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PROPOSED CHEMICAL PLANT INITIATED ACCIDENT SCENARIOS IN A S-I CYCLE PLANT COUPLED TO A PEBBLE BED MODULAR REACTOR
Table 2: Composition of the discharging gas
Gas
Mole fraction
Sulphuric acid, H 2 SO 4 0.0008
Water, H 2 O 0.4577
Sulphur trioxide, SO 3 0.1553
Sulphur dioxide, SO 2 0.2575
Oxygen, O 2 0.1287
Figure 10: Discharging gas for area = 0.02 m 2 break
Results are shown in Figures 11-13. These results are slight, largely because they only represent
the initial phase after the initiation of the accident. In Section 2, it is evident that the reaction rate
decreases as the amount of reactants in the section decreases. In Section 3, there are competing
effects, namely fewer input reactants available, but more reaction heat input. Thus, we see the
oscillatory behaviour shown in the figure. The magnitude of this oscillation is indeed small, however.
Due to an increase in reactor temperature, in Figure 13 the reactor power begins to decrease. This is
the expected behaviour of the PBMR due to the passively safe temperature feedback.
Figure 11: Extent of reaction in Section 2 for area = 0.02 m 2 break
384 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010