NRC SFST ISG-25: Pressure and Helium Leakage Testing of the Confinement Boundary of Spent Fuel Dry Storage Systems

The purpose of this interim staff guidance (ISG) is to supplement standard review plan guidance
for evaluating the helium leakage testing and ASME Code1
required pressure
(hydrostatic/pneumatic) testing that is specified for the dry storage system (DSS) confinement
boundary. These acceptance tests are necessary to clearly demonstrate that the DSS
confinement boundary has been fabricated in accordance with the design criteria, and that its
operation complies with the intended safety bases of the confinement system and regulatory
requirements. Specifically, a shop helium leakage test (i.e. leakage test performed at the
fabrication facility) should be performed to demonstrate that the DSS shell leak rate is within the
design limits. This is important to ensure that site boundary dose limits are met and an inert
helium environment is maintained for cooling of the spent nuclear fuel. Additionally, a shop
helium leakage test has been accepted to demonstrate confinement integrity for inaccessible
DSS shell welds that can not be visually examined during the ASME Code field pressure test
(i.e. pressure test performed by a Part 722
licensee during loading operations). This ISG
provides guidance to the staff and is not a regulatory requirement. Alternative approaches may
be used to demonstrate safety and compliance, as appropriately justified by an applicant.