Safety reactivity control

Ring expansion (6-7 membered ring) M-tert-Butoxycarbonyl-5-ethoxycarbonyl-4- perhydroazepinone 89% Safety and control of reactive ethyl diazoacetate reagent 2004/[54]... 

The 4S FR concept was proposed and developed by CRIEPI — Toshiba (Japan). Tlie main features of reactor design are a tall thin reactor core (an equivalent diameter 90 cm, length 4 m) and axially moveable radial reflector for compensation of bumup reactivity. Its reference design of 50 MW(e) was for 10 years of electric power output without refuelling and without the use of the safety rod for bum up reactivity control. Now, the CRIEPI — Toshiba team has proposed a new design variant for 24 years of full power operation without refuelling. It uses part of the reactivity worth of the safety-rod in addition to the radial reflector segments for bumup reactivity control. 

The core has heterogeneous arrangement and uses dispersion-type nuclear fuel. Core consists of a set of FA and sets of reactivity control and safety rods. FAs incorporate burnable poison (gadolinium) rods to compensate the core excessive reactivity. The core uses smooth-pin type fuel element with a clad ng made of zirconium alloy. 

Thus, the inherent core safety against partial movement of the reactivity control system is assured for the 4S core. 

IXX Safety Circuit aoraae the vertical safety rods (VSRU) and the horizontal control rods (HCR s)j however only the negative reactivity of the VSR s la counted for reactivity control for this safety system In most Instances (exceptions are noted In subsequent paragraphs )> relays are used In parallel vlth contacts connected In series to provide high reliability to trip on demand ... 

Criterion 20 - Protection system functions. The protection system shall be designed (1) to initiate automatically the operation of appropriate systems including the reactivity control systems, to assure that specified acceptable fuel design limits are not exceeded as a result of anticipated operational occurrences and (2) to sense accident conditions and to initiate the operation of systems and components important to safety. 

Criterion 29 - Protection against anticipated operational occurrences. The protection and reactivity control systems shall be designed to assure an extremely high probability of accomplishing their safety functions in the event of anticipated operational occurrences. 

On the upper unit of V-392 reactor 121 nozzles are provided for the members of reactivity control system and reactor emergency protection (CPS) in comparison with 61 nozzles in V-320 reactor. This gives a possibility to vary the number and arrangement of CPS members and to optimise each fuel cycle for reaching the best characteristics of the core safety and efficiency. 

The safety analysis should establish the design capabilities and protection system set points to ensure that the fundamental safety functions are always maintained. The design basis events are the basis for the design of the reactivity control systems, the reactor coolant system, the engineered safety features (for example, the emergency core cooling system, the containment system and containment protection... 

Reactivity control system X Reactor scram function RPS, scram valves, hydraulic insertion of control rods (non-safety scram backup via el mech drives), boron mjection system... 

Reactivity control Insertion of control rods, and RCP runback, + injection of boron active active Backup, ever-present, boron mjection is automated, safety-grade backup... 

Residual Heat Removal (RHR) and safety injection systems entirely within the containment building - are all inherent safety characteristics with respect to reactivity control, LOCA, and offsite releases respectively. 

Diverse Reactivity Control System X boron injection, via passive safety injection system... 

The calandria is penetrated vertically and horizontally by flux measurement and reactivity control devices, and by the in-core components of two safety shutdown systems. All reactivity control devices function in the low-pressure moderator. No reactivity control devices penetrate... 

On-power refuelling provides the principal means for controlling reactivity in the CANDU 6. Additional reactivity control, independent of the safety shutdown systems, is achieved through use of reactivity control mechanisms. These include light-water zone compartments, absorber rods, and adjuster rods all are located between fiiel channels within the low pressure heavy water moderator and do not penetrate the heat transport system pressure boundary. The reactor is controlled by the dual redundant computer control system. The overall station control system is described in Section 5.7.2.3. 

Reactivity control 1 Reactor regulating system 2 Shutdown system 1, shut-off rods 3 Shutdown system 2, Gd poison mjection 4 Loss or dilution of DjO moderator 1 A 2 P 3 P 4 P Power manoeuvres mclude ramp setback, stepback and tnp 2 and 3 are engmeered safety systems for tnp 1 can serve m an assisbng role to shutdown sy stems No 1 and 2 In 4 HjO from ECC or leakage or boilmg down of moderator leads to subcnticality... 

Reliable reactivity control and shutdown system Large safety margin. 

To obtain adequate reactivity control of the reactor for the seous UF experiment, these rotary control elements were replaced by linear boron vanes running vertically, which could be inserted into the beryllium reflector from the top and acted as a reactivity poison on insertion. Eight such vanes were provided four could be individually controlled for reactivity measurements and four ganged together and were controllied by ah air-driven solenoid to act as safeties in case of a scram shutdown. Each of these vanes was worth about 2S, so the total shutdown from the four safeties alone was nearly. 8. Since our operating plan demands two independent safety, scram mechanisms, the ram drop was also used as an additional scram independent of flie boron safety vanes. 

An active, fast and reliable reactivity control system is very essential for the safety of a nuclear reactor even though the reactor would have inherent safety characteristics. Nevertheless, sudden reactivity excursions carmot be totally excluded. Essential reactivity changes would not happen in a nuclear waste repository. The waste matrix is deeply subcritical by inherent properties of waste materials. No active reactivity control system is needed in nuclear waste repositories. 

Instrumentation For Reactivity Control 5.4.1 Rod Operating and Safety Circuits... 

The safety functions of a MSR are essentially the same as those for LWRs they include reactivity control, heat removal from the core, and radioactivity confinement. 

The minimum negative reactivity in the reactivity control devices available for insertion should be such that the degree of subcriticality assumed in the safety analysis report can be reached immediately after shutdown from any operational state and in any relevant accident conditions. 

Operability requirements for reactivity control devices, including requirements for redundancy or diversity as stated in the safety analysis report, and their position indicators should be stated for the various modes of normal operation. These operability requirements should specifically define the proper sequence and the actuation and insertion times for reactivity control devices. Operating times for reactivity control devices should be consistent with, or more conservative than, the design assumptions. 

The Class 1 electrical equipment, identified in Table 2.5.2-1 of Reference 4.4, has electrical surge withstand capability and can withstand electromagnetic interference, radio frequency interference and electrostatic discharge conditions that would exist before, during and after a Design Basis accident without loss of safety function for the time required to perform the safety function. SSCs required to perform the plant safety functions (reactivity control, core heat removal control, exposure to radioactive material, release of radioactive material) that could be vulnerable to these effects are classified as Class 1. 

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