NRC-20-0046, Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specifications to Utilize Neutron Absorbing Inserts in Criticality Safety Analysis for Fermi 2 Spent Fuel Storage Racks

Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specifications to Utilize Neutron Absorbing Inserts in Criticality Safety Analysis for Fermi 2 Spent Fuel Storage Racks

ML20212B303
Person / Time
Site:	Fermi
Issue date:	07/30/2020
From:	Peter Dietrich DTE Electric Company, DTE Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC-20-0046
Download: ML20212B303 (25)

Text

Peter Dietrich Senior Vice President and Chief Nuclear Officer DTE Energy Company 6400 N. Dixie Highway, Newport, MI 48166 Tel: 734.586.4153 Fax: 734.586.1431 Email: peter.dietrich@dteenergy.com July 30, 2020 NRC-20-0046 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Fermi 2 Power Plant NRC Docket No. 50-341 NRC License No. NPF-43

Subject:

Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specifications to Utilize Neutron Absorbing Inserts in Criticality Safety Analysis for Fermi 2 Spent Fuel Storage Racks

References:

1) DTE letter NRC-19-0004, License Amendment Request to Revise Technical Specifications to Utilize Neutron Absorbing Inserts in Criticality Safety Analysis for Fermi 2 Spent Fuel Storage Racks, dated September 5, 2019 (ML19248C679)

In Reference 1, DTE Electric Company (DTE) requested an amendment to the Renewed Facility Operating License NPF-43 for Fermi Unit 2 (Fermi 2) and its Appendix A, Technical Specifications (TS), in accordance with the provisions of 10 CFR 50.90, Application for amendment of license, construction permit, or early site permit. The Reference 1 submittal requested modification of the Renewed Facility Operating License to eliminate the License Renewal License Condition regarding the Boraflex material in the spent fuel pool (SFP) storage racks based upon a proposed alternative of installing neutron absorbing inserts (i.e., NETCO SNAP-IN rack inserts) in the racks containing Boraflex. The Reference 1 submittal also requested revision of TS requirements associated with the SFP storage racks based on approval of a new criticality safety analysis, including methodology. In an email from Mr. Surinder Arora to Ms. Margaret Offerle dated June 30, 2020, the NRC sent DTE a Request for Additional Information (RAI) regarding the license amendment request (LAR). The responses to the questions in the RAI are provided in Enclosure 1, with the exception of question NRR-SFNB-RAI-03. The response to question NRR-SFNB-RAI-03 will be provided by separate letter by August 31, 2020.

USNRC NRC-20-0046 Page 2 Enclosures 2 and 3 provide a revised version of a marked-up and clean TS page, respectively, based on the response to one of the RAIs (NRR-SFNB-RAI-06) in Enclosure 1.

The Reference 1 submittal contained a discussion of a planned monitoring program that would be implemented by DTE for the NETCO SNAP-IN@ rack inserts. Subsequently, DTE has identified improvements that could be made to the planned monitoring program. Enclosure 4 of this letter provides supplemental information regarding the insert monitoring program. In addition, Reference 1 provided insert installation schedule dates based on the project information at the time. Recent project reviews have led to changes in some schedule dates. The revised schedule dates are also provided in Enclosure 4 for information only.

No new commitments are being made in this submittal.

Should you have any questions or require additional information, please contact Ms. Margaret Offerle, Manager - Nuclear Licensing, at (734)586-5076.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on J rly 30, 20 Peter Dietrich Senior Vice President and Chief Nuclear Officer

Enclosures:

1) Response to Request for Additional Information

2) Revised Marked-up Page for TS Page 4.0-2

3) Revised Clean page for TS Page 4.0-2

4) Supplemental Information for the Proposed License Amendment cc: NRC Project Manager NRC Resident Office Regional Administrator, Region III Michigan Department of Environment, Great Lakes, and Energy

Enclosure 1 to NRC-20-0046 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Response to Request for Additional Information to NRC-20-0046 Page 1 Response to Request for Additional Information By letter dated September 5, 2019, ((Agencywide Documents Access Management System (ADAMS) Accession No. ML19248C679), DTE Energy Company (DTE), the licensee, submitted for staff review and approval a license amendment request (LAR) to the Fermi Unit 2 (Fermi 2)

Technical Specifications (TS). The proposed amendment includes: 1) a revision to the criticality safety analysis for the fuel handling building spent fuel pool; 2) additional requirements for the spent fuel pool storage racks in TS 4.3.1, Criticality; and 3) a requirement for the monitoring of the neutron absorber material in storage racks.

The Fermi 2 Renewed Facility Operating License NPF-43 issued on December 15, 2016 (ML16270A526) contains a License Condition regarding the Boraflex material in the spent fuel pool (SFP) storage racks. The License Condition is to discontinue reliance on the Boraflex material to perform a neutron absorption function by replacing the SFP storage racks containing Boraflex with racks containing Boral. As an alternative to rack replacement, DTE LAR proposes to utilize NETCO SNAP-IN rack inserts (here after referred to as inserts) in the racks containing Boraflex. A new criticality safety analysis has been performed by the licensee which takes no credit for the Boraflex material to perform a neutron absorption function and instead relies upon the neutron absorbing inserts. After this amendment the Fermi 2 SFP will have two rack designs; one with Boral the other with the inserts.

The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the submittal and determined that the following additional information is needed to complete its review.

NRR-SFNB Applicable Regulation and Guidance Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Appendix A, General Design Criteria for Nuclear Power Plants (GDC) 62, Prevention of criticality in fuel storage and handling, requires that, Criticality in the fuel storage and handling system shall be prevented by physical systems or processes, preferably by use of geometrically safe configurations.

NUREG 0800, Standard Review Plan, Section 9.1.1, Criticality Safety of Fresh and Spent Fuel Storage and Handling (ML070570006) and Section 9.1.2, New and Spent Fuel Storage (ML070550057) provide guidance regarding the specific acceptance criteria and review procedures to ensure that the proposed changes satisfy the requirements in 10 CFR 50.68 and GDC 62.

The NRC staff issued a memorandum dated August 19, 1998 (ML11088A013), also known as the Kopp Memo, containing staff guidance for performing the review of SFP nuclear criticality safety (NCS) analyses. This guidance supports determining compliance with GDC 62 and the existing guidance in SRP Sections 9.1.1 and 9.1.2. The principal objective of this guidance was to clarify and document staff positions that may have been incompletely or ambiguously stated in to NRC-20-0046 Page 2 previously issued safety evaluations (SEs) and other staff documents. A second purpose was to state staff positions on a number of strategies used in SFP NCS analyses at that time.

NRC Interim Staff Guidance (ISG) DSS ISG [Division of Safety System Interim Staff Guidance]

2010 01, Staff Guidance Regarding the Nuclear Criticality Safety Analysis for Spent Fuel Pools, Revision 0, was issued in October 2011 (ML110620086). The purpose of this ISG is to provide updated guidance to the NRC staff reviewers to address the increased complexity of recent SFP nuclear criticality analyses and operations. This ISG is intended to reiterate existing guidance, clarify ambiguity in existing guidance, and identify lessons learned based on the past submittals. Similar to the Kopp Memo, this guidance supports determining compliance with GDC 62, the existing guidance in SRP Sections 9.1.1 and 9.1.2, but also 10 CFR 50.68. The NRC staff notes that while Section 9.1.2 of NUREG 0800 is applicable, it is not concerned directly with fuel storage criticality safety considerations. Therefore, Section 9.1.1 contains the primary SRP guidance for reviewing the proposed changes in the license amendment request (LAR) as it relates to fuel storage criticality safety considerations.

Issue Fermi 2 is installing inserts in each cell of the remaining Boraflex storage racks to replace the function of the Boraflex. The inserts are chevron shaped neutron absorbing inserts. All inserts will have the same orientation, ensuring one leg of an insert will be between fuel assemblies.

The inserts extend over the full-length of the active fuel region of the stored assemblies. The inserts are manufactured from Rio Tinto Alcans BORALCAN' aluminum boron carbide metal matrix composite material with a minimum certified areal density of 0.0157 g B10/cm2. Fermi 2 credits the neutron absorbing capability of the inserts for its lifetime peak reactivity method to set the Fermi 2 SCCG TS limit to provide reasonable assurance that the k-effective (keff) of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity does not exceed 0.95, at a 95 percent probability, 95 percent confidence level, if flooded with unborated water.

NRR-SFNB-RAI-01 The licensee has proposed a TS SCCG Standard Cold Core Geometry (SCCG) limit of 1.30.

This is a reduction of its current TS SCCG limit of 1.31. Verify that there is no fuel currently at Fermi 2 with a SCCG keff greater than the proposed TS limit of 1.30?

DTE RESPONSE There is no fuel currently at Fermi 2 with a SCCG kinf greater than 1.30. Review of the fuel currently stored in the SFP, shown in Table 25 in NEDC-33889P, Revision 0 (Enclosure 4 of the LAR), as well as fuel currently in the reactor vessel, identified a current maximum of less than 1.27.

to NRC-20-0046 Page 3 NRR-SFNB-RAI-02 The modified Boraflex rack modules and the Boral rack modules will be adjacent to each other in the Fermi 2 SFP presumably at a the same spacing as between the Boraflex and Boral rack modules themselves. The analysis has not calculated a keff at the interface between the two rack module designs. Rather the analysis relies on engineering judgement that the two rack module designs are isolated from neutronic interactions The border between the modified Boraflex rack modules and the Boral rack modules is not what is usually considered isolated from neutronic interactions but rather consistent with other SFP rack designs that are interactive. With respect to the interface between the two rack module designs, provide the following information:

(a) Justify the conclusion that the modified Boraflex rack modules and the Boral rack modules are neutronically isolated from each other.

(b) What is the Boron-10 (10B) areal density (AD) of the Boral in the Boral racks?

(c) Does every periphery storage cell in the Boral storage modules have a Boral panel on the outside wall of the storage cell such that there will be both a Boral panel and an insert wing on the entire length of the boundary between the two rack module designs?

(d) The temperature sensitivity study performed to establish the most reactive temperature indicates increased moderation increases reactivity. Does the increased moderation due to the gap between the storage modules increase reactivity?

DTE RESPONSE (a) The intent of the phrase isolated from neutron interactions used in Assumption 11 of NEDC-33889P Revision 0, and LAR Enclosure 1 Section 3.2 bulleted item 5 was to describe the absorber configuration where both rack types have an absorber panel facing the other rack type. Thus, a neutron would have to traverse two absorber panels in order to interact with fuel bundles stored in an adjacent rack.

The Boral rack and Boraflex rack interface was not explicitly analyzed but was dispositioned as stated in Section 6.0 NEDC-33889P Revision 0. There should be no interface restrictions for the Boral rack and Boraflex rack interface with an absorber panel on both sides (per Assumption 11) because that case is bounded by the misloaded bundle case which is modeled along an edge of the Boraflex rack where there is no absorber.

In addition, as shown on the response to Item (b) below the 10B areal density in the Boral racks is more than 25% higher than the minimum areal density of the inserts credited in the Boraflex rack analysis. As such, using the same peak Standard Cold Core Geometry (SCCG) k-inf value limit of 1.30, then the Boral racks with the larger 10B areal density will have a lower nominal in-rack k-eff, which will lead to a lower kmax(95/95). Thus, the Boraflex analysis results will bound the Boral rack analysis results.

to NRC-20-0046 Page 4 (b) Detailed information regarding the 10B areal density (AD) of Boral in the Boral racks was provided in Enclosure 2 of DTE letter NRC-16-0061, DTE Response to NRC Generic Letter 2016-01, Monitoring of Neutron-Absorbing Materials in Spent Fuel Pools, dated October 11, 2016 (ML16286A280). This DTE letter was identified as Reference 2 in the proposed LAR. Per pages 1 and 2 of Enclosure 2 of NRC-16-0061, the minimum certified 10 B AD for the Boral racks is 0.020 g 10B per cm2.

(c) Each chevron-shaped insert in the Boraflex rack cells will be oriented such that one panel will face the Boral racks, and each Boral rack cell includes an absorber panel that faces the Boraflex racks.

As described in NEDC-33889P Revision 0 Assumption 11 and Section 6.0, the insert orientation ensures that insert absorber material is present along all interface locations between the Boraflex racks and the Boral racks. Additionally, each Boral rack cell adjacent to a Boraflex cell has Boral panels on all four sides. Thus, the Boraflex and Boral rack interface has absorber on both sides.

(d) The response to Item (a) clarifies the justification for not analyzing the interface between the Boraflex racks and the Boral racks. As shown in NEDC-33889P Revision 0, the low moderator temperature perturbation has a negligible impact on the results (approximately 10 pcm). As stated in the response to Item (a) the interface was not analyzed, but if it were the moderator temperature would have a negligible impact.

to NRC-20-0046 Page 5 NRR-SFNB-RAI-04 The Fermi 2 Accident Considerations Related to Criticality section 3.7.1 of Enclosure 1 lists No inserts on the rack periphery as an accident scenario. NEDC-33889P, Revision 0, treats no inserts on the rack periphery as a normal condition. Please clarify the difference.

DTE RESPONSE The information provided in Section 3.7.1 of Enclosure 1 of the LAR was intended to be consistent with Section 5 of NEDC-33889P, Revision 0 (Enclosure 4 of the LAR). NEDC-33889P describes biases associated with normal conditions in Section 5.5.2 and biases associated with abnormal/accident conditions in Section 5.5.3. After further review, it was determined that no inserts on the rack periphery should not have been included in the bulleted list of accident considerations in Section 3.7.1 of Enclosure 1 of the LAR. The condition of no inserts on the rack periphery is not an accident scenario; it is a normal condition as described in Section 5.1 of NEDC-33889P and as also shown in Figure 7 of NEDC-33889P. Section 5.5.2 of NEDC-33889P provides the analysis associated with this normal condition.

to NRC-20-0046 Page 6 NRR-SFNB-RAI-05 In order for the analysis to demonstrate there is reasonable assurance that the keff of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity does not exceed 0.95, at a 95 percent probability, 95 percent confidence level, if flooded with unborated water, the computer models must be appropriate to the system. With respect to the computer modeling of the actual SFP storage system, provide the following information:

• NEDC-33889P, Revision 0, Table 11, Fuel Parameter Ranges Studied in Spent Fuel Rack, lists the results of the parametric study performed to determine the limiting lattice. There are several instances where cases appear to be identical and yet they have different results. With respect to the information provided in Table 11, explain why the seemingly identical cases have different results.

DTE RESPONSE As indicated in NEDC-33889P Revision 0 Table 11 under the heading Bundle, lattices from 3 different bundles are analyzed for the design basis lattice selection which include one GE14 bundle (4371) and two GNF3 bundles (4350 and 4424). As shown in NEDC-33889P Table 8, the two GNF3 bundles considered in the analysis have different channel dimensions and unique identifiers.

Some lattice types for the two GNF3 bundles have the same fuel parameters by coincidence, but these lattices are associated with two GNF3 fuel assemblies that have different fuel channels (shown in Table 8). For example, Cases 28 and 30 have the same fuel parameters (lattice types, void fractions, enrichments, number of gadolinia rods, gadolinia concentrations, and exposures),

but the corresponding entries under the heading Bundle are for GNF3 bundles with different channels. In addition, a review of Cases 28 and 30 from NEDC-33889P Revision 0 Table 11 indicates that these cases have different gadolinia rod patterns, which is typical. Thus, Cases 28 and 30 are different lattices with different results.

NEDC-33889P Revision 0 Table 11 does not include any identical cases with different results.

to NRC-20-0046 Page 7 NRR-SFNB-RAI-06 The current Fermi 2 SFP capacity is 3590; which will not change if the current LAR is approved.

The licensee has stated they are not fully implementing the SFP storage capacity increase approved in the January 25, 2001, amendment which approved a Fermi 2 SFP storage capacity to 4608, which is listed in Fermi 2 TS 4.3.3. The current LAR does not include a change to TS 4.3.3 to reflect the reduced SFP storage capacity. Yet the licensee is taking credit for the reduced storage capacity as evident by the following statement, The strength evaluation of the reinforced concrete SFP for Fermi 2 includes evaluation of the final configuration following implementation of the third campaign associated with License Amendment No. 141 (see Section 3.10). The final configuration following campaign three represents the highest density storage configuration and therefore places the most load on the SFP floor from a design analysis. Since the current capacity from implementing only the first two campaigns of Amendment No. 141 is much less than that for the third campaign, the reduction in total fuel assembly weight substantially offsets the relatively small weight increase due to the inserts. Therefore the existing SFP structural evaluation remains bounding of the current configuration even once inserts are installed. Please justify not revising TS 4.3.3 to reflect the reduced storage capacity of the Fermi 2 SFP.

DTE RESPONSE The proposed LAR is associated with DTEs intent to install the neutron absorbing inserts as an alternative to implementing the third campaign of License Amendment No. 141. Following approval of the proposed LAR and successful completion of the installation of inserts, there would be no further need to implement the third campaign. The Fermi 2 SFP capacity would remain at its currency capacity of 3590, consistent with the capacity of the second campaign of License Amendment No. 141. To ensure consistency between the actual plant configuration and the Fermi 2 TS, DTE will revise TS 4.3.3 to reduce the capacity from 4608 fuel assemblies to 3590 fuel assemblies. The revised TS markup and clean pages showing the additional impact to TS 4.3.3 are provided in Enclosures 2 and 3 to this letter.

Although this RAI response adds an additional TS change (i.e., TS 4.3.3) from those originally proposed in the LAR, this additional TS change does not impact the conclusions of the Regulatory Analysis previously provided in the LAR (Section 4.0 of Enclosure 1), including the no significant hazards consideration. The reason that the previous Regulatory Analysis is not impacted is that the TS 4.3.3 change is more restrictive, is consistent with the current Fermi 2 SFP configuration, and is consistent with the second campaign configuration approved by the NRC in License Amendment No. 141. For similar reasons, there is also no impact on the environmental considerations in Section 5.0 of Enclosure 1 to the LAR.

to NRC-20-0046 Page 8 NRR-SFNB-RAI-07 While the licensee is taking credit for not fully implementing the SFP capacity increase, its logic in evaluating the weight increase in the SFP storage rack modules with the inserts requires explanation. A weight reduction in one area of the SFP does not ameliorate a weight increase in another. With respect to the evaluation of the SFP structure, please justify the impact of the inserts using an appropriate method.

DTE RESPONSE The original discussion in the proposed LAR was intended to provide a simple explanation for how the SFP rack configuration for the third campaign would result in higher overall loads than the SFP rack configuration for the second campaign including inserts. However, as described previously in the response to NRR-SFNB-RAI-06, DTE will include the reduction of the SFP capacity from that of the third campaign to that of the second campaign as part of the proposed LAR. As a result, an alternate means of justification is provided in this response.

As part of the ongoing design modification work associated with insert installation, further evaluations of the SFP reinforced concrete strength have been performed. The evaluations considered the controlling case for implementation of License Amendment No. 141 only through the second campaign. The additional weight due to the insert installation was added to this controlling case and the evaluation demonstrated adequate margin for strength of the SFP structure. Therefore, the evaluation does consider the weight increase from the inserts without crediting the difference in weight between the second and third campaigns.

to NRC-20-0046 Page 9 NRR-SFNB-RAI-08 The Fermi 2 Full Rack Insert Inspections/Testing section 3.8.4 of Enclosure 1 with respect to the wear inspection states, This collection of measurements will then be compared with the as-built thickness measurements of the removed insert to verify it has sustained uniform wear over its service life. This implies that so long as the wear is uniform it is acceptable. This is not the purpose of the wear inspection. The wear inspection is to determine if wear is occurring, and if it is occurring then to assess at what point the wear will adversely affect the inserts ability to perform its function as a NAM. Please clarify.

DTE RESPONSE The purpose of the wear inspection is to determine if any significant wear is occurring on an insert. Isolated wear, such as scratches beyond the acceptable manufacturing surface requirements would be identified during visual inspections for indications of wear along the length of the insert. This type of wear, if detected, would be evaluated but would be unlikely to adversely impact the ability of the insert to function as a neutron absorbing material due to its isolated and localized nature. In addition to the visual inspections for indications of wear along the length of the insert, thickness measurements will also be taken and compared to the as-manufactured thickness taken during the insert fabrication inspections. Established thickness change criteria will allow for verification that the thickness still exceeds the minimum required thickness assumed in the criticality safety analysis. The insert removal inspections for wear, collectively with the other monitoring activities described in Section 3.8 of Enclosure 1 of the LAR, will ensure that the inserts are capable of performing their intended function as a neutron absorbing material throughout their period of use. Therefore, the sentence in Section 3.8.4 which stated This collection of measurements will then be compared with the as-built thickness measurements of the removed insert to verify it has sustained uniform wear over its service life should have instead stated This collection of measurements will then be compared with the as-built thickness measurements of the removed insert to verify there is no impact on function due to sustained wear over its service life.

to NRC-20-0046 Page 10 NRR-SFNB-RAI-09 The submittal indicates the LAR was prepared consistent with Nuclear Energy Institute (NEI) 12-16, Revision 2, Draft B, Guidance for Performing Criticality Analyses of Fuel Storage at Light-Water Reactor Power Plants, dated January 2017 (ADAMS Accession No. ML17009A343). NEI 12-16 guidance stipulates licensees should institute controls to ensure the criticality analysis remains bounding on the licensees current and future operation, core and fuel designs. With respect to the controls Fermi 2 is implementing, provide the following information:

(a) A description of the administrative controls that are in place to ensure that no more than one rack insert is missing from any fuel storage rack at any one time.

(b) Describe the controls the licensee is putting in place to ensure that the conditions evaluated in the nuclear criticality safety analysis remain bounding to the current and future plant operating parameters and fuel designs.

DTE RESPONSE (a) As part of implementation activities associated with installation of the neutron absorbing inserts, the Fermi 2 plant procedure that establishes spent fuel pool storage rack management guidelines will be revised to ensure that no more than one rack insert is missing from any fuel storage rack at any one time.

(b) Fermi 2 has instituted plant procedures which implement the guidance of NEI 96-07, Revision 1, Guidelines for 10 CFR 50.59 Implementation. NEI 96-07 is endorsed by the NRC in Regulatory Guide (RG) 1.187 as an acceptable means for complying with the requirements in 10 CFR 50.59, Changes, tests, and experiments. Fermi 2 has also instituted plant procedures which implement the Standard Industry Design Process, IP-ENG-001. The Standard Industry Design Process includes interdisciplinary and interdepartmental reviews to ensure that impacts of potential changes to the facility are properly considered. In addition, Fermi 2 plant procedures governing the core reload design process explicitly identify that impact on fuel storage, including the spent fuel pool, is to be considered as part of the reload process. Collectively, these Fermi 2 plant procedures ensure that all changes are properly reviewed to determine potential impacts. Continued adherence to these procedures will ensure the criticality analysis remains bounding for current and future operation, core and fuel designs, in accordance with the guidance in NEI 12-16.

Future revisions to the criticality analysis, as necessary, will be performed in accordance with plant procedures, including those that determine whether prior NRC approval of such changes are required.

to NRC-20-0046 Page 11 NRR-NCSG Applicable Regulation and Guidance 10 CFR 50.68, Criticality accident requirements, provides the regulatory requirements for maintaining sub-criticality in the SFP. Specifically, 10 CFR 50.68(b)(4) states that the keff in the SFP:

must not exceed 0.95, at a 95 percent probability, 95 percent confidence level, if flooded with borated water, and the k-effective must remain below 1.0 (subcritical), at a 95 percent probability, 95 confidence level, if flooded with unborated water.

In order to demonstrate compliance with this regulation the licensee prepares and maintains its criticality safety analysis. One input to this analysis is the 10B AD of the neutron absorbing material (NAM) credited for criticality control in the SFP. Potential degradation of the NAM may lead to a decreased 10B AD and therefore it may not meet the assumption made for 10B AD in the criticality safety analysis.

Issue In its LAR, the licensee proposes to remove full length rack inserts for inspection on a periodic basis. Additionally, the licensee proposes to maintain at least 8 spare inserts in environmentally controlled conditions so that these inserts may be used to replace the ones pulled from the SFP for inspection. One of the full-length inserts will be used as a comparison during the full length insert inspection but the inspections do not require the same spare insert to be used for each comparison.

NRR-NCSG-RAI-01 The NRC staff requests the following information:

(a) A description of the environmental controls and storage conditions that will preclude visible damage, contamination, corrosion or oxidation with the exception of the compact, adherent, protective film of alumina in order to achieve reasonable assurance that the NAM will not experience degradation in storage that may impact the 10B AD or other material assumptions made in the criticality safety analysis.

(b) Confirmation that the coupons in the SFP will bound the condition (i.e. remain the leading indicator of degradation) of any spare insert that will be placed into the SFP and credited for criticality control.

(c) An explanation for how inspection results can be monitored and trended if a different spare insert can be used for comparison to the inserts removed from the SFP.

to NRC-20-0046 Page 12 DTE RESPONSE (a) Any spare inserts shall be held in controlled environmental conditions such that the full length insert remains devoid of visible damage, contamination, corrosion or oxidation with the exception of the compact, adherent, protective film of alumina which normally forms on aluminum as a result of exposure to air. At a minimum, this consists of the insert being kept in a storage container that protects it from possible unplanned and unwarranted deformation from any other objects or from possible contamination such as leaks, spills, etc. In addition, the container will be kept in a building that protects the insert from outdoor elements such as wind, rain, etc. that could contribute to surface contamination or corrosion.

Spare inserts will be stored in a DTE warehouse that meets the necessary storage requirements. The material master for the inserts calls for Storage Level C. The Fermi 2 plant procedure for material shipping, handling and storage has the following requirements for Storage Level C:

Items shall be stored within a fire-resistant, tear-resistant, weather-tight, and well-ventilated building or equivalent enclosure.

a. Precautions shall be taken against vandalism.

b. This area shall be situated and constructed so that it will not be subject to flooding.

The floor shall be pavement or equivalent and well drained.

c. Items shall be placed on pallets or shoring to permit air circulation.

Storage Level C does not have any temperature or humidity requirements.

Storage of spare inserts in a DTE warehouse meeting these procedural requirements will ensure the spare inserts will not experience degradation in storage. In addition, spare inserts shall be visually inspected prior to installation for any abnormal or excessive scratches or gouges that occur during storage/handling as described in the installation procedure.

Additionally, the installation tool has been designed and tested (during sizing and prototype testing) to preclude the introduction of scratches/gouges on the surface of the inserts. As a result of these storage and installation measures, the spare inserts, once installed in the SFP, will be consistent with the 10B AD and other material assumptions made in the criticality safety analysis.

(b) The coupon trees will be placed in the spent fuel pool racks prior to the installation of all inserts. This will ensure that the coupons remain the leading indicators of degradation.

Following each refueling outage, freshly discharged fuel assemblies will be placed in proximity to the coupon tree such that the gamma exposure and local temperatures are maximized. This will ensure that the coupons have been subjected to the most severe environmental conditions thus bounding the inserts service conditions in the entire spent fuel pool. Since the spare inserts will be installed in the pool at a much later date after the installation of the coupons (the first planned use of a spare insert would be following the 10-year insert removal inspection), the coupons will always lead the spare inserts in terms of service time and be a leading indicator of degradation.

to NRC-20-0046 Page 13 Spare inserts are merely extra inserts that are delivered with the production batch inserts and are manufactured to the requirements of the design drawings and purchase order requirements that include specifications for the surface condition to be free of defects. The coupons are made to the same requirements as the inserts such that they are representative of the manufactured inserts and the conditions tested during the material qualification program.

As stated in (a) above, spare inserts shall be visually inspected prior to installation for any abnormal or excessive scratches or gouges that occur during storage/handling as described in the installation procedure. This will ensure that the coupons will bound the condition of the spare inserts once they are placed into the SFP and thus credited in the criticality safety analyses.

(c) Each insert that is removed will be subjected to visual and dimensional inspections. Visual inspections will be performed to determine locations, if any, showing indications of local pitting corrosion or other anomalies. For the visual inspection only, the spare insert surface finish would be used as a visual guide to identify areas of discoloration or surface roughness that may be indicative of local pitting corrosion or wear, as long as they are stored in accordance with the conditions described in the response to part (a) above. Visual inspections are qualitative in nature and not subject to trending.

Thickness measurements made on the full length inserts must be compared to the as-manufactured thickness measurement during the final inspection (prior to shipment to Fermi Station) of that insert to determine any thickness change that occurred over the time frame that the insert was in-service. Any thickness change outside of the thickness change criteria (i.e., outside of the manufacturing tolerances) would require further investigation. Since the thickness change measurements on the full insert are specific to that insert removed for testing, trending is impractical.

Although trending of the full length insert inspections is not intended to be performed, the overall monitoring activities described in Section 3.8 of Enclosure 1 of the LAR do include trending. Specifically, trending of the coupon data will be performed.

Enclosure 2 to NRC-20-0046 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Revised Marked-up Page for TS Page 4.0-2

Design Features 4.0 4.0 DESIGN FEATURES 4.3 Fuel Storage (continued)

b. Kr, c 0.95 if fully flooded with unborated water, which includes an allowance for uncertainties as described in Section 9.1 of the UFSAR; and

c. The following nominal center to center distances between fuel assemblies placed in the various storage rack types, as applicable Replace with:

SDacinQ Rack TyDe BORALCANTM (inches) 6.22 High density storage racks that contain Boraflex as the neutron absorbing material 6.23 High density storage racks that contain Delete text Boral as the neutron absorbing material Delete text 11.9 x 6.6 Low density storage racks 10.5 Defective fuel assembly storage rack 4.3.2 Drainage The spent fuel storage pool is designed and shall be maintained to prevent inadvertent draining of the pool below elevation 660 ft 11.5 inches.

4.3.3 CaDacity The spent fuel storage pool is designed and shall be maintained with a storage capacity limited to no more thin 4608 fuel I assemblies.

Replace with:

3590 Note:

Items in red are changes proposed in original LAR Items in blue are additional changes proposed in RAI response FERMI - UNIT 2 4.0-2 Amendment No. I}fl,141 JAN Idrv 2001

Enclosure 3 to NRC-20-0046 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Revised Clean Page for TS Page 4.0-2

Design Features 4.0 4.0 DESIGN FEATURES 4.3 Fuel Storage (continued)

b. keff 0.95 if fully flooded with unborated water, which includes an allowance for uncertainties as described in Section 9.1 of the UFSAR; and

c. The following nominal center to center distances between fuel assemblies placed in the various storage rack types, as applicable Spacing Rack Type (inches) 6.22 High density storage racks that contain BORALCAN' as the neutron absorbing material 6.23 High density storage racks that contain Boral as the neutron absorbing material 4.3.2 Drainage The spent fuel storage pool is designed and shall be maintained to prevent inadvertent draining of the pool below elevation 660 ft 11.5 inches.

4.3.3 Capacity The spent fuel storage pool is designed and shall be maintained with a storage capacity limited to no more than 3590 fuel assemblies.

FERMI - UNIT 2 4.0-2 Amendment No. 134, 141

Enclosure 4 to NRC-20-0046 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Supplemental Information for the Proposed License Amendment to NRC-20-0046 Page 1 Supplemental Information for the Proposed License Amendment

1.0 BACKGROUND

On September 5, 2019, DTE Electric Company (DTE) submitted letter NRC-19-0004 (ML19248C679) requesting an amendment to the Renewed Facility Operating License NPF-43 for Fermi Unit 2 (Fermi 2) and its Appendix A, Technical Specifications (TS), in accordance with the provisions of 10 CFR 50.90, Application for amendment of license, construction permit, or early site permit. The license amendment request (LAR) submittal requested modification of the Renewed Facility Operating License to eliminate the License Renewal License Condition regarding the Boraflex material in the spent fuel pool (SFP) storage racks based upon a proposed alternative of installing neutron absorbing inserts (i.e., NETCO SNAP-IN rack inserts) in the racks containing Boraflex. The LAR also requested revision of TS requirements associated with the SFP storage racks based on approval of a new criticality safety analysis, including methodology. By email from Ms. Sujata Goetz dated October 8, 2019 (ML19319A007), the NRC stated that the request had been accepted for review.

The LAR contained a discussion of a planned monitoring program that would be implemented by DTE for the NETCO SNAP-IN rack inserts. Subsequently, DTE has identified improvements that could be made to the planned monitoring program. Section 2.0 below provides supplemental information regarding the insert monitoring program. In addition, the LAR provided insert installation schedule dates based on the project information at the time. Recent project reviews have led to changes in some schedule dates. The revised schedule dates are provided in Section 3.0 below for information only. As described in Section 4.0 below, the supplemental information in Sections 2.0 and 3.0 of this Enclosure does not impact the conclusions of the Regulatory Analysis, including the no significant hazards consideration, previously provided in the LAR.

2.0 CHANGES TO INSERT MONITORING PROGRAM 2.1 LAR Discussion of Retention Force and Stress Relaxation in the Absorber Rack Inserts The LAR provided information regarding the force required to remove an insert from a fuel storage rack cell once installed (i.e., the retention force). That force was required to be greater than or equal to 250 lbf which was based on Fermi 2 specific design criteria for seismic accelerations and stress relaxation. A 60 percent reduction in retention force was assumed based on the expected stress relaxation of the insert material. With this reduction, the inserts would still maintain a minimum 100 lbf of retention force within the cell (i.e., 60 percent reduction of the initial 250 lbf minimum retention force). The 100 lbf retention force was described as adequate to maintain the inserts in their required position under safe shutdown earthquake (SSE) conditions with margin, since an evaluation showed a retention force of 81 lbf is required to prevent upward movement of the insert during seismic events. The LAR described that the test results from the previous demonstration activities and the corresponding initial retention force criteria (i.e., 250 lbf) would ensure that the inserts remain in the installed location during fuel to NRC-20-0046 Page 2 moves and during a design basis seismic event. The monitoring program described in the LAR would also ensure that stress relaxation over time did not reduce the retention force below the minimum required during seismic events.

In addition to the consideration of seismic events, retention force was also referenced when considering fuel assembly movement during normal operations. The LAR described how the drag force, or interference between the fuel assembly and insert, during fuel movement activities is significantly less than 50 lbs based on experience from other plants. Similarly small drag forces are expected to be confirmed during the Fermi 2 testing by lack of fuel assembly interference. As a result, the LAR described that the maximum drag force will be significantly less than the retention force, such that there is adequate margin to ensure that an insert would not be removed during fuel assembly withdrawal even when considering stress relaxation. Despite this assurance, the LAR also included consideration of a missing insert in the criticality safety analysis in order to bound the potential for inadvertent insert removal during fuel assembly movement. Based on the expectation of minimal drag forces and the criticality safety analysis assumptions, monitoring of stress relaxation over time was not considered a programmatic requirement for normal fuel assembly movement activities, but rather only for the seismic considerations described above.

2.2 Updated Seismic Evaluation for Retention Force and Stress Relaxation The LAR stated that DTE may perform future refinement of the seismic evaluation to reduce the minimum required retention force to provide additional margin for stress relaxation. The updated seismic evaluation has now been performed. The evaluation was performed using a simplified dynamic analysis and applying a static coefficient factor. Since the insert is contained within the rack in both horizontal directions, the insert only has a single degree of freedom (i.e.,

only vertical displacement can occur). When determining the rigidity of the insert, the insert is analyzed as an elastic bar under axial load due to gravity. In addition, the weight of the insert is conservatively considered to be acting at the end of the insert rather than uniformly along the length.

The seismic evaluation demonstrated that the natural frequency of the insert was great enough that it was considered a rigid structure and the seismic zero period acceleration (ZPA) would be applicable in the vertical direction. The result was that no additional force beyond the weight of the insert itself is required to keep the insert in place during SSE conditions. Therefore, no specific retention force is required to be maintained throughout the installed lifetime of the insert. As a consequence, stress relaxation beyond the expected value of 60% has no impact on the ability of the insert to perform its safety function during SSE conditions.

2.3 Changes to Insert Monitoring Program The LAR included a section addressing the various activities to be included in the NETCO SNAP-IN rack insert monitoring program. Section 3.8.4 of the LAR described testing and inspections of the full rack inserts and included proposed pull testing requirements to monitor for stress relaxation. Pull testing was proposed to be used to confirm that adequate retention force to NRC-20-0046 Page 3 exists to meet the requirements for seismic events. As described above, the updated seismic evaluation demonstrates that no specific retention force is required (other than the weight of the insert itself). Since no specific retention force is required to be maintained, pull testing to confirm the retention force is not necessary. To avoid the potential for wear of the inserts due to unnecessary testing, DTE proposes to eliminate pull testing from the monitoring program. By not performing pull testing, dose to personnel from the testing will also be eliminated, which is consistent with as-low-as-reasonably-achievable (ALARA) principles.

Although periodic pull tests will not be performed, information on retention force will still be available from other activities that are being retained. First, the initial retention force of 250 lbf will be confirmed by testing as part of the insert installation activities. This confirmation by testing will either be performed on all inserts or on a sample basis. In addition, the long-term monitoring program will measure retention force when an insert is removed for the removal inspections (i.e., once per 10 years) described in the LAR. These long-term retention force measurements will still provide data regarding stress relaxation, even though it is no longer a critical parameter due to the new seismic evaluation.

3.0 CHANGES TO SCHEDULE INFORMATION The LAR provided the project schedule dates for prototype installation, the start of insert installation, and the end of insert installation. The dates provided in the LAR were for information only and were based on the planned schedule at that time. Subsequent project reviews have resulted in changes to these proposed schedule dates. The original and updated schedule dates are provided as follows for information only:

Prototype installation was scheduled to take place in October 2019. Prototype installation is now scheduled to take place in September 2020.

Start of insert installation was scheduled to begin in the summer of 2020. Installation is now scheduled to begin in January 2021.

End of insert installation was scheduled to be completed by the summer of 2021.

Installation is now scheduled to be completed by February 2023.

The changes in dates are an administrative project change and do not reflect technical changes or concerns. As before, the schedule dates are provided for information only and are based on the best available information at this time and subject to change.

The current schedule still supports completion of the project and implementation of the amendment, once approved by the NRC, well before the License Renewal License Condition deadline of March 20, 2025. Continued performance of the Boraflex prior to project completion is ensured by existing criticality safety analyses and existing Boraflex monitoring program activities.

to NRC-20-0046 Page 4 4.0 IMPACT TO REGULATORY ANALYSIS The supplemental information in this Enclosure does not impact the conclusions of the Regulatory Analysis previously provided in the LAR, including the no significant hazards consideration. In the previous evaluation, DTE concluded that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10 CFR 50.92(c),

and, accordingly, a finding of no significant hazards consideration is justified. Based on the considerations discussed in the LAR, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

The supplemental information in this Enclosure also does not impact the previously provided DTE evaluation of the proposed amendment for environmental considerations. Accordingly, the proposed amendment still meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), an environmental impact statement or environmental assessment is still not required for the proposed amendment.

In addition, the supplemental information does not add to or modify regulatory commitments previously identified in the LAR.