Containment steel shell

From the so called outer annulus (the space outside the containment between the containment steel shell and the reactor building concrete wall) air is sucked into the air ventilation stack. In case of the leakage into the outer annulus the airflow is switched to pass through the filter line with four sequential filters 1 prefiKer, 2 HEPA filter, 3" Kl impregnated active carbon filter, 4" HEPA filter. 

I) Concrete containment 2) Containment steel shell 3) Polar crane 4) Reactor pressure vessel S) Control rod drive mechanism 6) Spent fuel pool 7) Refuelling machine 8) Steam generator 9) Pressurizer 10) Pressurizer relief tank 11) Main coolant pump 12) Main steam line 13) Feedwater line 14) Concrete shield IS) Accumulator 16) Personnel lock 17) Mate rials lock 18) Lifting gantry 19) Fresh fuel assembly storage 20) Borated water storage tank 21) Residual heat cooler 22) Component cooler 23) Safety injection pump (By courtesy of Siemens/KWU)... 

If all the penetrations through the containment steel shell are closed according to design, the containment can be regarded as a closed physical and chemical system the operational leakages of the steel shell (which are very small) can be... 

Penetration through operational leaks in the containment steel shell... 

The piping which penetrates the containment steel shell (e. g. fresh air and exhaust air ducts) is automatically locked in the very early stages of an accident. Despite these measures, in risk studies it has to be assumed that one of these penetrations will fail to be closed, thus permitting the transport of radionuclides out of the containment. The TMI-2 accident demonstrated that such a situation may occur in reality in this event an open connection to the auxiliary building was the main pathway for the escape of fission product radionuclides from the containment to the environment. 

Concerning the transport of fission products out of the containment, the relative locations of the break in the primary system and of the open penetration in the containment steel shell are of great importance. It can always be assumed that these two positions are in different compartments so that the fission products have to travel a certain distance over which deposition may occur moreover, the time required to cover this distance provides an opportunity for chemical reactions to occur, in particular with respect to iodine. This time delay depends highly on the specific accident sequence, in particular on the rate of pressure increase within the containment and, thus, on the steam mass flow from the primary system to the containment. With a high degree of probability it can be assumed that the open penetration can be locked (e. g. by manual action) within a comparatively short time. 

The heat transport from the core melt into the sump water, as well as the production of permanent gases in the core melt - concrete interaction, will result in a pressure increase inside the closed containment. Provided that no measures for controlled depressurization are undertaken (see next section), then, according to the results of thermodynamic calculations, the steam-gas pressure within the containment would reach the postulated failure value of the containment steel shell of about 0.9 MPa after 5 to 10 days, depending on the accident sequence. Such an overpressure failure will not be a catastrophic burst of the shell, but rather the enlargement of the operational leaks to a size permitting the escape of gas and steam at a rate high enough to keep the pressure inside the containment at a... 

The late overpressure failure of the containment steel shell can be prevented by a controlled depressurization, in the course of which the gas-steam mixture escaping from the containment is directed to an additional system in which the radionuclides are retained. The purpose here is to further reduce the possibility of release of radionuclides to the environment as a consequence of a severe reactor accident. Practical application of this idea can be based on various principles an overview of the design of different systems was given by Schlueter and Schmitz (1990). 

The Loviisa NPP, owned and operated by Imatran Voima Oy (IVO), is a unique combination of the nuclear technologies from east and west with the Soviet V -440 reactor and the ice condenser containment (ICC). The Loviisa ICC is a double containment in which the pressure boundary of the containment is the free standing cylindrical pressure vessel with a dome inside the secondary containment. The containment design pressure is 0.17 MPa, and estimated ultimate failure pressure 0.32S MPa. The ice condenser is divided in the Loviisa NPP into two separate sections in contrary to a single ice section in the US and Japanese ice condenser containments. The other significant differences in the Loviisa ICC, compared to the US and Japanese ICC s, are that the total volume of the containment is much bigger, i.e it is of the size of dry containment, there are no air return fans for mixing the atmosphere of the whole containment and the external spray system of the containment steel shell have been installed at Loviisa. 

In Russian WWER-640/V-407 concept [8], at the outer surface of the containment steel shell, rectangular pockets are arranged in rows and columns. The pockets of each column are interconnected by vertical lines. A NC flow of cooling water from an external pool near the roof will be established. Steam is condensed at the cooled parts of the inner surface of the steel shell. The condensate is collected in the sump to allow for post accident recirculation. 

Fig. 2. Downs cell A, the steel shell, contains the fused bath B is the fire-brick lining C, four cylindrical graphite anodes project upward from the base of the cell, each surrounded by D, a diaphragm of iron gau2e, and E, a steel cathode. The four cathode cylinders are joined to form a single unit supported on cathode arms projecting through the cell walls and connected to F, the cathode bus bar. The diaphragms are suspended from G, the collector assembly, which is supported from steel beams spanning the cell top. For descriptions of H—M, see text.

Control of low-pressure injection during an anticipated transient without scram (ATV i Dry well steel shell to prevent melt-through in a Mark 1 containment... 

The two foot diameter spherical steel shell shown in Figure U- is lA inch thick and weighs about 165 pounds. A rectangular tray is used Inside the shield to carry 10 cups of primary explosive material. Each cup contains TO grams of lead azide in a typical application. Total weight of explosive is limited to 700 grams lead azide or equivalent (1, 3. ... 

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