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CONCEPTUAL DESIGN OF THE HTTR-IS NUCLEAR HYDROGEN PRODUCTION SYSTEM
Run 2 shows that reducing the actuation time of HTIV from 30 to 5 seconds could drop the
amount of the helium transportation by more than 60%. In addition, Run 3 shows that the interfacing
the actuation of HTIV and LTIV simultaneously is effective for the reduction of helium gas transport
from primary to secondary. Furthermore, Run 4, which sets the actuation time of HTIV larger than
LTIV would considerably reduce the amount of the helium transportation by more than 80%.
The results are due to the difference in differential pressure behaviour at IHX. Figure 5 shows the
influence of the isolation valves actuation sequence on the differential pressure behaviour at IHX,
which is defined as a subtraction from secondary to primary coolant pressure. Though the profile of
differential pressure behaviour at IHX is almost the same in all of the cases, occurrence time of the
peaks and their intensity are different in each case because of the momentum change difference which
are induced by the difference of isolation valves actuation time and occurrence time of secondary
circulator trip.
Differential pressure between
primary and secondary cooling system (MPa)
Figure 5: Influence of the isolation valve actuation
sequence on differential pressure behaviour at IHX
0.02
0.015
0.01
0.005
0
-0.005
Run 1
Run 2
-0.01
Run 3
Run 4
-0.015
15 20 25 30 35 40 45 50
Elapsed time from IHX heat transfer tube rupture (s)
Plant dynamics evaluation
The system behaviour during the IHXTR was evaluated. In this calculation, analytical conditions,
e.g. reactivity coefficients, total reactivity worth of control rods, etc., used in the HTTR safety review
were introduced. In addition, 20 and 30 seconds were selected for the actuation condition and time of
isolation valves based on the previous results of parametric studies. Acceptance criteria, established
in the original HTTR safety review (Saito, 1994) were used to assess the reactor safety. Figure 6 shows
the transient behaviour of evaluation items. As a beginning, heat transfer tube rupture induces helium
gas transportation from secondary to primary. After the pressure balance between the primary and
secondary cooling systems, primary helium gas flows into the secondary cooling system. Isolation
valves then simultaneously actuate and isolate the secondary cooling system. Reactor scrams by the
“secondary cooling system flow low” at 39 seconds. As calculation results show that evaluation items,
which are the primary coolant pressure, heat transfer tube temperature of PPWC and IHX and RPV
temperature do not exceed the acceptance criteria. In addition, maximum fuel temperature also does
not exceed the initial value and therefore the reactor core was not seriously damaged and was cooled
sufficiently.
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 393