Coolant density

Preexponential factor k0 Activation energy E Process molecular weight Process densities p0 and p Coolant density p/... 

The NucMA code developed in the RSC Kurchatov Institute, is meant to calculate SNF residual energy release both for separate SFA s and for the whole inventory of accumulated SFA s or its any sampling. The code can be used to calculate SRP s bumup, radionuclide composition and residual energy release. Radionuclide composition is determined as a function of bumup (or power generation) at the averaged reactor parameters, i.e. power, coolant density and temperatme. Besides, the code uses... 

A], A2 eigenvalues defined in equation (6-37) p, Pc density, mols/volume coolant density... 

In this case, cold (about 40°C) water enters the coolant circuit. Owing to this event, water subcooling at the fuel channel inlets will become larger, leading to an increase in the coolant density resulting from both a lower water temperature and a smaller void fraction in the fuel channels. 

Depending on the core conditions (power level), the reactivity feedback coefficient due to the coolant density may either be negative or slightly positive. Ingress of gas into the core is likely during injection by the hydroaccumulators. This also adds to the coolant density variations, which are bound to affect the reactivity. 

From a very fundamental point of view, a coolant must be capable of removing the heat from a reactor with a reasonable expenditure of pumping power. The heat removal rate per unit frontal area of coolant is simply the product of the coolant density, velocity, specific heat, and the temperature rise across the core, i.e., pvCp AT. Typical values of these parameters for water, helium, and sodium coolants are illustrated in Table 11. The coolant-gas velocities are generally consistent with a pumping power of 5 to 10% of the electrical output of the nuclear plant. 

The negative reactivity effects of coolant density and fuel temperature attenuate the power transient following control system faults. 

However, power reactors require significant amounts of reactivity (i.e., well above the amount needed to go prompt critical if added suddenly) that must be provided by movable control absorber devices (or removable poison dissolved in the piimaiy coolant) under the direction of a licensed operator and following jq>proved procedures during reactor start-up and the transition to equilibrium full-power operation. This positive reactivity is needed to compensate for losses associated widi increased core temperature, reduced coolant density including bubble void formation, and equilibrium fission product poison loads, especially Xe. Consequently, it is only possible to limit the amount of reactivity that could theoretically be inserted to small, intrinsically safe values when the reactor is already in the normal full-power operating mode with all movable control devices very near their maximum withdrawal positions (and when the dissolved poison concentration is close to zero). 

Many IPWR designs are neither pure PWRs or pure BWRs, but combine features of both systems as discussed in reference 8 for the specific case of the KWU-NHR 200-MW, district heating reactor. However, BWR-based designs that use bulk boiling are sensitive to coolant density fluctuations and are generally considered unsuitable for mobile applications, such as... 

Neutron-physical characteristics (temperature and coolant density reactivity effects, void reactivity effect and bum-up reactivity swing,), power flattening (peaking factors, approaches to reduce them)... 

The inherent safety features of the ELENA-NTEP are a negative temperature reactivity coefficient, a large secondary water inventory (68 m ), a near-zero bum-up reactivity swing, a very small (near iPeir) operating reactivity margin in the core, and negative coolant density and void reactivity effects. 

Reactivity coefficient on coolant temperature (taking into account coolant density changes), 1/C -47 X lO ... 

Reactivity coefficient on coolant density (without taking into account coolant temperature), l/(g/cm ) 0.21... 

Figure XV-9 shows the averaged axial power profiles at several moments during the core lifetime. At the beginning of core life (BOC), a bare sub-critical core becomes critical by inserting reflectors to reduce the neutron leakage. The peak power is at a lower part of the core. As the core bums, the reflector is gradually lifted up to cover fresher fuel parts at the middle of core life (MOC). At the end of core life (EOC), the reflector is almost at the top of the core. Otherwise negative, the coolant density reactivity coefficient and the coolant void reactivity effect are approaching zero at the EOC.

Different variants of the core load differ in temperature and coolant density reactivity coefficients, but their sign and the void reactivity effect are always negative. The bum-up reactivity swing for the fuel lifetime varies from -7.0 Pefifto 0 (for UN fuel). 

Reactivity control mechanism - Shutdown rod for reactor start-up and shutdown. - During operation, reactor power autonomously load follows by means of inherent physical processes without the need for any motion of control rods or any operator actions. - System temperatures change corresponding to reactivity feedbacks from fuel Doppler, fuel and cladding axial expansion, core radial expansion, and coolant density effects. - Control rods for possible line reactivity compensation during cycle. - Control rods also provide for diverse and independent shutdown. ... 

The high heavy liquid metal coolant density (Apb= 10400 Kg/m ) limits void growth and downward penetration following postulated heat exchanger (HX) tube rupture such that void is not transported to the core but instead rises benignly to the lead free surface through a deliberate escape channel between the HXs and the vessel wall and... 

System temperatures change corresponding to reactivity feedbacks from fuel Doppler, fuel and cladding axial expansion, core radial expansion, and coolant density effects. 

The performance of the SPINNOR reactors under ULOF is shown in Fig. XXVI-3 to XXVI-6. Figure XXVI-3 indicates that following the loss of pumping power in the primary system, the flow rates in primary system and at the primary side of the steam generator (SG) decrease and progress toward the level of natural circulation. It causes the increase of temperatures as shown in Fig. 4, and results in the negative feedbacks including, in the order of importance, coolant density decrease, fuel axial expansion, Doppler effect, and core radial expansion, as shown in Fig. XXVI-5. These feedbacks assure the decrease of reactor power to match the new coolant flow rate, as shown in Fig. XXVI-6. 

Reactivity coefficients - Fuel temperature - Coolant temperature - Coolant density -2x10 A(l/k)/k -2.2x10 A(l/k)/k -6xlO- A(l/k)/(g/cm )... 

The coolant coefficient is given in Equation 6.2.5 Hlhe term involving C is related to the coolant density variation. The terms involving. f. L. p and T are related to both the coolant density and temperature variations. 

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