Cold Water Reactivity Effect

Zero Power (Cold graphite hot uranium and water) -3 1  

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As a converse of the above, the addition of an excessive volume of relatively cold water to a low reactivity quicklime can result in drowning of the lime. Under such conditions, the surface of the quicklime particles hydrate, but the particles do not disintegrate effectively and relatively little primary nucleation occurs. Indeed, some of the quicklime may fail to slake fully, resulting in unsoundness and grit. 

Girardot and Holloway (1985) have investigated the effect of cold-water immersion on analgesic responsiveness to morphine in mature rats of different ages. This study indicates that chronic stress affects the reactivity to morphine in young mature rats but not in old rats. 

Criterion 28 - Reactivity limits. The reactivity control systems shall be designed with appropriate limits on the potential amount and rate of reactivity increase to assure that the effects of postulated reactivity accidents can neither (1) result in damage to the reactor coolant pressure boundary greater than limited local 5uelding nor (2) sufficiently disturb the core, its support structures or other reactor pressure vessel internals to impair significantly the capability to cool the core. These postulated reactivity accidents shall include consideration of rod ejection (imless prevented by positive means), rod dropout, steam line rupture, changes in reactor coolant temperatme and pressure, and cold water addition. 

During reactor operation, normally all five beat exchangers will be In use and the reactor will never be operated with fewer than four In use. If one assumes operation with four cells, the reactivity effects of suddenly cutting in" the fifth cell can be calculated. Actually, this will not be attempted during reactor operation and the probability of It occurring accidentally without a reactor scram Is vanishingly small. However, even If the cold water in the "down" cell were to be suddenly Injected... 

Such a failure would result in a rapid depressurization of the system. Any lowering of water density within the process tubes will result in a reactivity loss. Thus. the immediate effect would be a reduction in reactivity. The later addition of cold water to the lattice will result in a reactivity Increase from 3.1 to 3 6 per cent k depending on reactor conditions. In all cases I the incremental control held in safety rods and the ball 3X system are sufficient to control the excess reactivity. See Table. ... 

Related to the fail-safeness of the lattice on coolant loss is the converse effect of increasing the amount of water in the reactor. Either a cold water Insertion at reactor equilibrium level (whldh would Increase the coolant density and hence the amount of water in the process tubes) or flooding of the graphite structure can add reactivity. 

The calculation results are shown in Fig. 6.36. The power decreases to the decay heat level due to the reactivity feedback and reactor scram. Reverse flow occurs in the water rod channel because the buoyancy pressure drop dominates the pressure drop balance. Heat conduction to the water rods increases when the coolant temperature in the fuel channel increases. This implies that the water rods serve as a heat sink . As the coolant expands in the water rods due to heat-up, there is an increase in the flow rate downstream from the water rods, including the fuel channel inlet. Consequently, the fuel channel flow rate is maintained even though the coolant supply from the cold-leg has stopped. This is called the water source effect of the water rods. The heat sink and water source effects mitigate heat-up of the fuel rod cladding, and hence enable the AFS to have a realistic delay time. The hottest cladding temperature begins to decrease before the initiation of the AFS. The increase in the hottest cladding temperature is about 250°C while the criterion is 520°C. 

The AFS delay after detecting one of the actuation conditions is taken from that of the turbine driven RCIC system of BWRs. Its influence on the peak temperature for the loss of offsite power event is checked. Due to the water source effect of the water rods, the core coolabihty is not influenced by the AFS delay. On the other hand, the net reactivity tends to increase with the shorter AFS delay because the AFS supplies cold coolant to the core. The peak temperature is higher with the shorter AFS delay. The increase in the cladding temperatiue is about 450°C for a delay time of 15 s and 330°C for 100 s. In spite of the wide variatiOTi of the AFS delay that would cover the actual design point, the degree of the temperature variation is well below that of the safety margin to the criterion. 

This is also shown by the fact that for a single fuel element of the outer core zone submerged in cold water the value k ff = 0.895 has been calculated. On the other hand, for a given number of control rods this means putting a limitation on the reactivity reserve which can be put into the core. Without the use of burnable poisons operation of the core with a reasonable fuel burnup seems impossible because of the reasons described above. In principle, soluble poison could also be used effectively but this is presently not considered for the stuck-rod condition because of the conservative assumption that it could possibly be washed out of the core in case of an accident. Table III shows values of the effective... 

Red phosphorus is a term used to describe a variety of different forms, some of which are crystalline and all of which are more or less red in colour [1,3,40]. They show a range of densities from about 2.0 to 2.4 g/cc, and melting points in the range 585-610°C. The stabilities and reactivities of these red forms lie between those of the white and black forms, although they resemble the latter more closely. The vapour pressure of the red is much less than that of the white (Table 4.4). Samples of red phosphorus usually vaporise at about 450°C under atmospheric pressure. Purification of the red variety can be effected by boiling with distilled water followed by filtering and washing with cold [41]. 

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