ML21211A612

Attachment 3: Proposed Changed Page of HI-STORM FW FSAR

ML21211A612
Person / Time
Site:	07201032
Issue date:	07/30/2021
From:	Holtec
To:	Office of Nuclear Material Safety and Safeguards
Shared Package
ML21211A608	List: ML21211A609 ML21211A610 ML21211A611 ML21211A612
References
5018088
Download: ML21211A612 (1)

Text

Attachment 3 to Holtec Letter 5018088 The MPC incorporates a redundant closure system. The MPC upper lid is edge-welded (welds are depicted in the licensing drawing in Section 1.5) to the MPC outer shell. The lid is equipped with vent and drain ports that are utilized to remove moisture from the MPC and backfill the MPC with a specified amount of inert gas (helium). The vent and drain ports are closed tight and covered with a port cover (plate) that is seal welded before the closure ring is installed. The closure ring is a circular ring edge-welded to the MPC shell and upper lid; it covers the MPC lid-to shell weld and the vent and drain port cover plates. The MPC lid provides sufficient rigidity to allow the entire MPC loaded with SNF to be lifted by the suitably sized threaded anchor locations (TALs) in the MPC upper lid.

As discussed later in this section, the height of the MPC cavity plays a direct role in setting the amount of shielding available in the transfer cask. To maximize shielding and achieve ALARA within the constraints of a nuclear plant (such as crane capacity), it is necessary to minimize the cavity height of the MPC to the length of the fuel to be stored in it. Accordingly, the height of the MPC cavity is customized for each fuel type listed in Section 2.1. To further minimize MPC cavity height, cutouts in the MPC-89 lower lid may be made to accommodate DFCs that extend past the top of the basket. Table 3.2.1 provides the data to set the MPC cavity length as a small adder to the nominal fuel length (with any applicable NFH) to account for manufacturing tolerance, irradiation growth and thermal expansion effects.

For fuel assemblies that are shorter than the MPC cavity length (such as those without a control element in PWR SNF), a fuel shim may be utilized (as appropriate) between the fuel assembly and the MPC cavity to reduce the axial gap as prescribed by Table 3.2.1. A small axial clearance is provided to account for manufacturing tolerances and the irradiation and thermal growth of the fuel assemblies. The actual length of fuel shims (if required) will be determined on a site-specific and fuel assembly-specific basis.

All components of the MPC assemblyportions of MPC components that may come into contact with spent fuel pool water or the ambient environment are made from stainless steel alloy or aluminum/aluminum alloy materials. Prominent among the aluminum based materials used in the MPC is the Metamic-HT neutron absorber lattice that comprises the fuel basket. As discussed in Chapter 8, concerns regarding interaction of coated carbon steel materials and various MPC operating environments [1.2.1] are not applicable to the HI-STORM FW MPCs. All structural components in an MPC enclosure vessel shall be made of Alloy X, a designation whose origin, as explained in the HI-STORM 100 FSAR [1.1.3], lies in the U.S. DOEs repository program.

As explained in Appendix 1.A, Alloy X (as defined in this FSAR) may be one of the following materials.

• Type 316

• Type 316LN

• Type 304

• Type 304LN

• Duplex Stainless Alloy S31803 Any stainless steel part in an MPC may be fabricated from any of the acceptable Alloy X materials listed above.

HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 10 1-43