Steam hammer can occur in steam systems when some of the steam condenses into water in a horizontal section of the piping. The steam forcing the liquid water along the pipe forms a " slug " which impacts a valve of pipe fitting, creating a loud hammering noise and high pressure. Vacuum caused by condensation from thermal shock can also cause a steam hammer. Steam hammer of steam condensation induced water hammer (CIWH) was exhaustively investigated both experimentally and theoretically more than a decade ago because it can have radical negative effects in nuclear power plants. It is possible to theoretically explain the 2 millisecond duration 130 bar overpressure peaks with a special 6 equation multiphase thermohydraulic model, similar to RELAP.