ML090750027

Request for Additional Information Regarding Control Rod Drive Control System Replacement License Amendment

ML090750027
Person / Time
Site:	Three Mile Island
Issue date:	04/06/2009
From:	Peter Bamford Plant Licensing Branch 1
To:	Pardee C Exelon Nuclear
Bamford, Peter J., NRR/DORL 415-2833
References
TAC MD9762
Download: ML090750027 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 6. 2009 Mr. Charles Pardee President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

THREE MILE ISLAND NUCLEAR STATION, UNIT 1 - REQUEST FOR ADDITIONAL INFORMATION REGARDING CONTROL ROD DRIVE CONTROL SYSTEM REPLACEMENT LICENSE AMENDMENT (TAC NO. MD9762)

Dear Mr. Pardee:

By letter dated September 29, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML082800174), AmerGen Energy Company, LLC. (the licensee, now Exelon Generation Company, LLC) submitted a license amendment request regarding proposed changes to the technical specifications to reflect a planned replacement of the control rod drive control system for Three Mile Island Nuclear Station, Unit 1 (TMI-1).

The Nuclear Regulatory Commission staff has been reviewing the submittal and has determined that additional information is needed to complete its review. The specific questions are found in the enclosed request for additional information. The questions were sent via electronic transmission on March 13,2009, to Mr. Frank Mascitelli of your staff. The draft questions were sent to ensure that the questions were understandable, the regulatory basis for the questions was clear, and to determine if the information was previously docketed. The questions were discussed in teleconference with your staff on March 17, 2009, and March 24, 2009, and a clarifying sentence was added to question number four. It was agreed that a response would be submitted by May 6, 2009.

Please contact me at 301-415-2833, if you have any questions.

Sincerely,

~

Peter Bamford, Project Manager Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-289

Enclosure:

As stated cc: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 REQUEST FOR ADDITIONAL INFORMATION THREE MILE ISLAND NUCLEAR STATION, UNIT 1 CONTROL ROD DRIVE CONTROL SYSTEM REPLACEMENT AND AXIAL POWER SHAPING ROD REMOVAL DOCKET NO. 50-289 By letter dated September 29, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML082800174), AmerGen Energy Company, LLC, the Iicensee,1 submitted a license amendment request (LAR) for Three Mile Island Nuclear Station, Unit 1 (TMI-1). The licensee proposes to modify Technical Specifications (TSs) related to the Control Rod Drive Control System (CRDCS), Reactor Trip Breakers (RTBs) and Axial Power Shaping Rods (ASPRs). These proposed changes reflect a planned CRDCS upgrade to a digitally based system (DCRDCS) that will result in the replacement of the TMI-1 reactor trip breakers and elimination of the APSRs. In order for the NRC staff to complete its review of the LAR, a response to the following request for additional information is requested.

Background for questions 1-7: According to the LAR, the existing RTBs at TMI-1 are General Electric (GE) models AK-15 and AK-25 with direct current (DC) and alternating current (AC) control power. The proposed replacement breakers are Square D type Masterpact NT.

1.) The undervoltage (UV) device is used on GE AK type breakers to trip the breaker when loss of voltage occurs on the undervoltage device coil. The undervoltage device is used as a trip device because of the inference that it is fail safe i.e., it directly trips the breaker with mechanical action when all normal sources of control voltage have become unavailable for shunt trip type operations. The LAR indicates that the UV device on the Square D breakers is de-energized to trip. Describe how the undervoltage tripping circuit functions upon loss of control power in the proposed Square D breakers.

2.) GE Service Advisories and NRC Information Notice (IN) No. 88-38: "Failure of Undervoltage Trip Attachment on General Electric Circuit Breakers," document low design margins of the torque available to trip GE AK breakers with the UV device. The torque available to trip the General Electric AK type breakers by the UV device is critical to proper operation. Compare and contrast:

a) The torque available from the UV trip mechanism in the proposed Square D breakers and the existing GE breakers.

b) The torque available from the shunt trip mechanism in the proposed Square D breakers.

The operating license for TMI-1 has been transferred from AmerGen Energy Company, LLC to Exelon Generation Company, LLC as of January 8,2009.

Enclosure

-2 c) The torque required by the trip bar in the proposed Square D breakers and the existing GE breakers.

3.) The GE breakers had a response time of less than 80 milliseconds (ms) for operation.

Lubrication problems with the trip shaft roller bearings of the GE breakers resulted in slower response times. According to the LAR, the proposed Square D breakers have a response time (open) of 50 ms. Provide details on any planned actions to monitor degradation in the response time due to aging or other unknown failure mechanisms.

Will the response time of the automatic shunt trip feature and undervoltage trip be independently tested periodically to verify that the timing is less than or equal to that assumed in the safety analyses?

4.) The LAR indicates that a common mode failure for the Masterpact breakers due to radio frequency interference (RFI) or electromagnetic interference (EMI) was not credible since the undervoltage trip device and the shunt trip device are low impedance devices and are not susceptible to failures from EMI/RFI. Please summarize the results of the evaluation and/or testing done on the Masterpact breakers to show that the undervoltage/shunt coils are not susceptible to EMI/RFI. The Masterpact circuit breakers are typically equipped with Micrologic trip system to protect circuits and loads. This protective device has electronic components and a microprocessor. If the Micrologic trip system is used at TMI-1, then describe:

a. The testing conducted to verify that the protective system is not susceptible to RFI/EMI failures.

b. Planned actions to prevent unauthorized access and programming capabilities, local and remote, to the Micrologic system that could lead to inadvertent actuations of the system.

c. Planned actions to maintain control over the hardware, software and procedures used to test and calibrate the Micrologic protective system.

5.) According to the LAR, the shunt trip device for the proposed Square D breaker has a maximum rating of 137 Volts (V) DC for a nominal 125 VDC system. Will the shunt trip coils be subjected to voltages higher than their rating during battery float and charging conditions?

6.) The LAR provides DC ratings for the shunt trip device and AC ratings for the UV device.

In addition, the LAR describes the control power source for the non safety related existing and new Control Rod Drive Control System as the incoming sources for the RTBs. Describe the control power scheme for the operation of the new breakers and provide details on separation/isolation devices between safety and non-safety related portions of the control power.

7.) Provide a summary of failure modes and effects analysis performed for the Square D Masterpact NT breaker and the modified trip logic system.

8.) The final paragraph of Page 8 of Attachment 1 in part states that, "The DCRDCS does not perform a nuclear safety-related function and failure of the control system will not prevent the RPS from tripping the reactor." In this statement, does the term "failure"

-3 imply a complete loss of functionality, or are there other failure modes that do not involve a complete loss of functionality (e.g. ones where unintended operations are spontaneously initiated due to programmatic error) that could adversely impact the reactor protection system?

9.) The first paragraph of Page 10 of Attachment 1 in part states that, "changes to CRDM patching will only be available when the system is offline and requires recompiling the application software." In addition, the third paragraph of Page 10 of Attachment 1 in part states that, "to modify DCRDCS rod patching, the system must be offline with the reactor shutdown (all rods in)." Do these two sections refer to the same system, or different systems (Le., is "CRDM patching" the same as "DCRDCS rod patching")? Also, for these systems, please explain why it is not possible for patching to occur if system is online and/or if the reactor is not shutdown. Specifically is patching modification not physically possible, or is this restriction simply enforced by information technology policy?

April 6, 2009 Mr. Charles Pardee President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

THREE MILE ISLAND NUCLEAR STATION, UNIT 1 - REQUEST FOR ADDITIONAL INFORMATION REGARDING CONTROL ROD DRIVE CONTROL SYSTEM REPLACEMENT LICENSE AMENDMENT (TAC NO. MD9762)

Dear Mr. Pardee:

By letter dated September 29,2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML082800174), AmerGen Energy Company, LLC. (the licensee, now Exelon Generation Company, LLC) submitted a license amendment request regarding proposed changes to the technical specifications to reflect a planned replacement of the control rod drive control system for Three Mile Island Nuclear Station, Unit 1 (TMI-1).

The Nuclear Regulatory Commission staff has been reviewing the submittal and has determined that additional information is needed to complete its review. The specific questions are found in the enclosed request for additional information. The questions were sent via electronic transmission on March 13, 2009, to Mr. Frank Mascitelli of your staff. The draft questions were sent to ensure that the questions were understandable, the regulatory basis for the questions was clear, and to determine if the information was previously docketed. The questions were discussed in teleconference with your staff on March 17, 2009, and March 24,2009, and a clarifying sentence was added to question number four. It was agreed that a response would be submitted by May 6, 2009.

Please contact me at 301-415-2833, if you have any questions.

Sincerely,

/raj Peter Bamford, Project Manager Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-289

Enclosure:

As stated cc: Distribution via Listserv DISTRIBUTION:

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• WKemper** HChernoff DATE 03/24/2009 04/01/2009 03/10/2009 02/19/2009 04/06/2009 OFFICIAL RECORD COPY