|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(A), System Actuation|
|ENS 44016||10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation|
|LER closed by|
|IR 05000250/2008005 (29 January 2009)|
|2512008001R00 - NRC Website|
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)
A. REPORTABLE EVENT
Turkey Point Unit 4 manual reactor trip due to high water level in the 4A steam generator is being reported herein pursuant to 10 CFR 50.73 (a) (2)(iv) (A) as any event or condition that resulted in manual or automatic actuation of the reactor protection system.
B. INITIAL CONDITIONS
Turkey Point Unit 4 was in Mode 1.
C. DESCRIPTION OF EVENT
On February 29, 2008, Turkey Point Unit 4 was in Mode 1 at approximately 7% power. Power escalation was in progress following an automatic reactor trip that occurred on February 26, 2008 due to an under voltage condition on the electrical grid.
At 0447, following the turbine [EllS:TA] and main generator [EIIS:TB] synchronization in accordance with procedural guidance, the operator at the turbine controls was increasing load to 40 MWe in increments of 5-10 MWe. The procedure used for this evolution, 4-GOP-301, Hot Standby to Power Operation, did not specify loading rates or hold points, permitting the operators to determine loading rates based on plant conditions. During this power escalation evolution, the operating crew was performing an abnormally fast loading. The main generator was loaded to 40 MWe in less than 2 minutes causing frequent reactivity changes. The abnormally fast loading of the main generator shifted the Unit Supervisor's focus from overall oversight to peer checking a large number of reactivity changes.
While still increasing generator loading, following several procedural steps to ensure steam dump operation, the operating crew was in the process of placing the main feedwater controls in automatic. The steam generator [EllS:SG] levels had been oscillating even before the turbine and main generator synchronization. The operator at the feedwater controls was using the Main Feedwater Regulating [EllS:FRV] Bypass Valve to control steam generator levels. During the power escalation and turbine loading evolution he did not stabilize the SG levels and he did not communicate to the operating crew his concerns regarding controlling the SG levels. When he opened the 4A Main Feedwater Regulating Isolation valve, he observed increasing SG levels, which led him to believe that the higher steam generator level was caused by leak-by flow from the main feedwater isolation valve. At approximately 0449, per direction from the Unit Supervisor he closed the Main Feedwater Regulating Control Bypass Valve in an effort to reduce level in the steam generators. During that time, load was continually being increased until approximately 0450, which lead to additional level "swelling.
The steam generator level control issues prompted control room questions and communications for stabilizing the plant. The abnormally fast loading of the generator and the increased steam demand resulted in exacerbated steam generator level fluctuations causing the SG levels to "swell." The operator at the turbine controls promptly reduced load. At that time, the crew noticed that the 4A SG level had exceeded 75% NR, i.e., the procedural upper limit for initiating a manual reactor trip. At 0451, with Turkey Point Unit 4 reactor power at 10%, the operating crew initiated a manual reactor trip due to high level in the 4A steam generator.
The operators verified that the reactor and turbine were tripped and stabilized the plant in accordance with procedural guidance. There were no equipment issues, and no adverse effects on plant parameters.
In accordance with 10 CFR 50.72 (b) (2) (iv) (B), this event (Event Notification #44016) was reported to the Nuclear Regulatory Commission Operation Center on February 29, 2008 at 0547. This event is being reported herein pursuant to 10 CFR 50.73 (a) (2) (iv) (A) as any event or condition that resulted in manual or automatic actuation of the reactor protection system.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) 2008 - 001 -
D. EVENT ANALYSIS
The event was evaluated to determine the root cause and contributing casual factors.
The procedure used for this evolution, 4-GOP-301, Hot Standby to Power Operation, does not provide guidelines for the rate of initial loading of the main generator. The operating crew determines the loading rate based on their training and plant conditions. During this event, an abnormally fast generator loading was implemented, which exacerbated steam generator level fluctuations and resulted in the loss of the 4A steam generator level control.
The operator at the reactor controls (RCO) did not attend the just-in-time-training (JITT), due to operations personnel demands resulting from the dual unit trip, and therefore, did not benefit from the crew's training and practice session.
This changed crew dynamics for returning Unit 4 to power from the way they practiced in the plant's simulator.
The abnormally fast generator loading implemented by the operating crew focused the unit supervisor on peer checking the RCO as recommended in the Nuclear Administrative Procedure, NAP- 402, Conduct of Operations.
The requirement for frequent peer checks of the RCO weakened the unit supervisor's overall oversight role during the evolution of power escalation.
The turbine operator and senior reactor operator continued to increase turbine load while the steam generator level continued to increase after the Main Feed Regulating Bypass Valves were closed. The operator at the feedwater controls did not stabilize SG levels and did not communicate his concerns about the SG level control.
The root cause of the event is insufficient guidance for the initial loading of the main generator and for stabilizing power while preparing to transfer to automatic feed regulating valve control. Other factors which contributed to the root cause are: (1) not all the operating crew members attended the same JITT to practice this evolution, (2) the abnormally fast loading of the main generator shifted the Unit Supervisor's focus from overall oversight to peer checking a large number of reactivity changes, (3) a weakness in understanding the SG "shrink" and "swell" concept and, (4) failure to communicate the SG levels and trends to the rest of the operating crew members.
F. CORRECTIVE ACTIONS
Turkey Point is in the process of implementing procedural changes to provide guidance for ramp rates during turbine initial loading and appropriate hold points to ensure proper control of plant parameters.
Corrective actions to address the event's contributing factors have been entered in the Turkey Point Corrective Action program.
This event resulted in a manual reactor trip due to the excessive feedwater level in the 4A SG. The reactor power was at 10% at the time of the trip. There was no challenge to the integrity of the primary or secondary plant. The plant response during this event is bounded by an event assuming an increase of 200% feedwater flow analyzed in Turkey Point's Updated Final Safety Analysis Report. This event is not a safety significant event, and had no adverse effect on the health and safety of the public.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) H. � ADDITIONAL INFORMATION The condition report that includes the post trip report and the root cause evaluation is CR 2008-7157.
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Previous Similar Events
No similar events were found for the past two years.