Acceptance criteria

The acceptance criteria for all design basis accidents are as follows:

(a) Coolability criteria:

• Clad temperature to be less than 1473 K;

• Oxidation of clad surface should be less than 17%;

• Maximum energy deposition in fuel for fuel shattering shall not exceed 200 Cal/g;

• Maximum fuel temperature anywhere in the core shall not exceed UO2 melting temperature throughout a transient;

(b) Fuel failure criteria:

• Maximum energy deposition in fuel for fuel failure shall not exceed 140 Cal/g;

• Maximum clad surface temperature shall be 1073 K;

• The radially averaged fuel enthalpy, anywhere in the core, shall not exceed 586 J/g.

Actual calculations indicate that fuel clad temperatures do not exceed 1073 K in any design basis accident sequences mentioned above.

For the purpose of containment design, a double ended guillotine rupture of the 600 mm diameter inlet header has been considered a design basis accident. A large number of other accident scenarios would conventionally fall within the category of beyond design basis accidents (BDBA). However, even in these cases, including the case of an NPP blackout accompanied by failures of both independent fast acting shutdown systems (SDS-1 and SDS-2), it has been demonstrated that none of the acceptance criteria for design basis accidents as indicated above has been violated.

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