**3. Tasks for seismic re-evaluation and upgrading of operating NPPs**

Major tasks of the seismic re-evaluation and upgrading projects are


82 Nuclear Power – Practical Aspects

3. Adequate design;

7. Evaluation of safety; 8. Seismic housekeeping;

4. Use of qualified components;

beyond design basis earthquakes.

place for the case of earthquakes

a. for leading the plant to a safe shutdown state, i.e.

consequences would be below the required limits.

The seismic safety is ensured by the following complex activities:

2. Definition of the characteristics of the design basis earthquake;

9. Periodic safety assessment and subsequent upgrading if needed.

using a moderate level of seismic excitation for operational limit.

function have to sustain the earthquake loads without loss of function.

by the earthquake, like soil liquefaction;

5. Installation of seismic instrumentation;

1. Inherent and/or engineered safety features, safety systems and procedures have to be in


features and accident management measures in case of severe earthquakes.

6. Development of accident-prevention and accident-management procedures;


b. for maintaining at least one protection barrier to ensure that the radiological

2. Means, plans and procedures have to be in place for on-site and off-site emergency response to mitigate the consequences of accidents that result from failure of safety

1. Site investigations and evaluation of the site seismic hazard, including hazards caused

The basic safety functions, i.e. shut down, cooling and containment, have to be maintained for the earthquakes within the design basis envelope and with some extent for the severe

Traditionally the design of the nuclear facilities adapted the two-level concept: design for safety, using a high-level seismic excitation for design basis and design for production,

The design base earthquake has to be defined with quite low probability of exceedance during operating time. This earthquake is the Safe Shutdown Earthquake (SSE) as per U.S. terminology; see U.S. NRC 10CFR Part 50, Domestic Licensing of Production and Utilization Facilities (NRC, 1956). It is called *Sicherheitserdbeben*, i.e. safety earthquake in German Nuclear Safety Standards 2101 (Kerntechnische Ausschuss [KTA], 1990), it is the maximum design earthquake (MRZ) according to the Russian-Soviet terminology and it is called SL-2 earthquake level by the IAEA guideline NS-G-1.6 (IAEA, 2003b) [4]. Here the term of Design Base Earthquake (DBE) will be used. According to the international practice the annual probability of exceedance of the DBE is usually 10-4/year in case of nuclear power plants. The lower limit of the peak ground acceleration (PGA) of the DBE is set for 0.1g regardless of the site (article 2.7 of NS-G-1.6). The shutdown and cool-down of the reactor, the continuous heat removal from the irradiated fuel (in the reactor core and spent fuel pool), and the limitation of releases have to be ensured in this limit state. SSCs required for basic safety


The tasks are determined by the objective of the project as it has been shown above, i.e. resolution of qualification issues, ensuring the design basis compliance, etc.
