Operational control and scram procedures in process heat HTRs

Compared with an electricity generating HTR a process heat reactor differs greatly in relation to reactor control and safety procedures, as a result of the higher helium outlet temperatures, and the more complicated multi-purpose heat exchanger systems. The problems arising from the more complicated and sensitive technology are illustrated by the example of a 9500C reactor which heats a steam reformer between 9500C and 7500C and which produces super-heated steam between 7500C and 8000C helium temperature. For such a reactor the necessary differences of scheme of the operational control circuit mainly resulting from the different operating behaviour of the steam reformer and the steam generator units (during operation, starting and stopping the plant) are pointed out. Furthermore the scram procedures have to be designed carefully. Due to the high temperatures after some accidents, e.g. rupture of a steam tube the reactor must be cooled down rapidly, a procedure which causes severe conditions at the heat exchangers. This safety problem and first proposals for the layout of such a scram-=procedure are discussed. (author)