2CAN021503, Response to RAI Associated with the Elimination of Movement of Coontrol Element Assembly 18 from Surveillance Requirement 4.1.3.1.2 for the Remainder of Cycle 24
| ML15055A385 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/24/2015 |
| From: | Jeremy G. Browning Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2CAN021503 | |
| Download: ML15055A385 (7) | |
Text
s Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-3110 Jeremy G. Browning Vice President - Operations Arkansas Nuclear One 2CAN021503 February 24, 2015 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
License Amendment Request Supplement Response to RAI Associated with the Elimination of Movement of Control Element Assembly 18 from Surveillance Requirement 4.1.3.1.2 for the Remainder of Cycle 24 Arkansas Nuclear One, Unit 2 Docket No. 50-368 License No. NPF-6
REFERENCES:
- 1. Entergy letter dated February 6, 2015, Allowance to Eliminate Movement of Control Element Assembly 18 from Surveillance Requirement 4.1.3.1.2 for the Remainder of Cycle 24 (2CAN021501) (ML15041A068)
- 2. NRC email dated February 23, 2015, Request for Additional Information Related to License Amendment Request to Eliminate Movement of Control Element Assembly per SR 4.1.3.1.2 (TAC No. MF5698)
(2CNA021501)
Dear Sir or Madam:
By letter dated February 6, 2015 (Reference 1), Entergy Operations, Inc. (Entergy) submitted a request for an amendment to Arkansas Nuclear One, Unit 2 (ANO-2) Technical Specifications (TS) to eliminate exercising Control Element Assembly (CEA) 18 for the remainder of operating Cycle 24, currently scheduled to end September 20, 2015. The proposed amendment would modify a Note to Surveillance Requirement (SR) 4.1.3.1.2 such that CEA 18 may be excluded from SR performance for the remainder of Cycle 24.
In the course of its review, the NRC staff has determined that additional information is required to complete its evaluation of the request (Reference 2). Entergys response to the NRCs request for additional information (RAI) is included in attachment to this letter.
In accordance with 10 CFR 50.91(b)(1), a copy of this application is being provided to the designated Arkansas state official.
No new commitments have been identified in this letter.
2CAN021503 Page 2 of 2 If you have any questions or require additional information, please contact Stephenie Pyle at 479-858-4704.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on February 24, 2015.
Sincerely, ORIGINAL SIGNED BY JEREMY G. BROWNING JGB/dbb
Attachment:
RAI Response Related to CEA 18 Exercise cc: Mr. Marc L. Dapas Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector Arkansas Nuclear One P. O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Ms. Andrea E. George MS O-8B1 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. Bernard R. Bevill Arkansas Department of Health Radiation Control Section 4815 West Markham Street Slot #30 Little Rock, AR 72205
Attachment to 2CAN021503 RAI Response Related to CEA 18 Exercise
Attachment to 2CAN021503 Page 1 of 4 RAI Response Related to CEA 18 Exercise By letter dated February 6, 2015 (Reference 1), Entergy Operations, Inc. (Entergy) submitted a request for an amendment to Arkansas Nuclear One, Unit 2 (ANO-2) Technical Specifications (TS) to eliminate exercising Control Element Assembly (CEA) 18 for the remainder of operating Cycle 24, currently scheduled to end September 20, 2015. The proposed amendment would modify a Note to Surveillance Requirement (SR) 4.1.3.1.2 such that CEA 18 may be excluded from SR performance for the remainder of Cycle 24.
In the course of its review, the NRC staff has determined that additional information is required to complete its evaluation of the request (Reference 2). Entergys response to the NRCs request for additional information (RAI) is included below.
SRXB - RAI 1 In its LAR, the licensee states that the proposed amendment is necessary due to a degrading Upper Gripper Coil (UGC) which was initially identified while performing SR 4.1.3.1.2 in October 2014. The licensee noted further degradation of the UGC while performing the subsequent SR 4.1.3.1.2 in January 2015. Is there any other possible cause (other than the degradation of the UGC) for the difficulties encountered while performing SR 4.1.3.1.2? If so, describe the possible causes.
Response
The wide current trace described in Entergys February 6, 2015 (Reference 1), letter can be caused by degradation in the gripper coil or degradation of the firing circuit. The power switch components or the coil driver card could also fire the circuit improperly generating higher current draw and improper traces. The coil driver card failures typically result in a full firing of the circuitry even when not activated. A degraded power switch opto-isolator could also provide a similar trace. However, the increase in the current draw and the observed similar traces for a previous coil failure make the opto-isolator a secondary cause and not the most probable.
To troubleshoot and repair a failed opto-isolator or coil driver card requires use of the hold bus and the UGC to hold the rod in place while the power switch is removed. Further troubleshooting in this regard is not considered in the best interest of nuclear safety since the failure modes of the UGC previously described could result in a plant transient and/or shutdown (i.e., the rod would drop into the core if the UGC failed during troubleshooting efforts).
SRXB - RAI 2 In its LAR, the licensee states that troubleshooting identified several possible causes for the degradation of the UGC and that degradation could cause the rod to drop into the core. Could any of the identified degradation mechanisms prevent the rod from dropping into the core when the reactor trip breakers are opened?
Attachment to 2CAN021503 Page 2 of 4
Response
All postulated failure modes are associated with the coil and associated control circuitry. The Reactor Trip Circuit Breakers (RTCBs) are upstream of the control and power switch assemblies (reference electrical distribution diagram provided below). The RTCBs open upon an automatic or manual reactor trip signal, removing all power from both control and holding circuitry. All coils on each CEA subsequently de-energize resulting in all CEAs inserting into the core. This design is fail-safe in that a loss of power itself, regardless of whether a reactor trip signal has been generated, will result in the CEAs inserting into the core.
As described in Entergys original letter (Reference 1), the Control Element Drive Mechanism (CEDM) is an electromechanical device such that the various grippers associated with each CEA are magnetically coupled to the subject coil; there is no physical (mechanical) coupling between the CEDM circuit/coil and the associated gripper. Entergy stated in its Reference 1 letter that heating was the primary driver for coil degradation. This heating is associated with the internal heating of the coil windings. Any postulated failure mechanism that could prevent rod insertion (such as mechanical binding of the CEA itself) is not influenced or impacted by coil failure or, control or holding circuitry failures. Therefore, there are no postulated failure mechanisms where the coil or associated circuitry could physically prevent rod insertion once the RTCBs have opened.
In addition, the postulated failure modes would not affect the RTCBs. Although not directly related to the identified condition of CEA 18, the system is designed in accordance with single failure criteria such that all circuitry will be de-energized even if one RTCB fails to open upon a reactor trip, as can be seen in the below schematic.
The control circuitry does not impact the trip circuit breaker nor is there a failure mode associated with the control circuitry which would prevent the loss of holding power when the trip circuit breakers open. As described in Entergys original letter (Reference 1), the CEDM is an electromechanical device that uses induced magnetic fields to operate a mechanism for moving a CEA. The control circuity and/or power source interacts with the lifting device magnetically and is not electrically connected to the mechanical grippers which perform the actual movement of the CEA. The CEAs are designed to fail safe on loss of power. Therefore, once power is lost (normally by opening of the RTCBs), no failure mode exists within the CEDM control or power circuitry that could interfere with control rod insertion.
Attachment to 2CAN021503 Page 3 of 4 2B-7 2B-8 MOT MOT 480V, 3 , 60 Hz A B GENERATOR GEN GEN 240V, 3 , 60 Hz DSS CABINET 52-1/DSS 29-1/DSS 29-2/DSS 52-2/DSS DSS CABINET 2C-407 2C-408 MG CONTROL SYNCHRONIZATION PANEL TCB-9 REACTOR TCB-2 TCB-6 TCB-7 TCB-3 TRIP PPS K2 PPS K3 SWITCHGEAR TCB-1 TCB-5 TCB-8 TCB-4 PPS K1 PPS K4 UV-2 UV-1 UV-4 UV-3 C4 2C70 (C2) 2C71 (C3)
Subgroup Circuit CEA #1 Breakers SUBGROUP 1 - 10 SUBGROUP 11 - 20 A B C N
COIL DRIVE ALL PHASES PLUS GND ACTUATION LOGIC SHOWN, FOR TYPICAL SUBGROUP Y2 Y3 Y4 Y1 Y2, Y3, Y4 SIMILAR TO Y1 LC Y2 UG PD Y3 LT Y4 LG CEDMCS ELECTRICAL DISTRIBUTION SRXB - RAI 3 Are there are any other possible degradation mechanisms of the UGC that could prevent the rod from dropping into the core when the reactor trip breakers are opened?
Response
Please see response to SRXB - RAI 2 above.
Attachment to 2CAN021503 Page 4 of 4 SRXB - RAI 4 In its LAR, the licensee states that electrical problems will not prevent insertion of a CEA into the core when the reactor trip breakers are opened. The licensee also states that heating is the primary driver for the UGC degradation. Is it possible for the heating to cause some non-electrical failure that could prevent the rod from dropping into the core when the reactor trip breakers are opened?
Response
Please see response to SRXB - RAI 2 above.
SRXB - RAI 5 In its LAR, the licensee states that it performed calculations to show that adequate shutdown margin is available (per the current Core Operating Limits Report (COLR) requirement) assuming both CEA 18 and the single CEA of highest reactivity worth failed to insert. Please confirm that these calculations were performed using the NRC-approved methodologies currently used by ANO-2 to generate the COLR.
Response
The COLR is developed using the NRC approved methodologies listed in Section IV of the COLR. When performing TS surveillances to verify adequate Shutdown Margin (SDM) is present, plant procedures use models and methods approved for use by the NRC by acceptance of the Entergy topical report ENEAD-01-P-A, Qualification of Reactor Physics Methods for the Pressurized Water Reactors of the Entergy System (Reference 3). The calculations performed to assure adequate SDM would exist, assuming both CEA18 and the single CEA of highest reactivity worth failed to insert, utilized the same models and methods as those utilized to perform the TS surveillances.
REFERENCES
- 1. Entergy letter dated February 6, 2015, Allowance to Eliminate Movement of Control Element Assembly 18 from Surveillance Requirement 4.1.3.1.2 for the Remainder of Cycle 24 (2CAN021501) (ML15041A068)
- 2. NRC email dated February 18, 2015, Request for Additional Information Related to License Amendment Request to Eliminate Movement of Control Element Assembly per SR 4.1.3.1.2 (TAC No. MF5698) (2CNA021501)
- 3. NRC letter dated September 29, 1995, Topical Report ENEAD-01-P, Rev. 0, "Qualification of Reactor Physics Methods for Application to Pressurized Water Reactors of the Entergy System" (TAC NOs. M88565, M88566, and M88567) (0CNA099519)