A cold neutron source(CNS) is a reactor facility to slow down thermal neutrons into clod neutrons of 0.1-0.5 meV.If the cryogenic hydrogen loop leaks(including the moderator chamber)

and the injecting hydrogen contacts the inner surface of the vacuum containment

the thermal stress shall concentrate on the impacted zone by cryogenic hydrogen.A finite element stress analysis was conducted

and it was found that the maximum stresses are 195 and 213 MPa

corresponding to the impacted area of 1.0-2.25 cm2

respectively.The max stresses are less than the stress limit of the material.So it is concluded that the cryo-hydrogen injecting accident does not threat the safety of the vacuum containment.