ML14059A156

NRR E-mail Capture - Request for Additional Information for Use of Neutron Absorbing Inserts in Spent Fuel Pool Storage Racks (TAC Nos. MF2489 and MF2490)

ML14059A156
Person / Time
Site:	Quad Cities
Issue date:	02/28/2014
From:	Mozafari B Division of Operating Reactor Licensing
To:	Nicely K Exelon Corp
References
MF2489, MF2490
Download: ML14059A156 (5)

Text

NRR-PMDAPEm Resource From: Mozafari, Brenda Sent: Friday, February 28, 2014 8:12 AM To: Nicely, Ken M.:(GenCo-Nuc) (ken.nicely@exeloncorp.com)

Cc: Tate, Travis; Purnell, Blake; Lipa, Christine

Subject:

REQUEST FOR ADDITIONAL INFORMATION FOR USE OF NEUTRON ABSORBING INSERTS IN SPENT FUEL POOL STORAGE RACKS (TAC NOS. MF2489 AND MF2490)

Ken, By letter dated July 16, 2013, and supplemented by letter dated September 18, 2013, Exelon Generation Company, LLC (EGC) the licensee, requested to amend Facility Operating Licenses No.

DPR-29 and DPR-30 and revise the Quad Cities Nuclear Power Station, Units 1 and 2, Technical Specifications (TSs). A January 22, 2014, letter contained supplemental information to complete the acceptance review of the request. The proposed amendment would allow installation of the NETCO-SNAP-IN neutron absorbing rack inserts into the spent fuel pool storage rack cells as a measure for criticality control. Approval of this license amendment would allow the licensee to meet the k-effective criticality control requirements without reliance on Boraflex neutron absorber panels. To continue its review the NRC requests the licensee provide the following additional information. Because of the need for a quick turnaround after the clarification call conducted yesterday (2/26/14) we will need your responses as soon as March 30, 2014, to support the progress of the technical review. Ken, call me today to discuss any timing matter. These questions will be put in ADAMS as an official RAI.

Final RAI Requests

1) Section 3.1.3 of Attachment 1 to the July 16, 2013, letter indicates that following approval and implementation of the rack insert amendment there will be several storage cells that will not be usable for one reason or another. Explain how TS 4.3.3 is being revised to reflect the reduced SFP capacity.

2) For the Super Lattice cases there is very little margin to the regulatory limit. Section 3.4.2 of Attachment 1 to the July 16, 2013 letter, discusses mechanical wear of the inserts. While the section indicates that minimal insert mechanical wear is expected the minimum as-built areal density of the inserts is the same value as is being used in the NCS. This means that for the inserts which are installed at the minimum as-built areal densities can tolerate essentially no wear of any kind before the insert no longer has the requisite areal density to perform as analyzed. With that in mind provide the following:

a) Justification of the proposed wear surveillance. NRC staff considers one insert too limited of a sample size and recommends the licensee increase the sample size to three or more.

Additionally, the NRC staff considers the licensees proposed definition of high duty to be limited as it does not appear to consider the potential for a low number of fuel movements having a higher contact with the insert as being more limiting than a high number of fuel moves with essentially no contact with the insert.

b) Discuss whether the process of placing the inserts into the rack results in any wear on the insert.

3) Sections 3.9.3 and 3.9.4.2 of Attachment 1 to the July 16, 2013, letter discusses the long term surveillance program for the inserts. The specified acceptance criterion for Boron-10 (10B) areal density is 0.0116 gm/cm2. This is the minimum as-built/minimum certified areal density for the entire population of inserts. A coupon or insert could experience degradation and pass this 1

acceptance criterion if its as-built areal density was above 0.0116 gm/cm2. Explain how the surveillance program guarantees that any degradation is detected before it affects the safety function of the inserts installed in the SFP.

4) Section 2.3.1.1 of HI-2125245 Revision 4 mentions MOX fuel. Provide a description of the MOX fuel assemblies stored in the Quad Cities SFPs. Provide the justification of how the HI-2125245 analysis bounds those MOX fuel assemblies, include descriptions of the analysis that was performed in support of the justification.

5) Section 2.3.1.1.2 of HI-2125245, Revision 2 discusses the isotopic compositions used in the analysis. The text implies the analysis is modeling a number of short lived isotopes and volatile and gaseous isotopes not explicitly mentioned in the discussion of the analysis assumptions. Provide a justification for using these short lived, volatile, and gaseous isotopes as well.

6) Section 2.3.5.4 of HI-2125245, Revision 2 discusses the various fuel orientations within the storage cells that were considered. The report also indicates fuel assemblies at Quad Cities will have radial gradients based on actual fuel pin loading and rodded operation. It is not clear from Section 2.3.5.4 that the fuel orientations considered included the case where the most reactive quadrant of the fuel assemblies were all turned toward each other. Was this case considered in Section 2.3.5.4, and if so identify the case.

7) HI-2125245, Revision 2 discusses the effect of fuel channel bulging and bowing. This section indicates the reactivity effect is bounded by abnormal/accident scenarios. The presence of fuel channel bulging and bowing would be part of the normal condition of the SFP storage system and needs to be included in the estimation of reactivity under normal conditions. The NRC staff considers it inappropriate to use accident conditions to bound normal operating conditions, especially when the normal operating conditions would be the starting point for subsequent abnormal/accident scenarios. Revise the NCS to account for fuel channel bulging and bowing under normal conditions.

8) HI-2125245, Revision 2 discusses the normal conditions of fuel movements, inspections, and reconstitution operations. This section indicates the reactivity effect is bounded by abnormal/accident scenarios. It is not appropriate to use accident conditions to bound normal operating conditions. Revise the NCS to account for these normal operations, or clarify how those type of normal operations cannot occur coincident with abnormal/accident conditions. If abnormal/accident conditions can occur (dropped assembly) during normal operation they should also be considered in the accident analysis.

9) Section 2.6.7 of HI-2125245, Revision 2 discusses an incorrect orientation of an insert. If an incorrect orientation of an insert is accepted as-is following installation, then that orientation becomes the normal as-built configuration. With respect to incorrect orientation of an insert, provide post-installation measures that will be taken to verify that all inserts are orientated correctly.

10) The inserts are required to function and remain in place under design operational and accident conditions. Explain how the inserts will perform under required accident conditions (e.g., seismic event, dropped assembly, and heat up events, if applicable) and provide a basis for the conclusions.

11) Section 2.9 of HI-2125245, Revision 2 discusses reconstituted fuel assemblies. With respect to reconstituted fuel, provide the following information:

a) The text indicates that the current inventory of reconstituted fuel at QCNPS had fuel rods replaced with either like for like fuel rods or stainless steel. The analysis concludes there was no increase in reactivity for these legacy reconstituted fuel assemblies. Justify the basis for that conclusion.

b) The text indicates that future reconstitutions will only use stainless steel pins. Elsewhere in the analysis it is indicated that the Optima2 fuel assembly is under moderated. Replacing a fuel rod 2

with a stainless steel pin reduces the amount of under moderation. This potential increase in reactivity may be offset by the additional neutron absorption in the stainless steel pin. Describe any limitations on the number or material of the stainless steel pins. Explain how did those conclusions were reached.

12) HI-2125245, Revision 2 includes the results of numerous cases that were run to support the determination of the bounding lattice used in the analysis. However, from the information provided it is unclear to the NRC staff what the particular details of each case are and how they relate to current QCNPS fuel.

13) Section 2.3.1.4 of HI-2125245, Revision 2 discusses a series of calculations performed to demonstrate that certain simplifications in the SVEA-96 Optima2 fuel geometry as modeled in CASMO-4 (due to code limitations) do not have a significant impact on the calculated rack k-infinity.

The calculations were performed based on a single fuel lattice. Provide the technical basis for concluding that this finding of no significant impact will apply broadly to all expected lattices (i.e.,

lattices with different compositions, gadolinia loading, and locations of gadolinia pins).

14) Section 2.3.4.1 of HI-2125245, Revision 2 addresses fuel manufacturing tolerance biases for the SVEA-96 Optima2 fuel assembly. However, the tolerances associated with other fuel lattice types are not addressed. Provide a statement explaining why any potential increase in fuel manufacturing tolerance bias for a different fuel assembly design are not expected to be larger than the reactivity difference between the limiting lattice(s) for that fuel assembly design compared to the limiting SVEA-96 Optima2 lattice.

15) Revision 4 of HI-2125245 removed part of Section 2.7 as included in Revision 2, which discussed a new approach in which super-lattices could be used to qualify future lattices. However, super-lattices are still used in the analyses. Given that the super lattices result in significantly less margin to the regulatory limit, please indicate if the proposed revision to the current licensing basis of Quad Cities is to be based on the design basis lattice, or on the super lattices. Provide clarification.

16) Provide more detail for the technical basis and assumptions inherent in the criteria described in HI-2125245, Revision 2 to select lattices for evaluation using the in-rack k-infinity calculational method.

In particular, explain why more lattices were not selected for evaluation and why it is appropriate to conclude that the most limiting in-rack k-infinity will be found among the candidate lattices.

17) CASMO-4 is used to perform depletion calculations which provide the isotopic compositions used as inputs to the MCNP5-1.51 NCS analyses. Describe how CASMO-4 is qualified for performing depletion calculations with the SVEA-96 Optima2 fuel assembly; given that a different code is used for NRC-approved reload analysis methods. Address the fact that the documented CASMO-4 k-infinity values show a persistent bias relative to MCNP5-1.51 results for the same fuel lattices. If CASMO-4 is not formally qualified for this purpose, then explain why use of the 5% depletion uncertainty described in DSS-ISG-2010-01 remains applicable.

18) The screening calculations performed as reported in HI-2125245, Revision 2 assumes nominal operating conditions. After the design basis lattice is selected, then different operating conditions are investigated to establish a limiting set of design basis operating condition. Provide the technical basis for concluding that the limiting operating conditions used as input to the NCS analyses are solely a consequence of the fuel assembly geometry and/or fuel assembly design specific characteristics. In other words, if the design basis operating conditions differs for different fuel assembly designs, Explain how this changes the lattice(s) selected as a result of the screening calculations.

19) Control rod specifications are given in HI-2125245, Revision 2. Section 7.1.4 indicates that operation with the adjacent control rod inserted is one of the core operating parameters that has a 3

significant impact on the NCS analysis. Many BWR plants have had to replace installed control rods due to tip cracking and/or B-10 depletion. Identify if other types of control rods are currently used at Quad Cities, and if so, provide a justification for the assumption that the control rod specifications used bound all other control rod types in use at Quad Cities for the depletion parameters used as input in determination of the isotopic compositions for the NCS analyses.

20) Section 2.2.2 of HI-2125245, Revision 2 indicates that a validation of CASMO-4 to determine a bias and bias uncertainty is not necessary because CASMO-4 is not being used for the design basis k-eff calculations. CASMO-4 is being used to screen out lattices in order to limit the number of MCNP5-1.51 calculations that need to be performed. The underlying assumption is that any bias between CASMO-4 and MCNP5-1.51 results will tend to be consistent, so the relative values for CASMO-4 can be used to identify the most reactive lattices. Provide support for the assumption that the most reactive lattice determined by CASMO-4 will produce the maximum in-rack reactivity using MCNP5-1.51.

21) HI-2104790, Revision 1 provides a detailed description of the benchmarking of MCNP5-1.51, trend analysis, and statistical analysis as discussed in NUREG/CR-6698, Guide for Validation of Nuclear Criticality Safety Calculational Methodology, issued January 2001. It is not clear how the critical benchmarks and experiments bound the Area Of Applicability (AOA) for the fuel lattices being studied with respect to specific characteristics of the geometry of the SVEA-96 Optima2 lattice.

Provide a discussion of how the AOA is adequately bounded for the specific characteristics of the SVEA-96 Optima2 fuel lattice.

Brenda L. Mozafari Senior Project Manager, NRR/DORL U.S. Nuclear Regulatory Commission Dresden 2/3 and QuadCities 1/2 301-415-2020 email: brenda.mozafari@nrc.gov This e-mail and any attachments are confidential, may contain legal, professional or other privileged information, and are intended solely for the addressee. If you are not the intended recipient, do not use the information in this e-mail in any way, delete this e-mail and notify the sender. -EXCIP 4

Hearing Identifier: NRR_PMDA Email Number: 1129 Mail Envelope Properties (Brenda.Mozafari@nrc.gov20140228081100)

Subject:

REQUEST FOR ADDITIONAL INFORMATION FOR USE OF NEUTRON ABSORBING INSERTS IN SPENT FUEL POOL STORAGE RACKS (TAC NOS. MF2489 AND MF2490)

Sent Date: 2/28/2014 8:11:55 AM Received Date: 2/28/2014 8:11:00 AM From: Mozafari, Brenda Created By: Brenda.Mozafari@nrc.gov Recipients:

"Tate, Travis" <Travis.Tate@nrc.gov>

Tracking Status: None "Purnell, Blake" <Blake.Purnell@nrc.gov>

Tracking Status: None "Lipa, Christine" <Christine.Lipa@nrc.gov>

Tracking Status: None "Nicely, Ken M.:(GenCo-Nuc) (ken.nicely@exeloncorp.com)" <ken.nicely@exeloncorp.com>

Tracking Status: None Post Office:

Files Size Date & Time MESSAGE 13937 2/28/2014 8:11:00 AM Options Priority: Standard Return Notification: No Reply Requested: Yes Sensitivity: Normal Expiration Date:

Recipients Received: