ML11272A130

Request for Additional Information Regarding the Earthquake on August 23, 2011 and Restart Readiness Determination Plan

ML11272A130
Person / Time
Site:	North Anna
Issue date:	09/27/2011
From:	Grecheck E Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
11-544, FOIA/PA-2011-0357, FOIA/PA-2011-0359
Download: ML11272A130 (26)

Text

VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 10 CFR 100, Appendix A September 27, 2011 U.S. Nuclear Regulatory Commission Serial No.: 11-544 Attention: Document Control Desk NL&OS/ETS R3 Washington, DC 20555 Docket Nos.: 50-338/339 License Nos.: NPF-4/7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNITS I AND 2 REQUEST FOR ADDITIONAL INFORMATION REGARDING THE EARTHQUAKE ON AUGUST 23, 2011 AND RESTART READINESS DETERMINATION PLAN On August 23, 2011, at 1351 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.140555e-4 months <br />, with North Anna Power Station Units 1 and 2 operating at 100% power, a Magnitude 5.8 earthquake occurred approximately 5 miles from Mineral, Virginia. The epicenter was approximately 11 miles WSW of North Anna Power Station. Ground motion was felt and recognized as an earthquake by the Main Control Room operators at the station. Dominion has confirmed that the August 23, 2011 earthquake exceeded the spectral accelerations for the Operating Basis Earthquake (OBE) and Design Basis Earthquake (DBE) for North Anna Power Station Units 1 and 2. In accordance with 10 CFR 100, Appendix A, in a September 17, 2011 letter (Serial No.11-520), Dominion submitted a Summary Report of the August 23, 2011 Earthquake Response and Restart Readiness Determination Plan to permit NRC evaluation of, and concurrence with, Dominion's restart of North Anna Units 1 and 2 following completion of the near-term action items.

Dominion has concluded that upon completion of the near-term activities, discussed within the September 17, 2011 letter (Serial No.11-520), it will have been adequately demonstrated that no functional damage has occurred to those features necessary for continued operation without undue risk to the health and safety of the public. Hence, NRC concurrence was requested to restart both North Anna units upon completion of the remaining near-term action items.

In a September 14, 2011, letter sent prior to the submittal of Dominion's Restart Readiness Determination Plan, the NRC requested additional information regarding the earthquake as discussed in the public meeting held on September 8, 2011. Some of the requested information was provided in the September 17, 2011 letter; however Dominion is providing a specific docketed response to address the requested information.

Serial Number 11-544 Docket Nos. 50-338/339 Page 2 of 3 To facilitate NRC review, Dominion is providing completed responses to several of the NRC questions in the attachment to this letter. Specifically, responses to Fuels questions 2, 4, 5, 6, 7, and 9 and Reactor Systems questions 1 through 5 are provided.

Dominion's response to the remaining questions (Fuels questions 1, 3, and 8) will be provided as timely as possible.

If you have any questions or require additional information, please contact Mr. Thomas Shaub at (804) 273-2763.

Sincerely, E. S. Grecheck Vice President - Nuclear Development Attachment There are no Commitments made in this letter.

COMMONWEALTH OF VIRGINIA )

COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by E. S. Grecheck who is Vice President - Nuclear Development, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief.

Acknowledged before me this 4A day of .'FfJl.C" 2011.

My Commission Expires: ,1]*2)I

• Ginger Lynn Rutherford NOTARY PUBLIC Commonwealth of Virginia Reg. # 310847 My Commission Expires 4/30/2015

Serial Number 11-544 Docket Nos. 50-338/339 Page 3 of 3 cc: U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 NRC Senior Resident Inspector North Anna Power Station M. Khanna NRC Branch Chief- Mechanical and Civil Engineering U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9E3 11555 Rockville Pike Rockville, MD 20852-2738 R. E. Martin NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 P. G. Boyle NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 Mr. J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.

Suite 300 Glen Allen, Virginia 23060

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake ATTACHMENT Response to Request for Information August 23, 2011 Earthquake Fuels and Reactor Systems Virginia Electric and Power Company (Dominion)

North Anna Units I and 2

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 1 of 22 BACKGROUND The following requests for information are related to the 'earthquake of August 23, 2011, that occurred in the vicinity of the NAPS, as discussed in the public meeting held on September 8, 2011. The following questions are grouped according to the format of the NAPS Final Safety Analysis Report (FSAR).

To facilitate NRC review, Dominion is providing responses to several of the NRC questions in this letter. Specifically, response to Fuels questions 2, 4, 5, 6, 7, and 9 and Reactor Systems questions 1 through 5 are provided. Dominion's response to the remaining questions (Fuels questions 1, 3, and 8) will be provided as timely as possible.

NRC REQUEST FOR INFORMATION 4.0 Fuel

2. Describe the extent of fuel assembly inspections which will be performed to confirm the structural integrity of the fuel. Provide specific information on how the inspections will determine that there is no distortion of the fuel lattice array or rod cluster control assembly (RCCA) guide tubes that occurred as a result of the seismic event. Also provide information on guide tube drag and rod drop testing.

Dominion Response The EPRI NP-6695, "Guidelines for Nuclear Plant Response to an Earthquake," only mentions fuel and control rods briefly. Results of physical inspections of the plant indicate the seismic event damage is consistent with Intensity 0 on the EPRI seismic damage scale.

NP-6695 describes how prescribed inspections and tests are keyed to the severity of the earthquake. No specific inspections of fuel or associated components are specified in NP-6695 for Intensity 0 earthquakes. Since the earthquake did not produce any significant physical or functional damage to safety-related plant structures, systems and components (SSCs) and only limited damage to non-safety related, non-seismically designed SSCs that were examined following the event, there is reasonable assurance that there was no significant physical or functional damage to the fuel, and that the fuel remains functional and capable of performing its design functions. The inspections described herein provide additional confirmation that the earthquake resulted in no significant physical or functional damage to the fuel or fuel insert components, and that they remain fully functional and capable of performing their design basis functions.

Dominion, with input from AREVA, compiled a list of inspections to be conducted for fuel and fuel inserts in the new fuel storage racks and spent fuel pool, and during offload of the Unit 2 core, to verify the acceptability of the Unit 2 fuel for use or reuse. The Unit 2 fuel has been examined, and these inspections were used to assess the condition of the Unit 1 fuel. No inspections of Unit 1 fuel are planned subject to the Unit 2 fuel meeting the inspection criteria.

Miscellaneous Inspections to Support Fuel Inspections Before any fuel inspections were performed by station personnel in the spent fuel pool area the following inspections were performed:

,Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 2 of 22

• Prior to any movement of fuel assemblies for inspection, the handling equipment - including handling tools, new fuel elevator and bridge crane - was verified as operational using functional checkouts required in the fuel handling procedures.

• Slight movement of the racks had been postulated during a design basis earthquake (DBE).

The spent fuel storage rack arrays were inspected to confirm that the racks had not shifted significantly and that structural changes had not occurred during the earthquake. The indexing coordinates used on the bridge crane were verified to remain accurate by inserting and removing the dummy fuel assembly in two empty spent fuel cells in each rack. Videos of the rack cells taken after the earthquake were also compared with previously existing videos of the racks. There were no detectable structural changes of the storage racks.

" The dummy fuel assembly was lifted and visually inspected prior to its use for any other system checkouts or verification.

New Fuel Storaqe Prior to moving any fuel assemblies an inspection of the underneath portion of the new fuel storage area was conducted to ensure there was no damage or distortion that would lead to interferences between the fuel assemblies and the storage cells when raising the fuel assemblies. There were no Condition Reports initiated from that inspection that indicated conditions exist that would result in any adverse impact on the fuel.

At the time of the earthquake, there were eighteen new fuel assemblies in the new fuel storage area, eleven of which contained burnable poison rod assemblies (BPRAs). In addition, there was one new BPRA hanging from a support plate in a new fuel storage cell.

The eighteen fuel assemblies were free standing in their storage cells and thus able to move and contact the cell walls during a seismic event. These eighteen fuel assemblies were visually inspected for any evidence of impact between the storage cell and the grids or any other parts of the assembly. This inspection was more involved than the normal new fuel receipt inspections. AREVA provided recommendations on the scope and criteria to be used during these inspections. Inspections included verification that all visible quick disconnect locking lugs remained in the locked position, visual examination of the outer row of fuel rods for anomalies that might indicate deformation of the grids, visual inspection of rod to rod and rod to guide tube gaps to the extent possible, and visual inspection of inner grid strip straightness to the extent possible. Rod cluster control assemblies (RCCA) insertion force was measured for the seven new fuel assemblies that did not contain BPRAs at the time of the earthquake to ensure that there is no distortion of the guide tubes. (A spare, unirradiated RCCA was used for this purpose.) The eighteen assemblies were found to meet the inspection criteria.

The eleven BPRAs that were in new fuel assemblies were each lifted a short distance by hand and lowered back into the fuel assembly to ensure that they would self-seat. Additional inspections were performed on these eleven BPRAs in accordance with the AREVA recommendations, including inspections of the nuts and welds connecting the poison rodlets to the BPRA baseplates and, while the BPRAs were slightly raised, inspecting the BPRA rodlets for dents or abrasions to the extent possible. The BPRA that was hanging from the support plate was inspected when it was removed from the support plate and placed in a fuel assembly. AREVA provided separate inspection recommendations for this BPRA, which again included inspection of the connections of the rodlets to the baseplate, visual inspection of the rods for straightness (qualitative inspection while BPRA was hanging), and inspection

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 3 of 22 of the full length of the rods for dents, abrasions, or yielding. The inspected BPRAs were determined to meet the inspection criteria.

Spent Fuel Pool The spent fuel pool rack cells are 8.875 inches square on the inside. There is slightly less clearance between the fuel and the cell walls in the spent fuel racks compared to the new fuel storage cells, and the potential for fuel damage in the spent fuel pool is further reduced by hydraulic damping effects. Nevertheless, the following inspections were performed:

• Five new fuel assemblies scheduled for use in Unit 2 Cycle 22 that were placed into the spent fuel pool prior to the earthquake were video inspected for any signs of damage.

These fuel assemblies were inspected in accordance with the recommendations provided by AREVA, and the inspections included verification that all visible quick disconnect locking lugs remained in the locked position, visual examination of the outer row of fuel rods for anomalies that might indicate deformation of the grids, visual inspection of rod to rod and rod to guide tube gaps to the extent possible, and visual inspection of inner grid strap straightness to the extent possible.

• During preparation of the spent fuel pool prior to the Unit 2 offload, a pre-core offload fuel shuffle was performed. During this shuffle, a sample consisting of ten of these fuel assemblies was also video inspected for any signs of damage. When inspecting these irradiated fuel assemblies, Dominion's normal criteria for irradiated fuel inspections were used to assess the condition of the fuel.

The population of new fuel assemblies and fuel assemblies moved during the pre-core offload fuel shuffle that was inspected provides a representative sample of the fuel and storage locations across the spent fuel pool. The fuel assemblies examined during these inspections met the inspection criteria.

Unit 1 and Unit 2 Cores At the time of the seismic event on August 23, 2011 RCS coolant activity indicated zero fuel failures in the Unit 2 core and an estimated two failed fuel rods in the Unit 1 core. The Unit 1 and Unit 2 RCS coolant activity following shutdown was consistent with the known fuel condition at the time of the earthquake, and indicated that no fuel failures occurred in either unit as a result of the earthquake. Because there were no indications of fuel failures in the Unit 2 core, no fuel sipping inspections - which are used to identify fuel assemblies containing leaking fuel rods - were required.

Prior to the Unit 2 core offload, the tops of two fuel assemblies that did not contain inserts (either RCCAs or discrete BPRAs) were examined to ensure the quick disconnect mechanisms remained properly locked. The locking lug position was checked for one assembly in the interior of the core and for one assembly in a baffle core location in accordance with AREVA recommendations. The locking lugs were determined to be properly positioned.

Binocular visual inspections were performed on the 157 fuel assemblies in the Unit 2 core during the core offload. Such visual inspections are performed as part of the normal refueling outage work scope, to look for any damage or other fuel anomalies. The appearance of the

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 4 of 22 fuel assemblies during the North Anna 2 Cycle 21 core offload was consistent with fuel assemblies inspected during previous core offloads, with no observations of grid or fuel rod damage that would indicate any unusual interaction between adjacent fuel assemblies or between fuel assemblies and the core baffle.

The only fuel anomalies that were identified during the North Anna 2 core offload visual inspections were indications of excessive fuel rod bow in some second- and third-cycle assemblies. Twenty fuel assemblies (five assemblies scheduled for reuse in Cycle 22 and fifteen assemblies scheduled for discharge at the end of the current cycle) were identified as potentially having sufficient fuel rod bow to result in channel closure (rod-to-rod contact) or envelope violations (rods extending beyond the plane identified by the fuel assembly nozzles and grids). Consistent with Dominion's normal inspection practice, detailed video inspections were performed of each fuel assembly in which a possible anomalous condition was identified during the core offload. These detailed video inspections confirmed the presence of channel closure or envelope violations in ten of the twenty fuel assemblies that had been identified. All ten fuel assemblies with confirmed anomalies were scheduled for discharge at the end of Cycle 21. The existence of significant fuel rod bow, the number of potentially affected fuel assemblies identified by the binocular inspections, and the number of confirmed instances of channel closure or envelope violation are consistent with previous experience with fuel rod bow in the AREVA Advanced Mark-BW fuel design at both North Anna units.

There is no indication that the seismic activity that resulted in the Unit 2 shutdown affected the presence of this phenomenon in some fuel assemblies, the frequency of occurrence, or the magnitude of fuel rod bow.

Dominion fuel inspection procedures also require that a sampling of fuel assemblies be video inspected in detail after the offload. The fuel assemblies selected for this inspection were selected to provide an overview of the core, and included fuel assemblies from each reload batch in the core. The selected fuel also represented different types of power histories within each batch and different core locations (interior and baffle locations, and locations in each quadrant of the core). Prior to the earthquake, thirteen fuel assemblies had been selected for inspection during the North Anna 2 refueling outage. AREVA also recommended that video inspections be performed on twenty fuel assemblies that resided in or near baffle locations that are predicted to be most susceptible to seismic damage. During these video inspections, recommendations provided by AREVA (e.g., half-face video inspections, inspection of rod to rod gap, inspection of grids from above and below for inner grid strip straightness) were used to supplement Dominion's normal criteria for irradiated fuel inspections. Any reuse fuel assembly with an anomalous condition (i.e., identified during the offload visuals as potentially having significant fuel rod bow) was inspected in the same manner. The appearance of the North Anna 2 fuel assemblies was consistent with observations made during previous refueling outages. There were no indications of grid, fuel rod or fuel assembly deformation or damage. If the vertical acceleration had been sufficient to lift the core and compress the top nozzle hold down springs, some indications might have appeared on the springs or on the corner pads if the springs bottomed out. Inspections of the side of the nozzle when the video inspections were performed did not identify any such damage to the nozzles.

When the units tripped during the recent seismic event, RCCAs fully inserted. When RCCAs are removed from fuel assemblies, the design of the RCCA handling tool prevents inspection of the RCCA rodlets. To confirm that there is no distortion of the RCCA rodlets or the fuel assembly guide tubes, and that the RCCAs can still freely travel within the fuel assembly

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 5 of 22 guide tubes, RCCA drag loads were measured in the spent fuel pool. Measurements have been performed in the 48 fuel assemblies in which the RCCAs resided during Cycle 21.

Following the movement of the RCCAs into their host fuel assemblies for Cycle 22, additional measurements of drag loads were performed. The fuel assemblies in which the RCAs were placed for Cycle 22 were also in the North Anna 2 core at the time of the earthquake. The data from these measurements are currently being analyzed.

The RCCAs used at North Anna are a Westinghouse design in which the radial vanes are tack welded, and then brazed, to the central hubs. Over the years, there have been isolated incidents in the industry where an RCCA vane has separated from the central hub in this design. To provide additional confirmation that the seismic event did not compromise the RCCA integrity, prior to the handling of individual RCCAs (drag measurements, movement to other assemblies), a video inspection of the RCCA hubs was performed, with emphasis on the joints where the radial vanes are brazed to the RCCA central hubs. No indications of any cracks or other flaws were observed.

Post-latch drag testing and hot rod drops of the RCCAs are already required as part of the normal start-up activities, and will be performed on Unit 2 prior to the unit entering Mode 2.

In addition, hot rod drops of the RCCAs will be performed on Unit 1 prior to the unit entering Mode 2. These tests ensure the proper alignment of the RCCAs and fuel assemblies, ensure that the RCCAs move freely, ensure that the control rod drive mechanisms (CRDMs) are functional, and verify that the Technical Specifications requirements for RCCA insertion are satisfied.

Conclusions Inspections performed on the North Anna 2 fuel included:

• Detailed visual inspections of the new fuel assemblies and BPRAs that were in the new fuel storage area, including RCCA insertion force for assemblies that did not contain BPRAs at the time of the seismic event

• Detailed visual inspections of a sample of the new fuel assemblies and BPRAs that had already been placed in the spent fuel pool

• Visual inspections of a sample of fuel assemblies stored in the pool at the time of the seismic event

" Binocular inspections of the North Anna 2 fuel in core at the time of the seismic event, and detailed visual inspection of any anomalies identified during the core offload

• Detailed visual inspections of a representative sample of fuel assemblies from the Cycle 21 core

• Detailed visual inspections of fuel assemblies from the Cycle 21 core locations predicted to be most susceptible to damage during a seismic event

• Visual inspection of the RCCA hubs

• Control rod drag measurements of the fuel assemblies that contained RCCAs in Cycle 21 and the fuel assemblies that will contain RCCAs in Cycle 22 to confirm the operability of the fuel assembly guide tubes and RCCAs.

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 6 of 22 Reduction of the data from the control rod drag testing is currently in progress. The fuel assemblies met the inspection criteria of the additional visual inspections. The appearance of the fuel assemblies and fuel insert components was consistent with fuel assemblies inspected during previous refueling outages. There were no indications of deformation of or other damage to the fuel assemblies, fuel assembly grids or fuel rods, or to the BPRAs or RCCAs as a result of the August 23, 2011 seismic event that would adversely impact their ability to safely perform their design functions.

The fuel assemblies and insert components in North Anna Unit 1 are of the same design as the Unit 2 fuel and insert components that were inspected, and were subjected to the same seismic loads during the August 23, 2011 earthquake. The impact of the seismic loads on the Unit 1 fuel and inserts would therefore be similar to the impacts on the Unit 2 fuel and inserts. No damage to the Unit 2 fuel or inserts was identified by the visual inspections that were performed, so it is concluded that the North Anna 1 fuel and inserts were similarly not subjected to any loads or vibrations that would adversely impact their ability to continue to safely perform their design functions. To the extent possible, the restart of Unit 1 will include performance of the tests and verifications that are normally applied during startup from a refueling outage. Because the Unit 1 reactor vessel was not disassembled following the August 23, 2011 seismic event, post-latch drag testing of the RCCAs normally performed as part of reactor reassembly to provide a first indication that the RCCAs are aligned and moving freely cannot be performed for Unit 1. However, hot rod drop testing of the Unit 1 RCCAs will be performed in accordance with station procedures as a final confirmation of the full functionality of the RCCAs.

This information is also discussed in Dominion's letter dated September 27, 2011 (Serial No.

11-520A).

4. Describe the extent of inspections and testing which will be performed to demonstrate the operability of the control element drive mechanisms.

Dominion Response The Rod Control System was included in the system inspections, detailed in Dominion's September 17, 2011 letter (Serial No.11-520), and there was no observed significant physical or functional damage.

Operability of the control rod drive system will be verified by completion of Technical Specification required surveillance tests. These surveillance tests will be performed during the startup of North Anna Units 1 and 2. Logic timing and current order testing will also be performed to ensure operability of the Rod Control system. A description of each test that will be performed is described below.

Quarterly Control Rod Operability Test This test determines operability, by movement, of each full length RCCA in accordance with Technical Specification Surveillance Requirement 3.1.4.2. The testing proves operability of the Control Rod System when a startup is in progress by verifying that each Control Rod and Shutdown Rod withdraws at least 10 steps as indicated by the Individual Rod Position Indication (IRPI) System.

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 7 of 22 Rod Drop Time Test This test determines operability by measuring the drop time of each RCCA at full flow RCS conditions in order to verify that the time from initiation of the RCCA drop to the entry of the RCCA into the dashpot is less than or equal to the maximum time allowed by Technical Specification Surveillance Requirement 3.1.4.3.

Logic Timing and Current Order Testing Testing is performed to verify the Rod Control System zero bus and neutral bus to plant ground resistance, Logic and Power Cabinets power supply output voltage, Logic Cabinet overvoltage protection setpoints, Logic and Power Cabinets non-urgent alarm circuits, the Logic Cabinet failure detection circuits, and Slave Cycle Decoder timing.

Testing is performed to verify the Logic and Power Cabinets power supplies load auctioneering circuits and the Power Cabinets failure detection circuits. This testing also obtains data traces of coil current profiles and coil current timing orders.

5. Provide any nuclear fuel related information that has been gathered considering the Electric Power Research Institute (EPRI) guidance and recommendations found in EPRI report NP-6695 (reference 3). Specific information of interest is control rod drive mechanism operability as related to changes in core instrumentation readouts; changes in primary coolant radiation monitor values; changes in other parameters such as primary coolant flow, temperature, and pressure; loose parts monitoring equipment noise signatures; and primary coolant chemistry sample results.

Dominion Response Plant Computer System data relevant to the RCS was reviewed. Based on a review of this data, the global RCS response is consistent with a normal reactor trip from full power followed by an RCP trip and coastdown from the loss of power to the RCP supply buses.

Reactor power decreases from the initial value and at no time exceeds 100% power. RCS temperatures trend smoothly toward hot zero power values as expected with no perturbations. All control rods fully inserted into the core in the time required by Technical Specifications Section 3.1.4. No indication of loose parts in the core was noted.

Considering this information and the lack of any unexpected increases in RCS coolant activity or containment radiation monitor indications, the nuclear fuel suffered no adverse consequences from 'the seismic event.

Prior to the seismic event on August 23, 2011, RCS radiochemistry data indicated that two failed fuel rods were present in the North Anna Unit 1 core, and that the Unit 2 core was defect free. The radiochemistry data measured following the unit shutdowns in response to the seismic event were consistent with the fuel integrity status as identified during steady state operation. As a result of fuel cladding defects in Unit 1 identified before the seismic event, the RCS radiochemistry data for Unit 1 are consistent with expected response following a unit shutdown. Similarly, with no cladding defects identified in Unit 2, the results are consistent with the expected response. Therefore, the data do not suggest any additional failures occurred due to the seismic event.

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 8 of 22 North Anna 1 (Figures 1-4)

Prior to the seismic event, North Anna 1 was estimated to contain two failed fuel rods. These failures were identified by unexplained, sustained increases in the RCS xeon (Xe-133 and Xe-135) levels, and by increases in the ratio of these two isotopes. There had been no increase in steady state RCS iodine levels, which indicated that the fuel rod failures were very small or present in low power fuel. The fuel currently in use at both North Anna units has experienced some grid to fuel rod fretting failures in fuel in its third operating cycle, when the fuel is located in low power locations on the periphery of the core, and it was anticipated that the Unit 1 failures may have been caused by the same mechanism.

When North Anna 1 shut down in response to the seismic event, activity spikes were observed in the North Anna 1 RCS which were consistent with the pre-existing failures in the core. During normal steady state operation, most isotopes are measured 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after the sample is taken, although 1-131 is measured 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the sample is taken to allow decay of other isotopes that may interfere with an accurate measurement. Following transients, multiple samples are obtained and 1-131 is typically measured after only 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.

Spikes in the RCS xenon levels (Xe-1 33 and Xe-1 35) were observed immediately following the unit shutdown, along with spikes in the 24-hour Iodine (1-131 and the 1-133) levels. The magnitude of these increases was consistent with past North Anna experience with low power defects in the core. Cesium data (Cs-134 and Cs-137) measured following the shutdown indicate that the burn up of the fuel failures is in the 40-45 GWD/MTU range. As the low power fuel in the North Anna core is on the periphery of the core, and this fuel is typically in its third operating cycle, the cesium data are also consistent with releases from the pre-existing failures in low power fuel rods. An additional increase in the RCS Xe-133 was observed in early September; this corresponded to depressurization of the RCS, and did not represent an additional failure.

North Anna 2 (Figures 5-8)

Prior to the seismic event, the RCS radiochemistry data indicated that North Anna 2 was operating with no failed fuel.

When North Anna 2 shut down in response to the seismic event, there were no spikes in the RCS radiochemistry data. The Xe-133, Xe-135, 24-hour 1-131, and 1-133 values all decreased from their steady state operating levels, with no increases that suggest a previously unidentified failure existed or had occurred as a result of the seismic event. The 1-hour 1-131 data, while higher than the 24-hour 1-131 data, showed a similar trend. The initial data points were consistent with 1-hour data obtained earlier in the cycle, and subsequently decreased, with no increases indicating that failed fuel rods were present in the core.

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 9 of 22 Figure 1 North Anna Unit I Cycle 22 Measured RCS Xe-133 Vs. Time 1.00E+00 200

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 10 of 22 Figure 2 North Anna Unit I Cycle 22 Measured RCS Xe-135 Vs. Time 1.00E+00 200 a XE-135 A Xe-135 (Pressurized)

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 11 of 22 Figure 3 North Anna Unit I Cycle 22 Measured RCS 1-131 Vs. Time 1 .OE-01 200 1 .0E-02 1 OE-03 a.

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 12 of 22 Figure 4 North Anna Unit I Cycle 22 Measured RCS 1-133 Vs. Time 1 .00E-01 200 1 .00E-02 1 .0 0 E -0 3 -.----------------------------------------------------------------------

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 13 of 22 Figure 5 North Anna Unit 2 Cycle 21 Measured RCS Xe-133 Vs. Time 1.00E+00 200 33 33 (Pressurized) 1.00E-01 1.00E-02 0.

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 14 of 22 Figure 6 North Anna Unit 2 Cycle 21 Measured RCS Xe-135 Vs. Time 1.00E+01 200

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 15 of 22 Figure 7 North Anna Unit 2 Cycle 21 Measured RCS 1-131 Vs. Time 1.00E+00 200 1-hr 1-131 a 1-131 (24-hr)

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 16 of 22 Figure 8 North Anna Unit 2 Cycle 21 Measured RCS 1-133 Vs. Time 1.00E+01 200 1.00E+00 1.00E-01

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Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 17 of 22

6. Explain the rationale and extent of the operability determinations for the core components (fuel and control rods) and their support systems.

Dominion Response As explained in the response to Question 2, detailed visual inspections were performed on a sampling of fuel assemblies that represented the various fuel batches in the core, the different operating histories experienced by the fuel, and different regions of the core. These inspections, which included additional focus on the fuel assembly grids for possible indications that loads may have been exerted on the fuel that might affect the structural integrity of the grids, found no indications of grid, fuel rod or fuel assembly deformation or damage. Excessive fuel rod bow was identified in some second- and third-cycle fuel assemblies, but this is a known phenomenon in the AREVA Advanced Mark-BW fuel, and there was no indication that the seismic event affected the existence of this phenomenon, the number of assemblies affected by it, or the magnitude of fuel rod bow.

The hubs of the RCCAs were examined to confirm that the seismic event did not adversely impact the weld joining the radial vanes to the central hub. Drag testing was performed to confirm that there was no deformation of the fuel assembly guide tubes or control rods that would adversely impact the ability of the RCCAs to insert. For Unit 2, control rod drag measurements will be verified again when the RCCAs are latched to the drive shafts prior to unit startup. For Unit 1 and Unit 2, hot rod drop time measurements and rod operability testing will be performed prior to entering Mode 2 to verify operability of the RCCAs and compliance with Technical Specifications requirements.

The results of inspections performed to date on the Unit 2 fuel and RCCAs indicate that the

'fuel and insert components in core at the time of the seismic event were not subjected to loads or vibrations that would adversely impact their performance. The fuel and insert components in North Anna Unit 1 are of the same design as the fuel and insert components that were inspected in Unit 2. Therefore, the Unit 1 fuel assemblies were subjected to the same seismic loads during the August 23, 2011 earthquake, and would have not been subjected to any loads or vibrations that would adversely impact their ability to continue to safely perform their design functions. To the extent possible, the restart of Unit 1 will include performance of the tests and verifications that are normally applied during startup from a refueling outage. Because the Unit 1 reactor vessel was not disassembled following the August 23, 2011 seismic event, post-latch drag testing of the RCCAs normally performed as part of reactor reassembly to provide a first indication that the RCCAs are aligned and moving freely cannot be performed for Unit 1. However, hot rod drop testing of the Unit 1 RCCAs will be performed in accordance with station procedures as a final confirmation of the full functionality of the RCCAs.

7. Provide the final root cause analysis report on the cause of the reactor trips.

Dominion Response A summary of the Root Cause Evaluation is contained in Dominion's letter entitled, "Post-Earthquake Restart Readiness Determination Plan Status Update," dated September 27, 2011, Serial No. 11-520A.

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 18 of 22

9. Third-burned fuel assemblies are generally located along the core periphery in locations where seismic loading may be limiting. These assemblies are at end-of-life and would be discharged to the spent fuel pool (SFP) (no reinsertion). Are there any plans to do detailed investigations and measurements (including rod pulls, dismantling, hot cell examinations) on any of the third-burned fuel assemblies located at the core periphery of Unit 2?

Dominion Response Because visual inspections of the North Anna 2 fuel and insert components (including fuel and components that were in the core as well as those in the new and spent fuel storage areas at the time of the August 23, 2011 seismic event) have shown no indications of damage, detailed inspections that involve dismantling of the assembly and rod removal are not currently planned. No destructive (hot cell) examination of the fuel is considered necessary.

5.0 Reactor Systems

1. Describe the evaluations, inspections and analyses of the steam generators (SG) to ensure SG tube integrity?

Dominion Response EPRI Steam Generator Management Program Pressurized Water Reactor Steam Generator Examination Guidelines, Revision 7, Section 3.10 states that forced outage examinations shall be performed during plant shutdown subsequent to seismic occurrence greater than the OBE. The guidelines require performance of a 20% sample inspection of Unit 1 and Unit 2 steam generator (S/G) tubes.

On Unit 1, 100% of the "A" S/G tubes were inspected, which is greater than the 20%

required sample of the Unit 1 S/G tubes, and no adverse indications were identified as a result of the earthquake. Inspection of the Unit 1 "A" S/G secondary side components also revealed no damage resulting from the earthquake. Additional detail of the Unit 1 S/G inspection results is included in Dominion's letter dated September 27, 2011 (Serial No. 11-520A). The Unit 2 "A" and "C" S/Gs are being inspected in a similar fashion during the current refueling outage.

2. Discuss provisions to ensure that system pressure relief capabilities are maintained.

Dominion Response During the trip response on August 23, 2011, several pressure relief valves were called upon to provide overpressure protection for plant equipment. The loss of power to the secondary plant caused main steam power operated relief valves (PORVs) on each unit to operate.

Main Steam (MS) System pressure was maintained within operating limits and the valves controlled pressure as designed. The 1 st point feedwater heaters were isolated and the shell-side relief valves maintained pressure by cycling as the heaters cooled.

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 19 of 22 Approximately ninety (90) pressure relief valves have preventive maintenance testing and rebuild work scheduled during the current Unit 2 refueling outage. These valves constitute a representative sample of the entire station (e.g., critical relief valves are tested a minimum of every 5 years and a portion of valves in each system is tested during a given refueling outage.)

One pressurizer safety valve (2-RC-SV-2551C) and the five (5) main steam safety valves (MSSVs) from the Unit 2 "B" SG were sent offsite for as-found testing. ASME O&M code contains provisions for scope growth based on initial test results, which would require a larger sample pool if any issues are found. Results of testing show that the five (5) MSSVs and the pressurizer safety valve lifted within the as-found tolerance.

Class 2 and 3 safety and relief valve testing is governed by periodic test (PT) 2-PT-147.1.

This PT identified the initial population of relief valves required to be tested to ensure compliance with ASME O&M code. The potential scope in inspection growth described above applies to this entire pool of valves as well. If valves fail from the initial sample group, additional testing is required to ensure proper pressure protection exists.

The pressure relief valves called upon to operate during both unit trips did so and prevented their respective systems from exceeding their maximum design pressures. Pressure relief valves were walked down and visually inspected as part of the seismic response effort and no damage was noted. Testing results thus far have been consistent with previous outage results. No adverse trends in the test results have been identified and no failures have been attributed to seismic damage.

Safety valves for high pressure systems such as the RCS and MS are designed to withstand the combined forces of an earthquake in combination with the load applied to the valves when relieving pressure. Typically, the pressure relief loading far exceeds the loading from the seismic event and therefore the valves that were not called upon to actuate during the event were subjected to forces below their design limit.

The current scope of testing on Unit 2 and lack of testing failures due to earthquake induced damage provides a reasonable assurance that pressure relief valves throughout both units are properly providing overpressure protection

3. Discuss measures to verify overall reactor coolant system (RCS) pressure boundary integrity.

Dominion Response Safety Analysis Summary of Reactor Trip Data The Plant Computer System data was reviewed relative to the requirements of the North Anna UFSAR safety analyses. Based on a review of this data, the global RCS response is consistent with a normal reactor trip from full power followed by a Reactor Coolant Pump (RCP) trip coastdown from the loss of power to the supply buses. Although there were some core power variations prior to full control rod insertion during the seismic event, power decreased from the initial value at the onset of the earthquake and at no time exceeded 100% power. RCS temperatures trended smoothly toward hot-zero power values as expected with no perturbations. There were some variations in pressurizer pressure and

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 20 of 22 level early in the event whose validity could not be confirmed; however, the overall trends were reasonable and the magnitudes, even considering the variations, were well within safety analysis response values.

Safety analysis events most applicable to this event are included in UFSAR Sections 15.2.7 "Loss of External Electrical Load and/or Turbine Trip" (LOEL), 15.2.9 "Loss of Offsite Power to the Station Auxiliaries" (LOEL), and 15.3.4 "Complete Loss of Reactor Coolant Flow" (CLOF). Since the reactor trip, turbine trip and reactor coolant pump trips occurred at essentially the same time during the seismic event, the transient response was bounded by the safety analysis response for these events. In particular, safety analysis requirements relative to core cooling/DNB criteria, RCS and main steam pressure, and pressurizer level were met. It is also noted that the LOEL, which demonstrates long-term core cooling, only credits operation of the motor-operated Auxiliary Feedwater System (AFW) pumps and therefore bounds initial unavailability (due to a surveillance test being performed at the onset of the seismic event) of the Unit 1 turbine-driven AFW pump.

In summary, the plant response remained or was bounded by the North Anna UFSAR safety analyses. The integrity of the core is maintained by operation of the reactor protection system and natural circulation flow through the RCS loops and reactor core. In addition, pressure relief valves and/or sprays maintained primary and secondary pressures well below safety analysis allowable values.

Consistent with the EPRI-NP-6695, "Guidelines for Nuclear Plant Response to an Earthquake," North Anna developed a methodology for performing inspections to assess significant physical or functional earthquake-related damage to structures, systems, and components (SSCs). Using this methodology, inspections were performed on the Reactor Coolant, Emergency Core Cooling, and Residual Heat Removal Systems. The inspections did not identify any significant physical or functional damage to the Reactor Coolant, Emergency Core Cooling, and Residual Heat Removal systems that would render them incapable of performing their design functions. A more detailed discussion of the attributes of the inspections and tests performed on North Anna plant SSCs to assess the potential earthquake damage is contained in Dominion's letter dated September 17, 2011 (Serial No.11-520).

In addition to the normal in-service inspection nondestructive examination activities planned for the ongoing Unit 2 refueling outage, additional sampling of Unit 1 and 2 weld inspections were completed for piping and pipe supports, which included the pressurizer spray line, RCS drain lines, RCS pump seal injection line and safety injection lines. No adverse findings were identified.

Additional, programmatic inspections conducted on the Reactor Coolant, Emergency Core Cooling, and Residual Heat Removal Systems in accordance the Boric Acid Corrosion Control (BACC) program and the augmented ISI program have identified no issues resulting from the seismic event.

4. Describe the inspections, examinations and evaluations of the emergency core cooling systems (ECCS) that have been or will be performed to show that the ECCS

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 21 of 22 will continue to perform as designed, especially under simultaneous design basis earthquake loading and ECCS design basis seismic requirements.

Dominion Response See the response provided in Dominion's letter dated September 17, 2011 (Serial No.11-520) concerning the attributes of the plant inspections.

The High Head Safety Injection (HHSI) Pumps (also the normal RCS makeup pumps) operated throughout the event with no anomalies noted. Performance testing has been conducted on the HHSI and Low Head Safety Injection (LHSI) pumps including oil sampling and vibration monitoring. The pumps performed as expected during this testing and no degradation in pump performance trends was noted. Successful operation during the event and post-event testing, as well as the lack of damage found during inspections, ensures the ECCS continues to be able to perform its design functions.

GDC 2 requires that structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design basis for these structures, systems and components shall reflect:

1. Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated.

2. Appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena.

North Anna ECCS systems are designed to withstand the combined effect of the accident loads and a seismic event. However, the North Anna licensing basis does not include a simultaneous seismic event and a design basis accident.

5. Were there any complications in residual heat removal (RHR) following the earthquake? Did all RHR equipment perform as intended?

Dominion Response When the seismic event occurred, both units were at power and the RHR systems were not in service. The Unit 1 RHR system was placed in service one day after the event, on August 24, 2011 at 1506 hours0.0174 days <br />0.418 hours <br />0.00249 weeks <br />5.73033e-4 months <br />. The Unit 2 RHR system was placed in service two days after the event, on August 25, 2011 at 1745 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.639725e-4 months <br />.

In each case, the system performed satisfactorily, as expected, with no noted issues or concerns. Historical trending comparing each unit's RHR system parameters with those observed during the cool-downs for the dual-unit outage one year earlier shows similar values and trends for heat-removal performance and associated temperatures and flow rates.

Inspections were conducted, as detailed in item 3, and no damage resulting from the seismic event was found. There has been no observed degradation or changes in the performance

Serial Number 11-544 Docket Nos. 50-338/339 Response to Request for Information - 08/23/11 Earthquake Page 22 of 22 of either unit's RHR system. The RHR systems in both units have been operated subsequent to the August 23, 2011 earthquake and no system performance issues have been identified.