WATER LEVEL FLOOD DESIGN

The water level of the core decreases due to outflow of the primary coolant. It, however, remains at about 2m high level over the top of the core when both of the pressure equals. The water level 2m is enough for core flooding completely even if the ship inclines at 30 degrees, which is one of the design conditions mentioned previously. 

Based on the observed water level data at Phu Le station, water level along the Nam Dinh Coast is best fitted modeling by a mixed Gamma and Exponential distributions. In the frequency domain of interest for the design purpose of the sea flood defences (0.1 to 10 ) the tail of exceedance frequency curve is best modeled by exponential distribution ... 

Depending on the site characteristics water ingress can not be excluded a priori even at water levels below the design flood level. 

The second case-study deals with the design of a flood protection dike. The variable of interest is here the maximal water level Zc of the river in a given wection. For the exemplary purposes of this study, we suppose that Zc is related by a simple analytical formula to several input variables ... 

In the formula above, the term in brackets is the water level H, measured in m above the riverbed level. Possible quantities of interest for Zc are extreme quantiles, corresponding to very high probabilities (e.g. 0.99 or 0.999). These values allows to properly design a protection dike to cover flood risk. The case shown hereby is to be interpreted a toy example and the simplified analytical model given by Equation 14 is not representative of the models used by EDF to assess hydrological risk. 

The design basis flood is a series of parameters that maximize the challenge to plant safety as a consequence of a flood the parameters may be associated, for example, with the maximum water level, the maximum dynamic effect on the protection or the maximum rate of increase in water level... 

When sites are located along semi-enclosed bodies of water, such as river estuaries, the reference water level may depend on astronomical tides in combination with the river flow. In regions where extreme floods arise mainly from oceanographic causes, it is necessary only to choose an appropriate value for the river flow (not to be exceeded in tens of years) this should be considered in conjunction with the appropriate combination of probable maximum surge, tsunami, wind wave and tide to derive the design basis flood. In other cases, where the river flood is more important, the solution adopted should be appropriate to the particular case . 

An acceptable value for the limiting annual probability of exceedance should be established for the combinations of extreme events and the relevant reference water levels that are to be taken into account in deriving the coastal design basis flood for a nuclear power plant. Certain combinations of events can be excluded from consideration if ... 

The benefit of a risk-based approach, compared to the other approaches to design or decision making, is that it deals with outcomes. A risk-based approach enables informed choices to be made based on comparison of the expected outcomes and costs of alternative courses of action. This is distinct from, for example, a standards-based approach that focuses on the severity of the load that a particular flood defence is expected to withstand. Using a risk-based approach, risk assessment often involves more complete representation of the flood/erosion system. This more holistic approach will be able to account for (a) complex physical mechanisms, spatial, and temporal variations in natural hazards (e.g., natural variability in wind, wave, rainfall, and water level conditions) (b) descriptions based on sparse/incomplete data and (c) multiple stakeholders with differing, often conflicting, values and objectives. ... 

Ferreira and Soares describe the joint probability distribution function of longterm hydraulic conditions. Especially when the main interest is in the design of flood defence structures, the extreme conditions are important, which implies that the dependence between hydraulic conditions needs to be accounted for. The joint probability analysis of extreme waves and water levels thus is significant in order to estimate more accurately the extreme environmental loading on a coastal structure. Because wind setup (storm surge) and wave conditions depend on the same driving force, a strong dependence between them is observed under extreme conditions. 

If the vessel and its external support structure were designed for water-filled loads, flood the vessel with water before start of hot work to a level just below the work area... 

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