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PROPOSED CHEMICAL PLANT INITIATED ACCIDENT SCENARIOS IN A S-I CYCLE PLANT COUPLED TO A PEBBLE BED MODULAR REACTOR
Figure 2: Bunsen failure
This scenario highlights an important recurring theme in each of the scenarios presented in this
paper, namely that the sections of the chemical plant transform from continuous coupled reactors to
discontinuous batch reactors. A discontinuous batch reactor is shown in Figure 3.
• Reactant flow to reaction chambers shut off.
• Reaction chambers, evaporators and pre-heaters will shut down, along with any accompanying
heat sink.
• Continuous coupled reactor becomes discontinuous batch reactor.
Figure 3: Discontinuous reactor
Reactant flow feed pipe failure in a single section of the chemical plant
The reactant pipe flow failure scenarios are depicted in Figures 4 and 5. In these scenarios the
reactant flow to a single section is interrupted via pipe break. The primary reason for such a scenario
would be a pipe break leaving the Bunsen reactor or a heat exchanger failure. The immediate
consequence is failure of the pre-heater and evaporator of the section in question, as well as the
transformation of the section in question from a continuous reactor to a discontinuous batch reactor.
As the reactants deplete, these reactors will shutdown, eliminating the reaction component of the
nuclear reactor heat sink. Eventually either of these scenarios would lead to the shutdown of the
entire chemical plant, due to the interruption of the required cyclical nature. Thus, this scenario is a
pronounced partial loss-of-heat-sink accident progressing to a full loss-of-heat-sink accident. The
length of time it takes for this progression to occur is the amount of time it takes for the reactant in
the newly created discontinuous reactor to deplete.
• Reactant flow to single section shut off.
• Partial loss of heat sink (pre-heater/evaporation of a single section) progresses to total loss of
heat sink.
• Accident is more severe if it occurs in Section 2, due to rapidity of response.
380 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010