods to bring the reactor to the subcritical stage and then promptly withdrew the rods
in order to take the reactor to the critical stage and return power to the point of adding heat
(POAH). These actions constituted an unauthorized attempt to start up the reactor. It is
expected that recipients will review this information for applicability to their facilities and
consider actions, as appropriate. However, suggestions contained in this information notice
are not NRC requirements; therefore, no specific action or written response is required.
Description of Circumstances
On February 19, 1997, the licensee observed that the containment spray (CS) pump IC took
an abnormally long time to start during a surveillance test and at 10:40 a.m. declared the
pump inoperable. The Technical Specifications (TS) required that the CS pump be restored
to an operable status within the next 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> or that Unit 1 be in hot shutdown within the
following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. In the early morning of February 21, the licensee completed corrective
maintenance on the CS pump IC and initiated post-maintenance testing.
However, the
pump did not start within the zequired time and the licensee initiated additional
- A
troubleshooting efforts. Later that moming, a new operating crew began their first day of shift
duty after 3 days off. Although the 48-hour limiting condition for operations (LCO) would
expire in less than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, requiring entry into a 4-hour shutdown in accordance with the TS
action statement, no plan had been developed to support an orderly and controlled shutdown
of Unit 1.
At 10:40 a.m. on February 21, the 48-hour LCO expired and the licensee entered a 4-hour
shutdown action statement for Unit 1. At approximately 11:00 a.m., plant management, operations management, and operations supervisors held an informal discussion regarding
the status of the CS pump IC and when to initiate the Unit 1 shutdown. Ten minutes later, the shift engineer (SE) conducted a formal shutdown briefing.
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IN 97-62 August 6, 1997 At 12:09 p.m., control room operators began reducing power at 0.25-percent per minute. At
approximately 12:55 p.m., the licensee noted through a review of surveillance testing records
that the CS pump 1C should have been declared inoperable at 10:20 a.m. rather than at
10:40 a.m. on February 19th. As a result, Unit 1 was required to be in hot shutdown by
2:20 p.m. instead of 2:40 p.m. in order to comply with the TS. The licensee subsequently
increased the rate of power reduction to 0.5-percent per minute.
At approximately 2:05 p.m., with Unit 1 at 7-percent power, the SE directed the Unit
Supervisor (US) to maintain the reactor critical because he expected the CS pump to be
returned to service within a few minutes. The US and the primary nuclear station operator
(NSO) reviewed the steps in the plant shutdown procedure for taking the turbine off-line and
inserting control rods to establish power at or below the POAH, defined in the procedure as
0.025-percent power. The review consisted of the US's reading the relevant step aloud and
requesting the primary NSO to locate the point on the intermediate power range monitor
corresponding to 0.025-percent power. The primary NSO identified this point and then asked
the US if he wanted him to drive control rods in. The US responded by re-reading the
procedure step aloud, which states, "HOLD #363, ROD MOTION CONTROL' switch IN to
minimize dumping steam and establish power at or less than the Point of Adding Heat
(2.5x`102% IR)."
At 2:07 p.m., the main turbine was tripped and the primary NSO inserted control rods
continuously for 3 minutes and 48 seconds (232 steps) until power indicated 0.025-percent.
Reactor power continued to decrease as a result of the negative reactivity associated with the
control rod insertion and when power reached 0.01 percent, the primary NSO informed the
US that he intended to withdraw control rods to stabilize power at 0.025 percent. The
primary NSO then proceeded to withdraw control rods continuously for 1 minute and 45 seconds (84 steps) until he was directed to trip the reactor by the US. The SE directed the
US to trip the reactor because the CS pump had not been restored to service and Unit I was
required to be in hot shutdown within the next 6 minutes to comply with the TS.
Discussion
The NRC dispatched an AugmdEted Inspection Team AIT) to review the facts surrounding
the February 21 event at Zion Nuclear Plant. The findings and conclusions of this inspection
are documented in NRC Inspection Report 50-295/97006.
The AIT concluded that the US and SE did not exercise their respective responsibilities for
ensuring that shift activities were conducted in a controlled manner and became focused on
CS pump restoration activities and balance-of-plant problems. The shutdown briefing was
informal, poorly planned, and ineffective. Operations supervisors did not provide any
direction to the operating crew during the briefing regarding the decision point for proceeding
IN 97-62 August 6, 1997 to hot shutdown. The SE did not provide clear direction to the US regarding his intent to
keep the reactor critical after the main turbine had been tripped. Operations supervisors also
failed to inform the operating crew of the intent to keep the reactor critical.
Despite a number of communications and control room indications such as "low rod insertion
limit" annunciator, the "low-low rod insertion limit" annunciator, audible clicking of the group
rod position step counter, control banks "C" rod bottom lights, and control bank C and D rod
position indication, the US and the SE were unaware that the primary NSO had continuously
inserted control rods a total of 232 steps, which placed the reactor in a substantially
subcritical condition, and then continuously withdrew control rods 84 steps in an attempt to
re-establish power at the POAH.
Upon noting that the control bank "C" rod bottom lights were illuminated, the qualified nuclear
engineer (ONE) assigned to monitor the shutdown evolution asked the primary NSO "why
control rods had been driven in so far." The primary NSO replied, "This doesn't look right, but I am just following procedures." Approximately 7 minutes later, the ONE observed that
the primary NSO was withdrawing control rods, approached the operator, and stated that he
"did not like what the operator was doing." The primary NSO responded that he was
uncomfortable with what he was doing as well. However, neither the ONE nor the primary
NSO informed the US of their concerns about control rod manipulations.
The actions of the primary NSO in continuously withdrawing control rods with the intent of
taking the reactor to critical stage in order to re-establish power at the POAH reflected a
significant lack of understanding of proper control rod manipulations for a controlled approach
to criticality. Although he was concerned with the actions directed by a specific step in the
shutdown procedure, the primary NSO did not adequately communicate his concerns to the
US. The US also did not clarify the intent of the procedural step to the primary NSO.
Although the actual event did not pose a risk to the health and safety of the public, the event
was considered safety significant from a human performance perspective. With the Unit 1 reactor substantially subcritical, a licensed reactor operator withdrew control rods
continuously in an attempt to take the reactor to the critical stage, disregarding established
-procedural controls for conducting a safe7eactor startup. The rod manipulations were
conducted without the knowledge of operations supervisors. Proper manipulation of control
rods during reactor shutdowns and startups is fundamental to operational safety.
KJ
IN 97-62 August 6, 1997 This information notice requires no specific action or written response. If you have any
questions about information in this notice, please contact one of the technical contacts listed
below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Ma lee M. Slosson, Acting Direct
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts:
Thomas Koshy, NRR
301-415-1176 E-mail: txk@nrc.gov
Marc Dapas, Rill
(630) 829-9601 E-mail: mldl@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
<1'
Attachment
August 6, 1997 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
97-61
97-60
97-59
U.S. Department of
Health and Human
Services Letter, to
Medical Device Manu- facturers, on the
Year 2000 Problem
Incorrect Unreviewed
Safety Question Deter- mination Related to
Emergency Core Cooling
System Swapover from
the Injection Mode to
the Recirculation Mode
Fire Endurance Test
Results of Versawrap
Fire Barriers
Mechanical Integrity of
In-Situ Leach Injection
Wells and Piping
08/06/97
08/01/97
08/01/97
07/31/97
All U.S. Nuclear Regulatory
Commission medical licensees, veterinarians, and manu- facturers/distributors of
medical device
All holders of OLs or CPs
for pressurized-water
reactors
All holders of OLs or CPs
for nuclear power reactors
Holders of and Applicants
for Licenses for In-Situ
Leach Facilities
97-58
97-57 Leak Testing oV-Dackaging
Used in the Transport of
Radioactive Material
Possession Limits for
at the Environcare of
Utah Low-Level Radioactive
Waste Disposal Facility
07/30/97
07/28/97 Suppliers and users of .,
packaging for the trans- portation of radioactive
material required to per- form packaging leak tests
All licensees authorized
to possess special nuclear
material
97-56 OL = Operating License
CP = Construction Permit
IN 97-62 August 6, 1997 This information notice requires no specific action or written response. If you have any
questions about information in this notice, please contact one of the technical contacts listed
below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
original signed by S.H. Weiss for
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts:
Thomas Koshy, NRR
301-415-1176 E-mail: txk@nrc.gov
Marc Dapas, Rill
(630) 829-9601 E-mail: mldl@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Tech Editor has reviewed and concurred on 06127/97 DOCUMENT NAME: 97-62.IN *SEE PREVIOUS CONCURRENCE
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OFFICE JContacts
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I
NAME
TTKoshy* 7/17/97 COThomas*
AChaffee*
MSlosson
DATE
07/
/97
07/2/97
07/24/97
_/3[/97 G
OFFICIAL RECORD COPY
IN 97- July , 1997 This information notice requires no specific action or written response. If you have any
questions about information in this notice, please contact one of the technical contacts listed
below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts:
Thomas Koshy, NRR
301-415-1176 E-mail: txk@nrc.gov
Marc Dapas, Rill
(630) 829-9601 E-mail mldl@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
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REOD/OY
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Julyxx, 1997 inserted control rods a total of 232 steps, which placed the reactor in a substantially
subcritical condition, and then continuously withdrew control rods 84 steps in an attempt to
re-establish power at the POAH.
Upon noting that the control bank "C" rod bottom lights were illuminated, the qualified nuclear
engineer (QNE) assigned to monitor the shutdown evolution asked the primary NSO "why
control rods had been driven in so far." The primary NSO replied, "This doesn't look right, but I am just following procedures." Approximately 7 minutes later, the QNE observed that
the primary NSO was withdrawing control rods, approached the operator, and stated that he
"did not like what the operator was doing." The primary NSO responded that he was
uncomfortable with what he was doing as well. However, neither the QNE nor the primary
NSO informed the US of their concerns about control rod manipulations.
The actions of the primary NSO in continuously withdrawing control rods with the intent of
taking the reactor to critical stage in order to re-establish power at the POAH reflected a
significant lack of understanding of proper control rod manipulations for a controlled approach
to criticality. Although he was concerned with the actions directed by a specific step in the
shutdown procedure, the primary NSO did not adequately communicate his concerns to the
US. The US also did not clarify the intent of the procedural step to the primary NSO.
Although the actual event did not pose a risk to the health and safety of the public, the event
was considered safety significant from a human performance perspective. With the Unit 1 reactor substantially subcritical, a licensed reactor operator withdrew control rods
continuously in an attempt to take the reactor to the critical stage, disregarding established
procedural controls for conducting a safe reactor startup. The rod manipulations were
conducted without the knowledge of operations supervisors. Proper manipulation of control
rods during reactor shutdowns and startups is fundamental to operational safety.
This information notice requires no specific action or written response. If you have any
questions about information in this notice, please contact one of the technical contacts listed
below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts:
Marc Dapas, Rill
301-415-1176
630-829-9601 E-mail: txk@nrc.gov
E-mail: mldl@nrc.gov
DOCUMENT NAME: G:lN~rodin.r3 *SEE PREVIOUS CONCURRENCE
To receive a copy of this document, Indicate In the box: "v u Copy without attachment/enclosure
TF
Copy with attachmentlenclosure
v a No copy
OFFICE
Contacts
C:HHFB
(A)D:DRPM
NAME
TKoshy* 7/17/97 COThomas*
AChaffee
MSlosson
MDapas
DATE
07/ /97
07/2/97
/ /97
/ /97
OFFICIAL RECORD COPY
This information notice requires no specific action or written response. If you have any
questions about information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project
manager.
Marylee M. Slosson, Direcr
Division of Reactor Progr
Management
Office of Nuclear Reac r Regulation
Technical Contacts: Thomas Koshy, NRR
301-415-1176 E-mail: txk@nrc.gov
Marc Dapas, Rill
630-829-9601 E-mail: MLD1 @ nrc.gov
DOCUMENT NAME: G:\\IN\\rodin.r3 To isceive a copy of this document, Indicate In the box:
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NAME
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11Dapas
ICOThomas '"-k
DATE
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7/97
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OFFICE
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