Nuclear Production of Hydrogen, Fourth Information Exchange ...

USE OF PSA FOR DESIGN OF EMERGENCY MITIGATION SYSTEMS IN A HYDROGEN PRODUCTION PLANT
Figure 2: PSA covered area
Preliminary system design
Once the information necessary to mitigate sulphuric acid leakage within the area indicated above
was collected, a system was proposed which is composed of three protective barriers, which are
described below.
Primary system (isolation system)
The primary system is intended to isolate the major equipment in order to prevent reverse flow and
exhaust oxides in a gaseous state. It consists of a special “restraint type” valve (check) and two
motorised shutdown valves, arranged in series. The system includes a low pressure detector on the
main pipe that trips the sulphuric acid pumps, isolates the process and stops the helium flow into the
reactor and heaters (emergency system EAS-200).
One of the precursors of the critical event is the failure of isolation in any of the endpoints, either
from the pumping system to the heating train, from the decomposition reactor to the previous train,
or in the helium supply lines. This is because, in the former case, the flow of sulphuric acid to spill
will be greater than that permissible, in the second case there is an emission of sulphur oxides in a
gaseous state from the decomposition reactor and in the third the flow of helium through stagnant
heat exchangers would increase emissions.
The electrical support for this system is the emergency generator for the section of sulphuric acid
decomposition. The pressure detectors PI201 and PI202 trip the system on low pressure. The diagram
of the primary system is shown in Figure 3.
Neutralisation system
If for some reason the primary system failed, a leak of acidic compounds would occur that should be
treated to prevent formation of toxic clouds. The second barrier against toxic clouds proposed here is
a chemical mitigation system, which uses a calcium carbonate dilution as a neutralisation agent.
In this second system, an automatic hopper delivers calcium carbonate to a dilution water tank,
where an electric mixer stirs and homogenises the blend. To cover a possible mixer failure, a diesel
pump, with enough capacity to homogenise the tank contents by turbulent backflow, is also placed.
400 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010