  The Proton Improvement Plan-II (PIP-II) is a superconducting linear
accelerator being built at Fermilab that will provide 800 MeV proton beam for
neutrino production. The linac consists of a total of twenty-three (23)
cryomodules of five (5) different types. Cooling is required at 2K, 5K and 40K.
The Cryogenic Distribution System (CDS) consists of a Distribution Valve Box,
~285 m of cryogenic transfer line, modular Bayonet Cans to interface with
cryomodules, and a Turnaround Can. The cryogenic system must provide protection
from over-pressure by sizing pressure relief devices for all volumes and
process line circuits. The cryomodule cavity circuits have dual pressure
ratings, 4.1 bara when cold and 2.05 bara when warm (T>80K). Worst case
relieving cases will be identified. The methods for determining heat flux will
be presented. For the relieving occurring in the linac tunnel, flow must vent
to outside to avoid an oxygen deficiency hazard. Also, we will present vacuum
vessel relief sizing to protect the cryogenic distribution system vacuum shells
from over pressure during an internal line rupture. The project is funded by US
DOE Offices of Science, High Energy Physics.
