05000265/LER-2015-001
| Quad Cities Nuclear Power Station Unit 2 | |
| Event date: | 03-05-2015 |
|---|---|
| Report date: | 03-30-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2652015001R00 - NRC Website | |
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PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT IDENTIFICATION
Unit 1 HPCI Watertight Door Found Open Results in Unit 2 HPCI Inoperability
A. CONDITION PRIOR TO EVENT
Unit: 1 / 2 Reactor Mode: 5 / 1 Event Date: March 5, 2015 Event Time: 1900 Mode Name: Refueling / Power Operation Power Level: 000% / 100%
B. DESCRIPTION OF EVENT
On March 5, 2015, an individual identified that the Unit 1 High Pressure Coolant Injection (HPCI) watertight door [DR] was open with no one in attendance. This information was provided to the shift manager at 1900. The shift manager indicated that this information had not been reported previously to the shift and dispatched an equipment operator to verify the status of the watertight door. At 1915, the shift manager received the report from the equipment operator that the Unit 1 HPCI watertight door,was found shut and dogged.
As stated in the Updated Final Safety Analysis Report (UFSAR), section 3.4.1.2.2, the watertight door is a flood barrier to prevent water from entering the Unit 1 HPCI room from the reactor building basement. Flood protection is required to support operability of systems in the Technical Specifications. Due to the construction of the adjacent Unit 1 and Unit 2 HPCI rooms, there is no flood barrier between the two rooms. Therefore, a condition that results HPCI watertight door being found open, with no one in attendance, results in the unplanned inoperability of the Unit 2 HPCI, since the Unit 2 HPCI is required to be operable by Technical Specifications in Mode 1. The Unit 1 HPCI is not required to be operable with Unit 1 in Mode 5.
Because the Unit 2 HPCI was inoperable while Unit 2 was in the mode of applicability, this is a required report to the NRC by 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to: (D) Mitigate the consequences of an accident.
C. CAUSE OF EVENT
This condition was a result of a human performance deficiency for a worker to properly control the watertight door per station procedure. QCAP 0250-06, step D.1.a states, "It is the responsibility of the individual using the door to verify it is properly closed and "dogged" (latched).
It is unknown which persons or what workgroup would have been responsible for the control of this watertight door at this time. For a human performance deficiency, without understanding why it occurred from the involved party, we cannot establish an apparent cause or the circumstances. Because of this fact, briefings to the workforce were conducted by department heads and senior management. In addition, interim actions established periodic tours conducted by management to check the watertight doors, along with targeted observations by the outage standards team and nuclear oversight.
D. SAFETY ANALYSIS
System Design The HPCI system is designed to inject water into the Reactor Vessel under loss-of-coolant conditions which do not result in a rapid depressurization of the Reactor Vessel, such as a small break Loss of Coolant Accident (LOCA).
The internal flood protection measures described in the UFSAR establish that a single failure in a non-Class I system will not preclude safe shutdown of the affected Unit. In order to preclude safe shutdown of the affected Unit, such flooding would have to disable the core cooling pumps located in five completely separate areas of the Unit (i.e., Residual Heat Removal (RHR) corner rooms A and B; Core Spray corner rooms A and B; and the HPCI pump room.) However, each of these rooms is protected from adjacent areas by watertight doors and walls. Therefore, no single failure will cause flooding to more than one of these areas and no single failure of non-Class I systems will prevent safe shutdown of the affected Unit.
To support flood protection, watertight doors were constructed for each of the Emergency Core Cooling System (ECCS) pump compartments. These doors will prevent water in the torus room area from leaking into the pump compartment and will assure the availability of the ECCS in the event of a passive failure of the torus.
Safety Impact The aboVe statements from the UFSAR establish that the flood protection in the reactor building basement is based on a passive failure in the torus area, and that this passive failure is a safe shutdown event, not an accident described in Chapter 15 of the UFSAR. As such, this event would not be combined with a failure of the Reactor Coolant System (RCS) and would not require HPCI as part of any success path. HPCI is needed for those events where RCS inventory is lost while RCS pressure remains above the shutoff pressure for the low pressure injection systems. For these reasons, the open watertight dool: does not impact the safety function of HPCI.
This condition does not constitute a Safety System Functional Failure (SSFF) as the condition did not affect the function of HPCI to respond to a design basis event. As noted above, with the Unit 1 HPCI watertight door open, the ability of the HPCI to complete its specified safety function was not compromised.
An engineering analysis was performed that demonstrated this event did not constitute a SSFF. (Reference NEI 99-02, Revision 7, Regulatory Assessment Performance Indicator Guideline, Section 2.2, Mitigating Systems Cornerstone, Safety System Functional Failures, Clarifying Notes, Engineering analyses.) As such, this event will not be reported in the NRC Performance Indicator (PI) for safety system functional failures since an engineering analysis was performed which determined that the system was capable of performing its safety function with the identified degraded condition.
Risk Insights Using the plant PRA, risk is unaffected since the Unit 2 HPCI was maintained available. As a result, there is no change in Core Damage Frequency (CDF) due to the Unit 1 HPCI watertight door being found open.
E. CORRECTIVE ACTIONS
Immediate:
- Verified the watertight door was shut and dogged.
- Established tour requirements to check watertight door status.
Follow-up:
- Briefings to the workforce conducted by department heads and senior management for individuals on site.
F. PREVIOUS OCCURRENCES
The station events database, LERs, and INPO Consolidated Event System (ICES) were reviewed for similar events at Quad Cities Nuclear Power Station. This event was caused by a human performance failure to close a watertight door.
No previous occurrences were identified in this search applicable to the circumstances of this event.
G. COMPONENT FAILURE DATA
Failed Equipment: N/A Component Manufacturer: N/A Component Model Number: N/A Component Part Number: N/A This event has not been reported to ICES since there was no equipment failure.