Analysis of self-shielding regions of nuclear reactors under conditions of uncertain initial data

Conclusions

We now formulate the basic results on the solution of problems with constraints on the safety functionals.

• 1. Problems with constraints on safety functionals under conditions of uncertainty in the information about external disturbances can always be reduced to two deterministic problems corresponding to optimistic and pessimistic scenarios of events, where the initial data are determined uniquely. This conclusion concerns both problems of optimal design of selfshielded reactors and problems of constructing the region of internal self-shielding.

• 2. If the safety functionals in an accident situation (or under conditions of superposition of accident regimes) reach maximum values in a new stationary state, established as a result of actuation of reactivity feedbacks (or emergency shielding), then there is no uncertainty in determining the boundary of the region of self-shielding, i.e., the boundaries of regions corresponding to optimistic scenarios of the development of accident situations are identical to the boundaries of regions corresponding to pessimistic scenarios.

  As the amplitude of a disturbance increases and therefore the maximum of the safety functionals shifts in time from the region of a transient regime into a region of a steady-state regime, the uncertainty in the boundary of the region of selfshielding decreases.

• 3. When solving problems under conditions of uncertainty of initial data which are not associated with external disturbances, an uncertainty is always present in the boundary of the region of self-shielding, i.e., the boundary is diffuse.

  In closing, we note that such problems are solved at the final stages of the design of the new-generation self-shielded nuclear reactors for the purpose of making a deterministic substantiation of their safety.