When establishing the basic design concept for a white tank, there are a number of local conditions to be considered:

— height of the reference groundwater level (and/or height of accumulating seepage water)

— height of the minimum groundwater level before starting use

— chemical composition of the groundwater.

If there are any liquid factors to be dealt with from inside, the following must also be established:

— maximum possible height of the liquid level surface

— chemical composition of the liquid

— maximum possible temperature of the liquid

— duration of the liquid load.

Particular attention must be paid to limiting any water or other liquids escaping in the event of an incident.

Establishing categories of use under the WU guidelines cannot be applied directly to nuclear power plants, particularly because of what is required in the event of an incident. Instead, unique findings must be made for each individual structure, broken down by structural components, such as floor slab, walls and so on, if possible.

In terms of groundwater loads from outside, we need to define to what extent limited local access of groundwater can be accepted:

— in the phase of structural works, shell and core

— before commissioning

— in use

— during and after incidents.

Requirements for liquid stresses from inside must be defined analogously.

Except in the event of an incident, external structures should be designed and dimensioned in accordance with the DAfStb guidelines on concrete structures when dealing with water pollutants [102].

Design principles

If separating cracks arise in WU structures, these can admit large quantities of water [103]. Even fine cracks usually admit more water than can be displaced by air from the inside. How much water gets in depends mainly on how wide a crack is, how thick a structure is and how high the water level is.

When dealing with separating cracks, the design principles which can be used for nuclear power plant structures exposed to standing groundwater are:

— avoiding separating cracks

— designing to waterproof cracks on schedule prior to commissioning

— cracks waterproofing through self-healing

— designing to run off penetrating water.

Whether individual design principles can be implemented must be considered in the light of the construction timetable.

The design principles selected must be justified and recorded, and the findings made must be included in contracts between the parties involved.