The LOFT pressurizer spray and surge line piping was analyzed for a 450/sup 0/F step change in fluid temperature. This transient was chosen to conservatively represent several pressurizer operating transients that had not previously been analyzed. These include temperature transients resulting from a 300/sup 0/F ..delta..T between pressurizer temperature and cold leg temperature, injection of a cooled (70/sup 0/F) slug of stagnant fluid into the hot (540/sup 0/F) spray line piping, and inflow of 100/sup 0/F primary coolant system water into the hot (480/sup 0/F) surge line piping.