IR 05000261/1991021
| ML14182A243 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 01/09/1992 |
| From: | Merriweather N, Shymlock M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML14182A240 | List: |
| References | |
| 50-261-91-21, NUDOCS 9201270050 | |
| Download: ML14182A243 (42) | |
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R UNITED STATES NUCLEAR REGULATORY COMMISSION REGION 11 101 MARIETTA STREET, ATLANTA, GEORGIA 30323 Report Nos.:
50-261/91-21 Licensee: Carolina Power and Light Company P. 0. Box 1551 Raleigh, NC 27602 Docket Nos.: 50-261 License No.: DPR-23 Facility Name: H. B. Robinson 2 Inspection Conducted: September 23, 1991 - October 25, 1991 Team Leader:
N.'Merriw ather, Team Leader bate Signed Team Members: R. Moore, NRC J. Dick, AECL L. Garner, NRC L. Maggio, EPM M. Miller, NRC J. Lindley, AECL Approved by:
M. Shymlock, Chief Date Signed Plant Systems Section Engineering Branch Division of Reactor Safety SUMMARY Scope:
This special, announced inspection was conducted in -the areas of design of electrical systems and related engineering activitie NRC Temporary Instruction 2515/107,
"Electrical Distribution System Functional Inspection (EDSFI)", issued October 9, 1990, provided guidance for the inspection Results:
The electrical distribution system at H. B. Robinson was capable of performing its intended functions under normal and postulated accident condition In the areas inspected, three unresolved items and one deviation were identifie The unresolved items involved:
marginal service water flow rate to diesels for 110% power (Findina 91-21-02),
E1/E2 equipment room ambient conditiors not evaluated (Finding 91-21-03),
and failure to establish surveillance procedures which adequately incorporate EDG loading requirements 911.01270050 9 2011 PDR. ADOC~
K 5O026
stated in the Technical Specifications (Finding 91-21-09).
The deviation (Finding 91-21-05) involved a failure to implement procedures for sampling the EDG fuel oil in accordance with a previous commitment to the NR Other team findings were in the areas of design calculations and documentation, electrical maintenance practices, and testing. A summary of team findings is provided in Appendix The team considered the licensee's design activities to be proactive in pursuing a design concern related to analyzing the fast bus transfer scheme and this was considered a strengt SUMMARY An Electrical Distribution System (EDS) functional inspection was conducted at the H. B. Robinson nuclear station over the period September 23 through October 25, 199 Led by Region II, the team was comprised of Region I inspectors, the senior resident inspector, and supplemented by contracted design engineer The team reviewed the Robinson EDS design with regard to compliance with regulations and licensing commitments, -design engineering standards, and accepted engineering practice.The process involved an examination of the application of EDS equipment in total system design from the non-safety switchyard to the safety-related load; a review of the as-built material condition of the EDS; a review of EDS maintenance and testing activities; a review of the design and operation of EDS mechanical support systems; and an assessment of the engineering and technical activities related to the ED The team concluded the Robinson EDS was adequately designed and maintained to accomplish its intended safety function. EDS material condition was good, and engineering and technical support for the EDS was adequat There is limited margin for future load growth on the emergency busses..The team noted that the licensee was aware of the limitations of the EDS and had mechanisms in place to monitor and control future load growth. It was the team's understanding that a project had been initiated to investigate possible alternatives to increase the emergency system margins. The team considered this action to be a strengt The team concluded that the Design Basis Reconstitution Program in conjunction with the PRA was a strength in resolving issues related to GDC 17 and single failure criteria. Although the grid load flow studies were not developed with controls equivalent to the calculation control program, the team concluded the studies were a strengt The studies provided the dispatcher adequate information on capacity and configuration requirements to support the switchyard voltage at Robinson Unit 2 for all accident conditions, thereby supplementing the intent of GDC 17 requirements for offsite circuit The team had several findings in the areas of design, maintenance and testin The findings did not indicate programmatic problems and had only limited safety significance, however, they should be given appropriate attention for timely resolutio These findings are discussed in the following paragraphs and summarized in Appendix The team identified that a mis-coordination existed on certain non-safety breakers in the 120 VAC instrument bus system which could render safety-related buses inoperable under a seismic event. The team noted that the licensee was well. aware of current industry issues and NRC Notices regarding fast bus transfer schemes and had taken action on the concern by authorizing a bus transfer dynamic simulation study. The team considered this action to be a strength. The team noted that the available service water flow to the EDG heat exchangers was less than recommended by the vendo This could impact EDG capacity with high lake water temperature and EDG load greater than 2500 K The team observed that the analysis was nonconservative with respect to modeling of the EDG heat exchanger This is considered to be an unresolved ite The team identified the safety-related electrical equipment room ambient temperature conditions had not been adequately analyzed. This is an unresolved item. The condition of the underground fuel-oil piping was indeterminant due to the failure of the galvanic corrosion protection syste Two examples of poor maintenance practices regarding sealing of spare cable ends and labeling electrical equipment were identified. The team identified problems with MOVs which involved a potential undetectable MOV failure mode that may not have been previously analyzed and two undersized motor starters in the RHR system for MOVs 744A and B. The team also identified that the EDGs had not been tested at nameplate rating (3125 kva) as required by In a dissenting opinion, licensee management stated their belief that the applicable operational surveillance test procedures tested the EDGs as required by Technical Specifications. This is considered to be an unresolved ite Within the areas inspected, one deviation was identified. The deviation involved the licensee's failure to implement a previous commitment to industry standards relating to EDG fuel oil storage tank samplin Not withstanding the above, the team concluded that the Robinson EDS was operable, E&TS was adequate to support EDS activities, and adequate design controls existed for ED.0 INTRODUCTION Previous NRC inspections of Nuclear Power Plants and various licensee event reports have identified conditions in the electrical distribution systems at various operating plants that could compromise the design safety margins of the plants. This resulted in part from a lack of proper E&TS, which resulted in the introduction of various design deficiencies during the initial design or during subsequent design modifications of the station EDS. Examples of some of these deficiencies were unmonitored and uncontrolled load growth. on safety-related buses, inadequate modifica tions, technically inadequate calculations, incorrect facility configuration, inadequate testing, improper application of commercial grade components, lack of fuse control, and improperly installed electrical connection The primary objective of this inspection was to assess the capacity of the H. B. Robinson EDS to perform its intended functions during plant operating and accident condition A secondary objective was to assess the capability and performance of the licensee's engineering organization in providing engineering and technical support for EDS activitie The team reviewed the Robinson.EDS design with respect to regulatory requirements, licensing commitments and pertinent industry standard The EDS components reviewed included the EDG and auxiliary support systems; the offsite circuits from the 115 and 230 kV switchyard, the startup and unit auxiliary transformers, the 4.16 kV switchgear and related equipment; the 480 VAC switchgear, load centers and motor control centers, the 125 VDC batteries, chargers and distribution systems; the 120 VAC distribution systems, HVAC for EDS equipment spaces; protective relaying and coordination; AC grounding and penetration protectio Additionally, the mechanical systems which are required to support the EDG were specifically examined. These included the air start system, lube oil system, fuel oil system, and water cooling syste There were two unique aspects of the Robinson EDS. The first was the use of 480 VAC emergency buses and 480 VAC ED The second aspect was that Robinson was not originally designed to meet GDC-17 with respect to 2 independent offsite circuits supplying the emergency bus. The licensee had implemented measures to meet the intent of GDC-1 Within this report FINDINGS are.identified and are defined as follows:
FINDINGS are facts.or conclusions related to how well the electrical distribution system meets its intended functio FINDINGS may indicate a requirement or an accepted industry practice that was not fully implemente FINDINGS may indicate discrepancies or omissions in documents where these problems could credibly result in the intended function being compromise The licensee's working knowledge of the design as well as their control of design documents may be the subjects of FINDING FINDINGS typically make statements about the need for corrective action.0 ELECTRICAL SYSTEMS 2. EDS Description The Robinson Nuclear Station was connected to the CP&L high voltage grid transmission system through two switchyards. Electrical energy generated by the main generator at 22 kV is transmitted to three single phase transformers by an isolated phase bus duct. These transformers step the voltage up to 230 kV and are connected to a 230 kV switchyard. The 230 kV switchyard is connected to five outgoing lines and to an adjacent 115 kV switchyard through two 300 MVA auto-transformer The 230 kV switchyard is of the breaker and a half design and the 115 kV switchyard is a split bus design incorporating two bus sectionalizing breaker The 115 kV switchyard has three outgoing lines. The. coal fired HBR-1 and a gas turbine generator are located adjacent to the nuclear unit but are not considered part of the off-site syste The supply to the station auxiliaries is provided by a 22 kV/4.16 kV unit auxiliary transformer connected to the main generator isolated phase bus and by a 115 kV/4.16 kV start-up transformer connected to the 115 kV switchyar During normal operation, the main generator through the unit auxiliary transformer supplies power to four of five 4.16 kV buses and the 115 kV offsite system, through the startup transformer, supplies power to the remaining bu Following a main generator trip these 4.16 kV buses normally energized by the unit auxiliary transformer are automatically transferred to the startup transforme The two Class 1E 480 VAC safety related buses (El & E2)
are normally connected to separate 4.16 kV buses via stepdown transformers. Bus E2 is connected to a 4.16 kV bus which is energized by the 115/4.16 kV startup transformer and bus El obtains power from a 4.16 kV bus energized by the 22/4.16 kV unit auxiliary transforme Two onsite safety related emergency diesel generators are connected via output circuit breakers to the 480 VAC safety related buses. Each EDG has a continuous rating of 2500 KW and a short term rating of 2750 KW at power factor. The continuous rating is based on a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> duty cycle while the short term rating is based on one 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> operation in any 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period. The EDGs are capable of starting a single 900 KW motor and produce power at 480 VAC. They are connected to redundant class 1E buse If a loss of bus voltage occurs the EDGs are automatically started and their circuit breakers closed. Blackout loads are automatically recon nected to the buses in sequenc The Class 1E 125 VDC system is split into two groups; each group comprised of one battery, two battery chargers, one DC motor. control center and two DC panel boards. The batteries are located within a single room with a metal protective barrier between them. The group 'A' battery has a rating of 525 A-H and the group 'B' battery a rating of 170 A-H. Based on load profiles each battery has sufficient capacity for 60 minutes of operation under emergency conditions without re-chargin Two class 1E 120 VAC main instrument buses are associated with each redundant trai These buses supply secondary-buses which have both safety and non-safety loads connected through isolating devices. On each train one main bus is supplied from a class 1E 480 VAC motor control center through a 7.5 kVA constant voltage transformer and the other main bus is supplied from a DC to AC inverter, also rated at 7.5 kVA, which is connected to a class 1E 125 VDC battery. An alternate supply to each bus is provided from one non-class 1E 480 VAC MCC. Transfer to this supply is manual only and is provided for maintenance purpose No automatic transfers to alternate sources are provided for these buse. EDS Review The team reviewed the adequacy of offsite power sources that supply power to the ED Calculations and analyses were reviewed to insure that electrical power of acceptable voltage, current, and frequency would be available to safety related equipment supplied by the EDS. The design ratings were compared to the equipment ratings to verify that acceptable margins existed. Additionally, plant walkdowns of the offsite and onsite power sources were performed to verify that equipment nameplate ratings and the installed configuration corresponds to the design requirements and is in agreement with the facility document The non-safety related medium voltage 4.16 kV and 480 VAC safety buses and their connected loads were reviewed to assess voltage adequacy, load current and short circuit current capabilities, equipment ratings, protective relaying, circuit breaker.coordination, cable sizing, and voltage relay applications. Also reviewed were load flow studies, testing and surveillance, General Design Criteria 17 compliance with single failure criterion, adequacy of the fast bus transfer scheme in terms of any effects on the safety systems, and applicable-separation requirement The Emergency Diesel Generators were reviewed to assess the EDG sizing adequacy and the transient and steady state loading capabilit The safety-related 120 VAC and 125 VDC systems were reviewed for short circuit capability, loading, minimum and maximum expected operating voltage,.and equipment sizing and ratings (e.g., batteries, chargers, transformers and inverters).
The specific components and portions of the EDS reviewed and the team's conclusions are discussed in the following paragraph.1 Conclusions The team concluded that the 115/230 kV system provided stable off-site power to the plant 480 VAC safety related buse The 480 VAC safety related distribution system was adequately designe No operability concerns were identified by the tea The EDGs were adequately sized, however, the licensee's EDG load studies indicated loading in excess of the continuous rating in some case Electrical calculations associated with the Class 1E 480 VAC system demonstrated that there is sufficient capacity-and voltage level to support the necessary safety-related load Equipment was rated properly for short circuit dut There was limited margin for future load growth on the emergency buses. The licensee was aware of load growth limitations and had established a mechanism for evaluation, monitoring, and control of future load growt Additionally, a project was initiated to investigate possible actions to increase the emergency system margin The team considers the licensee's action to be a strengt Protective relays and relay coordination were satisfactory. The licensee's actions in regard to the fast bus transfer dynamic analysis i-ndicated that the licensee is keeping abreast of industry issues involving the EDS and is seeking solutions to identified problem The team identified an occurrence of inadequate breaker coordination in the 120 VAC instrument bus syste.A seismic event could cause two non-safety loads in both trains to short circuit which could lead to the de-energizing of both instrument buses. This was considered to have minor safety significanc The team identified minor deficiencies in the 120 VAC calculations related to the establishment of the loads on the instrument buse.2 Offsite Power 2. Grid stability and reliability The team reviewed the licensee design to assure a reliable source of offsite power to the emergency buses. The stability of the offsite power source to support the plant during maximum expected loads on the transmission system was adequat In cases where the grid conditions potentially compromised the reliability of the offsite power supply to onsite emergency buses, due to lack of adequate grid voltage or capacity, appropriate contingency measures had been established to ensure reliable power to the emergency buse These measures are discussed in the following paragraph To assure that the transmission system was maintained in a configuration to support the voltage at Robinson the Nuclear Engineering Department had a formal agreement with the Transmission and Distribution Department to conduct engineering studies of the transmission system and develop voltag schedules for various network scenarios and configurations to maintain proper offsite capacity levels. These conditions were proceduralized in System Planning and Operations Procedure DTRM-GP-22 utilized by the system dispatcher. DTRM-GP-22 provided the dispatcher guidance for eastern area loads up to 9000 MW. The eastern area peak was approximately 8500 MW set on July 23, 199 In the event that adequate voltage and capacity to support Robinson could not be achieved the Transmission Department procedures required the dispatcher notify the plant operato Upon notification that the voltage could not be maintained the plant offsite
source would be declared inoperable and the emergency bus would be loaded on the diese The operator's actions were described in Abnormal Operating Procedure AOP-027, Operating with Degraded System Voltag In addition, CP&L established a working'committee which included both NED and T&D to review operating procedures and actual operation of the system and if necessary make recommendations for change The team considers the licensee's formal interaction with Transmission and Distribution and the resulting procedures and schedules developed to assure a reliable offsite power supply to be a strengt The team reviewed the transmission grid analysis which established minimum and maximum switchyard voltages to verify adequate voltages were availabl for safety-related components. It was determined that the minimum switch yard voltage required to support a LOCA had been established by NED as 112.9 Kv (see calculation RNP-E-8.002, Rev. 1).
For margin, 113.7.kV was used by the transmission department as the minimum allowable system voltage. They have taken this value, performed analysis, and established requirements (operation of capacitor banks and/or operation of the Darlington Plant IC turbines) to assure this voltage will be me These requirements were formalized in system dispatcher instruction DTRM-GP-2 The maximum expected high voltage levels occurred during light-load grid conditions. Several factors tended to raise.the voltage levels seen on the power system during light-load periods. Examination of less typical combinations of factors demonstrated the Robinson 115 kV bus voltage may reach 119 k During light load periods (spring/fall in the early morning)
high voltages have been experienced on bus E Bus E2 is normally connected to the grid via 4.16 kV bus 3 and the Start-up trans former. Most other buses were powered from the generator via the Unit Auxiliary transforme Procedure AOP-031, Operation with High Switchyard Voltage, was established to avoid these overvoltages.. If high voltage was present on bus E2, the AOP required for a realignment on the 4.16 kV system and/or increasing load on bus E2 to increase the loading on the SAT, thereby reducing voltage on bus E Other means of reducing these overvoltages, such as reducing the Unit minimum MVAR output limit, were being examine The team investigated the minimum number of transmission lines required to be energized to assure plant voltages during a LOC The team concluded there was an adequate number of transmission lines supporting Robinson Unit 2. The number of transmission lines required to support a LOCA was dependent on a variety of system conditions such as system load, operating plants, energized transmission lines, and energized capacitor bank The Darlington IC electric generating plant was the most important source for assuring adequate voltage during a system peak particularly if Unit 1 and/or the capacitor banks were unavailabl Due to this apparent reliance on the Darlington plant, the team was concerned if the trans mission network would support Robinson Unit 2 without Darlingto In
response the licensee performed an analysis assessing the impact on Robinson Unit 2 from postulated failure of Darlington 230 kV bus and its ability to supply power from the Darlington plant and other transmission sources connected with this bu Under this condition, the licensee demonstrated adequate voltage would be available i~n the switchyard in the event a LOCA were to occur at Unit 2. This analysis resolved the team's concerns on the issu. Degraded Grid Voltage Protection The team reviewed the degraded grid voltage protection scheme and was concerned with the protection relay setpoints. The degraded grid voltage relays were set to disconnect the 480 VAC emergency buses from offsite power and transfer the buses to their associated emergency diesel generators at 415 plus or minus 4 Volts. The problem with this setpoint was it allowed operation of continuous-duty motors at voltages less than their minimum rating (typically 90 percent of nameplate rating).
The DBR determined that the degraded grid voltage setting was originally based on minimum contactor pick-up voltage requirements at the MCC leve As a result the licensee established operator intervention under abnormal operating procedure A0P-027, when responding to a low voltage alarm at 115 kV (plus or minus 1 kV).
The operator was procedurally required to monitor the 480 V emergency bus voltage and transfer the buses to their respective diesel generators should the voltage continue to decrease to the analyzed limit for maintaining minimum rated voltage at safety-related motor The licensee was-relying on manual operator action for a function that should be an automatic relay functio This was an interim corrective action and the licensee has been communicating with NRC in development of long term corrective actions. The licensee was proceeding to alleviate the need for operator intervention by replacing degraded grid relays with new relays. The new relays support a setpoint increase with lower pickup to dropout rati Also, the licensee was performing an analysis to determine an appropriate setpoint upon which a TS Change Request will be submitted to the NRC. The team concluded this issue was being adequately addresse.3 Medium Voltage and Safety Related 480 Volt Systems 2. General Design Criteria 17 Certain provisions of GDC-17, such as two independent circuits from the transmission network to the onsite electrical distribution system and the current definition of an electrical system single failure, were not incorporated in the design of HBR-The licensee's DBR Program in conjunction with the PRA was an acceptable method to identify and resolve issues related to GDC-17 and the single failure criteria. Examples where these methods were applied were reviewed by the team and found to be acceptable. The licensee's transmission system load flow studies provided
the dispatcher with the necessary information on capacity and configura tion requirements to support plant operations under accident condition. Validation and Verification of Computer Programs The team reviewed the results of the licensee's validation and verification analysis for the computer software used by.design to perform various electrical calculations (e.g., short circuit, voltage drop, and load flow analysis), draft time current curves, and calculate raceway percent fill and seismic loadin In general, the validation and verification program was found to be adequat However, the team found that the CAMS software used to calculate raceway percent fill and seismic loading had not been validated or verified prior to its use as required by Nuclear Engineering procedure. In response to this finding the licensee developed a Design Guide (DG-V.78)
and completed the validation and benchmarking for the CAMS software features prior to the end of the inspectio The team reviewed the completed Design Guide and the benchmarking results of CAMS and found them to be adequate to verify all program feature. Fast Bus Transfer The team reviewed the fast bus transfer scheme which provided automatic transfer from the unit auxiliary transformer to the start-up transformer upon a reactor or turbine trip, opening of generator output breakers, manual operator transfer, or generator/transformer fault tri The transfer control scheme was adequate, however, the team was concerned that the fast bus transfer scheme had not been analyzed for possible excessive difference in voltage between the auxiliary load bus and the incoming power source. Additionally, transfer time (cycles per second)
has not been determined. These issues are current industry issue The licensee was cognizant of the issues and related NRC generic communications and has demonstrated an approach to the resolution by authorizing EBASCO to perform a bus transfer dynamic simulation stud The licensee's demonstrated knowledge of the industry issues, and the proactive investigation and scheduling of a computer bus transfer analysis were considered a strengt. Cable Ampacity Ratings The licensee's calculation, RNP-E-5.004, "Analysis for Power Cable Ampacity Study," indicated certain safety related AC power cables were carrying load currents in excess of their evaluated ampacities.. This was based on maximum ambient temperature (40 C) under LOCA conditions assuming cable trays contain over 43 conductors which requires maximum derating per IPCEA P-46-42 This would result in a loss of cable life based on exceeding the 75 C cable conductor temperatur The overloaded cables were replaced. Based on the number of cases of marginal ampacity revealed by this analysis the licensee had initiated an engineering project PCN 88-192/04, to further evaluate and resolve the marginal cables and further analyze safety related 480 volt, 120/208 VAC, 120 VAC, and 125 VDC cables
in the Reactor Auxiliary Building and the containment. The study was limited to areas containing safety related cables. The team concluded the licensee's actions to resolve this issue were appropriate. No operability concerns were evident although this could be a factor in plant life extension evaluation. Short Circuit Calculations The team concluded that there is little margin for future EDS load growth based on short circuit calculation The team reviewed computer program ASDOP calculation RNP-E-8.002, Re for short circuit on 4.16 kV buses 1,2,3,and 4; 480 VAC dedicated shutdown buses; 480 VAC safety-related buses El and E2; 480 VAC MCCs 5 and 6; and 208 VAC MCCs 9 and 1 The analyzed cases demonstrated adequate margin on the buses with no EDGs contributing to the short circui The licensee also analyzed the case with one EDG being exercised on either bus El or E2. The results of this calculation demonstrated bus ratings were exceede The licensee recalculated short circuits at El and E2 taking credit for internal circuit breaker impedances and less conservative voltage level The recalculation found bus El for symmetrical short circuit to be the worst case with a calculated value of 84.5 KA symmetrical and a rating of 85 KA symmetrica This provides a margin of only.5 percent for future growt. Voltage Drop Calculations The team found the calculations for postulated worst case loading to be adequate with acceptable margins. However, the demonstrated margins show that future load growth is.limite The team reviewed ASDOP calculation RNP-E-8.002, Rev.1 for voltage drop on non-safety 4.16 kV buses 1, 2, 3, and 4; 480 VAC dedicated shutdown DS bus; safety related buses El and E2 and safety related 480 VAC MCCs 5, 6, 16, and 18; and safety.related 208 VAC MCCs 9 and 10. The minimum steady state voltages with 115 kV switchyard voltages at minimum predicted value of 113.7 kV for buses El and E2 are calculated at 444 VAC and 446 VAC, respectively. 'Bus El with 444 Volts calculated and with a minimum require ment of 429 volts had a positive margin of 3.5 percent. Bus E2 with 446 VAC calculated and minimum required of 428 volts had a positive margin of 4.2 percent. Safety-related 480 VAC MCCs 5,6,16, and 18. with calculated values 436, 439, 440, and 442, and with required minimum values of 420, 423, 419, and 419 have positive margins of 3.8%,
3.8%,
5.0%,
and 5.5%,
respectively. The 208. VAC MCCs 9 and 10 with calculated values 189 and 188, and with minimum required 180 and 181 have positive margins of 5.0%
and 3.9%, respectivel The minimum transient "ride-through" voltages for emergency buses considers minimum allowed motor terminal voltages while starting safety related motors during LOCA with the switchyard at 113.7 kV. Buses El and E2 with calculated voltage of 408 VAC and 410 VAC, and both with minimum required 362 VAC had margins of 12.7% and 13.3%, respectively. The 480 VAC MCCs 5, 6, 16, and 18 with calculated. values 399, 403, 384, and 385
and minimum required values 353, 356, 351, and 351 had positive margins of 13.0%, 13.2%, 9.4% and 9.7%. The 208 VAC MCCs 9 and 10 with calculated values of 173 and 172 and with required values 158 and 159 had positive margins of 9.5% and 8.2 %.
2. Load Capacity Calculations The team reviewed ASDOP calculation RNP-E-8.002, Rev.1 for loading on the unit auxiliary and start-up transformers; non-safety 4.16 kV buses 1, 2, 3, and 4; 480 VAC non-safety related buses 1, 2A, 2B, 3, 4, and 5;,480 VAC dedicated shutdown DS bus; safety related emergency 480 VAC buses El and E2; and MCC 9 and 10 480/208 VAC transformers. The team found loading to be adequate but noted safety-related buses El and E2 were marginal. Bus El with a 4000 A continuous rating and 3977 A calculated load had a.6%
margin. Bus E2 with 4000.A continuous rating and a 3923 A calculated had a 1.9% margi The 4.16 kV buses 1, 2, 3, and 4 were marginal with calculated 3,114, 3,114, 2,816, and 2,816; and with maximum allowed currents of 3,257 A (value based on transformers being restrictive component associated with the bus); the margins were 4.4%, 4.4%,
13.5%,
and 13.5%, respectivel The team considered the margins adequate for postulated worst case loading; however, as stated earlier for short circuit and voltage levels, there was little margin for future load growth. The team.noted the licensee had initiated project PCN 88-084/100 to investigate possible alternatives to increase load, voltage, and short circuit margins for the entire electrical distribution syste The licensee had a load tracking program in place per Design Guide DG V.10 which required that all proposed load changes to the electrical dis tribution system be evaluated, prior to implementation, to ensure these changes will not significantly reduce available margin.The team considered this program to be adequat. Control Circuit Voltage Drop The team reviewed voltage drop in control circuit loop analysis for 4.16 kV switchgear control circuits, control circuits on El and E2 buses, control circuits for 480 VAC, and safety related control circuits for 208 VAC safety related motor control centers. The team found the analysis to be adequat. Buses El and E2 Circuit Breaker Coordination The team reviewed circuit breaker coordination at the 480 VAC safety buses El and E2 and down to the connected MCCs and their loads..These calculations demonstrated coordination was acceptabl.3.10 Medium Voltage Protective Relayin The team reviewed the protective relaying schemes and the protective relay settings for the non-safety related 4.16 kV switchgear and found it satisfactor.4 Emergency Diesel Generators 2. Static and Dynamic Loading Analysis The team reviewed the licensee's calculation RNP-E-8.016, Static and Dynamic Loading, which verified the appropriate sizing of the EDG The calculation evaluated the postulated worst case loading conditions, loss of coolant accident plus simultaneous loss of off-site power with only one EDG available, which embraced all other emergency operating condition The calculation utilized electrical data provided either by equipment manufacturers or standard NEMA motor dat The EDG manufacturer (Colt)
performed the dynamic loading analysis of the EDGs, using.its own computer program. The team considered the methodology used for both calculations to be satisfactory and the conclusion appropriat The dynamic analysis verified the minimum EDG output terminal voltage during the loading sequence was 81 percent of its nominal 480 V value and the maximum frequency drop was below 5 percen These values were within the criteria provided in Appendix A of IEEE Standard 387-1984 and were therefore considered satisfactory. Data from the transient analysis was used to verify that voltages on buses supplied from the EDGs did.not dro below minimum allowable levels during the EDG loading sequenc All bus voltages were found to remain within the. acceptance criteria except for two 208 V buse The' licensee stated this was a transient di~p and
.therefore motors on the buses would not stop operating; however, they were planning the installation of new transformers to rectify the proble The-static analysis determined the maximum total load on EDG 'A' was 2500 KW and on EDG 'B' was 2528 KW. The maximum loads occurred at a time of forty (40)
minutes following the LOCA/LOOP even The surveillance tests on the EDGs did not load EDG 'B' to the maximum value shown by the cal culation. The licensee indicated that steps will be taken to modify the tests and also to revise the UFSAR to reflect the load values shown in the calculatio The static analysis verified that the EDG was capable of starting the largest motor when all other safety related loads were operatin. EDG Protection The team reviewed four recent calculations relating to EDG protectio These covered:
EDG ground overvoltage rel-ay, EDG reverse power relay settings, EDG voltage permissive relay (27)
set points and EDG neutral grounding resistor sizin The calculations indicated that the existing protective devices meet the calculated requirements. The team considered the calculations to be technically accurate and well prepare The licensee indicated that two additional calculations were planned to evaluate EDG ground overvoltage relay setpoints and -EDG voltage controlled overcurrent relay setpoint. EDG Load Sequencing System The team reviewed the EDG load sequencing system and noted that an acceptable design was in plac New digital, solid state, class 1E qualified Agastat timing relays had been installed. These provide.greater accuracy and less drift than the original pneumatic relay Interposing relays operating off of 120 VAC instrument buses were used to operate the motor feeder breaker.5 Class 1E Low Voltage AC Systems The team reviewed Class 1E 120 VAC Vital Bus calculations and identified minor deficiencie For example, the method of establishing channel loading relied on measurements rather than manufacturer's data. Secondly the minimum voltage at devices connected to the system had not been determined. The licensee stated that an instrument bus upgrade project was underway which will address these deficiencies and the overall configuration of the syste The team reviewed the Instrument Bus Channel Loading Calculation, RNP-E-1.003, which established loading on each channel based on measurements taken over a 3 month period. This calculation verified that the loads on each main bus were conservatively below the rated values of the.associated CVTs and inverters under all normal operating condition The inverter on the 'B' train was restricted to a 5 kVA rating because of the limited capacity of the 125 VDC batter The licensee demonstrated that loads under accident conditions would not change significantly from normal condition The team reviewed a coordination study for the 120 VAC instrument buses calculation RN1.07-E-37-F, which verified protective device coordination was achieved, with two exception These exceptions were of minor safety significance and related to the circuit breakers.which feed buses IB7 and IB9.from IB2 and IB4 respectively. Circuit breakers to non-safety loads connected to 1IB7 and IB9 have the same rating (30A)
as the feeder breakers. The team postulated that in the event of an earthquake, short circuits could occur in the non-safety loads and because of the non coordination, the breakers supplying IB7 and IB9 would trip thus completely de-energizing the buses. In response to the team's concern the licensee evaluated the safety loads supplied from IB7 and IB The licensee was able to demonstrate that sufficient instrumentation would remain available to put the plant into a safe condition utilizing power from the other instrument buse The licensee indicated that new 50A circuit breakers to supply instrument buses IB7 and IB9 would be installed. The lack of coordination is a identified as a team finding (see Appendix A, Finding 91-21-01).
The team reviewed a preliminary calculation, "Instrument Bus Voltage Evaluation" RNP-E-1.005, which determined whether bus voltages, would remain within the established criteria when new instrumentation and control loads were added during refueling outage #1 The calculation
demonstrated that the bus voltages would remain above the minimum values provided that the loads, on each channel did not exceed the stated CVT and inverter load limit The given limits enveloped the existing loads as calculated in RNP-E-1.003 and the applicable calculation verified that when the new loads were taken into account, adequate margin still.existe The team concluded that the system had adequate capacity based on the data presente.6 Class 1E 125 VDC System The team reviewed six calculations for the class 1E 125 VDC system. These included:
short circuit study, load profile and battery sizing, DC voltage profile, minimum inverter voltage verification and battery charger sizing. These calculations were evaluated against the requirements of IEEE Standards 485-1983 and 946-1985 and found to be acceptabl The licensee indicated that future plans call for the re-habilitation of the 125 VDC system including the creation of separate battery rooms and the removal of the 125 VDC distribution gear from the battery roo The team considers that this would be a positive ste The team determined that the present system was adequate in terms of capacity and protectio.7 Containment-Electrical Penetrations The team asked for assurance that the containment electrical penetrations were capable of:
a) continuously carrying full load currents and b)
withstanding short circuit current In response the licensee provided two hand calculations. One evaluated a 350 Hp motor (HVH fan) supplied from the class 1E 480 VAC switchgear and the other a 10 Hp motor supplied from a 480 VAC MCC. The results of both calculations.verified the ratings of the penetrations were not exceeded. The team reviewed the calculations and found them to be technically accurat The team noted that the licensee's DBR project included a study that will assess all penetrations in terms of individual full load current and short circuit current capability. *.The study will be based on the original penetration manufacturer's data, the station load data and the.bus short circuit level The team reviewed the scope of work document and a preliminary first copy of the assessment and concluded that the approach being followed was appropriate. The team also noted that the requirements for containment penetration leakage detection, and environmental and seismic qualification of the penetrations had been adequately addresse.8 Grounding of AC Systems The Robinson plant utilized a high resistance grounding. system which allowed continued operation with a single ground fault. Ground detection relays provided annunciation but no automatic trip. The class 1E systems'
grounding will be analyzed as an element of the DBR project which will analyze the overall grounding system. This analysis will determine if the original design was adequat The team evaluated the EDG neutral
grounding resistor and relay selection calculations and found them to be acceptable. A study prepared by the licensee in response to a question by the team indicated that the station ground protection schemes were adequat.0 MECHANICAL SYSTEMS The team reviewed and evaluated the adequacy of mechanical systems required to support EDS during normal operations and postulated accident These systems included the EDG and EDG. support systems, e.g. diesel fuel oil storage and transfer, air start, cooling water, lubrication oil, and the air exhaust and intake systems. Also reviewed was the plant service water interface with the EDGs. The team reviewed the HVAC for spaces containing safety related electrical equipment.to determine if equipment ambient conditions were maintained in accordance with vendor recommenda tions. Additionally, the anticipated accident mechanical loads which were used in the licensee analysis of the EDG loading were reviewe Documents reviewed included applicable portions of the UFSAR, engineering and vendor documentation, operating and maintenance procedures, mechanical system calculations and. drawings, pump performance curves, equipment performance data sheets, and EDS related modification packages. The team verified that the licensee had documentation reviewed and approved by design to support the seismic qualification of EDS components. However, the adequacy of this documentation. was not assessed as part of this inspectio.1 Conclusions The team concluded that the.design and operation of the mechanical systems supporting the EDS were adequat However, a number of items were found which merit further attention by the licensee. In the EDG accident load analysis, the containment fans may draw more power than stated in the calculation assumption which would reduce available loading margi The available service water flow to the EDG heat exchangers was less than recommended by the vendor. This could impact EDG capacity with high lake water temperature ( >95 degrees F) and EDG load greater than 2500 KW (100 to 110 percent load).
The licensee's analysis for ventilation of the E1/E2 safety related electrical equipment rooms under normal and accident conditions was found to be inadequat The heat loads had not been analyzed to determine ambient temperatures and the subsequent.impact on equipment. The licensee has initiated an analysis of this conditio The licensee was unable to determine the status of the EDG underground fuel oil piping with respect to galvanic corrosion protectio The team was concerned with the condition of this piping due to the possibility of corrosion induced reduction in pipe wall thickness which could affect the seismic load capacity of the line The licensee initiated action to address this concer Performance of fuel oil sampling was not in accordance with industry standard practice related to ensuring a representative storage tank sample. The licensee initiated action to address this issu.2 EDG Loading The team reviewed the licensee's postulated mechanical equipment loading values used in the EDG loading calculation. This consisted of reviewing equipment performance data and determining accident condition loads then translating these into electrical load values. The results were generally close to the values computed by the license.3 EDG Support Systems The systems required to support the operation of. the diesel generators were the jacket water, air starting, lubricating oil, combustion air intake, combustion exhaust, and the instrumentation for the alarm and trip function The team noted that lubricating oil pressures could be lower than the pressure in the jacket water system so that any leakage could be into the lubricating oil system which was opposed to normal industry practic Water forms emulsions which clog passages and could prevent, proper lubrication, and was the cause of major repair work on EDG 'A' in the pas The UFSAR indicates that the air start system for each diesel engine is sufficient for a 10 second attempt to start followed by 7 cold start Although the team identified minor inaccuracies in the verifying docu mentation, the air start capacity was essentially as state.4 Plant Service Water Interface The service water flow for the EDG heat exchangers was less than the manufacturer recommendations. The licensee had previously identified this condition and developed evaluations to address this issue concluding that the available flow was adequate for all postulated condition While the team agreed that adequate service water flow existed for most conditions, there was uncertainty regarding the adequacy of flow during high lake water temperatures and EDG load greater than 2500 KW. A recent transient analysis (discussed in paragraph 2.4.1) indicated the possibility of EDG loading greater than 2500 KW during certain accident scenario The EDG manufacturer's flow recommendation for 95 degrees F service water (SW)
was 600 gpm for operation at 100% electrical power (2500 KW output)
and 700 gpm for 110% electrical power (2750 KW output).
SW verification tests have shown that the SW flow rate to each EDG following a LOCA would be in the order of 550 gpm. A number of analyses were performed.to verify the functional capability of the EDG's with the reduced SW flow rate The analyses submitted to the team for inspection were based on a variety of assumptions, some of which were conservative in the context of ensuring adequate cooling flow, and others which were not. All analyses used the data from a manufacturer's drawing specifying the EDG heat exchanger conditions and performance, (Dwg 11 905 210) but for which the supporting manufacturer's thermal analysis was apparently not locatabl Essential information for the use of this drawing include its purpose i.e. design, testing, installation., mid-life performance, et each of which would require different margins on the parameters and the test conditions under which the measurements were mad Furthermore, the actual heat loads to be dissipated by the heat exchangers depend.on specifics of the diesel installation and any modification The analyses assumed the design drawing information was the result of manufacturer testin Thi assumption was inaccurate. The.manufacturer could not verify that a 11 percent load test had been performed. This test would have supported the licensee's conclusion regarding adequate service water flow for EDG operation greater than 2500 K The manufacturer's representative also said that fouling factor information should have been communicated to the heat exchanger fabricator along with Drawing 11 905 210, but doubted that Colt would have retained any formal record of that transfer. The fabricator, ITT Standard, could not be contacted for more informatio Actual installed heat exchangers'
performance data was not used in the analyse The licensee's analysis did not verify that service-water flow was sufficient to support EDG loading between 100 and 110 percent load when heat sink temperature was 95 degrees Predictions for cases with conditions close to those expected following LOCA's indicate LO and JW temperatures will be near or above alarm thresholds. Operation in this range permits very little margin for error. This margin may have been eroded by inaccuracies.in the design informatio These inaccuracies challenge the accuracy of the' licensee's overall conclusion (see Appendix A, Finding 91-21-02). Heating, Ventilation, and Air Conditioning The team reviewed HVAC design for the EDG rooms and other safety related equipment spaces to ensure ambient conditions were maintained within equipment design requirements. With the exception of the E1/E2 equipment room, the HVAC was adequately designe The original HVAC design for the E1/E2 room was based on contamination control rather the ambient temperatur The redundant buses powering vital equipment, as well as Reactor Protection and Safeguards Logic Cabinets, were located in this.Auxillary Building room. The licensee had not evaluated ambient conditions in this space and potential impact on safety related equipment due to rising room temperatures resulting from loss of ventilatio Room ventilation is lost during a loss of offsite powe Following identification of this issue by the team, the licensee initiated an analysis of the room heat loads and potential -ambient conditions during postulated accident conditions. The analysis provided by the licensee during the inspection was not fully conclusive..Although no operability issue was evident the issue required further evaluatio The licensee stated testing to accurately determine heat loads would be accomplished and the results evaluated to determine if further action is required (
Appendix A, Finding 91-21-03).
3.6 EDG Fuel Oil Storage and Transfer System 3. Inventory and Fuel Consumption The fuel oil system consisted of a diesel fuel oil storage tank, two transfer pumps, two independent underground FO-transfer lines to each day tank in each EDG room, piping from the day tank to the engines and connecting underground piping between tank Operating procedures required a minimum FO storage of 21,000 gallons in the DFOST and 15,000 gallons in the I-C Turbine FO tank. The capacities of those tanks was 25,000 gallons in the former and 95,000 gallons in the latter. With a DFOST low level alarm at 20,000 gallons, and assurance that fuel inventories in the I-C Turbine FO tank were always well above the required minimum 15,000 gallons, a minimum total inventory of 35,000 gallons was available. The team concluded that fuel storage requirements were me. Miscellaneous Fuel Oil Issues The team identified two issues related to the diesel fuel oi The first issue was the indeterminate condition of the underground fuel oil piping due to malfunction of the system which provided galvanic corrosion protection for this pipin A cathodic protection system was installed in 1982 which began to malfunction in 1988 and was discontinued in 199 The licensee was unable to determine what methodology was provided for galvanic corrosion protection on the original piping installatio Additionally the licensee could not verify the integrity of the pipin Galvanic corrosion could result in pipe wall thinning which would impact the seismic integrity of the piping. The licensee had already initiated actions to evaluate the Cathodic Protection System functionalit The licensee further stated that examination of a portion of the piping had been scheduled for 1992 (see Appendix A, Finding 91-21-04).
The second issue was related to the licensee's methodology for sampling of the EDG fuel oil storage tanks. The team concluded that the methodology used did not result in a representative sample of the tank contents. The applicable industry standard requires sampling at various levels within the tank. The licensee sample is drawn from a location 15 inches in from the tank side and 15 inches above the tank botto The licensee stated that their methodology was adequate based on a history of samples from this location being within the acceptance criteri The team disagreed
that this basis justified deviation from industry practice to which the licensee was committe The licensee initiated actions to acquire sampling' equipment which would more accurately determine if the current method is equivalent to industry guidance (see Appendix A, Finding 91-21-05).
4.0 MAINTENANCE, TESTING, CALIBRATION, AND CONFIGURATION CONTROL The team performed walkdown inspections of the EDS to identify the material condition of the electrical equipment and panel Portions of the "as installed" configuration of the EDS were examined to determine its compliance with design drawings and documents. The electrical maintenance program, procedures, surveillances, and work orders were reviewed to ensure the EDS was being properly maintained to function for the life of the plan Data sheets from completed calibration and surveillance procedures were reviewed to verify the EDS operates in accordance with design specifications and requirements. The method used for fuse control configuration was examined to ensure correct sizes and types were installed. Preliminary relay setting drawings were reviewed to determine if the licensee was in the process of developing and implementing an effective program for controlling setpoints for protective relays, over load relays, circuit breakers, and switchgea Testing and surveillance procedures for the emergency diesels generators were reviewed to determine if specifications are being me.1 Conclusions In the area of configuration control the team found that the Nuclear Engineering Department was in the process of upgrading the electrical drawings; developing new one-line drawings for the 480 V Class 1E MCCs; developing "relay setting" drawings; and implementing *a fuse control progra The overall material condition of the EDS was found satisfactory except for spare electrical leads. The ends of spare cables, wires, leads, and conductors were not always securely taped (capped) to last for the life of the plant. Additionally, examples were identified of improperly labeled electrical panels. The team identified that the Class 1E motor starters for two safety related RHR MOVs were undersize The team identified examples of potential undetectable failures in plant MOV The licensee initiated an investigation of this conditio In the area of maintenance the team noted the licensee was still using check lists for preventive maintenance procedures. This was identified as a weakness during the NRC Maintenance Team Inspection. However, the team verified the switchgear was being maintained in a PM program. and the protective relays were calibrated on a scheduled basi In the area of testing and surveillance the team identified that the EDGS had not been tested at nameplate ratin This was identified as an unresolved ite In addition the EDG's surveillance procedures do not
require load acceptance and/or rejection be verified. In another area, the team identified that DC ground indication trending had not been performe.2 Equipment Walkdowns The electrical components examined during inspection walkdowns included fuses, protective relays, motor starters, circuit breakers, switchgear, batteries, chargers, inverters, cables, cable trays, transformers, panels, and cubicles. The associated components, equipment, and panels in the following electrical systems and areas were inspected:
The safety related 125 VDC system, batteries, chargers, power panels, and 120 VAC inverter *
The safety related 480 V buses, switchgear, protective relays, and motor control center *
The 4.16 kV switchgear, cubicles, panels, and load center *
The 480,V emergency diesel generators and control panel *
The main step-up, the unit auxiliary, and the startup transformer *
The 230/115 kV main switchyar Walkdown inspections were conducted by the team to determine the EDS conformance to design requirement Design drawings used for the field inspections reflected the "as-installed" configuratio Specific atten tion was directed to. the Class 1E MCCs since modifications were recently installed. The team examined the fuses, motor starters, transformers, circuit breakers, and cubicles in three different MCC The material condition of the electrical panels, MCCs, switchgear cubicles, and relay panels was satisfactory except for cables and wires and MCC compartment label The ends of some spare cables, wires, leads, and conductors were not securely taped to last for the life of the plan In addition, the team observed several examples in which MCC compartment labels did not agree with descriptions on the electrical line-up procedure The licensee initiated a project to upgrade identification of plant equipment in the first quarter of 199 The team identified the spare cable terminations and MCC label issues as poor maintenance practices (see Appendix A, Finding 91-21-06).
During the inspection of safety related MCCs 5 and 6, the team identified that the motor starters in compartments 1J and 12J respectively did not appear to be sized to match the circuit breakers. The licensee confirmed that the motor starters for RHR valves 744A and 744B were undersized and would be replaced with the correct size (see Appendix A, Finding 91-21-07).
The team reviewed the wiring drawings for these valves with
licensee's engineering personnel and determined that no method for identifying a tripped overload relay was available to the plant operator A tripped overload relay in a motor starter-circuit would prevent the valve from operating. The team identified this condition as a potential undetectable failure for the MOVs (see Appendix A, Finding 91-21-08).
The electrical drawings used during the walkdowns had several minor errors such as the location of component The. licensee agreed, the drawings needed to be upgraded and stated an upgrade program was in process. The licensee was also in the process of developing one-line drawings for the 480 V MCC The team reviewed these preliminary drawings and considered them to be appropriate, particularly in support of maintenance activitie.3 Equipment Maintenance, Testing, and Calibration The team inspected the maintenance program to ensure. that the EDS was being properly maintained to function for the life of the plant. The calibrations, testing, -surveillances, and completed work orders were reviewed to determine if the EDS was operating within design requirements and technical specifications. Maintenance was performed by two group The high voltage (230/115 kV) equipment and main switchyard were serviced by an offsite "Transmission Group'" The Electrical/Maintenance Department on site performed all other maintenance activities for the low voltage equipment and EDG. Preventive and Predictive Maintenance In early 1991, the licensee initiated a project to review preventive maintenance (PM),
predictive, and monitoring activities necessary for safety related and balance of plant system. The review had been completed for the 480 and 120/208 VAC and 125 VDC system The EDG review was in progress. Resolution of the recommended changes/additions to the PM program were scheduled for completion by December 31, 1993. Examples of vendor recommendations not currently contained in PM procedures include failure to verify generator brush spring tension and measurement of ring eccentricity as described in the vendor instruction manual n B, dated March 196 These specific examples and other examples were identified by the licensee's PM review projec. MCCs, Protective Relays, and Switchgear The team reviewed the maintenance and calibration programs for both the Transmission Group and the Maintenance Departmen PM and calibration procedures were reviewed to determine content and details. The Transmis sion Group had completed calibration cards verifying the protective relays for the 230/115 kV switchyard were calibrated and maintained in the PM progra The.Maintenance Department PM procedures used brief "check lists" to identify required wor The use of these check lists was identified as a weakness by the NRC Maintenance Team in Inspection Report 50-261/90-10 dated August 9, 199 The PM schedule and completed work orders were reviewed to verify that the 480 V and the 4.16 kV switchgear was maintained on scheduled basi Completed calibration data sheets and relay settings were reviewed to verify the protective relays had been calibrate The material condition of the switchgear indicated regular maintenance was satisfactorily performed. The material condition of the motor control centers was goo The NED was in the process of developing a fuse control progra The licensee stated the program for Class 1E application would be completed for the next refueling outage (Spring 1992).
The team reviewed the preliminary contents and concluded the fuse control program described would be sufficient for ensuring the correct size and type of fuses are specified. Overall the team determined that NED had good programs and engineers to support maintenance activitie. EDG Surveillance The team reviewed EDG surveillance test activities to determine if the EDGs met design and TS requirement During the review of completed surveillance tests, the team identified that the EDGs had not been tested at nameplate rating as required by TS 4.6. Both the slow speed and rapid speed start surveillance tests, OST-401 and 409, required the EDGs to be loaded to 2500 KW. The TS requirement was for assumption of load up to the nameplate rating which is 2500 KW at 80 percent power factor and 3125 kVA. Based on this information the team concluded the licensee has apparently not been testing the EDGs as required by TS (see Appendix A, Finding 91-21-09).
Review of startup and factory test reports demonstrated that the generator had not been tested to 3125 kVA. In May of 1987, special test SP-776 and SP-777.was performed to measure the A and B EDGs governors character istics. During these tests the A and B EDGs were tested to 3014 kVA and 3172 kVA respectively which enveloped the nameplate rating only for the BEDG but enveloped both the A and B EDGs anticipated maximum accident kVA loading of 2880 kVA and 2886 kVA (calculation RNP.E-8.002 revision 1).
Since neither OST-401, nor 409 functionally test the EDGs to anticipated maximum accident kVA loading, the functional capability of the EDGs to provide accident kVA loads had not been demonstrated since the special tests discussed above. Vendor. information indicated that the generators were capable of supplying several hundred additional kVA without modifi cations. The licensee stated that the appropriate OSTs would be revised to test the.EDGs to a kVA equivalent to the nameplate rating. The testing would be implemented by December 9, 199 The team also noted that the present test procedures did not perform other testing such as load acceptance and rejection tests and extended.time run tests which are routinely performed in the industr Generally, such testing is required by TS or commitment to Regulatory Guide 1.108; however, HB Robinson was not committed to this Regulatory Guide nor was such testing required by the T The licensee stated their intention to review the value of such testing for possible incorporation into their
testing program. Additionally, as discussed in section 2.4.1, the EDG was not periodically tested to verify performance above 2500 KW which the static load analysis, discussed in paragraph 2.4.1, demonstrated was a possible accident load conditio On September 14, 1991, the licensee identified that established surveillance test procedures had not fully tested each loss of.voltage load shed channel (TS Table 3.5-3, item 3.a).
They also identified that testing had not completely demonstrated the load shed function upon a simulated loss of all normal AC coincident with a safety injection signal (TS 4..6.1.2).
Additional information concerning this item and the associated Waivers of Compliance which allowed continued operation 's contained 'in NRC Inspection Report N /91-2 The team reviewed the loss of voltage, the. degraded voltage and load sequencing test procedures. Test deficiencies other than those already identified by the licensee were not identifie.0 ENGINEERING AND TECHNICAL SUPPORT The team assessed the licensee's capability and performance regarding eng.ineering and technical support associated with the EDS. The basis for this assessment included the following areas; technical organizations and interfaces, problem identification and resolution, support of routine EDS related activities, and modification.1 Conclusions Engineering and technical support for EDS related activities and design controls for EDS systems and components were adequate to monitor and maintain the functional integrity of the EDS as designe Engineering organizations were adequately staffed to provide EDS suppor Responsi bilities and interfaces for engineering organizations 'were appropriately defined and documented. The-team concluded the engineering and technical support organizations demonstrated a good knowledge level regarding the EDS and associated components. Documentation of plant activities demon strated engineering involvement in problem identification and resolution as well as routine plant activitie Appropriate design controls were implemented on EDS related modification.2 Organization and Staff Engineering and technical support for EDS related activities was provided by onsite and offsite engineering organization The Nuclear Engineering Department,was designated as. the design authority and was located primarily offsite with a smaller onsite branch staf Technical Support was the onsite technical authority and included System Engineering as the largest grou System engineers provided the focal point for technical support of EDS related activities, interfacing with the plant staff, NED, and vendor technical representative The Technical Support staff of approximately 70 personnel included 35 percent contractor Review of
plant activities during this inspection indicated that staff size was adequate to provide required technical support for the EDS Responsibilities for engineering groups were appropriately defined and documented in plant memorandum and guidance manuals. General knowledge of the Technical Support and NED staffs was good. This was demonstrated by staff response to team inquiries regarding systems'
and components'
design, configuration, testing, and maintenance. Additionally, the team observed that interfaces were effective between NED and Technical Suppor Overall, adequate programs were developed to provide technical support of EDS activitie Performance by the engineering organizations indicated appropriate implementation of these program.3 Problem Identification and Resolution The team assessed engineering and technical support involvement in problem identification and resolution activitie Involvement was assessed by review of deficiency reporting programs and trending activities related to the ED Deficiency reporting documentation from the previous five year period was reviewed. Resolution of identified deficiencies was adequat Cause analysis for deficiencies was generally adequat An exception was FRs which. programmatically did not require cause analysis, and inconsis tent cause analysis on corrective maintenance work request An upgrade of the corrective action program in December, 1990 has. improved cause analysis activity for deficiency reporting processe Several examples demonstrated engineering involvement in problem identification and resolution. SCRs88-015.and 89-002 identified water in EDG cylinders. Extensive investigation activities demonstrated technical staff involvement in eventual resolution of the proble SCR 90-020 identified a problem associated with the Auxiliary Building smoke alarms being activated by.the exhaust smoke generated by an EDG fast start. The technical evaluation of. this condition was detailed and comprehensiv A PIR dated June 13,1990 was initiated by a System Engineer to identify the malfunction of the cathodic protection system for the underground fuel oil piping. POER 88-02 addressed a series of overspeed trips on both EDGs in 1987 and 198 A comprehensive -evaluation of EDG design and operating characteristics by Technical Support resulted in corrective maintenance which eliminated the proble An additional indication of involvement in problem identification was the large percentage of ACRs which were initiated by Technical Support organizations in 199 The team reviewed trending activities performed by the engineering staf The system engineers accomplish trending for assigned system Fuel oil pumps and valves are trended by the ISI progra High EDG exhaust cylinder temperatures were identified as a result of trending and was under investigatio An apparent decrease in fuel oil transfer pump capability was also identified which was attributed to inappropriate testing methodology. In general, review of deficiency reporting processes and trending activities demonstrated appropriate involvement of the
engineering and-technical support organizations in problem identification and resolutio.4 Routine Plant Activities Engineering and technical support involvement in routine plant activities was reviewed by the tea Routine involvement included maintenance, testing, and operations activities. Additional routine involvement was provided by an EDG system team which routinely reviews EDG performance and activities. An electrical systems team was developing preventive main tenance procedures for the generator component of the EDG. Review of maintenance documentation demonstrated frequent requests for engineering assistance in accomplishing maintenance task Preventive maintenance, which included periodic disassembly of EDG components for inspection and testing, was supported by the licensee's technical staff and vendor technical representatives during performance. Surveillance testing of the EDGs demonstrated interface of operations, maintenance, and technical staffs in recording and evaluation of performance informatio Overall, review of maintenance, testing and operational documentation demonstrated appropriate engineering and technical support involvement in routine activitie.5 Modifications The teams review of EDS related modifications included electrical and mechanical modifications developed and implemented within the previous 10 year perio Temporary modification activity: was also reviewe The following modifications were. reviewed:
MOD 955 EDG Upgrades MOD 763 Add New Pressure Taps for Controlling EDG Air Compressors MOD 921 EDG.Room Ventilation Louvers Modifications MOD 922 Remove Trip Function from MCC 5 Transfer Switch Breakers MOD 939 Protective Equipment Upgrade MCC 5,6,9,10 Safety Evaluations were appropriately detailed and post modification testing was adequate. Overall, design development and implementation was adequate. An exception was MOD 939 in which relay trip setpoints for MCCs were inadequate to preclude spurious trips. This error was identified during post modification testing and a comprehensive root cause analysis was performe The cause was identified to be an inaccurate design document referenced to determine setpoint Documentation of modifica tions had improved over the time period reviewe A good practice noted in the more recent modifications (MOD 955)
was the designation of organizational responsibilities for various aspects of the design change within the modification packag The team reviewed temporary modification controls and available examples of temporary modifications related to the ED The licensee's procedures
provided adequate controls for temporary modification Temporary Modification 91-718 installed an electrical jumper around "A" station battery cell 5 This was the only EDS related temporary modificatio Appropriate design controls were implemented. A temporary modification to provide cooling water to the EDGs for maintenance runs during the outage was accomplished via a special procedure, SP-947 dated November 19, 199 Design controls were adequate for control of this temporary modificatio The licensee's approved design control program permitted use of special procedures for implementation of this temporary modificatio Based on the sample of modifications reviewed, adequate design controls were implemented for EDS related modification activitie.0 EXIT MEETING The team met with the licensee's representatives (denoted in Appendix C)
at the conclusion of the inspection on October 25, 1991, at the plant site. The findings were discussed at that tim No dissenting comments were received at that time however the licensee's management met with the Senior Resident Inspector on November 1, 1991 to dissent with the finding related to inadequate surveillance testing of the ED The licensee's stated position was that the applicable operational surveillance test procedures, OST 401 and 409, tested the EDGs as required by T The Senior Resident Inspector observed an attempt to test the A EDG to nameplate rating on December 9, 199 The test was accomplished, but caused high voltages on the equipment due to lack of load on the El bu Due to plant configuration, voltage will be even higher on the E2 bus, therefore that test was suspended pending further study of how it should be performed without equipment damag NRC management has determined this item will be designated as unresolved pending further review by the NRC to determine the true intent of the TS surveillance requirement. Licensee representatives were informed of this decision just prior to report completion. Proprietary information is not contained i.n this repor APPENDIX A FINDINGS FINDING 91-21-01:
Inadequate Coordination Between Safety and Non-Safety Circuit Breakers on the 120 VAC Vital Bus System (para. 2.5)
DESCRIPTION:
The team noted that the supplies to instrument buses IB7 and IB9, from instrument buses IB2 and IB4 respectively, were through 30A circuit breakers and that non-safety loads connected to IB7 and IB9 also utilized 30A breaker The team postulated that in the event of an earthquake both non-safety loads could fail short-circuit and because of lack of coordination the feeder breakers may trip, thus completely de-energizing both IB7 and IB The design calculation RN107-E-37-F, "Coordination Study for Instrument Buses,"
issued in 1986 had recognized the lack of coordination and had recommended changing the feeder breakers to new ones with a 50A rating with a corresponding increase in cable size. These recommendations had not been implemented at the time of the inspectio In response to the team's concern the licensee conducted an investigation into the effects on the station if the above situation developed. The licensee was able to demonstrate that the plant could be shutdown safely and that the auxiliary systems required for heat removal would remain available with instrumentation power provided by the remaining buse The team accepted the licensee's position but was concerned that the above scenario had not been recognized by the license The team noted that the licensee had initiated a long term "Instrument Bus Upgrade" project (PCN 85 -
032/04) which proposes hardware changes and a possible system re-configuration under which the present problem would have been corrected. However the licensee indicated that they would not wait for the results of this project but would initiate action to purchase new 50A circuit breaker SAFETY SIGNIFICANCE:
A maximum hypothetical earthquake could result in the failure of redundant safety buse Appendix A
Finding 91-21-02:
Marginal Service Water Flow Rate to.Diesels for 110% Power (para. 3.4)
This finding is identified as an unresolved ite DESCRIPTION:
Service water flow rates to the diesels for cooling under LOCA conditions have been shown by tests to be below the manufacturer's recommendatio While the manufacturer has documented a need for 600 gpm of 95 degrees F service water at 100% power operation and 700 gpm of 95 degrees service water at 110% power, the special SW tests showed that the maximum available flow to be expected under LOCA conditions would be in the order of 550 gp The question of whether the lower SW flow rates are acceptable hinges on the performance of the heat exchanger As no in-service tests of the heat exchangers are available (Reference D3-1),
calculations were performed to ascertain whether the measured SW flow rates were sufficient under LOCA condition A summary of the status of the calculations was given in the DBD validation report. The team disagreed with the validation conclusion that adequate SW is available for 110% powe Actual installed heat exchangers' performance data was not used in the analysis of low service water flow condition The analyses were based on ideal conditions related to a factory tested newly assembled EDG which may not be accurate for the present installed conditio The conclusion that 550 gpm flow was adequate permits operation of EDG support systems in the alarm range at greater than the 100 percent EDG continuous rating of 2500 kw.. In the alarm range the margin for error is limited before damage to the EDG could occur with subsequent impact on the EDG. safety function. Calculation non-conservative assumptions discussed above may have consumed the available safety margin before instrument errors have been accounted for. Additionally, a recent licensee EDG loading analysis indicated possible loading above the continuous loading value. Based on the potential for greater than 100 percent continuous rating load in conjunction with. high lake temperatures, the team concluded this specific scenario required more accurate analysis to verify the EDG could meet its required safety function under these condition SAFETY SIGNIFICANCE:
A recently completed transient analysis by the licensee indicated that in certain scenarios EDG may be required to provide between 100 and 110 percent loa The licensee's analysis did not verify that service water flow was sufficient to support this EDG loading when heat sink temperature was 95 degrees Appendix A
Finding 91-21-03:
E1/E2 Equipment Room Ambient Conditions Not Evaluated (para. 3.5)
This finding is identified as an unresolved ite DESCRIPTION:
The redundant 480 VAC safety-related buses, El and E2, are located.in the same room in the auxiliary building. Equipment in this room included safety-related equipment breakers and inverters for vital control power and Reactor Protection and Safeguards Logic Cabinet The ambient temperatures resulting from electrical equipment heat loads had not been analyzed to determine potential impact on equipment performance or if temperatures remained within equipment design requirements in normal and accident condition Ventilation in this room is non-safety, i.e. lost on a loss of offsite powe Following NRC questions, the licensee initiated an evaluation of heat loads in this space for normal and abnormal conditions. An analysis based on industry reference values for equipment heat loads was performe Additionally, an analysis based on informal testing accomplished in 1985 was performe The results of these analyses varied considerably. The former indicated an ambient temperature of 136 degrees F in 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, leveling at 166 degrees in 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> The latter analysis indicated 126 degrees F in 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, leveling at 144 degrees in 100'hours. The difference in the computed heat loads was the cause of the variation. The industry reference heat loads were 52 KW, the test based value was 17 K The team concluded that, although no operability issue was evident, further analysis was required to more accurately determine the -heat loads and subsequent ambient temperatures. This was based on two factors: 1) the large variation in computed heat loads, and 2) the test was an uncontrolled, informal activity which required several assumptions to be made *regarding actual ventilation flow and accuracy of instrumentation use The license stated during the inspection that a controlled test would be performed and evaluation of equipment impact accomplished by the end of 199 SAFETY SIGNIFICANCE:
Electrical equipment performance could be impacted when exposed to high ambient temperatures. This could require derating or other compensatory measures to assure adequate equipment functionalit Appendix A
Finding 91-21-04:
Corrosion Protection of Underground Fue.l Oil Piping (par.6.2)
DESCRIPTION:
The cathodic protection system was installed in 1981 to prevent galvanic corrosion from piping to groun However, the system is known to have been operating outside of its original specification since August 1988 and thus the duration of protection has only been about 7 years. The Licensee was unable to provide documentation which specified what provisions for galvanic corrosion had been made at the time of the original installatio As a result, the licensee was unabl.e to determine the present condition. of.:the underground fuel piping. Degradation of the cathodic protection system in.1988 appeared to have been caused by installation of concrete in the yar The licensee stated that a sample of the underground fuel oil piping would be inspected during the 1992 refueling outage. Further action will be based on inspection result The. licensee scheduled a technical representative to review the onsite cathodic protection system and upgrade the site staff knowledge of the syste SAFETY SIGNIFICANCE:
If corroded the underground piping could be susceptible to failure during a seismic event which could result in loss of fuel oil between the storage tanks and the EDG day tank Appendix A
- Finding 91-21-05:
Fuel Oil Sampling Methodology (para. 3.6.2)
This finding will be identified as a deviatio DESCRIPTION:
Sampling of the fuel oil in the diesel fuel oil storage tank (0FOST) was performed at a single location near the bottom of the tank. The-idustry standard methodology for sampling, to which the licensee.is committed, ensures that the sample is representative of the tank contents by sampling at different tank elevations or by circulating tank contents prior-to samplin Deviation from the methods described in the industry standard, ASTM 0270, are acceptable with appropriate justificatio No justification for this deviation,. either comparative testing or other demonstration of equivalency, was documente TECHNICAL REQUIREMENTS:
Regulatory Guide 1.137, C.2, states that ASTM D270 should be used to sample fuel oil in tanks and the purpose was to obtain a representative sample of tank content SAFETY SIGNIFICANCE:
Failure to ensure representative testing of the diesel fuel could cause degradation of fuel oil to go unnoticed and lead to a failure of the diesel generators in an emergency situatio Appendix A
FINDING 91-21-06:
Examples of Poor Maintenance Practices (para 4.2)
DESCRIPTION:
The team conducted walkdown inspections of the electrical panels, motor control centers, switchgear, and relay racks to determine the material condition of the equipment and the wiring. During these walkdowns the following deficiencies were identifie A number of spare electrical cables, wires, leads, and conductors ends were not securely taped to last for the life of the plant. In several instances the tape appeared to be loose. The functional description on MCC compartment labels may vary substantially from that contained in OP-603 and in some cases are technically incorrec *The licensee stated the standard practice for terminating spare cables and conductors 'at the site has been to wrap the ends with tap The licensee agreed with the team's finding that somespare cables and conductors ends are not up to standard As a result of this finding the licensee initiated ACR 91-37 ACR 91-370 required the practice of terminating spare wires be investigated and resolution be determine In addition Work Requests WR/JO 91-APHG1, 91-APHH1, 91-APHI1, 91-APHJ1, and APHK1 all dated October 23, 1991, had been written for corrective actio The functional description on MCC compartment labels may vary substantially from that contained in OP-603 and in some cases are technically incorrect. An example of the former was MCC compartment label which read "SAT SUCTION VLV SI-845B" whereas OP-603 referred to this compartment as "SPRAY ADDITIVE TANK OUTLET ISOL. SI-845B."
An example of the latter involved a spelling error on a MCC label (section misspelled as suction) resulting in an MOV compartment label of "AUX. FWP SUCTION VA. V2-20A." The OP-603 reference, "Motor Driven AFW Pump Discharge Cross-Connect V2-20A," was technically correc The licensee initiated a project to upgrade identification of plant equipment in the first quarter of 199 This project will include mechanical components such as valves as well as electrical components such as MCC and electrical distribution panel breaker labels. However, the licensee.has not determined the style, type or means of attachment of labels to be used nor developed a schedule for the labeling of electrical component SAFETY SIGNIFICANCE:
Spare dangling electrical conductors could potentially cause a short resulting in the failure of a safety syste In addition these conductors could potentially shock plant personnel if voltage was presen Incorrect or inconsistent labeling could result in improper component isolation for maintenance or maintenance on incorrect equipmen Appendix A
FINDING 91-21-07:
The Motor Starters For Motor Operated RHR Valves 744A And 744B Are Undersized (para. 4.2)
DESCRIPTION:
The team identified that in MCC 5 Compartment 1J and MCC 6 Compartment 12J 50 ampere motor protector circuit breakers were feeding Size 1 motor starter The licensee was requested to verify that this configuration was correct. The licensee's engineering staff performed an Operability Determination 91-022.to analyze this condition. The licensee determined the motor starters should be a Size 2. The licensee analyzed the affect of having undersized motor starter in the circuits. and concluded that the valves were operabl However, the licensee stated the motor starters will be replaced with Size 2 starters no later than refueling outage N.
Until then, the existing motor starters are to be inspected each time the valves are cycled. The team agreed with the licensee's analysis and proposed corrective actio SAFETY SIGNIFICANCE:
A failure of the motor starters would prevent the motor operated RHR Valves, 744A and/or 744B from cycling which could compromise the Low Head Safety Injection flow pat Appendix A
FINDING 91-21-08:
Undetectable Failure Mechanism on MOVs (para. 4.2)
DESCRIPTION:
The team identified that there is no indication provided to plant operators to detect a tripped overload relay in a motor starter circui This was identified by the team during the review of the motor starters for MOV 744A and MOV 744B. The power to the position indication lights (OPEN and CLOSED) is fed directly from the fuse side of the circui It is not interlocked to the overload relay and therefore the position lights can not be used. The licensee agreed with the team that a tripped overload relay could not be identifie The licensee was requested to address this concern by the tea The-licensee stated that an adverse condition report (ACR)
would be issued to investigate this concer However, the licensee stated that the MOV circuits were of original plant design and did not represent an operability concer The team considered this finding as a potential "undetectable failure."
SAFETY SIGNIFICANCE:
A tripped overload relay would not be detected and the valve would be inoperable due to a loss of electrical powe Appendix A
Finding 91-21-09:
EDGs Not Tested at Name Plate Rating as Required by TS 4.6. (para. 4.3.3)
This finding is identified as an unresolved item, Failure to meet TS require ments for EDG testin DESCRIPTION:
TS 4.6.1.1 requires operation of the EDGs with an assumption of load up to the nameplate rating. The EDG's nameplate specified a rating of 2500 KW at 80 percent power factor and 3125 kVA. OST 401 and 409 which implemented this TS requirement tested the EDGs at 2500 KW at an unspecified power factor or kVA loading. Subsequently, the licensee attempted tests at 3125kVA. and found this caused very high voltages on equipment due to light loading on the E buses., It is not the NRCs intention to cause the licensee to push test conditions to the point of causing equipment damage. Therefore the correct intention of the TS surveillance requirement needs further consideration by the NRC and CP&L. This item will be considered unresolve SAFETY SIGNIFICANCE:
Failure to perform testing of the generator at the nameplate rating of 3125 kVA could result in a failure to detect degradation of the alternator, i.e. the EDG's ability to carry accident load APPENDIX B ACRONYMS AND ABBREVIATIONS A
Amperes ACR Adverse Condition Report AECL Atomic Energy of Canada Limited A-H Amp-Hours AFW Auxiliary Feed Water ANSI American National Standards Institute AOP Abnormal Operating Procedure ASTM American Society of Testingand Material C
.Celsius CP&L Carolina Power & Light C CVT Constant Voltage Transformer CWD Control Wiring Diagrams DBD Design Basis Document DCP Design Change Packages DBR DesignBase Reconstitution DFOST Diesel Fuel Oil Storage Tank DR Deviation Reports DS Dedicated Shutdown EBASCO Licensee architect-Engineer EDG Emergency Diesel Generator EDS Electrical Distribution System EDSFI Electrical Distribution System Functional Inspection EPM Electrical Planning and Management ESF Engineered Safeguard Feature E&TS Engineering and Technical Support EWR Engineering Work Request ff fouling factor FO Fuel Oil FR Field Report GDC General Design Criteria HBR-1 H.B. Robinson coal-fired plant Hp Brake Horsepower HVAC Heating Ventilation and Air Conditioning IEEE Institute of Electrical & Electronics Engineers ISI Inservice Inspection JW Jacket Water KW kilowatts kV kilovolts kVA Kilovolt-amperes LERs Licensee Event Reports LO Lubrication Oil LOCA Loss of Coolant Accident LOOP Loss of Off-site Power MCC Motor Control Center MOV Motor Operated Valve MVA Mega Volt-amperes
Appendix B
MW Megawatts NED Nuclear Engineering Department NEMA National Electrical Manufacturers Association NSR Non Safety Related OST Operating Surveillance Test PIR Plant Improvement Request P&ID Process and Instrumentation Drawings POER Plant Operating Experience Report PM Preventive Maintenance POM Plant Operating Manual PRA Probabilistic Risk Assessment PT Periodic Test RHR Residual Heat Removal RNP Robinson Nuclear Plant SAT Start-up Transformer SCR Significant Condition Report SW Service Water SP Special Procedure SQUG Seismic Qualification Users Group T&D Transmission & Distribution TS Technical Specification UFSAR Updated Final Safety Analysis Report VAC Volts Alternating Current VDC Volts Direct Current
APPENDIX C PERSONS CONTACTED Licensee Employees
- G. Attarian Electrical, Unit Manager, NED
- T. Bowman Engineer, NED
- R. Chambers Plant General Manager, Robinson Nuclear Project
- G. Chappell Civil-Mechanical Supervisor, NED
- C. Coffman Engineer Technical Support
- D. Dykesterhouse Engineer, NED
- S. Farmer Manager, Engineering Programs, Technical Support
- W. Flanagan Manager, Operations
- S. Gupta Engineer, NED M. Hammack, Senior Engineer, NE *B. Hynds Engineer, NED
- P. Jenny Compliance Engineer,,Regulatory Compliance G. Kirven, System Engineer, Technical Support F. Legette Senior Control Operator, Operations
- A. Lucas Manager, NED
- L. Lynch Supervisor Quality Control
- M. Macon
'Engineer, NED
- A. McCauley Manager, Electrical Maintenance, Technical Support J. McDaniel, Senior Engineer, NED
- R. Parsons Manager, Engineering Support, NED
- M. Payne Electrician First Class, Maintenance J. Pierce, Senior Engineer, NED
- R. Smith Manager, Maintenance
- K. Strouzas Engineer, NED
- G. Vaughn Vice President, Nuclear Services
- J. Windham Electrician First Class, Maintenance
- Attended exit meeting