L-12-361, Response to NRC Bulletin 2012-01, Design Vulnerability in Electric Power System
| ML12300A066 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 10/25/2012 |
| From: | Harden P FirstEnergy Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-12-361, BL-12-001 | |
| Download: ML12300A066 (16) | |
Text
FENOC October 25, 2012 l-12-361 10 CFR50.54(f)
ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Beaver Valley Power Station, Unit Nos. 1 and 2 Docket No. 50-334, license No. DPR-66 Docket No. 50-412, license No. NPF-.73 Response to NRC Bulletin 2012-01, "Design Vulnerability in Electric Power System" On July 27,2012, the Nuclear Regulatory Commission (NRC) staff issued Bulletin 2012-01, "Design Vulnerability in Electric Power System," requesting information on electric power system design, to determine if further regulatory action is warranted.
licensees are required to provide a written response in accordance with 10 CFR 50.54(f) within 90 days of the date of the bulletin.
FirstEnergy Nuclear Operating Company hereby provides the requested information for the Beaver Valley Power Station (BVPS), Unit Nos. 1 and 2, as an attachment.
There are no regulatory commitments contained in this submittal. If there are any questions or if additional information is required, please contact Mr. Thomas A. lentz, Manager - Fleet licensing, at 330-315-6810.
I declare under penalty of perjury that the foregoing is true and correct. Executed on
. October ~s ,2012.
rden, Vice President - Beaver Valley Power Station'
Attachment:
Response to NRC Bulletin 2012-01 for Beaver Valley Power Station, Unit Nos. 1 and 2 cc: NRC Region I Administrator NRC Resident Inspector NRC Project Manager Director, Pennsylvania Bureau of Radiation Protection, Department of Environmental Protection (BRP/DEP) .
BVPS Site BRP/DEP Representative
Attachment L-12-361 Response to NRC Bulletin 2012-01 for Beaver Valley Power Station, Unit Nos. 1 and 2 Page 1 of 15 Nuclear Regulatory Commission (NRC)Bulletin 2012-01, "Design Vulnerability in Electric Power System," requested information regarding single-phase open~circuit conditions or high impedance ground fault conditions. The NRC-requested information is identified using bolded and italicized text, followed by the FirstEnergy Nuclear Operating Company (FENOe) response. The following outline identifies the order the NRC requests are addressed in, with similar items grouped together...
Outline of Bulletin 'Response:
- System Description - NRC Items 2., 1.d,. 2.a, 2.c
- System Protection - NRC Items 1., 1.a, 2.b, 2.d
- Consequences - NRC Items 1.b, 1.c, 2.e
- Figure 1*- Simplified One-Line Diagram
- Tables:
- Table 1 - ESF Buses Continuously Powered From Offsite Power Source(s)
- Table 2 - ESF Buses Not Continuously Powered From Offsite Power Source(s)
- Table 3 - Major ESF Bus Loads Normally Powered From* Offsite Power Source(s)
- Table 4 -Offsite Power Transformers
- Table 5 - Protective Devices Note: Throughout this response, the content applies to both Beaver Valley Power Station (BVPS) Unit 1 and Unit 2, unless specifically noted otherwise. _
Attachment L-12-361 Page 2 of 15
System Description
Items 2., 1.d, 2.a, and 2.c request system descriptions and are grouped in this section:
2.* Briefly describe the operating configuration of the ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) at power (normal operating condition).
Response
See Figure 1 for a simplified one-line diagram, which provides necessary information from Updated Final Safety Analysis Report (UFSAR) Figures 8.3-1 for each unit, along with Figure 8.4-1 for Unit 1, and Figure 8.3-3 forUnit 2.
Power to station auxiliary loads (including the engineered safety feature (ESF) buses) is available from four station service transformers. Two Unit1 Station Service Transformers (USSTs) supply power from the main generator; two System Station Servi~e Transformers (SSSTs) supply power from the 138 kV switchyard. The primary side of each SSST is connected through separate breakers to separate buses in the 138 kV switchyard. When at power (normal operating condition), station ser\lice power may be supplied by.the main generator, the 138kV switchyard, or a combination of both.
Each train of ESF buses receives power from a non-ESF 4.16 kV bus* that is aligned to one of the four station service transformers. Although these* buses are permitted to be aligned to the 138 kV switchyard via the SSSTs, this is not the normal operating configuration. When at power (normal operating condition), station auxiliary loads are typically aligned to the main generator via the USSTs.
1.d. Describe theoffsite power transformer (e.g., start-up, reserve, station auxiliary) winding and grounding configurations.
Response
See Table 4 for offsite power transformer winding and grounding configurations.
1 In the Unit 1 UFSAR, these are referred to simply as the Station Service Transformers.
Attachment L-12-361 Page 3 of 15 2.a. Are the ESF buses powered by offsite power sources?
If so, explain what major loads are connected to the buses including their ratings.
Response>:
When at power (normal operating condition), ESF buses are permitted to be powered from the 138 kV switchyard via the SSSTs; however, this is not the normal alignment.
ESF buses are normally aligned to the main generator via the USSfs.
Therefore,Table 1 "Essential Buses Continuously Powered From Offsite Power Source(s)"*and Table 3 "Major ESF Bus Loads Normally Powered From Offsite Power Source(s)" 'are not applicable to BVPS.' Table 2 lists the ESF buses not continuously powered from offsite power sources. ,. '
.2.c. Confirm that the operating configuration of the ESF buses Is consistent with the current licensing basis.
Describe any changes In'offslte power source alignment to the ESF buses from the original plant licensing.
Response
The operating configurations of the ESF buses shown in Table 2 were verified to be consistent with the current licensing basis as described in the UFSAR. With respect to the normal offsite power alignment, no relevant changes have been made since the original plant, licensing.
Attachment L-12-361 Page 4 of 15 System Protection Items 1., 1.a, 2.b, and 2.d request information regarding electrical system protection, and are grouped in this section:
- 1. Given the requirements above, describe how the protection scheme for ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) is
. designed to detect and automatically respond to a slngle-phase open circuit condition or high impedance ground fault condition on a credited off-site. power circuit or anQther power sources [sic].
Response
Consistent with the current licensing basis and General Design Criterion (GDC) 1'1; the existing electrical protection system will separate the ESF buses from a connected:: . ,
failed offsite source due to a loss of voltage or a sustained, balanced degraded grid':
voltage. The protection scheme was not specifically designed to detect a single..:phase open circuit in a three phase system. Detection of a single-phase open-circuit condition was not requii'ed for licensing of the plant.
The response of the electrical protection system to a single-phase open-circuit condition (with or without a ground) depends on the electrical power alignment at the time the '
open phase occurs.
Normal Alignment When at power (normal operating condition), station auxiliary power is typically supplied from the,main generator through the USSTs, and the SSSTs are unloaded. In this alignment, a single-phase open-circuit condition in the offsite power supply will not be .
detected by the electrical protection system for the ESF buses,because the ESF buses will continue to receive stable, balanced power from the main generator.
Startup/Shutdown/Alternate Alignment During plant startup and shutdown, station auxiliary power is typically supplied from the 138 kV switchyard via the SSSTs. This alignment may also be used when at power (normal operating condition); however, this is uncommon. When station auxiliary loads are aligned to the SSSTs, a single-phase open circuit upstream of the SSSTs mayor may not be detected by the electrical protection system. The protection system
Attachment L-12-361 Page 5 of 15 response is dependent on plant conditions and the specifics of the open circuit failure; relevant details include the load on the SSST and whether the open conductor becomes grounded when the failure occurs.
Backfeed Alignment During shutdown, station auxiliary power may be supplied from the 345 kV switchyard through the main transformer and USSTs. In this alignment, a single-phase open circuit in the 345 kV switchyard mayor may not be detected by the electrical protection system. The protection system response is dependent on plant conditions and the specifics of the open circuit failure; relevant details include the load on the main transformer and whether the open conductor becomes grounded when a failure occurs.
An open phase between the main transformer and a USST is not considered to be' credible'due to the robustness of the accompanying isophase bus connection.
High Impedance Ground Faults (with or without an open phase)
Ground 'fault protection is provided for the 4.16 kV ESF buses and their associated offsite power circuits. This protection consists of relays and circuit breakers that, ,
automatically operate to isolate ground faults. Ground alarms are provided for the',
normally ungrounded 480 V ESF buses. The ground protection/alarm setpoints are chosen to provide sensitive ground protection/detection while maintaining appropriate protective device coordination and minimi2;ing spurious actuation for normally expected electrical transients.
1.a. The sensitivity of protective devices to detect abnormal operating conditions and the basis for the protective device setpolnt(s).
Response
Consistent with the current licensing basis and GDC 17, existing electrical protective devices are designed to detect design basis conditions like a loss of voltage or a degraded voltage but were not designed to detect a single-phase open-circuit condition.
Table 5 lists the undervoltage protective devices and ,the basis for the device setpoints ..
Existing electrical protective devices are designed to detect ground faults of sufficient magnitude. Table 5 lists ground protection/alarms on the ESF buses and the basis for the device setpoints.
Attachment L-12-361 Page 6 of 15 2.b. If the ESF buses are not powered by offslte power sources, explain how the surveillance tests are performed to verify that a single-phase open circuit condition or high Impedance ground fault condition on an off-site power circuit is detected.
Response
a Periodic surveillances are in place to specifically monitor for single-phase open-circuit condition in the offsite power supply. Daily walkdowns are performed to visually inspect the transmission lines and connections between the 138 kV switchyard and the system station service transformers.
Previous plant experience has demonstrated that a single-phase open-circuit on the primary side of an unloaded system station service transformer yields a small voltage
.lmbalanc.9 on the secondary side of the transformer. Operator rounds periodically (approximately every eight hours) check for voltage imbalances on the secondary sides of the transformers. The same checks are performed immediately preceding any planned transfers to the offsite power supply. Operating procedures*address actions to be taken if a voltage imbalance is detected.
There are no surveillances to specifically monitor for a high..impedance ground fault without an open phase. Ground faults of sufficient magnitude are expected to be detected by the electrical protection scheme regardless of Whether the ESF buses are
. aligned to the offsite power source.
2.d. Do the plant operating procedures, Including off-normal
.operating procedures, specifically call for verification of the voltages on all three phases of the ESF buses~ .
Response
Yes, weekly surveillance procedures call for measurement of three-phase voltages at the 4.16 kV and 480 V ESF buses. These surveillances are performed for all operating modes and electrical power alignments.
Attachment L-12-361 Page-7 of 15 Consequences Items 1.b, 1.c, and 2.e request information regarding the electrical consequences of an event, and are grouped in this section:
1.b. The differences, (if any) of the consequences of a loaded (i.e., ESF bus normally aligned to offslte power transformer) or unloaded (e.g., ESF buses normally aligned to unit auxiliary transformer) power source.
Response
When station auxiliary loads (including ESF buses) are aligned to the main generator, via the USSTs, a single-phase open circuit in the offsite ,power supply is not expectetfto be detected by the electrical protection scheme. However, because station auxiliary'" ' ;
loads will continue to receive balanced, stable power from the main generator, the ,-,,; ',"
condition is not anticipated to have an Immediate, adverse effect on plant operation::';:' "
and/or equipment. In this alignment, the open-circuit condition is expected to be ,;r,,! .
detected by the periodic surveillances described in response to 2.b. ::i -:; , .. ,
, If station auxiliary loads are aligned to the offslte power supply, the electrical protection',:,
scheme mayor may not detect a single-phase open-circuit condition. The responsEfof the electrical protection scheme and the effect on plant equipment is dependent on plant conditions and the specifics of the open circuit failure; relevant details include the' ,
load on the offsite power transformer and whether the open conductor becomes grounded when the failure occurs. If the condition is not automatically detected, plant operators may be required to identify that the offsite power supply is inoperable and take manual action to separate station auxiliary loads from the degraded power source.
Regardless of the offsite power alignment, ground faults of sufficient magnitude are expected to be detected and isolated by the electrical protection scheme.
r' Attachment L-12-361 Page 8 of 15 1.c. If the design does not detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offslte power circuit or another power sources, describe the consequences of such an event and the plant response.
Response
The current licensing basis does not credit the electrical protection system to detect and automatically respond to a single-phase open-circuit condition in the offsite power supply. Because the electrical protection scheme is not credited to detect and automatically respond to a single-phase open-circuit condition, an open phase fault was not included in the design criteria for either the loss of voltage or degraded voltage .relay schemes. ,(
Since open-phase detection Was 'not credited in the design or licensing basis, no design basis calculations or design documents previously considered this condition. It is ",: "
possible to provide a generic assessment of the consequences of an open-phase event using information from operating experience and guidance from published literature(:'* .-
However, such an assessment cannot be formally credited as the basis for an accurate' response, because the consequences of an open-phase event are highly dependent on the specific characteristics of each plant electrical system. An analysis that takes into account those characteristics would be necessary to develop a detailed response.
The following is provided as a high-level description of the possible consequences of an open-phase event: ..
In the normal alignm~nt through the USSTs, a single-phase open circuit or a high impedance grou'nd fault in the offslte power supply is not expected to have an immediate, adverse effect on plant operation and/or equipment, because station auxiliary loads will continue to receive balanced, stable power from the main generator.
In this alignment, the open-circuit condition is expected to be detected by the periodic surveillances described in response to 2.b.
In the less common alignment where station auxiliary loads are aligned to the offsite power supply, the consequences of a single-phase open circuit or high Impedance ground fault have not been fully analyzed. If the condition is not automatically detected by the electrical protection system, plant operators may be required to identify that the offsite power supply is Inoperable and take manual action to separate station auxiliary loads from the degraded power source. Without detailed analysis to support an
Attachment L-12-361 Page 9 of 15
.alternate conclusion, for a worst-case scenario, it is conservatively assumed that one of twoESF trains could be made inoperable.
2.e. If a common or single offsite circuit Is used to supply redundant ESF buses, explain why a failure, such .a$ a single-phase open circuit or high Impedance ground fault condition, would not adversely affect redundant ESF buses.
Response
This request is not applicable .. Redundant ESF buses are supplied by independent*
offsite power circuits.
AttachmelJt L-12-361 Page 10 of 15 Figure 1 Simplified One-line Diasram - Beaver Valley Power Station Unit 1 at Unit 2
~
k Main Generator, 138kV SkV 138kV ,
t Transformer. and ~
SWitchyard y rV"1"Y"\
SSST USST USST SSST No - normally open N~ ~O I' I' Nd) ~O ESF Buses I' T ESF Buses TrainA Train B rE~G I) 4kV Buses . I) ~ EDG~
NO t )
1', ) )
)
~NO )
I.A...A.I u.L \.A.I..A.I \.A..W I.A...A.I v..W T, T, T, T, T, T, r II ._,
\
480V Buses
Attachment L-1.2-361 Page 11 of 15 Tables Table 1- ESF Buses Continuously Powered From Offslte Power Source(s)
Original licensing basis Description of ESF Bus Power Source ESF Bus Name (normal operating condition) configuration (VIN)
N1A N/A N1A Table Z - ESF Buses Not Continuously Powered From Offslte Power Source(s)
Original licensing basis Description of ESF Bus Power Source ESF Bus Name (normal operating condition) configuration (YIN)
Unit 1 Unit Station Service Transfonner 1C (TR-1C) 4KVS-1AE,4BOVUS-1-B Y Unit Station Service Transfonner 1D (TR-1 D) 4KVS-1DF,4BOVUS-1-9 Y UnitZ Unit Station Service Transfonner 2C (TR-2C) 4KVS-2AE, 4BOVUS-2-8 Y Unit ~tation Service Transfonner 2D (TR-2D) 4KVS-2DF, 4BOVUS-2-9 Y Table 3 - Major ESF Bus Loads Nonnally Powered From Offslte Power Source(s)
ESFBus Load Voltage Level Rating (HP)
N/A N/A N1A N/A
Attachment L-12-361 Page 120f 15 Table 4
- Offslte Power Transformers T
MVA Size Voltage Rating Transformer Windlni Confi.curatlon (Coollng*) (Primary/Secondary) Grounding Configuration Unit 1 System Station Service Three winding, 19.2125.6/32 MVA 138 k'P/4.36 kVl4.36 kV Solidly grounded primary, Transformer 1A (TR-1A) Wye-Wye-Wye (OAlFOAlFOA) resistance grounded secondary System Station Service Three winding, 19.2125.6/32 MVA 138 kV/4.36 kVl4.36 kV Solidly grounded primary, Transformer 1B (TR-1B) Wye-Wye-Wye (OAIFOAIFOA) resistance grounded secondary Unit Station Service Three winding, 19.2125.6/32 MVA 22 kV/4.36 kVl4.36 kV Resistance grounded Transformer 1C (TR-1C) Oelta-Wye-Wye (OAlFOAlFOA) secondary Unit Station Service Three winding, 19.2125.6/32 MVA 22 kV/4.36 kVl4.36 kV Resistance grounded Transformer 10 (TR-10) Oelta-Wye-Wye (OAlFOAlFOA) secondary Main Generator Step-Up Two winding, 945MVA 21.5 kV/345 kV Solidly grounded Transformer CTR-MT1) Oelta-Wye (FOA) secondary Unit 2 System Station Service Three winding, 19.2125.6/32 MVA 138 kV/4.36 kV/4.36 kV Solidly grounded primary, Transformer 2A (TR-2A) Wye-Wye-Wye (OAlFOAlFOA) - resistance grounded secondary System Station Service Three winding, 19.2125.6/32 MVA 138 kV/4.36 kVl4.36 kV Solidly grounded primary, Transformer 2B (TR-2B) Wye-Wye-Wye (OAlFOAlFOA) resistance grounded secondary Unit Station Service Three winding, 19.2125.6/32 MVA 22 kV/4.36kVl4.36 kV Resistance grounded Transformer 2C (TR-2C) Oelta-Wye-Wye (OAlFOAlFOA) secondary Unit Station Service Three winding, 19.2125.6/32 MVA 22 kV/4.36 kVl4.36 kV Resistance grounded Transformer 20 (TR-20) Oelta-Wye-Wye (OAlFOAlFOA) secondary Main Generator Step-Up Two winding, 945MVA 21.5kV/345kV Solidly grounded Transformer (TR-MT-2) Oelta-Wye (FOA) secondary
~ MVA =Megavolt Ampere
- OA/FA/FOA =Oil Air I Forced Air I Forced Oil Air
§ kV =kilovolt
Attachment L-12-361 Page 13 of 15 Table 5 - Protective Devices Protective UV Protection Zone Device Logic Setpoint (Nominal) Basis for Setpoint Unit 1 4.16 kV Degraded 20f2 3899 V" (93.7% of . The degraded voltage relays are designed to detect ESF Bus Voltage 4160 V). sustained undervoltage conditions. The voltage setpoint is 90 seconds chosen to erisure that at least 90% of the rated voltage is
- available at motor terminals. Voltages are monitored by two single-phase relays.
4.16 kV Loss of 1 of 1 3122 V (75% of The loss-of';'voltage relays are designed to detect significant ESF Bus Voltage 4160 V). undervoltage conditions. The voltage and time delay 1 second settings are chosen to preclude relay actuation during normally expected voltage transients (e.g. motor starts and bus transfers). A three-phase relay operates on the difference between the positive sequence and the negative sequence voltage.
480 V Degraded 20f2 450 V (93.7% of 480 V). The degraded voltage relays are designed to detect ESF Bus Voltage 90.1 seconds sustained undervoltage conditions. The voltage setpoint is chosen to ensure that at least 90% of the rated voltage is available at motor terminals. Voltages are monitored by two single-phase relays.
480 V Loss of 1 of 1 360 V (75% of 480 V). The loss-of-voltage relays detect Significant undervoltage ESF Bus Voltage 29.5 seconds conditions. The voltage and time delay settings are chosen to preclude relay actuation during normally expected voltage transients (e.g. motor starts and bus transfers). A three-phase relay operates on the difference between the positive sequence and the negative sequence voltage.
V =Volts
Attachment L-12-361 Page 14 of 15 Protective UV Protection ZOne Device Logic Setpolnt (Nominal) Basis for Setpoint 4.16 kV Ground NlA 10An The setpoint is selected to provide sensitive ground ESF Bus Supply Differential 0.1 seconds protection for the cables supplying the 4kV ESF buses. The time delay is sufficient to avoid spurious operation during nonnally expected. electrical transients.
4.16 kV Ground N/A 30A The setpoint is selected to provide sensitive ground ESF Bus Supply Overcurrent 0.3 seconds protection for the.cables supplying the 4 kV buses while coordinating with the ground protection for the ESF motors.
4.16 kV Ground N/A 10A The setpoint is selected to provide sensitive ground ESF Motors Overcurrent 0.1 secOnds protection for the 4 kV ESF motors. The time delay is sufficient to avoid spurious operation during normally expected electrical transients.
480 V Ground NlA 16V The 480 V ESF buses are ungrounded. The alarm setpoint ESF Bus Alann 1 second is chosen to be sufficiently sensitive to detect a ground fault without resulting in nuisance alanns.
Unit 2 4.16 kV Degraded 20f2 3888.5 V (93.5% of The degraded voltage relays are designed to detect ESF Bus Voltage 4160 V), sustained undervoltage conditions. The voltage setpoint is 90.1 seconds chosen to ensure that at least 90% of the rated voltage is available at motor tenninals. Voltages are monitored by two single-phase relays.
4.16 kV Loss of 20f2 3122 V (75% of The loss-of-voltage relays are designed to detect Significant ESF Bus Voltage 4160 V), undervoltage conditions. The voltage and time delay 1 second settings are chosen to preclude relay actuation during nonnally expected voltage transients (e.g. motor starts and bus transfers). Three-phase relays operate on the difference between the positive sequence voltage and the negatiVe sequence voltage.
11" A =Amperes
Attachment L-12-361 Page 15 of 15 Protective UV Protection Zone Device Logic Setpolnt (Nominal) Basis for Setpoint 480 V Degraded 20f2 448.4 V (93.4% of The degraded voltage relays are designed to detect ESF Bus Voltage 480 V), sustained undervoltage conditions. The voltage setpoint is 90.1 seconds chos~m to ensure that at least 90% of the rated voltage is available at motor terminals. Voltages are monitored by two single-phase relays.
480 V Loss of 20f2 336 V (70% of 480 V), The loss-of-voltage relays are designed to detect significant ESF Bus Voltage 5 seconds undervoltage conditions. The voltage and time delay settings are chosen to preclude relay actuation during normally expected voltage transients (e.g. motor starts and bus transfers). A three-phase voltage relay operates in conjunction with a single-phase voltage relay. The three-phase relay monitors the difference between the positive sequence voltage and the negative sequence voltage.
4.16 kV Ground N/A 254._4 A, 255.3 A The setpoint is selected to provide sensitive ground ESF Bus Supply Differential prote9tion for the cable~ supplying the 4 kV ESF buses.
4.16 kV Ground N/A 40 A, 30A The setpoint is selected to provide sensitive ground ESF Bus Supply Overcurrent 0.4 seconds, protection for the cables supplying the 4 kV buses while 0.3 seconds coordinating with the ground protection for the ESF motors.
4.16 kV Ground NlA 10A The setpoint is selected to provide sensitive ground ESF Motors Overcurrent 0.1 seconds protection for the 4 kV ESF motors. The time delay is sufficient to avoid spurious operation during normally expected electrical transients.
480 V Ground N/A 15V The 480 V ESF buses are ungrounded. The alarm setpoint ESF Bus Alarm 1 second is chosen to be sufficiently sensitive to detect a ground fault without resulting in nuisance alarms.