ML082130140

Request for Additional Information Related to Related to Request for License Amendment to Allow Ganged Rod Drive Capability of the Rod Control Management System Tac Nos. MD7900 and MD7901)

ML082130140
Person / Time
Site:	LaSalle
Issue date:	08/01/2008
From:	Sands S NRC/NRR/ADRO/DORL/LPLIII-2
To:	Pardee C Exelon Generation Co
Sands S,NRR/DORL, 415-3154
References
TAC MD7900, TAC MD7901
Download: ML082130140 (6)

Text

August 1, 2008 Mr. Charles G. Pardee Chief Nuclear Officer and Senior Vice President Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LASALLE COUNTY STATION, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO REQUEST FOR LICENSE AMENDMENT TO ALLOW GANGED ROD DRIVE CAPABILITY OF THE ROD CONTROL MANAGEMENT SYSTEM (TAC NOS. MD7900 AND MD7901)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated August 14, 2007, as supplemented by letter dated May 13, 2008, Exelon Generation Company, LLC submitted a request to allow ganged rod-drive capability of the Rod Control Management System, for the LaSalle County Station, Units 1 and 2.

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on July 21, 2008, it was agreed that you would provide a response 30 days from the date of this letter.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC=s goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-3154.

Sincerely,

/RA/

Stephen P. Sands, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-374

Enclosure:

Request for Additional Information cc w/encl: See next page

Mr. Charles G. Pardee August 1, 2008 Chief Nuclear Officer and Senior Vice President Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LASALLE COUNTY STATION, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO REQUEST FOR LICENSE AMENDMENT TO ALLOW GANGED ROD DRIVE CAPABILITY OF THE ROD CONTROL MANAGEMENT SYSTEM (TAC NOS. MD7900 AND MD7901)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated August 14, 2007, as supplemented by letter dated May 13, 2008, Exelon Generation Company, LLC submitted a request to allow ganged rod-drive capability of the Rod Control Management System, for the LaSalle County Station, Units 1 and 2.

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on July 21, 2008, it was agreed that you would provide a response 30 days from the date of this letter.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC=s goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-3154.

Sincerely,

/RA/

Stephen P. Sands, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-374

Enclosure:

Request for Additional Information DISTRIBUTION:

PUBLIC RidsNrrBCGCranston RidsNrrBCWKemper LPL3-2 R/F RidsNrrDorlLpl3-2 RidsAcrsAcnw&mMailCenter RidsNrrPMSSands RidsNrrLATHarris RidsNrrDorlDpr RidsOgcRp RidsRgn3MailCenter ADAMS Accession Number: ML082130140 OFFICE LPL3-2/PM LPL3-2/LA LPL3-2/BC NAME SSands THarris RGibbs (MDavid for)

DATE 7/31/08 7/31/08 8/1/08 OFFICIAL RECORD COPY

LaSalle County Station, Units 1 and 2 cc:

Site Vice President - LaSalle County Station Robert Cushing, Chief, Public Utilities Division Exelon Generation Company, LLC Illinois Attorney General's Office 2601 North 21st Road 100 W. Randolph Street Marseilles, IL 61341-9757 Chicago, IL 60601 Illinois Emergency Management Plant Manager - LaSalle County Station Agency Exelon Generation Company, LLC Division of Disaster Assistance &

2601 North 21st Road Preparedness Marseilles, IL 61341-9757 1035 Outer Park Dr Springfield, IL 62704 Manager Regulatory Assurance - LaSalle Exelon Generation Company, LLC Document Control Desk - Licensing 2601 North 21st Road Exelon Generation Company, LLC Marseilles, IL 61341-9757 4300 Winfield Road Warrenville, IL 60555 U.S. Nuclear Regulatory Commission LaSalle Resident Inspectors Office Senior Vice President - Operations Support 2605 North 21st Road Exelon Generation Company, LLC Marseilles, IL 61341-9756 4300 Winfield Road Warrenville, IL 60555 Phillip P. Steptoe, Esquire Sidley and Austin Director - Licensing and Regulatory Affairs One First National Plaza Exelon Generation Company, LLC Chicago, IL 60603 4300 Winfield Road Warrenville, IL 60555 Assistant Attorney General 100 W. Randolph St. Suite 12 Vice President - Regulatory Affairs Chicago, IL 60601 Exelon Generation Company, LLC 4300 Winfield Road Chairman Warrenville, IL 60555 LaSalle County Board 707 Etna Road Associate General Counsel Ottawa, IL 61350 Exelon Generation Company, LLC 4300 Winfield Road Attorney General Warrenville, IL 60555 500 S. Second Street Springfield, IL 62701 Manager Licensing - Braidwood, Byron, and LaSalle Chairman Exelon Generation Company, LLC Illinois Commerce Commission 4300 Winfield Road 527 E. Capitol Avenue, Leland Building Warrenville, IL 60555 Springfield, IL 62706 Senior Vice President - Midwest Operations Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

REQUEST FOR ADDITIONAL INFORMATION LASALLE COUNTY STATION, UNITS 1 AND 2 DOCKET NOS. 50-373 AND 50-374 In reviewing the Exelon Generation Company=s (Exelon=s) submittal dated August 14, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML072360042) , as supplemented by letter dated May 13, 2008 (ADAMS Accession No. ML081340270), related to Exelons proposed amendment request that Ganged Control Rod Drive Capability be permitted in lieu of the current single rod movement utilizing the rod control management system (RCMS), for the LaSalle County Station (LSCS), Units 1 and 2, the Nuclear Regulatory Commission (NRC) staff has determined that the following information is needed in order to complete its review:

EICB-1 Section 1.2, 1st Paragraph: EGC is replacing the original Rod Worth Minimizer (RWM) and the Reactor Manual Control System (RMCS), which is comprised of the Rod Drive Control System (RDCS) and the Rod Position Indication System (RPIS) with a new Rod Control Management System (RCMS). The current RMCS uses discrete digital electronics and dynamic logic to control rod motion. The replacement RCMS system will be a digital microprocessor-based system. The new system will also incorporate the RWM within the system, eliminating the need for a separate RWM computer.

The original design feature included separate computer for the RWM function, however, the proposed design incorporates the RWM and all the subsystems of the RMCS in a single microprocessor based system. Please summarize the failure modes for the new system, and describe the consequences that result from these failures. This description should include justification that these consequences will not put the plant into a new and unanalyzed state.

EICB-2 Sections 1.3 2nd Paragraph, and Section 3.1.2 1st Paragraph, and Section 3.1.3: The software can be subject to common-mode failure, and therefore, credit cannot be taken for soft interlocks due to software failure. In addition, system indications of rod position could be lost.

Please respond to the following items that could result from a common-mode failure:

A. Rod block logic is part of the RCMS and is subject to common-cause failure due to software errors. Ganged-rod withdrawal at power is possible due to malfunctioning of RBM. Describe the diverse, non-RCMS equipment, systems, and controls that will be used to recognize and respond to a ganged-rod withdrawal-at-power event due to a common-cause software failure. This description should also indicate if the resultant excess reactivity addition is bounded by current accident analyses.

B. The RDCS, RPIS, and the RWM are all controlled and all the indications are displayed by the same computer system. Failure of software may lead to loss of RPIS.

Enclosure

Please describe the backup indication system available to the plant operating personnel under such an event. If no such backup system is available, please explain what actions the operators would take in the event of such a software failure.

EICB-3 Section 3.2.2 - Comparison of New RCMS to Existing RMCS: The last paragraph on page 10 of 49, states that, The use of the flat-panel touch screen displays instead of the discrete indicators creates a fundamental change to the human system interface. The last paragraph of this section states, As is the case with the existing RMCS and RWM, the components for the replacement RCMS are not safety-related or seismic, but are seismically installed in the cabinets and panels to satisfy seismic Il/I concerns, where required.

The touch-screen visual display unit (VDU) is not seismically qualified and is, therefore, subject to multiple spurious actuations in case of a seismic event. Please explain why such an event could not place the plant in a new unanalyzed condition.

EICB-4 Section 3.2.5 External Communication Interfaces: Has a Cyber Security Assessment been performed or is one planned to be implemented at LSCS, Units 1 and 2. If not, how do you plan on insuring Cyber Security for this system?

EICB-5 Section 3.3.4: The second paragraph states, From a software perspective, the NUMAC process that was used for development and validation of the RCMS software, as described in Section 3.2.7 above, yields software that has a low probability of failure. However, any software-based system can generate random faults. Based on the development and validation process, there is a very low probability of a common-mode failure in those areas that are tested in the V&V testing process. Because of this low probability of a common-mode failure, random errors are assumed in only one program of one component.

Given the NRC concern that software design errors are a credible source of common-mode failures (i.e., as discussed in Branch Technical Position HICB-19, "Guidance for Evaluation of Defense-in-Depth and Diversity in Digital Computer-Based Instrumentation and Control Systems"), please justify or revise the statement regarding the low probability of failure, consistent with the guidance in HICB-19. In addition, identify the key defense-in-depth and diversity elements that will be employed to demonstrate that the potential vulnerabilities associated with common-mode software failures have been adequately addressed.

EICB-6 The licensee has stated that the new RCMS pushbuttons are slightly smaller than the current pushbuttons, providing a smaller target for a seismic event. Please provide justification for the conclusion that these smaller switches have similar or better seismic withstand capability, as compared with the existing switches. Compare mechanical rigidity and spring strength, and any other pertinent design characteristics to back up the justification.

The licensee has stated that In the event of a seismic event, these displays are adequately mounted to the H13-P603 panel and are not sensitive to falling objects or debris from other systems. Please confirm that all the equipment in the vicinity and above the VDU touch-screen is mounted seismically to protect the VDUs from falling debris and causing spurious selection of rods for movement.

EICB- 7 Following two-way messages provide communication between Level 4 and Level 3 equipment:

• Messages sent to RCMS Controller by the PPC Over the Data Connection

• Messages sent to RCMS Controller by the PPC Over the Status Connection

• Messages sent to RCMS Controller by the RWM Sequence Computer Please confirm that all the communication data is predefined and any data which is not predefined will be ignored by the receiving system. How is unrecognized data handled within the receiving system? Does every message have the same message field structure and sequence, including message identification, status information, data bits etc., in the same location in every message. Every datum should be included in every transmit cycle, whether it has changed since the previous transmission or not, to ensure deterministic system behavior.

Appendix B, Section 5, monitoring of boundary interfaces provides guidance on setting up the boundary interfaces with security components such as firewalls, network intrusion detection system, host intrusion detector systems etc. Please describe your boundary interfaces and their compliance with NEI 04-04.

Appendix B, Section 7, variations on the model provides further guidance for deviations from the 4 layer model. Since LaSalle is deviating from this model, please describe how LaSalle meets the guidance of this section of NEI 04-04 [Nuclear Energy Institute].

SRXB - 1 The AREVA licensing methodology seems to imply that the Control Rod Withdrawal Error (CRWE) is analyzed using CASMO4/MICROBURN-B2, which is NRC-approved, and capable of analyzing slow transients.

Please explain why the low-power CRWE evaluation was performed using RAMONA 5-FA.

Additionally, justify the use of RAMONA5-FA to analyze this transient in terms of the codes qualification. Demonstrate that the code is capable of modeling this transient and predicting conservative results. Alternatively, provide similar analytic results using your NRC-approved accident/design-basis accident analysis methodology.

SRXB - 2 In the text of the Low Power CRWE Evaluation, it is discussed that the single rod Gang G-09A had the largest decrease in MCPR (Minimum Critical Power Ratio), and that the same trend is demonstrated for the BOC-B [Beginning of Cycle] sequence withdrawals in that fewer rods in a gang results in a larger change in the MCPR.

Please identify the relevant nuclear and thermal-hydraulic phenomena and/or initial condition assumptions that cause this trend.

SRXB - 3 While the report states that single rod Gang G-09A had the largest decrease in MCPR, the first three figures of Section 3 do not seem to identify rod gangs by size, as does Figure 3.4. Please provide information clarifying this issue.

SRXB - 4 The fractional LHGR [Linear Heat Generation Rate] comparisons provided in Section 4 present results from only a selected set of rod gangs. Please explain why the LHGR comparisons of the remaining gangs were omitted, particularly with respect to some of the remaining gangs toward the center of the core.

SRXB - 5 Because you are implementing a new reactivity control system, the hardware-specific conclusions that allow licensees to treat uncontrolled control rod withdrawal errors as an infrequent event may no longer be acceptable, because the staff may not be reasonably assured that the new RCMS is robust enough that only the presented and evaluated single failures could occur, and that occurrence of these single failures would not result in an uncontrolled control rod withdrawal. This conclusion may be applicable to both single and ganged rod withdrawals, both at low-power and/or startup conditions, and at full power (at full power, because the RBM system appears to interact with the RCMS to achieve a rod block). In consideration of this, you are requested to provide the following additional information:

1) Propose an alternative means to provide adequate assurance that the aforementioned reactivity and power distribution anomalies would not leave the plant in an unacceptable condition. Your present basis implies acceptability based on a low frequency of occurrences, with little regard to possible consequences. Additional consideration of consequences is suggested.

2) Explain how the NRC is reasonably assured of the following:

2a) Only low-worth gangs of multiple rods will be designed. What defines "low-worth," and how is the NRC assured that your core design will consistently contain low-worth gangs?

2b) Rod gangs will not be designed for at-power operation. How is the NRC assured that gangs of multiple rods will not be available for withdrawal above the RBM automatic bypass setpoint?