ML14106A133

Issuance of Amendment No. 198, Request to Adopt TSTF-535, Revision 0, Revise Shutdown Margin Definition to Address Advanced Fuel Designs, as Part of Consolidated Line Item Improvement Process

ML14106A133
Person / Time
Site:	Grand Gulf
Issue date:	06/30/2014
From:	Wang A Plant Licensing Branch IV
To:	Entergy Operations
Wang A
References
TAC MF3174
Download: ML14106A133 (15)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 June 30, 2014 Vice President, Operations Entergy Operations, Inc.

Grand Gulf Nuclear Station P.O. Box 756 Port Gibson, MS 39150

SUBJECT:

GRAND GULF NUCLEAR STATION, UNIT 1 -ISSUANCE OF AMENDMENT RE: TECHNICAL SPECIFICATION CHANGES CONSISTENT WITH TSTF-535, REVISION 0, "REVISE SHUTDOWN MARGIN DEFINITION TO ADDRESS ADVANCED FUEL DESIGNS" (TAC NO. MF3174)

Dear Sir or Madam:

The U.S. Nuclear Regulatory Commission has issued the enclosed Amendment No. 198 to Facility Operating License No. NPF-29 for the Grand Gulf Nuclear Station, Unit 1. This amendment consists of changes to the Technical Specifications (TSs) in response to your application dated November 8, 2013.

The amendment adopts Technical Specification Task Force (TSTF) change traveler TSTF-535, Revision 0, "Revise Shutdown Margin Definition to Address Advanced Fuel Designs," into the TSs. Prior to the amendment, the plant's shutdown margin (SDM}, the amount of reactivity by which the reactor is subcritical, was calculated using a shutdown moderator temperature of 68 degrees Fahrenheit (°F). This value was conservative for standard fuel designs. However, new, advanced boiling-water reactor fuel designs can have a higher reactivity at moderator shutdown temperatures above 68 °F. Therefore, the amendment implements TSTF-535, Revision 0, which modifies the TSs to require the SDM to be calculated at whatever moderator temperature produces the maximum reactivity (i.e., greater than or equal to 68 °F). This TS improvement is part of the Consolidated Line Item Improvement Process and has been requested with no modifications.

A copy of our related Safety Evaluation is also enclosed. The Notice of Issuance will be included in the Commission's next biweekly Federal Register notice.

Sincerely, OJ(i;}l\. ~J wu~

Alan Wang, Project Manager Plant Licensing IV-2 and Decommissioning Transition Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-416

Enclosures:

1. Amendment No. 198 to NPF-29

2. Safety Evaluation cc w/encls: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 ENTERGY OPERATIONS, INC.

SYSTEM ENERGY RESOURCES, INC.

SOUTH MISSISSIPPI ELECTRIC POWER ASSOCIATION ENTERGY MISSISSIPPI, INC.

DOCKET NO. 50-416 GRAND GULF NUCLEAR STATION, UNIT 1 AMENDMENT TO FACILITY OPERATING LICENSE Amendment No. 198 License No. NPF-29

1. The Nuclear Regulatory Commission (the Commission) has found that:

A. The application for amendment by Entergy Operations, Inc. (the licensee), dated November 8, 2013, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commission's rules and regulations set forth in 10 CFR Chapter I; B. The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commission's regulations; D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commission's regulations and all applicable requirements have been satisfied.

Enclosure 1

2. Accordingly, the license is amended by changes to the Technical Specifications as indicated in the attachment to this license amendment, and Paragraph 2.C.(2) of Facility Operating License No. NPF-29 is hereby amended to read as follows:

(2) Technical Specifications The Technical Specifications contained in Appendix A and the Environmental Protection Plan contained in Appendix B, as revised through Amendment No. 198 are hereby incorporated in the license. Entergy Operations, Inc. shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan.

3. This license amendment is effective as of its date of issuance and shall be implemented within 60 days from the date of issuance.

FOR THE NUCLEAR REGULATORY COMMISSION Douglas A. Broaddus, Chief Plant Licensing IV-2 and Decommissioning Transition Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Attachment:

Changes to the Facility Operating License No. NPF-29 and the Technical Specifications Date of Issuance: June 30, 2014

ATTACHMENT TO LICENSE AMENDMENT NO. 198 FACILITY OPERATING LICENSE NO. NPF-29 DOCKET NO. 50-416 Replace the following pages of the Facility Operating License No. NPF-29 and the Appendix A, Technical Specifications with the attached revised pages. The revised pages are identified by amendment number and contain marginal lines indicating the areas of change.

Facility Operating License Remove Technical Specifications Remove 1.0-6 1.0-6

(b) SERI is required to notify the NRC in writing prior to any change in (i) the terms or conditions of any new or existing sale or lease agreements executed as part of the above authorized financial transactions, (ii) the GGNS Unit 1 operating agreement, (iii) the existing property insurance coverage for GGNS Unit 1 that would materially alter the representations and conditions set forth in the Staff's Safety Evaluation Report dated December 19, 1988 attached to Amendment No. 54.

In addition, SERI is required to notify the NRC of any action by a lessor or other successor in interest to SERI that may have an effect on the operation of the facility.

C. The license shall be deemed to contain and is subject to the conditions specified in the Commission's regulations set forth in 10CFR Chapter I and is subject to all applicable provisions of the Act and to the rules, regulations, and orders of the Commission now or hereafter in effect; and is subject to the additional conditions specified or incorporated below:

(1) Maximum Power Level Entergy Operations, Inc. is authorized to operate the facility at reactor core power levels not in excess of 4408 megawatts thermal (100 percent power) in accordance with the conditions specified herein.

(2) Technical Specifications The Technical Specifications contained in Appendix A and the Environmental Protection Plan contained in Appendix B, as revised through Amendment No. 198 are hereby incorporated into this license. Entergy Operations, Inc. shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan.

During Cycle 19, GGNS will conduct monitoring of the Oscillation Power Range Monitor (OPRM) . During this time, the OPRM Upscale function (Function 2.f of Technical Specification Table 3.3.1.1-1) will be disabled and operated in an "indicate only" mode and technical specification requirements will not apply to this function. During such time, Backup Stability Protection measures will be implemented via GGNS procedures to provide an alternate method to detect and suppress reactor core thermal hydraulic instability oscillations. Once monitoring has been successfully completed, the OPRM Upscale function will be enabled and technical specification requirements will be applied to the function; no further operating with this function in an "indicate only" mode will be conducted.

4 Amendment No. 198

Definitions 1.1 1.1 Definitions (continued)

SHUTDOWN MARGIN (SDM) SDM shall be the amount of reactivity by which the reactor is subcritical or would be subcritical throughout the operating cycle assuming that:

a. The reactor is xenon freei

b. The moderator temperature is 2 68°F, corresponding to the most reactive statei and

c. All control rods are fully inserted except for the single control rod of highest reactivity worth, which is assumed to be fully withdrawn.

With control rods not capable of being fully inserted, the reactivity worth of these control rods must be accounted for in the determination of SDM.

STAGGERED TEST BASIS A STAGGERED TEST BASIS shall consist of the testing of one of the systems, subsystems, channels, or other designated components during the interval specified by the Surveillance Frequency, so that all systems, subsystems, channels, or other designated components are tested during n Surveillance Frequency intervals, where n is the total number of systems, subsystems, channels, or other designated components in the associated function.

THERMAL POWER THERMAL POWER shall be the total reactor core heat transfer rate to the reactor coolant.

GRAND GULF 1.0-6 Amendment No. ~, 198

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 198 TO FACILITY OPERATING LICENSE NO. NPF-29 ENTERGY OPERATIONS. INC .. ET AL.

GRAND GULF NUCLEAR STATION. UNIT 1 DOCKET NO. 50-416

1.0 INTRODUCTION

By letter dated November 8, 2013 (Agencywide Documents Access and Management System (ADAMS Accession No. ML13337A592), Entergy Operations, Inc. (Entergy, the licensee),

proposed changes to the Technical Specifications (TSs) for the Grand Gulf Nuclear Station, Unit 1 (GGNS). Specifically, the licensee requested to adopt U.S. Nuclear Regulatory Commission (NRC)-approved Technical Specifications Task Force (TSTF) Change Traveler TSTF-535, Revision 0, "Revise Shutdown Margin Definition to Address Advanced Fuel Designs," dated August 8, 2011 (ADAMS Accession No. ML112200436).

The proposed change would revise the TS definition of shutdown margin (SDM) to require calculation of SDM at the reactor moderator temperature corresponding to the most reactive state throughout the operating cycle (68 degrees Fahrenheit (°F) or higher). The purpose is to address newer boiling-water reactor (BWR) fuel designs, which may be more reactive at shutdown temperatures above 68 °F.

The licensee stated that the license amendment request is consistent with NRC-approved TSTF-535, Revision 0. The availability of this TS improvement was announced in the Federal Register on February 26, 2013 (78 FR 131 00), as part of the consolidated line item improvement process.

2.0 REGULATORY EVALUATION

2.1 Background In water-moderated reactors, water is used to slow down, or moderate, high-energy fast neutrons to low-energy thermal neutrons through multiple scattering interactions. The low-energy thermal neutrons are much more likely to cause fission when absorbed by the fuel.

However, not all of the thermal neutrons are absorbed by the fuel; a portion of them are instead Enclosure 2

absorbed by the water moderator. The amount of moderator and fuel that is present in the core heavily influences the fractions of thermal neutrons that are absorbed.

Water-moderated reactors are designed such that they tend to operate in what is known as an under-moderated condition. In this condition, the ratio of the moderator-to-fuel in the core is small enough that the overall effectiveness of water as a moderator decreases with increasing temperature. As temperature increases, fewer neutrons are absorbed in the moderator due to the decrease in its density (i.e., lost to the reaction). At the same time, this increase in reactivity is overshadowed by fewer neutrons being moderated (i.e., slowed enough to cause fissions),

which reduces overall reactivity. The result is a decrease in power and temperature which produces a negative reactivity feedback effect so that the reactor becomes self-regulating.

However, if the amount of moderator becomes too large with respect to the amount of fuel, the reactor can enter an over-moderated condition. In this condition, the overall effectiveness of water as a moderator increases with the temperature. The number of neutrons moderated (i.e.,

slowed down) enough to fission outweighs the loss of neutrons being absorbed in the moderator. This causes an increase in power that leads to a further increase in temperature creating a potentially dangerous positive reactivity feedback cycle.

As practical examples in support of the proposed changes to the definition of SDM, TSTF-535, Revision 0, discusses SDM with regard to fuel assembly-GE14 (GE14) and Global Nuclear Fuel-2 (GNF2) fuels. TSTF-535, Revision 0, indicated that for historical fuel products leading up to and including GE14, the maximum reactivity condition for SDM always occurred at a moderator temperature of 68 °F. These fuel products were designed to keep the core under-moderated when all control rods were inserted, except for the single most reactive rod. In cores with GNF2 fuel, TSTF-535, Revision 0, projected that the maximum reactivity condition at the beginning of the cycle remains at 68 °F, but later in the cycle, the most limiting SDM may occur at a higher temperature. Thus the GNF2 fuel design could potentially cause an over-moderated condition in the core.

2.2 Technical Specification Changes Entergy's adoption of TSTF-535, Revision 0, for GGNS proposes to revise the TS definition of SDM to require calculation of SDM at the reactor moderator temperature corresponding to the most reactive state throughout the operating cycle (68°F or higher).

The current definition of "SHUTDOWN MARGIN (SDM)" in TS 1.1, "Definitions," states:

SDM shall be the amount of reactivity by which the reactor is subcritical or would be subcritical assuming that:

a. The reactor is xenon free;

b. The moderator temperature is 68°F; and

c. All control rods are fully inserted except for the single control rod of the highest reactivity worth, which is assumed to be fully withdrawn. With

control rods not capable of being fully inserted, the reactivity worth of these control rods must be accounted for in the determination of SDM.

The revised definition of "SHUTDOWN MARGIN (SDM)" in TS 1.1, "Definitions," would state SDM shall be the amount of reactivity by which the reactor is subcritical or would be subcritical throughout the operating cycle assuming that:

a. The reactor is xenon free;

b. The moderator temperature is<:: 68°F, corresponding to the most reactive state; and

c. All control rods are fully inserted except for the single control rod of the highest reactivity worth, which is assumed to be fully withdrawn. With control rods not capable of being fully inserted, the reactivity worth of these control rods must be accounted for in the determination of SDM.

2.3 Regulatory Review Title 10 of the Code of Federal Regulations (1 0 CFR), Part 50, Appendix A, General Design Criterion (GDC) 26, "Reactivity control system redundancy and capability," and GDC 27, "Combined reactivity control systems capability," respectively, require that reactivity within the core be controllable to ensure subcriticality is achievable and maintainable under cold conditions. Reactivity must also have appropriate margin for stuck rods, and within the core, it must be controllable to assure that under postulated accident conditions the capability to cool the core is maintained.

Among other things, 10 CFR 50.36(c)(2)(ii) requires, in part, the establishment of a limiting condition for operations (LCOs) for "[a] process variable, design feature, or operating restriction that is an initial condition of a design-basis accident or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier."

The TS definition of SDM and the LCOs placed on SDM serve, in part, to satisfy GDCs 26 and

27. They ensure there is always sufficient negative reactivity worth available to offset the positive reactivity worth of changes in moderator and fuel temperature, the decay of fission product poisons, the failure of a control rod to insert, and reactivity insertion accidents. Given this margin, the core can be held subcritical for conditions of normal operation, including anticipated operational occurrences.

Section 3.1.2.3.7, "Criterion 26- Reactivity Control System Redundancy and Capability,"

of the UFSAR discusses how the GGNS meets Criterion 26 and Section 3.1.2.3.,

"Criterion 27- Combined Reactivity Control Systems Capability," of the UFSAR discusses how the GGNS meets Criterion 27. With respect to the proposed change to the definition of SDM, these sections of the GGNS UFSAR describes two systems, consisting of moveable control rods (UFSAR Subsection 4.6) and recirculation flow control (UFSAR Subsection 5.4.1 ), in conjunction with the standby liquid control system (UFSAR Subsection 9.3.5), that are provided to meet the intent of GDC 26 and GDC 27

criteria. These systems provide assurance that the reactor core can be made and held subcritical from normal operation and from normal anticipated operational transients, by at least two reactivity control systems and that malfunction of a reactivity control system will not result in unacceptable damage to the fuel, or disrupt the core to the point of preventing core standby cooling if needed. Operational control of reactivity is provided by a combination:

• Movable control rods and their control;

• Reactor coolant recirculation flow control; and

• Nuclear design (including the burnable poison Gadolinium) that assures that sufficient reactivity compensation is always available to make the reactor subcritical from its most reactive condition including compensation for positive and negative reactivity changes from nuclear coefficients, fuel depletion and fission products transients and buildup even with the most reactive control rod fully withdrawn.

3.0 TECHNICAL EVALUATION

3.1 Current Definition of Shutdown Margin In BWR plants, the control rods are used to hold the reactor core subcritical under cold conditions. The control rod negative reactivity worth must be sufficient to ensure the core is subcritical by a margin known as the SDM. It is the additional amount of negative reactivity worth needed to maintain the core subcritical by offsetting the positive reactivity worth that can occur during the operating cycle due to changes in moderator and fuel temperature, the decay of fission product poisons, the failure of a control rod to insert, and reactivity insertion accidents.

Specifically, Section 1.1, "Definitions," of the STS defines SDM, in part, as the amount of reactivity by which the reactor is subcritical or would be subcritical assuming that ( 1) the reactor is xenon free, (2) the moderator temperature is 68 °F, and (3) all control rods are fully inserted except for the rod of highest worth, which is assumed to be fully withdrawn.

The three criteria provided in the definition help exemplify what has traditionally been the most reactive design condition for a reactor core. Xenon is a neutron poison produced by fission product decay and its presence in the core adds negative reactivity worth. Assuming the core is xenon free removes a positive reactivity offset and is representative of fresh fuel at the beginning-of-core.

The minimum temperature the reactor moderator is anticipated to experience is 68 °F, making it the point at which the moderator will be at its densest and therefore capable of providing the highest positive reactivity worth. By assuming the highest worth rod is fully withdrawn, the core can be designed with adequate shutdown margin to ensure it remains safely shutdown even in the event of a stuck control rod, as required by GDC 26 and 27.

Determination of the SDM under the aforementioned conditions yields a conservative result that, along with the requirements set forth in Section 3.1.1 of the TS, helps ensure:

a. the reactor can be made subcritical from all operating conditions and transients and design basis events,

b. the reactivity transients associated with postulated accident conditions are controllable within acceptable limits, and

c. the reactor will be maintained sufficiently subcritical to preclude inadvertent criticality in the shutdown condition.

3.2 Proposed Definition of Shutdown Margin The specified moderator temperature of 68 oF facilitates the maximum reactivity condition only if the core exists in an under-moderated condition. In addition to burnable poisons, many modern fuel designs also incorporate partial length rods for increased neutron economy which are employed in order to extend the operating cycle. Both of these affect the ratio of moderator to fuel. The strong local absorption effects of the burnable poisons in fresh fuel make the core under-moderated. As burnable poisons are depleted during the fuel cycle, the core becomes less under-moderated, potentially leading to a slightly over-moderated condition wherein the core will be more reactive at a moderator temperature higher than the 68 oF specified in the SDM definition. Thus, the maximum core reactivity condition and the most limiting SDM may occur later in the fuel cycle at a temperature greater than 68 °F. Consequently, calculation of the SDM at the currently defined moderator temperature of 68 oF may not accurately determine the available margin.

TSTF-535, Revision 0, therefore proposed a change to the definition of SDM to enable calculation of the SDM at a reactor moderator temperature of 68 oF or a higher temperature corresponding to the most reactive state throughout the operating cycle. SDM would be calculated using the appropriate limiting conditions for all fuel types at any time in core life.

In support of the proposed change, TSTF-535, Revision 0, cited the requirements for SDM as specified in Global Nuclear Fuel topical report NED0-24011-A, Revision 18, "General Electric Standard Application for Reactor Fuel (GESTAR II)," April 2011 (ADAMS Accession No. ML111120046). Section 3.2.4.1 of GESTAR II states, in part, that The core must be capable of being made subcritical, with margin, in the most reactive condition throughout the operating cycle with the most reactive control rod fully withdrawn and all other rods fully inserted.

TSTF-535, Revision 0, also cited SRP Section 4.3, which states the following concerning the review of control systems and SDM:

The adequacy of the control systems to assure that the reactor can be returned to and maintained in the cold shutdown condition at any time during operation.

The applicant shall discuss shutdown margins (SDM). Shutdown margins need to be demonstrated by the applicant throughout the fuel cycle.

Although the licensing basis requirements for SDM in GESTAR II are only applicable for cores licensed with Global Nuclear Fuel methods, they are consistent with the review procedures set forth in the SRP, which are provided to help ensure compliance with GDCs 26 and 27.

TSTF-535, Revision 0, stated that while the SRP does not prescribe the temperature at which the minimum SDM should be determined, the requirement of shutting down the reactor and maintaining it in a shutdown condition "at any time during operation" suggests that considering a range of thermal and exposure conditions would be appropriate in the determination of the minimum SDM. Because newer fuel designs employ elements such as partial-length rods and burnable absorbers, which may cause the maximum core reactivity conditions and the most limiting SDM to occur later in the fuel cycle at a temperature greater than 68 °F, the NRC staff agrees with the TSTF-535, Revision 0, assessment in this regard. Additionally, the NRC staff finds that allowing calculation of the SDM at the most limiting core reactivity condition is prudent with respect to ensuring compliance with GDCs 26 and 27 and concludes that the proposed changes to the GGNS TSs are acceptable.

The impetus for TSTF-535, Revision 0, was to provide for a more broadly applicable SDM definition in recognition of modern fuel designs, for which the core may not be in its most reactive condition at 68 °F. The proposed language will require the licensee to consider all temperatures equal to or exceeding 68 °F, and all times in the operating cycle. This change places an additional responsibility on the licensee to identify the most limiting time-in-cycle and temperature, a change that is more conservative than the current definition and will ensure the licensee maintains adequate SDM as required by its current licensing basis. Therefore, the NRC staff concludes the change is acceptable for the GGNS. The NRC staff also concludes that the revised definition is consistent with the 10 CFR 50.36 requirements pertaining to LCOs, because it ensures that the LCOs for SDM consider a broadly conservative range of potential initial conditions in the anticipated operational occurrence analyses.

3.3 Summary The NRC staff has reviewed the licensee's requested implementation of the TSTF-535, Revision 0, proposed revisions to the definition of SDM. Based on the considerations discussed above, the NRC staff concludes that the proposed revisions are acceptable and will provide a conservative and improved approach to the calculation of SDM that ensures use of the appropriate limiting conditions for all fuel types at any time in the life of the core. The NRC staff concludes that the proposed revisions serve to satisfy the requirements set forth in GDCs 26 and 27, as discussed in NUREG-0800, Section 4.3, "Nuclear Design." Additionally, the NRC staff concludes that the proposed revisions to the definition of SDM will require the licensee to calculate SDM in consideration of the most limiting conditions in the core. Based on the above, the revised SDM definition is acceptable for use with any current fuel design at RBS.

4.0 STATE CONSULTATION

In accordance with the Commission's regulations, the Mississippi State official was notified of the proposed issuance of the amendment. The State official had no comments.

5.0 ENVIRONMENTAL CONSIDERATION

The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no

significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding published in the Federal Register on March 4, 2014 (79 FR 12244). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

6.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) there is reasonable assurance that such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor: A. Wang Date: June 30, 2014

ML14106A133 OFFICE NRR/DORLILPL4-2/PM NRR/DORLILPL4-2/LA NRR/DSS/STSB/BC NAME A Wang JBurkhardt REIIiott DATE 05/06/14 05/01/14 06/11/14 OFFICE OGC NRR/DORLILPL4-2/BC N RR/DORLILPL4-2/PM NAME BMizuno DBroaddus A Wang DATE 06/24/14 06/30/14 06/30/14