Effective fuel temperature of wwer-1000

. The main temperature characteristics of a pressurized water reactor are distinguished, supporting its safety and reliable operation. The special role of the uranium fuel effective temperature is emphasized and the accuracy of the analytical determination of the power effect is increased. The calculation of the temperature distribution along the radius of the fuel rod was carried out taking into account the temperature dependence of the thermal conductivity UO 2 . The design procedure was corrected for using the Finca-Ronchi dependence for the thermal conductivity of 95% density of the theoretical one.


Primary temperature characteristics of reactor
These include the following integral and differential characteristics [1,2].
The temperature effect of reactivity (TER), which is defined by the difference of reactivity, caused by the same temperature change from the cold to the hot state of all materials in reactor core (RC).The initial temperature of the cold reactor is set to 20-40 °C.Hot reactor temperature varies with a minimum controlled power level due to external heat sources.Fuel reactivity effect is responsible for forming the neutron spectrum and its leakage.
The power reactivity effect (PRE) N U is determined by the mean or effective temperature of uranium fuel eff T and the actual presence an isotope 238 U in it.Due to the Doppler effect, there are resonance levels of the uranium isotope broadening with temperature rise, which increases the neutron absorption probability, thereby reducing reactivity.The higher the fuel temperature and the lower its concentration, the greater the effect.Also, magnitude N U is important for to assess the mode extension fuel campaign using the power effect reactivity.U reactivity coefficients determine self-regulation, self-protection, reliability and safety of the nuclear reactor.Both coefficients to provide these nuclear reactor properties must be negative: the first is near the operative point, the second is on the entire range of power transient.
The fuel effective absolute temperature is determined by the exact integral formula

Characteristic comparison on the coefficient of thermal conductivity
The method of direct explicit calculation T r T is presented in handbooks [3,4].Research activity was based on the results [5], where the theoretical dependence of the thermal conductivity UO 2 was used as the equation: There is also the empirical formula: where .
The equations ( 3) -( 6) are presented in Fig. 1 and show the necessity of the coefficients adjustment in dependence (5).

Updating of the design formula for the fuel block
We take the Fink-Ronchy formula (6) as the main dependence for the coefficient of the thermal conductivity UO 2 and approximate it by the trigonometric function ( 5

Analysis of results
Carrying out estimations on the proposed dependencies allows us to draw the following conclusions: x the approximation formula for determining the effective fuel temperature (2) is in error slightly more than 3%; x the acceptable trigonometric approximation (7) of the Fink-Ronchi formula has been received; it will allow calculating the radial temperature distribution using the temperature dependence of the uranium dioxide thermal conductivity (8); x comparison with the known results of thermal design for the reactor fuel rods (WWER-1000 [9]) showed slightly lower values of the temperature field; this indicates, first of all, the necessity of using the effect of density changes and deviations from stoichiometry, which requires further analysis.
the fuel block; max T temperatures on the axis of the fuel block; c T temperatures on the surface of the fuel block.
: a O W/(m•K); a .; b . .More recent works are recommended to use the Fink-Ronchy formula to determine the thermal conductivity with density of 95%: