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Figure 5. Core mass balance for 0.50% and 100% 238 U<br />

in the fertile material input for Vfertile/Vfissile = 2<br />

1 000 000<br />

Loaded mass in reactor (kg)<br />

100 000<br />

10 000<br />

1 000<br />

100<br />

10<br />

1<br />

TH<br />

32<br />

PA<br />

33<br />

U2<br />

33<br />

U2<br />

34<br />

U2<br />

35<br />

U2<br />

36<br />

U2<br />

38<br />

PU<br />

38<br />

PU<br />

39<br />

PU<br />

40<br />

PU<br />

41<br />

PU<br />

42<br />

AM<br />

41<br />

AM<br />

43<br />

100%Th 50% Th 50% U 100% U<br />

NP<br />

37<br />

CM<br />

42<br />

CM<br />

43<br />

CM<br />

44<br />

CM<br />

45<br />

5. A major safety asset: core drainage<br />

The salt is at its maximum reactivity in the graphite. A safe fallback position can thus be<br />

obtained by draining the core. As the fuel is liquid, it can be extracted from the core at any moment.<br />

For this, we adopted a concept proposed by EdF and the CEA, which consists in placing a drain tank<br />

under the core, which is permanently connected to it. Salt is confined within the core by a helium<br />

back-pressure (Figure 6). One therefore need simply interrupt the electric power supply to the He<br />

compressor for gravity drainage of the core. This feature, allied with the considerable thermal inertia<br />

of the reactor and the difficulty of rapidly inserting reactivity, should make the reactor particularly<br />

safe.<br />

Figure 6. Core drainage principle<br />

Thermal detector<br />

Reactor<br />

Salt<br />

Compressor<br />

He<br />

264

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