To fulfil Argentina’s regulations, a set of accidental sequences associated with potential exposure of the personnel and population has been identified. The annual probability of occurrence of each identified sequence is calculated using event trees and fault trees. Failure analysis systematically covers all failures and accidental sequences that can be foreseen, including combinations of failures. In these analyses, an assumption is being made that safety functions are not operable.

The dose to the critical group that would result from the release and dispersion of radioactive nuclides is calculated using accepted methods. Meteorological conditions and their probabilities are being considered. No credit is taken for any countermeasure, such as evacuation.

According to Argentina’s regulations, no accidental sequence with radiological consequences for the public shall have an annual probability of occurrence that, when plotted against the calculated effective dose, results in a point located in the unacceptable region shown in Fig. III-4 [III-7].

If the number N of accidental sequences is greater than 10, the allowed annual probability shall be divided by N/10, in order to keep the overall risk below 10-6 per reactor per year.

III-5. PROVISIONS FOR SAFETY UNDER EXTERNAL EVENTS

The safety design features of CAREM intended to cope with external events and external/internal event combinations are described in detail in [III-8].

Seismic considerations for the CAREM have been developed at the basic engineering level, with the objective of achieving an enveloping design that could qualify for a variety of possible siting conditions.

The philosophy and terminology of the Argentine regulations have been adopted for seismic design. The applicable regulation is AR 3.10.1 “Protection contra terremotos en reactores nucleares de potencia” [III-9]. This norm defines two seismic levels for design purposes:

(1) ‘Severe earthquake’, similar to the safe shutdown earthquake defined by the US NRC and to the L-S2 earthquake level of the IAEA guides [III-10];

(2) ‘Probable earthquake’, similar to the operating basis earthquake defined by the US NRC and to the L-S1 earthquake level of the IAEA guides.

As the targeted sites are located in a moderate seismic zone, the effective peak ground acceleration (PGA) of a severe earthquake was defined as 0.4g.

The IAEA Safety Standards and Guides regarding seismic design have been adopted [III-10]. Combinations with internal events are also considered. For example, a combination of DBA (LOCA with the break of a primary pipe of maximum diameter) with NPP blackout and probable earthquake is considered in the CAREM design.