4.187. Penetrations through the containment for electrical power cables and instrument cables should be leaktight. Means for ensuring the leaktightness of these penetrations may be based on the following:

(a) Pressure glass penetrations. The pressure glass design consists of studs embedded in a pressurized disc of glass flanged to the containment. Cables are connected to the studs, which extend on both sides of the glass disc and provide continuity for the electric power. The glass ensures electrical isolation between the studs and acts as a sealant. The design should include double seals on the flange to ensure the leaktightness of the assembly. These penetrations should be removable and individually testable for leaktightness at the design pressure.

(b) Pressurized and continuously pressure monitored penetrations. For pressurized penetrations, the pressurization should normally be higher than the internal pressure in the containment for design basis accidents, so that leaktightness can be tested continuously. In any case, the pressure should not be lower than the pressure used in the containment leak rate test. The effects of increase in temperature on the design pressure of the fluid inside the penetrations should be assessed and taken into account in the design of the penetrations.

(c) Injected sealant penetrations. Penetrations of this type should be leak testable in integrated leak tests.

4.188. Preference should be given to designs of electrical penetrations that allow each penetration to be tested individually.

4.189. Heat produced by the electrical cables should be taken into account in selecting the materials for electrical penetrations. The materials used should be heat resistant and non-flammable. Penetrations using sealant injection should be at least flame retardant.