Information Notice 1996-69, Operator Actions Affecting Reactivity
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
December 20, 1996
NRC INFORMATION NOTICE 96-69: OPERATOR ACTIONS AFFECTING REACTIVITY
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 operating events that have affected reactivity. 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 information notice are not
NRC requirements; therefore, no specific action or written response is required.
Background
Generic Letter 85-05, "Inadvertent Boron Dilution Events," dated January 31, 1985, was used
to indicate the staffs position that resulted from the evaluation of Generic Issue 22,
"Inadvertent Boron Dilution Events." The generic letter considers an unmitigated boron
dilution event as a serious breakdown in the licensee's ability to control its plant and strongly
urges each licensee to assure itself that adequate protection against boron dilution events
exists in its plants. However, the consequences are not severe enough to warrant backfitting
requirements for boron dilution events at operating reactors.
In the past several years, this year in particular, there have been numerous events where
operator actions inappropriately affected reactivity. This information notice highlights several
recent events in which poor command and control during reactivity evolutions have led to
unanticipated conditions.
Description of Circumstances
Byron Unit I
On June 12, 1996, the licensee made four dilutions of the reactor coolant system. Only the
first dilution was calculated in advance. At the time, Byron Unit I was in cold shutdown for a
refueling outage. Fuel had been reloaded into the core, and the reactor head was in
position. The reactor coolant loops were isolated to support steam generator tube inspection
and repair. The reactor coolant system (RCS) boron concentration was 1,984 parts per
million (ppm). The RCS silica concentration was elevated at 4 ppm.
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IN 96-69 December 20, 1996 A series of dilutions was planned to reduce silica levels and bring the RCS boron
concentration closer to the 1,600 ppm starting point for the planned dilution to criticality. The
target RCS boron concentration was 1,700 ppm.
The operations staff added approximately 7,600 liters [2,000 gallons] of pure, unborated
water from the primary water storage tank through a feed-and-bleed dilution. A reactor
operator calculated the expected boron concentration after this dilution to be no less than
1,837 ppm. The subsequent chemistry sample results indicated a boron concentration of
1,942 ppm.
On the basis of the chemistry sample result, the reactor operators performed a second
dilution of 7,600 liters [2,000 gallons] without conducting formal calculations expecting to
achieve a boron concentration of around 1,800 ppm. The chemistry sample after the second
dilution indicated a boron concentration of 1,877 ppm. Based on this and a subsequent
chemistry sample, but without formal calculations, the reactor operators made two additional
dilutions of 15,200 liters [4,000 gallons] each, expecting a final boron concentration of greater
than 1,700 ppm. The chemistry sample results after the fourth dilution indicated a boron
concentration of 1,521 ppm. The reactor operators added borated water to increase the
boron concentration to about 1,585 ppm to ensure adequate shutdown margin. The
licensee's Technical Specifications require a 1.3-percent shutdown margin, which the
licensee indicated was about 1,164 ppm boron.
The licensee determined that the sample line was not adequately purged before the first
three samples were obtained. However, the sample valve was left open for about 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />
before the fourth sample was taken, which allowed the line to be adequately purged; thus a
representative sample was obtained.
Washington Nuclear Project No. 2
On June 27, 19°6, the reactor achieved criticality at Step 8-3 in the rod pull sequence.
Criticality was expected at Step 12-18 of the rod pull sequence, with an acceptable range of
achieving criticality (+/- 10 my,)
between Steps 11-12 and 14-20. Achieving criticality at
Step 8-3 was outside the licensee's self-imposed acceptable range of values and was
approximately 16 mk,,,,, before the calculated estimated critical position. In accordance
with plant procedures, operators manually inserted control rods-to shut-down the reactor.
The estimated critical position calculated for the startup was performed using an
inappropriate parameter for the plant conditions. The nuclear engineer selected an incorrect
parameter for xenon dependence. The reactor was shutdown for a short period of time and
xenon did not completely decay and was incorrectly accounted for in the calculation.
During the approach to criticality, members of the control room staff were involved with
activities related to shift turnover, this may have distracted personnel involved with the
startup.
KY 11 IN 96-69
December 20, 1996 St. Lucie Unit 1
On January 22, 1996, while performing a routine manual boron dilution of the reactor coolant
system, the board reactor controls operator (RCO) was distracted leading to an over dilution
with reactor power reaching 101 percent. During the evolution the RCO responded to a
secondary plant annunciator and lost track of the routine dilution. He then requested to be
relieved by the desk RCO while he prepared his lunch. During the turnover, there was no
discussion of the dilution in progress which continued for seven minutes until the board RCO
returned and realized his error. The operators took prompt corrective action of stopping the
dilution and initiating manual boration.
Discussion
At Byron, an inadequate sampling procedure and inadequate calculations of boron
concentration led to an unexpected dilution of 179 ppm below the target boron concentration
of 1,700 ppm. The licensee determined the chemistry sample procedure to be deficient.
This deficiency was originally noted during review of procedures for post-accident sampling;
however, the chemistry staff failed to recognize the implications on routine sampling. The
licensee's dilution procedure was deficient, also, In that It did not have provisions for dilutions
with the loop stop isolation valves closed. The operators calculated the reduced volume for
the dilution calculations and attributed the differences in expected and sample boron
concentrations to the conservative reactor coolant system volume used in the calculation.
The reactor operators continued with successive dilutions based on the original calculation
and the sample concentrations but failed to adequately question the higher than expected
sample values and to perform acceptable calculations between dilutions in order to determine
the additional dilution amounts.
At Washington Nuclear Project No. 2, Shift Nuclear Engineers, because of inadequate
training on a recent software modification, incorrectly selected a parameter which resulted in
the wrong estimated critical position. These engineers and operators suspected a problem
with the estimated critical position but did not effectively resolve their concerns or express
them to higher management. The engineers did perform an independent verification which
confirmed the estimated value; however, they used the same software and input parameters.
During the startup, the control room staff realized that the reactor would go critical outside
their self-imposed +/- 10 mk,,,,. reactivity band; however, they continued the startup
because of their interpretation of a poorly written startup procedure. The likelihood of
achieving early criticality was not communicated to upper management, either. When
criticality was achieved, operators then acted conservatively and manually shut down the
reactor.
At St. Lucie Unit 1, the board RCO exhibited inattentiveness to a routine evolution affecting
reactivity. The RCO initiated the dilution without notifying other control room personnel and
failed to discuss the evolution in progress with his temporary replacement prior to exiting the
IN 96-69 December 20, 1996 control room. As a result, the senior reactor operator and the other operators were unaware
that a reactivity addition was taking place. Upon returning to the control room, the RCO
noted an alarm which was due to increasing reactor coolant system pressure, realized his
error, and took prompt corrective actions.
Both the Byron and the Washington Nuclear Project events involved a lack of questioning
attitude that would have allowed the operators to suspend the ongoing evolutions affecting
reactivity until they had an understanding of the unexpected plant indications. Furthermore, all three events contained inappropriate command and control over activities associated with
reactivity manipulations.
Additional details of these events can be found in the following inspection reports: Byron
Unit I IR 50-454/96-05; 50-455/96-05 dated July 31, 1996 [9608120029]; Washington
Nuclear Project No. 2 IR 50-397/96-16 dated September 12, 1996 [96091902751; and
St. Lucie IR 50-247/96-03 dated February 22, 1996 [96071502941.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/Thomas
T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: N. D. Hilton, Rill
M. S. Miller, Ril
(815) 234-5451
(407) 464-7822 E-mail: ndh@nrc.gov
E-mail: msm@nrc.gov
R. C. Barr, RIV
S. S. Koenick, NRR
(509) 377-2627
(301) 415-2841 E-mail: rcb3@nrc.gov
E-mail: ssk2@nrc.gov
Attachments: List of Recently Issued NRC Information Notices
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IN 96-69 December 20, 1996 control room. As a result, the senior reactor operator and the other operators were unaware
that a reactivity addition was taking place. Upon returning to the control room, the RCO
noted an alarm which was due to increasing reactor coolant system pressure, realized his
error, and took prompt corrective actions.
Both the Byron and the Washington Nuclear Project events involved a lack of questioning
attitude that would have allowed the operators to suspend the ongoing evolutions affecting
reactivity until they had an understanding of the unexpected plant indications. Furthermore, all three events contained inappropriate command and control over activities associated with
reactivity manipulations.
Additional details of these events can be found in the following inspection reports: Byron
Unit I IR 50-454/96-05; 50-455/96-05 dated July 31, 1996 [9608120029]; Washington
Nuclear Project No. 2 IR 50-397/96-16 dated September 12, 1996 [9609190275]; and
St. Lucie IR 50-247/96-03 dated February 22, 1996 [9607150294].
This information notice requires no specific action or written response. If you have any
questions about the 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 D.B. Matthews
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
N. D. Hilton, Rill
(815) 234-5451 E-mail: ndhenrc.gov
M. S. Miller, RII
(407) 464-7822 E-mail: msm@nrc.gov
R. C. Barr, RIV
(509) 377-2627 E-mail: rcb3@nrc.gov
S. S. Koenick, NRR
(301) 415-2841 E-mail: ssk2@nrc.gov
Attachments: List of Recently Issued NRC Information Notices
Tech Editor has reviewed and concurred on 9/24/96 OFC
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DOCUMENT NAME: 96-69.1N
IN 96- December
, 1996 At St. Lucie Unit 1, the board RCO exhibited inattentiveness to a routine
evolution affecting reactivity. The RCO initiated the dilution without
notifying other control room personnel and failed to discuss the evolution in
progress with his temporary replacement prior to exiting the control room. As
a result, the senior reactor operator and the other operators were unaware
that a reactivity addition was taking place. Upon returning to the control
room, the RCO noted an alarm which was due to increasing reactor coolant
system pressure, realized his error, and took prompt corrective actions.
Both the Byron and the Washington Nuclear Project events involved a lack of
questioning attitude that would have allowed the operators to suspend the
ongoing evolutions affecting reactivity until they had an understanding of the
unexpected plant indications. Furthermore, all three events contained
inappropriate command and control over activities associated with reactivity
manipulations.
Additional details of these events can be found in the following inspection
reports:
Byron Unit 1 IR 50-454/96-05; 50-455/96-05 dated July 31, 1996
[9608120029]: Washington Nuclear Project No. 2 IR 50-397/96-16 dated September
12, 1996 [9609190275]; and St. Lucie IR 50-247/96-03 dated February 22. 1996
[9607150294].
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: N. D. Hilton, RIII
M. S. Miller, RII
(815) 234-5451
(407) 464-7822 E-mail: ndh@nrc.gov
E-mail: msm@nrc.gov
R. C. Barr, RIV
S. S. Koenick. NRR
(509) 377-2627
(301) 415-2841 E-mail:
rcb3@nrc.gov
E-mail: ssk2@nrc.gov
Attachments:
List of Recently Issued NRC Information Notices
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IN 96- December
, 1996 This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
N. D. Hilton, Rill
(815) 234-5451 E-mail: ndh@nrc.gov
M. S. Miller, Ril
(407) 464-7822 E-mail: msmenrc.gov
R. C. Barr, RIV
(509) 377-2627 E-mail: rcb3@nrc.gov
S. S. Koenick, NRR
(301) 415-2841 E-mail: ssk2@nrc.gov
Attachments: List of Recently Issued NRC Information Noticed
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DOCUMENT NAME: G:\\SSK2\\REACTIVE.RV3
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Attachment
December 20, 1996 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
96-68
96-67
96-66
96-65
96-64
Incorrect Effective Diaphragm
Area Values in Vendor Manual
Result in Potential Failure
of Pneumatic Diaphragm
Actuators
Vulnerability of Emergency
Diesel Generators to Fuel
Oil/Lubricating Oil Incom- patibility
Recent Misadministrations
Caused by Incorrect Cali- brations of Strontium-90
Eye Applicators
Undetected Accumulation
of Gas in Reactor Coolant
System and Inaccurate
Reactor Water Level
Indication During Shutdown
Modifications to Con- tainment Blowout Panels
Without Appropriate
Design Controls
12/19/96
12/19/96
12/13/96
12/11/96
12/10/96
All holders of OLs
or CPs for nuclear
power reactors
All holders of OLs
or CPs for nuclear
power reactors
All U.S. Nuclear
Regulatory Commission
Medical Use Licensees
authorized to use
eye applicators
All holders of OLs
or CPs for nuclear
power reactors
All holders of OLs
or CPs for nuclear
reactors
OL = Operating License
CP = Construction Permit