Containment isolation system

USNRC (1985) Reliability analysis of containment isolation systems , NUREG/CR-4220. 

Direct bypass of the containment (for example, due to a steam generator tube rupture or to an interfacing systems LOCA which discharges outside the containment) and failure of the containment isolation system should be addressed in the analysis. This would normally be included in the definition of the PDSs. 

Safety injection system Containment spray system Containment hydrogen recombiner system Containment isolation system Auxiliary feedwater system... 

The containment system includes the reactor building, which encloses the reactor and other nuclear steam supply system components, and the containment isolation system. 

Flatness Control 1 Containment isolation system 2 Containment hner P The isolation system automatically butUms up the containment ventilation system, wall penetrations of process pipmg and airlocks and hatches... 

The remaining safety-grade functions are performed by the reactor protection system (it initiates opening of the scram valves to achieve a reactor scram), the containment isolation system (it initiates isolation of the containment by closing isolation valves), the reactor vessel safety valves (based on pressure-activated components), and the passive reactor pool cooling function. These functions are not needed for the protection of the core, however. 

In summary, the containment isolation system is designed to conform to the requirements of NUREG-0737 and meet the overall guidance identified in SRP 6.2.4, Rev. 2. These documents... 

The containment isolation system (CIS) provides the means of isolating the various fluid systems passing through the containment walls as required to prevent the release of radioactivity to the outside environment. Design bases of the CIS consider several factors. Subsequent to an accident which may release radionuclides within the containment, there must be a barrier in all pipes or ducts that penetrate the containment. Leakage from the containment through these pipes or ducts which penetrate the containment is minimized by a double barrier. This double barrier ensures that failure of a single active... 

On a rise in pressure or a release of radioactivity to the containment, the containment isolation system would dose all penetrations open to the outside atmosphere, mainly the containment ventilation system. This is a subsystem of the containment safety system. 

The maj or function of the containment isolation system of the AP1000 is to preserve the integrity of the contaimnent boundary and prevent the release of radioactivity to the environment, when required, but at all other times to allow the passage of fluids through the containment boundary. To achieve this, fluid lines penetrating the primary containment boundary are isolated in the event of an accident. When isolated, this prevents or limits the release of radioactivity to the environment. 

The containment isolation system consists of the piping, valves, and actuators that isolate die containment. 

The chemical and volume control system valves are stainless steel for compatibility with the borated reactor coolant. All the isolation valves are actuated by the containment isolation system in addition, they can all be actuated manually from the main control room. The containment isolation valves are described in Section 9.3.6.3.7 of Reference 6.1 a summary description is provided below. 

Containment isolation valves are provided on either side of containment penetrations. The normal residual heat removal system has two containment penetrations the normal residual heat removal system suction line penetration, and the normal residual heat removal system discharge line penetration. Both penetrations are provided with contaimnent valves inside and outside containment, which are actuated by the containment isolation system. 

The liquid radioactive waste system must be capable of being isolated by the containment isolation system. 

The VFS containment penetrations include containment isolation valves on both side of containment. These containment isolation valves have air operators. The valves are designed to fail closed in the event of loss of electrical power or air pressure. The valves are actuated by the containment isolation system. 

Towards this objective, a theoretical model has been developed and based on this model, the response of the system has been estimated using the indigenously developed computer code CAPCIS (Code for Analysis of Passive Containment Isolation System). The numerical analysis performed takes into account the pressure transient because of the postulated initiating event (PIE) and the solution includes determination of levels in the two compartments of the isolation tank and the cumulative volumetric spill into the ventilation duct at any point of time during the transient. A case of a 200% break in inlet header is considered for the analysis and the pressure transient for the considered PIE is numerically simulated as shown in Fig. 10. Figure 11 shows the volumetric spillover during the entire transient. 

This subsection should present relevant information on the containment (or confinement) systems incorporated to localize the effects of accidents, and should include, among other things the heat removal systems of the containment, the functional design of the secondary containment, the containment isolation system, the protection of the containment against overpressure and underpressure, where provided, the control of combustible gas in the containment, the containment spray system and the containment leakage testing system. Further discussion on matters to be covered in this subsection of the SAR is provided in Ref. [28]. 

Radionuclide management features work in concert with energy management features and the containment isolation system to limit the radiological consequences of accidental conditions. Examples of radionuclide management features include double-containment systems which trap any radioactive leakage between the two envelopes, containment structures upon which radionuclides plate out are deposited), suppression pools that dissolve or entrain airborne molecular or particulate radioactive materials as the atmosphere is forced through the pool, spray systems, and particulate filter systems. 

The I C safety systems include those systems that provide the protection functions. These functions are typically provided by a system known as the reactor protection system, or by the I C subsystems of special safety systems, such as reactor shutdown systems, the emergency core cooling system and containment isolation systems. I C safety systems may also fulfil post-accident monitoring functions and support functions (for example, essential data communication systems for the protection systems or the special safety systems). 

---