ML18194A742
| ML18194A742 | |
| Person / Time | |
|---|---|
| Site: | NuScale |
| Issue date: | 07/13/2018 |
| From: | NRC |
| To: | NRC/NRO/DLSE/LB1 |
| References | |
| Download: ML18194A742 (4) | |
Text
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, General Design Criteria (GDC) 62 requires fuel assemblies in the fuel storage and handling system to be held sub-critical through the use of physical systems or processes. For the NuScale design the applicant utilizes a neutron absorbing material as the primary means to prevent re-criticality. The applicant has chosen to address GDC 62 primarily in Technical Report TR-0816-49833-P, Rev 0 "Fuel Storage Rack Analysis." The technical report describes the fuel storage racks and provides analyses to demonstrate that the fuel storage racks meet GDC 62. The staff finds that TR-0816-49833-P does not contain information on how neutron absorbing material is qualified. Qualification testing should ensure that the neutron absorber is suitable during fabrication, shipping, construction, and operation. Additionally, the staff finds that the technical report does not impose process controls to ensure that the manufactured material meets the safety functions described in TR-0816-49833-P. Qualification reports, processes controls, and verification testing have been previously required by the staff for the Metamic and Maxus neutron absorbing materials. The staff provides four issues below that should be addressed by the applicant. The four issues are: material fabrication, environmental compatibility, material structural adequacy, neutron absorption properties. The applicant should revise Technical Report TR-0816-49833-P to address the staff concerns. The staff notes that regulatory guidance on the qualification of neutron absorber material may be found in Interim Staff Guidance document SFST-ISG-23 Revision 0, "Application of ASTM Standard Practice C1671-07 when performing technical reviews of spent fuel storage and transportation packaging licensing actions," and ASTM C-1671-07, "Qualification and Acceptance of Boron Based Metallic Neutron Absorbers for Nuclear Criticality Control for Dry Cask Storage System and Transportation Packaging." The staff acknowledges that SFST-ISG-23 and ASTM C1671-07 contain some aspects which are specific to dry spent fuel storage, however the majority of content in both documents are generic. Additional conditions or clarifications on the use of SFST-ISG-23 and ASTM C1671-07 are provided alongside the discussion of the four issues that should be addressed. The staff would consider the use of SFST-ISG-23, ASTM C1671-07, and the modifications below as an acceptable method of addressing the staff concerns in meeting GDC 62. Issue A - Material Fabrication The key processes and controls on the key processes should be described. Key processes should include neutron absorber material fabrication methods (e.g., extrusion, stir casting, compaction process, etc.), whether cladding is used, raw material specifications, etc. Process controls should include particle size distribution limitations, heat treatment ranges, ratio of B 4C to Al, minimum density, contamination controls, etc. The process controls shall prevent changes to the fabrication process which could impact the credited safety function or introduce new degradation mechanisms. In addition, Technical Report TR-0816-49833-P, Section 3.4.1.3.2, "Neutron Absorber Material Specification," should be expanded to describe acceptance testing which will verify that key process controls were met during fabrication. Revise FSAR Section 9.1.1 or Technical Report TR-0816-49833-P to describe how the material fabrication will be controlled to ensure that the manufactured product is consistent with the licensing basis. Alternatively, the applicant may commit to meeting ASTM C1671-07 (in particular Section 5.2.7, "Key Processes and Process Controls") subject to the conditions on ASTM C1671-07 in SFST-ISG-23, with the modifications shown in the attached marked up version of ISG-23.
Issue B - Environmental Compatibility Neutron absorber material qualification testing should demonstrate that the material is suitable for use in the spent fuel pool environment for the lifetime of the component. Qualification testing should verify that the safety functions of the neutron absorber are not impaired by radiation damage, borated water, or boiling temperatures. Testing should verify that prolonged immersion in spent fuel pool water will not result in the formation of gas pockets (hydrogen or steam) which can interfere with spent fuel assembly withdrawal or may impact subcriticality. Revise FSAR Section 9.1.1 or Technical Report TR-0816-49833-P to describe how the material will be qualified for environmental compatibility. Alternatively, the applicant may commit to meeting ASTM C1671-07 (in particular Section 5.2.3, "Environmental Qualification Tests") subject to the conditions on ASTM C1671-07 in SFST-ISG-23, with the modifications shown in the attached marked up version of ISG-23. Issue C - Material Structural Adequacy If the material is not credited with a structural design function, testing shall demonstrate that the neutron absorber has sufficient strength and ductility to prevent cracking, fracture, or other significant damage during fabrication, shipping, and operation. Revise FSAR Section 9.1.1 or Technical Report TR-0816-49833-P to describe how the material will be qualified for structural adequacy. Alternatively, the applicant may commit to meeting ASTM C1671-07 (in particular Section 5.2.6, "Mechanical, Absorber Uniformity, and Other Qualification Testing") subject to the conditions on ASTM C1671-07 in SFST-ISG-23. Issue D - Neutron Absorption Properties Neutron absorber material qualification testing should demonstrate that the material has sufficient neutron absorption properties to achieve its design function. Uniformity of the neutron absorber, measurement uncertainties, and biases should be assessed during qualification. The assessments shall be used to demonstrate that the neutron attenuation measurements of the production material is sufficiently conservative. The applicant should define neutron attenuation acceptance criteria and methods of assessing bias and uncertainty for the production material. The acceptance criteria and methods shall be used to verify that the production material meets the licensing basis. Revise FSAR Section 9.1.1 or Technical Report TR-0816-49833-P to describe how the material will be qualified for neutron absorption properties. Alternatively, the applicant may commit to meeting ASTM C1671-07 (in particular Section 5.2.6, "Mechanical, Absorber Uniformity, and Other Qualification Testing," and Section 5.3, "Neutron Absorber Material Acceptance Testing") subject to the conditions on ASTM C1671-07 in SFST-ISG-23, with the modifications shown in the attached marked up version of ISG-23.