**3.2. Methodologies for re-evaluation of seismic safety**

The methodologies for the seismic re-evaluation and re-qualification are as follows:


86 Nuclear Power – Practical Aspects


earthquake hit the plant,

due to seismic interactions (falling down, flooding, fire).

The quantification of the margins has three aspects:

*3.1.4. Recent beyond design base studies* 

analysis can also be effective in this case.

bringing the reactor into stable (hot or cold) shutdown condition. Those non-safety classified SSCs have to be also considered damage/failure of which can disable certain safety functions


According to the IAEA design requirements NS-R-1 (IAEA, 2000), *the seismic design of the plant shall provide for a sufficient safety margin to protect against seismic events.* This means that the abrupt lost of function has to be excluded by the design even if the earthquake demand exceed the design base one (see also NS-R-1.6 paragraph 2.39 regarding 'cliff-edge' effect).

According to the novel requirements, the capability of the new plants to withstand the loads and conditions of the design basis extension has to be ensured by the design provisions. In case of new plants, a minimum configuration of SSCs for ensuring the shutdown and subcriticality of the reactor, heat removal to the ultimate heat sink and the containment have to remain functional for the accident management purposes. A margin type evaluation has to be performed for demonstration the beyond design base capabilities of the new plants (1.4 times the SSE loads as per EUR requirements and 1.67 times of the SSE loads in the U.S. practice). Best

The plant safety re-assessment after a strong earthquake requires an overall checking the post-event condition of all SSCs, even those non-safety classified SSCs, since both the safety and operability have to be demonstrated. The possible analysis and testing/inspection methods should be selected and applied in accordance with safety relevance and impact on the operation (Nomoto, 2000). According to (Kassawara, 2008), the probabilistic margin

Recently, the availability of severe accident management provisions become of great importance. The scope of stress tests covers review of compliance with design base requirements, demonstration of beyond design base capacity (avoidance of the cliff-edge effect) and identification of plant vulnerability/damage state and development of severe accident management measures and guidelines. Generally, some margin type analyses have been performed in the participating countries for the possible minimum configurations needed for shutdown and heat removal of the reactor and spent fuel and protection of the containment. Identification of seismic interactions (fires, flooding, logistical obstacles) became important since these can affect the function of the SSCs within the minimum configuration, inhibit the connections of provisory power and cooling lines, impeding the implementation of Severe Accident Management/mitigation measures as it is to see in the country reports at the European Nuclear Safety Regulators Group site (ENSREG, 2012).


estimate methods can be used for the justification beyond design base capabilities.

