ML13004A265
| ML13004A265 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 10/15/2010 |
| From: | David Beaulieu Division of Policy and Rulemaking |
| To: | Lawrence Criscione NRC/RES/DRA |
| Shared Package | |
| ML130040225 | List:
|
| References | |
| FOIA/PA-2012-0259 | |
| Download: ML13004A265 (7) | |
Text
1 Criscione, Lawrence From:
Sent:
To:
Subject:
Attachments:
Beaulieu, David Friday, October 15, 2010 2:54 PM Criscione, Lawrence IN Regarding 2003 Callaway Event IN Reactivity.docx
- Larry, I am the project manager in NRR responsible for information notices (IN). Attached is the draft information notice (IN) that discusses the 2003 reactor shutdown at Callaway. While RES is not on concurrence for the IN, given your involvement with the issue I am e-mailing you the draft IN and will consider any comments you may choose to provide. Please do not feel obligated to provide comments. If providing comments would violate your settlement agreement with your former employer, that is a matter between you and your former employer.
I am your point of contact for any comments you may choose to provide. Please let me know whether you intend to provide comments so I can plan accordingly. Feel free to call me.
Dave X) \\-
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, DC 20555-001 NRC INFORMATION NOTICE 2010-XX:
OPERATOR PERFORMANCE ISSUES INVOLVING REACTIVITY MANAGEMENT AT NUCLEAR POWER PLANTS ADDRESSEES All holders of operating licenses for nuclear power reactors under the provisions of 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.
PURPOSE The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees of events in which deficiencies with reactivity management planning and implementation resulted in transients or unexpected conditions. The NRC expects recipients to review the information for applicability to their facilities and to 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 Callaway Plant During a Callaway Plant shutdown in October 2003, the control room operators did not effectively control reactivity during low-power operations. The event began on the morning of October 20, 2003, when the Callaway Plant experienced an inverter failure on a safety-related bus that put the unit in a 24-hour technical specification action to restore the inverter or be in Mode 3 (hot standby) within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The next morning, operators initiated a plant shutdown at approximately 10 percent per hour. With the main turbine on line and with turbine bypass valves closed, operators attempted to stabilize the plant at approximately 8-percent power. Per procedure, operators opened the turbine drain valves, which increased main steam flow, reducing reactor coolant temperature and adding positive reactivity. In addition, negative reactivity was being inserted by xenon buildup, decreasing reactor power. The net effect was that reactor coolant temperature decreased by approximately 10 degrees Fahrenheit over a half-hour period. Operators did not withdraw control rods or dilute boron concentration to stabilize reactor power or reactor coolant temperature. As a result of the lowering temperature, the pressurizer level lowered enough to cause letdown to isolate and the reactor coolant temperature went below the minimum temperature for criticality for several minutes. With power at approximately 5 percent, the operators manually tripped the main turbine. Tripping the main turbine reduced main steam flow, increasing reactor coolant temperature and adding negative ML101810282
IN 2010-XX Page 2 of 5 reactivity, which together with the addition of negative reactivity by xenon buildup, caused the reactor to become subcritical. Tripping the main turbine permitted the turbine bypass valves to open and control steam pressure, causing reactor coolant temperature and pressurizer level to return to normal. Operators did not insert the control rods until almost 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the reactor became subcritical.
A subsequent review of this plant shutdown found that control room operators did not effectively control reactivity to maintain the reactor in the desired condition during low-power operations by properly anticipating, controlling, and responding to changing plant parameters. Operators did not use control rods or boron concentration-two means that operators can directly control the amount and timing of reactivity changes-to adjust for reactivity changes by xenon buildup and reactor coolant temperature changes. As a result, (1) operators did not effectively stabilize and hold the plant at a low power level, (2) operators did not shut down the reactor in a deliberate manner (e.g., by inserting control rod banks), but rather the reactor became subcritical because of xenon buildup and the increase in reactor coolant temperature resulting from the operators manually tripping the main turbine, and (3) operators did not insert control rods for nearly 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the reactor became subcritical to provide assurance that the reactor remained shut down.
Operator performance in not effectively controlling reactivity was attributable, in part, to weaknesses with management oversight, training, and procedural guidance. The just-in-time training did not cover plant operations below 10-percent power and did not include operation after the point where the operators tripped the main turbine. The reactivity management plan did not address the possibility that the expected reactivity change from tripping the main turbine together with the xenon buildup could cause the reactor to become subcritical. The licensee's initial post-shutdown review did not identify and evaluate the atypical manner that the reactor became subcritical and whether operators sufficiently anticipated and accounted for xenon.
This omission delayed application of the lessons learned to operator qualification and requalification training and significantly delayed procedure changes to address weaknesses in operator control of reactivity during low-power operation. Additional information is available in "Callaway Plant-NRC Integrated Inspection Report 05000483/2007003," dated August 2, 2007, which can be found on the NRC's public Web site in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML072140876.
River Bend Station On March 8, 2008, with River Bend Station at 25-percent power, control room operators were withdrawing control rods to increase reactor power. The operating procedure for plant startup directs operators to withdraw control rods a using a withdrawal sequence specified in a reactivity control plan that is provided to them by licensee reactor engineering. However, the dedicated reactor operator at the controls stated an incorrect target position when reading aloud a rod movement step in the reactivity control plan. As a result, this operator individually withdrew six consecutive rods to position 24 rather than the target position 20 specified in the reactivity control plan. The dedicated peer-check reactor operator did not identify that the stated target position was incorrect because he could not readily see the reactivity control plan that was resting on the lap of the reactor operator at the controls. The operator at the controls halted the withdrawal of the seventh rod at position 18 after the dedicated peer-check reactor operator identified the error. The licensee determined that the reactor operator at the controls
IN 2010-XX Page 3 of 5 and the peer-checker did not follow the procedures to prevent human performance errors and that the senior reactor operator did not maintain effective oversight of the activity. Additional information is available in "River Bend Station-NRC Integrated Inspection Report 05000458/2008002," dated May 9, 2008 (ADAMS Accession No. ML081300838).
Diablo Canyon Power Plant, Unit 2 In August 2009, Diablo Canyon Power Plant Unit 2 was shut down in order to troubleshoot and repair a main transformer bushing. In preparation for the shutdown, the control room operators performed simulator training on a ramp downpower using a draft copy of a ramp plan provided via e-mail by reactor engineering. Before the actual shutdown, a revised ramp plan was provided by reactor engineering, approved by the operations manager, and issued in the shift orders. This revised ramp plan was also e-mailed to all shift members. The oncoming shift foreman and shift manager did not review the approved ramp plan located in the shift orders nor did they review the ramp plan as part of the reactivity brief. Operators began the ramp downpower using the original (unapproved) draft ramp plan. After the first 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of the downpower, the control room operator questioned plant conditions that were inconsistent with the simulator scenario and contacted the reactor engineer. The reactor engineer provided a copy of the approved ramp plan. No reactivity manipulations outside of the approved plan had been made. Operators continued the downpower using the approved ramp plan.
The licensee performed an apparent cause evaluation and determined that the shift foreman did not validate that the ramp plan in use was the same as the one that the operations manager had approved. Licensee corrective actions included revising existing procedures to require validation of the ramp plan by the shift foreman and shift manager during the reactivity briefing.
Additional information is available in "Diablo Canyon Power Plant-NRC Integrated Inspection Report 05000275/2009005 and 05000323/2009005," dated February 3, 2010 (ADAMS Accession No. ML100341199).
Arkansas Nuclear One On April 25, 2010, following the completion of a refueling outage, Arkansas Nuclear One, Unit 1 was at approximately 20-percent reactor power determined by heat balance (approximately 30-percent reactor power indicated on nuclear instrumentation (NI)) and holding to allow instrumentation and controls (I&C) technicians to calibrate the NI, which involves adjusting the gain on the NI excore detectors so that NI indicated reactor power level matches the reactor power determined by heat balance. To prevent the integrated control system (ICS) from automatically moving control rods in response to the changing input of NI reactor power level from the gain adjustment, the calibration procedure first directs a control room operator to place the control rod station in manual. The I&C technician who was implementing the procedure stated to a control room operator, "We are ready to place ICS to manual." The control room operator responded, "ICS is in manual." However, this exchange did not result in the operator placing the control rod station in manual and it remained in automatic. When I&C technicians subsequently adjusted the gain on the NIs, control rods automatically withdrew for approximately 38 seconds and resulted in an automatic reactor trip because of high reactor power (49.55 percent NI indicated reactor power) and high RCS pressure. The rapid event succession did not afford operators time to complete diagnosis of the rod withdrawal and initiate manual corrective action.
IN 2010-XX Page 4 of 5 The causes of the event included failure to follow the NI calibration procedure, miscommunication between the I&C technician and the reactor operator, failure to conduct a pre-job brief, and lack of supervisory oversight. Additional information is available in "Arkansas Nuclear One-NRC Integrated Inspection Report 05000313/2010003 and 05000368/2010003,"
dated August 5, 2010 (ADAMS Accession No. ML102180209).
BACKGROUND The following are related NRC generic communications:
NRC IN 92-39, "Unplanned Return to Criticality during Reactor Shutdown," dated May 13, 1992, discussed events involving unplanned returns to criticality caused by the cooldown of the reactor coolant system during reactor shutdowns (ADAMS Accession No. ML031200314).
NRC IN 96-69, "Operator Actions Affecting Reactivity," dated December 20,-1996, highlighted several events in which poor command and control during reactivity evolutions have led to unanticipated and unintended plant conditions (ADAMS Accession No. ML031050475).
DISCUSSION One of the most important responsibilities of an on-duty licensed reactor operator and senior reactor operator is reactivity management in order to maintain the reactor in the desired condition, consistent with plant technical specifications, by properly anticipating, controlling, and responding to changing plant parameters. Reactivity management involves establishing and implementing procedures for operators to use in determining the effects on reactivity of plant changes, and to operate the controls associated with plant equipment that could affect reactivity. Although there is no specific NRC requirement, before conducting planned evolutions involving reactivity changes (e.g., power decreases and increases), many licensee reactor engineering staffs prepare a reactivity management plan that helps control room operators maintain the reactor in the desired condition by providing expected plant responses and expected alarms. Required training is expected to give licensed operators an understanding of facility operating characteristics during steady-state and transient conditions, including causes and effects of temperature, pressure, coolant chemistry, and load changes, as well as, operating limitations and their bases. Licensee post-transient reviews are important for determining the cause of transients or unexpected plant responses and for taking corrective actions, such as procedure changes and training, to prevent recurrence.
During one of the events discussed above, after the reactor became subcritical through xenon buildup and a reactor coolant temperature increase, operators delayed inserting control rods to establish adequate shutdown margin for nearly 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. NRC IN 92-39 discusses an event in which, after the operators brought the reactor subcritical by inserting control rods, an inadvertent unplanned return to criticality occurred because operators delayed actions to continue inserting control rods while changing shifts. Although not specifically required, licensees may revise procedures and train operators so that, after the reactor becomes subcritical, the operators will
IN 2010-XX Page 5 of 5 proceed without delay to establish adequate shutdown margin by inserting control rods or adding boron.
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 project manager.
Timothy J. McGinty, Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation Technical
Contact:
Geoffrey Miller 817-860-8141 Qeoffrev.miller(c&nrc.qov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ML101810282 OFFICE BC:DRP:R-IV Tech Editor IOLB:DIRS BC:IOLB:DIRS D:DIRS NAME GMiIler Chsu LVick JMcHale FBrown DATE 9/4/10e-mail OFFICE BC:SRXB:DSS OGC(NLO)
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I OFFICE LA:PGCB:NRR PM:PGCB:NRR BC:PGCB:NRR D:DPR:NRR NAME CHawes J
DBeaulieu SRosenberg TMcGinty OFFICE I