Rupture of process gas feedline

Any process heat plant design implies piping through the containment to connect the reactor vessel with the chemical plant. The fracture of a pipe could result in the accumulation of a flammable gas mixture in the containment. Precautions must be taken to minimize the risk of a fire or gas explosion such as avoidance of explosive gas ingress, proper detection devices, inerting, sufficient safety distances, appropriate layout of secondary coolant boundary, explosion-proofed wall, plant isolation valve. For the PNP-500, the use of two concentric pipes for the process gas carrying lines were recommended. Alternatives are concrete channels around the gas lines or inerting of the containment [10]. 

As part of the PNP safety program. Interatom has studied the process gas ii ress into the containment for the scenario of a depressurization plus process gas pipe rupture. Various containment volumes as well as times for the process gas pipes have been examined showing that the equilibrium pressure will be in the range of 0.16 - 0.24 MPa at temperatures 

Under the assumption of a reformer tube rupture creating a leak size of 80 cm with process gas to escape into the containment over 20 s before the stream is automatically cutoff, an estimated 3 % of flie containment volume is occupied by the process gas. Furthermore, pessimistically assuming that a stoichiometric mixture is formed and explodes, results in an overpressure of 46 kPa within 3 s which is expected to cause no damage to the containment [10]. 

Safety assurance in the design of the HTTR steam reforming system against fire or explosion of flammable product gas mixtures is the task of the secondary helium piping system which is designed to limit gas ingress by means of a combination of containment vessel isolation valves and emergency shutoff valve in the process gas feed line [33]. 

The release of product or feed gas into the envirorunent and the formation of a free flammable gas cloud could result in heat radiation and blast wave impact from fire / explosion. For the German PNP design, it was proposed to ensure that the gas be routed through inerted charmels away from the gasifier and flared at a safe spot. This measure, however, requires additional components in the confinement, e.g., to allow for a separation of the coal dust from the gas mixture and a cooling of the mixture [25]. 

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