05000483/LER-2003-007
| Callaway Plant Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4832003007R01 - NRC Website | |
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I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
This event is being reported under multiple criteria. It is being reported under:
- 10CFR50.73(a)(2)(i)(B), a condition prohibited by Technical Specifications
- 10CFR50.73(a)(2)(vii), common-cause Inoperability where a single condition caused two independent trains to become inoperable in a single system designed to mitigate the consequences of an accident.
Initially this event was also classified as reportable per 10CFR50.73(a)(2)(v)(D), as an event or condition that could have prevented fulfillment of a safety function to mitigate the consequences of an accident. Subsequent evaluations have determined the dose to Control Room personnel would not have exceeded the FSAR reported value. The ability to maintain dose levels to Control Room personnel below the FSAR and regulatory limits demonstrates that this event did not represent a safety system functional failure.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
Callaway Plant was in Mode 1 at 100 percent power.
C. STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS THAT WERE INOPERABLE AT THE START
OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
Not applicable for this event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES
On July 17, 2003 with Callaway Plant operating at 100 percent power, an error was discovered in Request For Resolutions (RFR) 14826 and 16672 that had approved leaving the Health Physics (HP) Access entrance doors 32201 and Hot Lab Door 32282 open.
These doors are pressure boundary doors between the Control Building and the Communication Corridor and are required to be closed during a Control Room Ventilation Isolation. Following a Control Room Ventilation Isolation, the HP Access Control fan coil unit SGKO3 would cause air in the HP Access Control area to commingle with portions of the Control Building that are credited in the Control Room radiological consequences analysis of record.
With the doors open, air from the HP Access Control area must be considered to be outside air in the radiological consequences analysis.
The entrance to HP Access is a high traffic area and the entrance doors are a set of large missile doors that serve as a fire and pressure boundary. Revision A of RFR 14826 was performed in 1994 and approved leaving the HP Access area doors open to reduce repeat door maintenance and the chance for personnel injury from these heavy doors.
Radiological Engineering and the HVAC System Engineer had performed a review and concluded that leaving the doors to HP Access open would not affect the Licensing Bases analysis. These reviews did not identify that SGKO3 continues to operate after a Control Room Ventilation Isolation Signal (CRVIS) and that operation of SGKO3 following a CRVIS would cause air from the HP Access Control area to commingle with portions of the Control Building credited in the Licensing Bases radiological consequences analysis of record for the Control Room. It was identified that having these doors open would impact the Fire Protection plan and required a Fire Barrier Integrity Record to be generated. This record documented the requirement for a continuous fire watch with these doors propped open. One additional action required by RFR 14826, was to establish controls that required the HP Access doors to be closed upon declaration of a plant emergency. At that time, Key Issue was located within the HP Access area and the requirements to close the HP Access doors and act as fire watch, were assigned to the Security individuals manning Key Issue. Unfortunately, during the RFR review process neither engineering group identified the disallowed air flow path associated with SGKO3.
In 1998, Revision B of RFR 14826 was issued. Key Issue had been relocated outside of HP Access and Revision B addressed re-assignment of fire watch and door closure responsibilities. In Revision B it was determined that propping the doors open did not require a compensatory fire watch per current plant procedures, but that the doors would still require closure during plant emergencies. Thus, Security personnel still retained the requirement to close the HP Access doors during plant emergencies. In Revision B, the errors in air flow pathways from Revision A were not identified and were carried forward into Revision B. Additionally, in both Revisions A and B, accurate response times for closing the HP Access doors were not determined.
In 1996, RFR 16672 performed a similar evaluation which allowed Hot Lab door 32282 to remain open.
On 7/17/03, when it was identified that leaving the doors at HP Access open created a pathway for outside air to commingle with portions of the Control Building credited in the analysis of record, the doors were closed and a plant bulletin was issued notifying plant staff that these doors were to remain closed except during normal entrance and egress. Additionally, instructions were issued to Health Physics and Security personnel to maintain the doors closed.
An evaluation was performed to quantify the impact of the open doors on post-accident consequences to Control Room personnel. The responsibility to close the doors post-accident was assigned to a Security Officer. Emergency declarations occur within 15 minutes of an event, and it was determined that upon declaration of an emergency, a Security Officer would close the doors within 10 minutes. The evaluation conducted was therefore performed assuming that a pathway for outside air to commingle with Control Building air was available for the first 25 minutes of the event, with the 25 minutes being comprised of:
- time from event initiation to emergency declaration — 15 minutes
- time from emergency declaration to door closure — 10 minutes Utilizing licensing basis assumptions determined post-LOCA thyroid dose to Control Room personnel would be approximately 31.5 REM. This represents a more than minimal increase of accident consequences above the Final Safety Analysis Report (FSAR) reported value of 25.55 REM. Additionally, this exceeds the GDC 19 regulatory limit of 30 REM. These results were determined on 8/8/03, and this event was reported as 8-hour Event Notification#40053 for an Unanalyzed Condition per 10CFR50.72(b)(3)(ii)(B) at 1254 CDT, 8/8/03.
Additional evaluation utilizing as-found values from Callaway's ILRT results determined that post-LOCA thyroid dose to Control Room personnel would be approximately 11.7 REM. This is below the FSAR reported value of 25.55 REM, as well as the GDC 19 regulatory limit of 30 REM, thereby demonstrating the safety function to protect Control Room personnel was maintained for the period in question.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL ERROR
During plant walkdowns and design reviews in preparation for responding to NRC Generic Letter on Control Room habitability, a problem was identified regarding doors 32201 and 32282 at HP Access.
II. EVENT DRIVEN INFORMATION
A. SAFETY SYSTEMS THAT RESPONDED
Not Applicable for this event.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
Per Technical Specification 3.7.10 Bases, the Control Room Emergency Ventilation System (CRVES) is designed to maintain the control room environment for 30 days of continuous occupancy after a Design Basis Accident (DBA) without exceeding a 5 REM whole body dose to the control room staff. The 30 REM thyroid dose is considered equivalent to the 5 REM whole body dose. With the doors initially open at HP Access, and a door closure response time of 25 minutes, an evaluation performed by Safety Analysis shows that the thyroid dose to control room operators with door 32201 or 32282 open for the initial 25 minutes following a large break LOCA, is approximately 31.5 REM.
This represents a more than minimal increase in accident consequences described in Callaway's FSAR and exceeds the GDC 19 regulatory thyroid dose limit of 30 REM. .
Due to exceeding the thyroid dose limit stipulated in T/S 3.7.10 Bases, this event rendered the CRVES inoperable and constituted a violation of T/S 3.7.10. NUREG 1022 only requires an evaluation period of 3 years, thus this event represents a violation of T/S 3.7.10 for the 3 year period from 7/17/00 until 7/17/03 when the problem was identified and rectified.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
As was previously discussed, an evaluation was performed to quantify the impact of the open doors on post-accident radiological consequences. The results indicated that the open doors would result in a more than minimal increase in accident consequences as described in Callaway's FSAR. Additionally, the regulatory limit of GDC 19 would be exceeded. This evaluation was performed using the radiological consequence analysis methodology currently described in Callaway's FSAR.
Additional evaluations were performed using ICRP 30 Dose Conversion Factors (DCF). This evaluation concluded that post-accident consequences would be 22.2 Rem to the thyroid. This value would be bounded by the FSAR reported value and the GDC 19 regulatory limit. Additionally, it was noted that Regulatory Guide 1.195 would allow licensees, with prior NRC approval to use a thyroid dose limit of 50 Rem. Callaway has submitted a License Amendment Request to obtain NRC approval for the use of ICRP 30 DCFs.
Although the Regulatory Guide 1.195 dose limit and ICRP 30 DCFs are not currently part of Callaway's Licensing bases, they do demonstrate the limited safety implications of this event.
III. CAUSE OF THE EVENT
The cause was an error in an assumption in Engineering Evaluations which concluded that leaving the doors open would not affect the Licensing Bases analyses.
IV. CORRECTIVE ACTIONS
Corrective actions were to close the doors, plus issue a plant bulletin to maintain the doors closed. Signs were added to the doors indicating the requirement to maintain the doors closed. Specific instructions were provided to Health Physics personnel to maintain the doors closed. Additionally, Security officers have been informed that these doors are to remain closed at all times, and they will check these doors while on patrol.
The Licensing Impact Review (LIR) form used by engineering personnel to screen proposed plant changes has been revised since RFRs 14826 and 16672 were dispositioned. A new section of questions regarding Control Room Habitability has been added to the LIR form.
V. PREVIOUS SIMILAR EVENTS
A review of Callaway LER's from 2000 until present did not reveal any similar events.
A review of the Callaway Action Request System (CARS) was performed covering the last three years. Using key word "HP Access doors" and "blocked doors" text searches, no CARs were identified that revealed potential breaches of the Control Building pressure boundary, and thus potential violations similar to the issue addressed in this LER.
VI. � ADDITIONAL INFORMATION The system and component codes listed below respectively.
are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 System: � Not applicable for this event.
Component: � DR