05000483/LER-2008-003
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4832008003R00 - NRC Website | |
- I.�DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
10CFR50.73(a)(2)(iv)(A) requires reporting of any event or condition that resulted in a manual or automatic actuation of any of the systems listed in 10CFR50.73(a)(2)(iv)(B). The systems listed below are relevant to this LER:
(1) Reactor protection system (RPS) including: reactor scram and reactor trip.
(6) PWR auxiliary or emergency feedwater system.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
Prior to the event, the plant was being cooled down for a scheduled refueling shutdown. The plant was in MODE 4, and RCS temperature was less than 350°F. Operators had reached the step in the procedure that allowed closing the MSIVs and opening the MSIV bypass valves.
C. STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS THAT WERE INOPERABLE AT THE
START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
- During the event the Plant Process Computer's alarm manager task had failed. This may have hindered the crew's ability to identify various alarms that are not provided by the annunciators.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES
At 0500 CST on 10/11/08, plant operators had reached the step in performance of their procedures for plant shutdown to Refuel 16 when they were allowed to close and bypass steam flow around the Main Steam Isolation valves (MSIVs) [EIIS system: SB component ISV]. Once the MSIVs were closed, the reactor coolant system (RCS) [EIIS system: AB] cooldown rate stopped and a slight heatup started. In order to restore cooling and prevent re-entry into MODE 3, an attempt to open the 'A' MSIV was made by the Balance of Plant (BOP) operator. The BOP operator then proceeded to open the 'A' Atmospheric Steam Dump (ASD) [EIIS system; SB component RV] to restore cooling. The BOP operator did not inform the crew of the actions he had taken to open the 'A' MSIV prior to opening the 'A' ASD.
It is important to recognize that during the previous plant refueling outage (Refuel 15), the hydraulic type MSIV actuators installed in the plant were replaced with a newer process fluid type of actuator.
The motive force is different in the newer actuators, such that at lower pressures a longer response time is required for the valve to open. The operators were trained on the operation of the new valves.
The operator expected a slow response. When the valve did not respond in 20 to 30 seconds, the operator assumed that the system pressure was too low to operate the valve.
Shortly after the 'A' ASD was opened, the 'A' MSIV stroked open. The crew was unaware that the `A' MSIV had opened. This caused the 'A' Steam Generator (SG) level to swell, resulting in a P-14 FWIS (Feedwater Isolation) actuation [EIIS system; JE / BA] at 0505. The P-14 FWIS isolated feed water to the SGs. Plant operators then took action to recover from the FWIS in accordance with off normal operating procedures. The 'B' Motor Driven Auxiliary Feedwater Pump (MDAFP) [EIIS system: SJ] was started to restore SG levels. However, the level in the 'A' SG could not be restored due to steam rate and cold Auxiliary Feedwater addition. The level lowered to the Narrow Range (NR) SG level Low-Low setpoint of 17%, which resulted in a Reactor Trip signal [EIIS system: JC] and an Auxiliary Feedwater Actuation Signal (AFAS)[EIIS system JE] at 0508. All control rods had been previously inserted into the core as part of the shutdown sequence. 'A' SG water level was restored and 'A' Residual Heat Removal (RHR) [EIIS system BP] cooling was placed into service.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL ERROR
As noted previously, events began as the plant was being cooled down for shutdown into a refueling outage. There were no Safety System failures or procedural errors that lead to this event OTG-ZZ- 00006, Plant Cooldown Hot Standby to Cold Shutdown, is the only procedure utilized for the cooldown of the plant from Normal Operating Temperature and Pressure (NOP/NOT). This procedure did not contain a provision to ensure that another heat sink (e.g. ASDs or RHR) is in service prior to closing the MSIVs.
II.� EVENT DRIVEN INFORMATION
A. SAFETY SYSTEMS THAT RESPONDED
All safety systems functioned per design.
The FWIS Actuation occurred as designed in response to the P-14 SG Hi level Protective Interlock Setpoint being reached during MODE 4. The Reactor Trip System Actuation and Auxiliary Feedwater Actuation Signal that subsequently occurred due to SG Low-Low Water Level (NR) Trip also occurred per design. Subsequent to the FWIS actuation, in accordance with Off-Normal Operating Procedures, the 'IV Motor Driven Auxiliary Feedwater pump (MDAFP) was started to restore SG water level. Manually starting the 'EV MDAFP is considered an actuation of the Auxiliary Feedwater System.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
There were no Safety System inoperability concerns during this event. All systems functioned normally.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
The first portion of events described in this LER can be best characterized by comparison with the Loss of Load heatup event analyzed in FSAR Section 15.2.� Following closure of the MSIVs, when a slight heat up of the RCS occurred as previously described, the plant was in a configuration comparable to what is analyzed in the Loss of Load event. During this heatup portion of the transient, plant conditions were bounded by the FSAR Section 15.2 Loss of Load transient, which is evaluated during MODE 1, at full power. The events described in this LER occurred during MODE 4 with all control rods fully inserted and the RCS heat loads well below the analyzed condition.
The second transient of the events described in this LER occurred when the MSIV and the ASD were both open at the same time, resulting in a temporary excessive cool down and depressurization of the `A' SG. This portion of the event is best represented by the analyzed condition of a steamline break (SLB) while the plant is at Hot Zero Power (HZP). The reason for selecting the postulated SLB at HZP accident analysis is because it results in a rapid loss of pressure and an excessive cooldown of the RCS.
The postulated SLB at HZP as analyzed in FSAR Section 15.1 represents a much larger cool doWn than this event produced, and it also assumes that the most reactive control rod is stuck out. The SLB at HZP bounds the transient for this event because the reactor was already shut down with all of the control rods inserted, and temperature (approximately 340°F) was far below the HZP accident analysis value.
The third transient during this event occurred when the SG appeared to overfill because of depressurization of the SG. This caused the FWIS. This portion of the event is best represented by the accident analysis of a feedwater malfunction transient from hot full power (HFP), which is presented in FSAR Section 15.1. This accident analysis bounds the third transient of this event, because the reactor was at zero power with all control rods fully inserted, and the temperature was well below the temperature for HFP.
The last transient of this event occurred when the SG water level reached the low-low level set point and initiated a reactor trip signal. This portion of the event is best represented by the accident analysis of a loss of normal feedwater transient from HFP, which is presented in FSAR Section 15.2. The conditions that existed during the events described in this LER were bounded by the licensing bases analyses because the licensing bases analyses assume HFP.
The events described in this LER occurred at zero power with all of the control rods fully inserted and the RCS temperature below that of HFP. The events described in this LER are therefore bounded by the analyses presented in Sections 15.1 and 15.2 of the Callaway FSAR, and consequently do not represent any unanalyzed conditions, nor were they safety significant.
, III.C CAUSE(S) OF THE EVENT AND CORRECTIVE ACTION(S) Causes of the event were determined to be:
- OTG-ZZ-00006, Plant Cooldown Hot Standby to Cold Shutdown, is the only procedure utilized for the cooldown of the plant from NOP/NOT. This procedure did not contain a provision to ensure that another heat sink (e.g. ASDs or RHR) is in service prior to closing the MSIVs. OTG-ZZ-00006 will be revised to ensure that prior to closing MSIVs another heat sink is in service.
- The BOP operator did not inform the crew prior to opening the MSIV. If crew had known of this action they would have had an opportunity to stop opening of the MSIV by using other cooldown methods as discussed in Pre-Evolution Practice (PREP) training. This is a human performance issue. Individual coaching was performed.
- The Shift Manager and Control Room Supervisor did not provide effective oversight as unplanned activities caused a loss of focus. Remedial actions taken were to discuss the importance of crew teamwork when unplanned activities and distractions occur, and to incorporate the details of this event into future licensed operator training as operating experience.
IV. PREVIOUS SIMILAR EVENTS
A search was performed for past applicable events concerning inadvertent P-14 FWIS Actuations followed by a Reactor Trip Signal. Other P-14 FWIS Actuations followed by Reactor Trip Actuations have occurred at Callaway Plant; however, none have occurred in MODE 4 while cooling down or have similar equipment issues. The events have some commonality in that they involve a human performance element.
An external operating experience search was also performed. None of the event results from that search had similar equipment issues; therefore, they are not considered to be relevant.
V. ADDITIONAL INFORMATION
None