Fast shutdown

Thermal loads upon the process heat exchanger do not allow rapid temperature change rates. Therefore in case of the demand for a decay heat removal system after a fast shutdown of the reactor, an auxiliary cooling system should be used rather than the main cooling system. In addition, much of the decay heat would be removed via the core surfaces to the liner cooling system [10]. 

After reactor fast shutdown, it was maintained isothermal at a temperature of 250 °C, i e at least 40 C above the oxygen saturation temperature in the pnmary sodium when the rate of impurities was maximum (15 ppm... 

On start-up in 1994, following the long BCS shutdown, a significant increase in the frequency of bell re-inflation on IHX-RCPE 02 EX was observed (up to around one re-inflation per day) As a result of the fast shutdown of 17/12/94, the leak rate from the bell increased significantly to reach a value close to the threshold set by the operator (160 mbar/day) This justified shutdown of the reactor... 

Figure 1-1. Drawing of the CPI pile. Scram - this term means fast shutdown of a reactoK various explanations have been proposed for its origin. The most credited one assumes that it derives from the abbreviated name of the CPI safety rod which could be actuated by an axe. In the original design sketches of the pile, the position of the operator of the axe was indicated by SCRAM, the abbreviation of Safety Control Rod Ax Man. The designated operator was the physicist Norman Hilberry, subsequently Director of the Argonne Laboratory. His colleagues used the name Mister Scram. The drawing is courtesy of Prof. Raymond Murray.

In core 3.5 X 10 fast shutdown Prevent releases from the fuel... 

The fast shutdown trigger levels and the corresponding time delays considered in the analyses (including errors) are of the order of magnitude indicated in Table 4-1 and Figure 4-1. 

Table 4-1. Fast shutdown signals and corresponding delays (core safety limits, p = 5.51 MPa (2250 psig)...

Origin of fast shutdown Trigger level in the analyses Time delay (s)... 

Overall, the reactivity available for a fast shutdown t q)ically ranges between 6 per cent (under hot conditions and zero power conditions) and 9 per cent (at full power). 

The reactivity of the complex of control rods is typically of the order of 10 per cent. The reactivity available for fast shutdown, however, depends on the position of the rods (e.g. rods are usually inserted under zero power and hot circuit conditions, but less often inserted under full power conditions), on the axial shape of the neutron flux and on the core burn-up. Moreover, in order to evaluate the reactivity available for a fast shutdown, the assumption is usually made that the most reactive rod stays stuck in its position (generally it is considered completely extracted). 

The fast shutdown is quick (< 2 s) actuated by the slowing down of the primary recirculation. The actuation signals vary according to design preference and they may comprise loss of pump speed, inadequacy of their electric power supply (voltage and frequency) and reduction of recirculation flow rate. 

As far as ATWS accidents are concerned, usually a duplicated and diversified fast shutdown system is required, see US Code of Federal Regulations (2006) and the EUR criteria (see the pertinent Appendix). 

The presence of a signiflcant neutron flux together with a fast shutdown actuation signal (Anticipated Transient Without Scram (ATWS) case, that is a transient with the failure of the scram to operate). 

The fast shutdown of the TMI-2 reactor, in the conditions described, occurs in the following way. The increase of primary water temperature causes the expansion of the water itself which can expand in the pressurizer, which, as it has been said, is connected to the primary circuit by a pipe and is only partially filled with water the other part of it is full of steam, as in a pressure cooker (see Figure A17-2). 

Fast shutdown Fast insertion in the nuclear reactor core of negative reactivity, thus causing the immediate stop of the fission chain reaction. 

Interrupted on April 23 for a few days by a fast shutdown that occurred as a result of faulty water flow control following the activation of a turbine-driven feedwater pump, this period of steady state operation ended, running solely on the B train turbo-generator. The A train transformer was shut down as the analysis made periodically of the cooling oil of the transformer had revealed that a preventive internal inspection was required. 

Operating procedures rather than autonatio Interlocks will be relied upon to preclude unsafe or faulty operation in the following Instances a. To ensure adequate fast shutdown at all times up to 20 rods must remain fully withdrawn and In the safety assignment. Preselection of these rods shall be made with lockable switches. 

The fast shutdown functions were not impeded to any measurable extent. This was proved by comparative measurements taken in April 1986 and February 1987. A basic inspection and functional testing programme for the shutdown systems and other internals was carried out in the framework of other functional tests on the reactor in order to corroborate the recent findings. 

Each absorbing element (AE) consists of a cluster of rods linked by a structural element (namely, spider ), so the cluster moves as a single unit. Absorber rods fit into the guide tubes. The absorber material is the commonly used Ag-In-Cd alloy. Absorbing elements (AE) are used for reactivity control during normal operation (adjust and control system) and to produce a sudden interruption of the nuclear chain reaction when required (fast shutdown system). 

Many of the elements are for the fast shutdown system during normal operation they are kept in the upper position. They are designed to obtain a minimal dropping time, so that it takes only a few seconds to completely insert absorbing rods inside the core. In CAREM-25, this system has a minimum worth of 3500 pcm, with one rod unavailable. 

The fast shutdown of the reactor is achieved with a similar system to Winfrlth (ref. 6). Development has revealed that, for the valve size chosen, a capacity several times that required for a single rod Is possible. The larger designs of reactor generally use like... 

Most of research reactors use gravity to insert the control elements when fast shutdown is required. The electromagnetic clutch is supplied with electric current by the magnet power supply, which also acts as a fast cut-off device when a scram is initiated by the protection system. 

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