NRC Issues Report on Special Inspection of Improper Control Rod Movement at Zion Unit 1




801 Warrenville Road, Lisle IL 60532

CONTACT:    Jan Strasma (630) 829-9663/e-mail:
Angela Dauginas (630) 829-9662/e-mail:


April 30, 1997


The Nuclear Regulatory Commission staff has issued the report of the Augmented Inspection Team which reviewed the improper control rod movements during a shutdown February 21 at Unit 1 of the Zion Nuclear Power Station. The Commonwealth Edison Co. plant is at Zion, Illinois.

The team concluded that the actual incident did not pose a risk to the health and safety of the public, but that it had safety significance from a human performance perspective.

While the Unit 1 reactor was shut down, an NRC-licensed reactor operator withdrew control rods continuously in an attempt to take the reactor critical [i.e., producing energy], disregarding established procedural controls for conducting a safe reactor startup.

Control rod movements were stopped before startup occurred, and the reactor has remained shut down, pending completion of the utility's performance improvement program.

The team inspection focussed on gathering information about the incident and did not evaluate the findings for possible violations of NRC requirements. A subsequent inspection has been conducted to review the incident for possible enforcement action. A written report of this inspection will be issued at a later date.

Attached is the summary section from the Augmented Inspection Team report. The full report is on the NRC's internet web site.

NRC Augmented Inspection Team Report -- Zion Unit 1

8.0 Summary of Findings and Conclusions

During their review of the February 21 shutdown event, the team developed a number of findings and conclusions. These are discussed in detail in the report. This section summarizes the team's more significant findings and conclusions.

  1. The more significant root causes for this event included:

    a total breakdown in command and control by operations supervision,

    inadequate communications between operators, operations supervision, operations management, and nuclear engineering department personnel,

    the failure of operations supervision, operations management, and plant management to provide clear direction to the operating crew regarding the planned shutdown,

    the failure to pre-plan the shutdown evolution,

    licensed operator training deficiencies, and

    the existence of a number of control room distractions during shift activities.

  1. Operations supervision did not properly exercise its oversight responsibilities for ensuring that shift activities were conducted in a controlled manner and became focused on containment spray pump restoration activities and balance of plant problems. As a result, operations supervision was unaware of improper control rod manipulations.

  2. Despite the almost continuous presence in the control room of operations and/or plant management during shift activities, including the shutdown evolution, no direction was provided to operations supervision to correct the command and control deficiencies, communication problems, lack of teamwork, and control room distractions which collectively precipitated this event. This inaction by management conveyed tacit approval of the existing control room conditions to operations supervision.

  3. The actions of the primary nuclear station operator (NSO) in continuously withdrawing control rods to re-establish power at the point-of-adding-heat (POAH) reflected a significant lack of understanding of reactor physics and proper control rod manipulations for a controlled approach to criticality. The actions of the primary NSO were also contrary to instructions in the plant startup procedure.

  4. Regarding command and control deficiencies:

    The shutdown briefing was informal, poorly planned, and ineffective. Operations supervision did not provide any direction to the operating crew during the briefing regarding the decision point for proceeding to hot shutdown.

    Despite a number of control room indications and communications, operations supervision was 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 withdrew control rods 84 steps in an attempt to re-establish power at the POAH. [POAH - point of adding heat, a very low power level where enough energy is produced to add heat to the reactor cooling water.]

    Operations supervision failed to exercise their responsibility to minimize control room distractions with the potential to adversely impact the ability of operators to safely conduct plant evolutions.

  5. Regarding communications deficiencies:

    The shift engineer did not provide clear direction to the US regarding his intent to keep the Unit 1 reactor critical after the main turbine had been tripped. Operations supervision also failed to inform the operating crew of the intent to keep the reactor critical.

    The primary NSO did not adequately communicate and seek resolution of concerns he had with the actions directed by a specific step in the shutdown procedure. The unit supervisor (US) also did not clarify the intent of this procedural step for the primary NSO. This was one of the major contributing causes of the event.

    The qualified nuclear engineer assigned to monitor the shutdown evolution did not adequately communicate his concerns with observed control rod manipulations to operations supervision.

    On a number of occasions, the operating crew did not exercise proper three-way communications.

    Ineffective communications between plant management, operations management, and operations supervision contributed to poor planning for the shutdown evolution.

    The significance of the event was not communicated to licensee management in a timely manner, and licensee management did not effectively communicate expectations that the primary NSO, US, and shift engineer involved in the shutdown be removed from licensed duties.

  6. Operations management did not appreciate the significance of the actions of the primary NSO in continually withdrawing control rods in an attempt to take the reactor critical. This was evident in the deliberate decision by operations management to return the involved licensed operators to licensed duties.

  7. Immediate corrective actions were inadequate in that licensed operators directly involved in the event resumed licensed duties.

  8. Operations supervision did not ensure that planned reactivity changes were accomplished in a controlled manner and that the effects of these changes were understood and appropriately monitored.

  9. The AIT identified a number of precursor events with root causes related to poor communications, weak command and control, and poor reactivity management. Due to the absence of corrective actions in some cases, and ineffective corrective actions in other cases, the licensee failed to correct the underlying problems which contributed to these events.

  10. The licensed operator requalification training program was deficient in that it did not include training on shutdown evolutions that involve establishing and maintaining power at the POAH.

  11. The overall level of knowledge among licensed operators pertaining to reactivity management and reactor physics specific to plant response to continuous control rod withdrawal and inspection evolutions, was adequate.

Page Last Reviewed/Updated Wednesday, March 24, 2021