Safety case core components

The cask provides the shielding, inert environment, confinement, component grappling, andl.4-kW(t) cooling capability required to handle sodium-wetted, irradiated core components. Its inside diameter isabout 8 in. The dolly provides traverse drive, cask elevation, and seismic-restraint functions. The control system provides the control consoles, motor control equipment, and all interconnecting cables. Control of the transfer cask is semiautomatic that is, key operations are automatically performed after the operator initiates a command. Interlocks are incorporated to meet safety requirements. Status lights indicate the exact machine conditions during all operations and manual overrides permit the operator to complete key operations in case of a control system failure. 

The core components of a typical Level 5/6 (see Fig. 8.1) safety case are ... 

In normal conditions of operation, therefore, a nuclear power reactor system can respond to the requirements of the electrical power grid system, and the rate at which power can be increased will be dictated by the mechanical limits of the components, rather than by the reactor physics of the core. However, all reactors have systems by which shutdown rods can be—and in many cases are— automatically forced into the core to avoid circumstances that could endanger the plant ( Scram —said to have been formed from the term Safety Control Rod Axe Man at the first man-made reactor, Stagg Field, Chicago). 

Examinations that necessitate the disassembly of components (such as the disassembly of pumps or valves to volumetricaUy examine large bolting, or the removal of fuel or of core support structures in reactor vessels in order to examine welds or nozzle radius sections) may be deferred until the end of each inspection interval except in cases where, on the basis of results of examinations conducted on analogous components, an earlier inspection is necessary. This should in no way diminish the requirements on the frequency of examinations formulated in the relevant design codes (for example, those of the American Society of Mechanical Engineers or the German Nuclear Safety Standards Commission). 

The reactor cooling system is composed of the MCS, ACS and VCS as schematically shown in Fig. 1. The MCS is operated in normal operation condition to remove heat from the core and send it into the environment. The ACS and VCS have incorporated safety features. The ACS is initiated to operate in case of a reactor scram. Besides one out of two components of VCS has sufficient capacity to remove residual heat, the ACS is provided to cool down the core and core support structure. A helically coiled intermediate heat exchanger (IHX) whose heat-resistant material is Hastelloy-XR developed by the JAERI has been installed in S tember 1994. Nuclear heat application tests using the HTTR, are planned to be carried out, and accordingly a heat utilizaticxi system will be connected to the IHX. The fuel fabricaticm started in June 1995 and will complete in 1997. 

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