05000461/LER-2014-003
| Docket Number | |
| Event date: | 06-22-2014 |
|---|---|
| Report date: | 09-12-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4612014003R00 - NRC Website | |
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
PLANT AND SYSTEM IDENTIFICATION
General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in text as [XX].
EVENT IDENTIFICATION
Misapplication of Support System Technical Specification Requirements Resulted in Implementation of Non- Conservative Guidance for Removal of Essential Switchgear Heat Removal System from Service
A. Plant Operating Conditions Before the Event
Unit: 1 Event Date: 6/24/14 Mode: 1 Mode Name: Power Operation
B. DESCRIPTION OF EVENT
Event Time: 1400 CDT Reactor Power: 97.8 percent A planned system outage of the safety-related Division 1 Essential Switchgear Heat Removal (VX) system began on 6/22/14 at 2015 hours0.0233 days <br />0.56 hours <br />0.00333 weeks <br />7.667075e-4 months <br />, and was restored to service on 6/25/14 at 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />.
During the outage, a NRC inspector questioned the station practice of entering the actions of the Clinton Power Station (CPS) Operational Requirements Manual (ORM) 2.4.9, Essential Switchgear Room (VX) Ventilation, when the VX system is inoperable without entering any Technical Specification (TS) Limiting Condition for Operation (LCO) Conditions and Required Actions for the systems that the safety-related non-TS VX system supports.
ORM 2.4.9 requires that the areas cooled by the Divisions 1, 2 and 3 VX systems be maintained less than 95 degrees Fahrenheit (F) when the equipment in the associated area is required to be operable. This is satisfied by verifying area temperatures less than or equal to 95 degrees F every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Should temperatures be observed to be above 95 degrees F, then ORM 2.4.9 directs that temperatures should be restored to less than the limit within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, or place the safety-related VX cooling coil [CCL] into service. If area temperatures increase to greater than 104 degrees F, then the ORM directs action to restore the area temperatures within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and declare the affected equipment in the area inoperable. The essential areas that the VX system supports include the Divisions 1, 2 and 3 switchgear [EB] [ED] areas, the Divisions 1, 2, 3 and 4 battery [EJ] rooms, cable spreading rooms, and the Divisions 1, 2 and 4 inverter [EF] rooms.
As a result of the question and until the station resolved the acceptability of the practice, Operations issued Night Order 2014-04 on 6/27/14, to direct operators to declare the following systems inoperable any time a safety-related divisional VX system is not functional in its ability to maintain area temperatures: Divisional DC Sources (TS LCOs 3.8.4 and 3.8.5); Divisional Inverters (TS LCOs 3.8.7 and 3.8.8); and Electrical Power Distribution Systems (TS LCOs 3.8.9 and 3.8.10). The Night Order remains in effect pending resolution for this event.
On 7/17/14 during investigation of this issue, the station determined that TS LCO 3.8.4 and TS LCO 3.8.9 should have been entered on 6/22/14. The required restoration time for an inoperable Division 1 DC source or an inoperable Division 1 AC electrical distribution subsystem is 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> respectively, otherwise the plant is required to be in Mode 3 within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> (that is, 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> and 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> respectively from entering the LCO actions).
During this event, the Division 1 VX system was out of service for 63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> and 45 minutes; therefore the required time allowed by Technical Specifications was exceeded and this event is reportable as a condition prohibited by Technical Specifications per 10 CFR 50.73(a)(2)(i)(B).
The CPS TS has never had any explicit requirements for the VX system; however, the Updated Safety Analysis Report describes the VX system. In accordance with the design basis, functionality of the VX system is required for ensuring adequate heat removal to limit the maximum temperatures in the essential areas consistent with equipment ambient temperature ratings and requirements under normal or abnormal station conditions.
Clinton Pc .ilatiatation, Unit 1 05000461 For the switchgear cooling portion of the VX system, independent redundant cooling trains are provided for each of the three divisional switchgear areas with one train being non-safety-related and the other safety-related. The non- safety-related train has a cooling coil supplied with cooling water from the plant chilled water system [KM]. The redundant safety-related train contains a direct expansion refrigeration unit [RFU] supplied with cooling water from either the safety-related shutdown service water (SX) system [BI] or non-safety-related plant service water (VVS) system [KG], depending on plant conditions. The safety-related and non-safety-related cooling trains utilize a common supply air distribution network. The safety-related cooling train is utilized during abnormal (accident) conditions or upon failure of the non-safety related switchgear heat removal train.
The Bases for TS Surveillance Requirements 3.7.1.2 and 3.7.2.1 for verifying SX valve positions supports the position that if both the non-safety-related and safety-related VX subsystems were to become inoperable, the actions for the SX system would be entered and the actions in the supported system LCO may be delayed per LCO 3.0.6. This position is based on the fact that the SX system is the ultimate cooling medium for the electrical equipment and that if an SX subsystem is inoperable, then the associated equipment is also inoperable. LCO 3.0.6 allows 'When a supported system LCO is not met solely due to a support system LCO not being met, the Conditions and Required Actions associated with this supported system are not required to be entered. Only the support system LCO actions are required to be entered." It should be noted that VX is not a TS system and thus LCO 3.0.6 does not apply to the VX system.
CPS has followed the practice of not entering TS Required Actions for maintenance activities affecting the safety- related portion of the VX system since 2001 when the station implemented procedural requirements allowing VX system outage time up to 14 days without declaring the affected divisional equipment inoperable as long as the redundant VX subsystem is operable and the safety-related VX chillers on the other divisions are operable. If both the safety-related and non-safety-related VX subsystems become inoperable, then the actions of the SX system may be entered and the actions of the supported TS system delayed per LCO 3.0.6.
In 2005, a revision to the ORM was implemented to require area temperatures to be maintained below limits. Shortly following that revision, procedural requirements were changed to not enter any TS actions as long as area temperatures were kept below the ORM limits.
The station has determined that current station practices (stemming from procedure changes made in 2001 and a revision to the ORM made in 2005) were the result of the misapplication of support system TS LCO requirements. In this instance, the station applied LCO 3.0.6 guidance to a non-TS support system (that is, VX) as it would to TS support systems. This resulted in the guidance contained in procedures and ORM 2.4.9 to be non-conservative.
During the investigation of this event, a letter from the NRC to Clinton Power Station in August 1989 was found that provided the position regarding inoperability of systems (including the VX system) providing a support function. The position in the letter indicates that the TS definition of operability and the remedial actions for the supported equipment apply when the VX system is not capable of performing its specified function.
A review of the station narrative logs was performed to identify previous occasions when the station did not enter TS LCO 3.8.4 and/or TS LCO 3.8.9 when VX was removed from service in excess of TS requirements. This review identified that on seven additional occasions in the last three years use of ORM 2.4.9 has resulted in exceeding the required time allowed by TS.
During each of these outages, and the outage from 6/22/14 to 6/25/14, the temperatures did not exceed the design basis temperature for the affected areas. In addition, there were no instances of both Divisions 1 and 2 of the VX system being inoperable at the same time.
Issue Reports 1674754 and 1683023 were initiated to document and investigate this event.
C. CAUSE OF EVENT
The apparent cause of this event is misapplication of support system TS LCO requirements to the VX system which resulted in the implementation of non-conservative guidance into station practices in 2001 and 2005 due to misunderstanding of the licensing basis. In addition, the station did not know that there was a letter from the NRC issued in August 1989 on the subject of support system inoperability when changes to procedures and the ORM were made in 2001 and 2005.
D. SAFETY CONSEQUENCES
This event had no actual nuclear safety consequences. During each of the VX system outages when TS LCO 3.8.4 and TS LCO 3.8.9 were not entered, temperatures for the affected areas were monitored and never exceeded the design basis temperatures. Also, there were no instances of Divisions 1 and 2 of the VX system being inoperable at the same time.
In the event of the safety-related VX systems being inoperable, the plant areas cooled by the divisional VX systems are also provided cooling from non-safety-related Switchgear Heat Removal equipment. Thus cooling and functionality of the associated electrical equipment will be provided for many plant transients and accidents.
While there are events that can disable both the safety-related and non-safety-related switchgear heat removal systems for the associated electrical equipment areas, equipment functionality will be sustained for a period of time because of the relatively low electrical heat loads in the switchgear rooms combined with large surface areas for walls, floors and ceilings of the rooms. These structural elements are generally constructed of relatively thick reinforced concrete and would serve as a massive heat sink to limit room temperature increases for shorter duration losses of switchgear heat removal. In the longer term, temperature increases could be limited by recovery of either safety-related or non-safety-related switchgear heat removal systems or other measures such as opening doors to allow cooler external air to enter the switchgear rooms.
E. CORRECTIVE ACTIONS
ORM 2.4.9 will be revised to delete requirements that are currently in place and references this ORM will be removed from procedures.
The Bases for TS Surveillance Requirements 3.7.1.2 and 3.7.2.1 will be revised to remove the allowance to declare SX inoperable when a supported ventilation system is inoperable.
A briefing will be conducted for appropriate personnel to reinforce the definition of operable-operability to address the lack of knowledge of TS support system requirements as applied to non-TS support systems.
F. PREVIOUS OCCURRENCES
None
G. COMPONENT FAILURE DATA
Not applicable, no components failed during this event.