Criteria for evaluation of effectiveness of nuclear-reactor safety barriers

Abstract

According to general safety regulations OPB-88 [1], the system of barriers to the entry of ionizing radiation and radioactive materials into the environment includes the fuel matrix and fuel-element jacket, the boundary of the core-coolant loop, and hermetic protection of the containment systems. The conditions on the number of quality of the barriers are established in the design documentation for the reactor installation and depend on a number of factors: the reactor type and power, fuel type, specific thermal load, operating conditions, etc. It is obvious that the ensuring of acceptable radiation parameters at an acceptable distance from the reactor (for example, at the boundary of the protection zone) under conditions of normal operation and in emergencies is an attainable goal. The importance and, accordingly, the required effectiveness of safety barriers can be evaluated by examining in accordance with IAEA data [2] the development of an accident as a realization of the possible transitions from normal operation to a severe emergency with subsequent breaching (failure) of the safety barriers. Let u(j, k) be the normalized measure of the loss of integrity of the j-th safety barrier in an initial event k: u(], k) = 0 when the barrier is in a state of integrity and u(j, k) = 1 with total failure of the safety barrier. Then, ifp(k) is the probability of an initial event k, the effective measure of the loss of integrity of a safety barrier (its transmittance) can be estimated as