Method for evaluating burnout margin in nuclear power units

FIELD: power engineering; evaluating burnout margin in nuclear power units.

SUBSTANCE: proposed method intended for use in VVER or RBMK, or other similar reactor units includes setting of desired operating parameters at inlet of fuel assembly, power supply to fuel assembly, variation of fuel assembly power, measurement of wall temperature of fuel element (or simulator thereof), detection of burnout moment by comparing wall temperatures at different power values of fuel assembly, evaluation of burnout margin by comparing critical heat flux and heat fluxes at rated parameters of fuel assembly, burnout being recognized by first wall temperature increase disproportional relative to power variation. Power is supplied to separate groups of fuel elements and/or separate fuel elements (or simulators thereof); this power supplied to separate groups of fuel elements and/or to separate fuel elements is varied to ensure conditions at fuel element outlet equal to those preset , where G is water flow through fuel element, kg/s; iout, iin is coolant enthalpy at fuel element outlet and inlet, respectively, kJ/kg; Nδi is power released at balanced fuel elements (or simulators thereof) where burnout is not detected, kW; n is number of balanced fuel elements; Nbrn.i is power released at fuel elements (or element) where burnout is detected; m is number of fuel elements where burnout is detected, m ≥ 1; d is fuel element diameter, mm.

EFFECT: enhanced precision of evaluating burnout margin for nuclear power plant channels.

1 cl, 2 dwg

 

The invention relates to energy and can be used to determine the reserves before the crisis, the heat transfer in nuclear power plants (NPP), for example, VVER or RBMK.

There is a method of determining the reserves before the crisis of heat transfer, namely, that required operational parameters at the entrance of the fuel Assembly (FA), bring power to the fuel assemblies, change the power assemblies, measure the wall temperature of the fuel rods (fuel simulators), determine the time of onset of the crisis by comparing the temperatures of the walls at various capacities Assembly, determine the critical power for various parameters at the entrance of the Assembly, determine the reserves before the crisis, the heat transfer by comparing the critical power Assembly and power Assembly at a nominal parameters and the crisis of heat transfer take first, compared with the normal mode of heat removal, disproportionate change power, the temperature of the wall associated with the deterioration of heat transfer from the simulator TVEL (Paavani, Web Operational modes VVER), Energoatomizdat, 1988, s).

The assumption that the conditions of crisis are formed by the totality of flow parameters, forms the basis of the hypothesis of global conditions. In this case, the reserves before the crisis is determined by the critical power.

kr) depend on the distribution of the heat flux along the length of a fuel rod, and the power can be significantly lower than for a fuel rod with a uniform dissipation (P.L. Kirillov, Sands O.L., Pometia R.S., she MET “calculation of the critical power of steam generating channels with nonuniform dissipation length”, Teploenergetika, No. 5, 1981). Critical power Assembly depends on its length, placement of the fuel rods in the cross section, etc.

The closest to the technical nature of the proposed method is a way of determining the reserves before the crisis, the heat transfer in the channels of the NPP, which consists in the fact that the required operational parameters at the entrance of the fuel Assembly, bring power to the fuel assemblies, change the power on FA, measure the wall temperature of the fuel rods (fuel simulators), determine the time of onset of the crisis by comparing the temperatures of the walls at various capacities Assembly, determine the reserves before the crisis, the heat transfer by comparing KTP and heat flow at rated parameters output Assembly, and the crisis of heat transfer take first, compared with the standards is determined as being the mode of heat removal, disproportionate power change the temperature of the wall associated with the deterioration of heat transfer from the simulator TVEL (1. Wastrels and other Investigation of critical heat flux in bundles of rods in the reactors of VVER type. In Proc. of the Workshop TF-74. Study of critical heat flux in bundles of rods. M: the Council for mutual economic assistance. The standing Committee on the use of atomic energy for peaceful purposes. 1974, 2. Aaaall, Respublika. The study of heat transfer crisis on the model of FAS alternative fuel for VVER-1000. Preprint IPPE-2774. Obninsk - 1999).

To determine (obtain) dependence of the form qkr=f(P, ρ W, x) vary the conditions (length, inlet water temperature, water flow, etc.), repeat all the operations described above, and determine the KTP at other options and get the dependence of the form qkr=f(P, ρ W, x). Using megacache analysis to define the local settings in the individual cells of the Assembly are determined KTP (qkr) in these local settings are the stocks before the crisis, as the ratio of the critical heat flux from the surface of the fuel elements in this section (qLok) - qkr/qLok. This is a “local” approach. To determine qkrthere are both the table and the various settlement zavisimost and (P.L. Kirillov, Bobkov VP, she MET and other “Skeleton table for critical heat flow”. Atomic energy, 1991, CH, No. 1, p.18-28; Boltenko EA,, Katan IB, Satina O.A. “Calculation of heat transfer crisis at different flow conditions//Thermophysical aspects of the safety of VVER. Proceedings of the international workshop. Thermophysics. 90, 2xvolumes, edited by Placitella. Obninsk: IPPE jist. 1991, Vol.2, s-319). The definition of reserves before the crisis, the heat transfer is possible on the basis of different methods (Planillo, Ussuri, Vpopov Handbook of thermal-hydraulic calculations (nuclear reactors, heat exchangers, steam generators, M.: Energoatomizdat, 1990)). In all methods use the values of KTP, obtained as described above (prototype).

The main disadvantage of this method is that factor, defined as qkr/qLokmakes sense only for fixed, unchanging nominal parameters and cannot be implemented, both in normal operation and in transitional or emergency situations.

The technical result, which directed the present invention is to improve the accuracy of determination of reserves before the crisis in the channels of the NPP and is that power down to the individual groups and(or) individual fuel rods (fuel simulators), change the power supplied from the nutrient groups TVEL and(or) individual fuel rods, so the conditions at the exit of the Assembly were equal beforehand set

,

where G is the rate of flow through the Assembly FA, kg/s;

io, iI- enthalpy fluid outlet and inlet Assembly, kJ/kg;

i- power allocated to balance the fuel rods (fuel simulators), which is not determined by the crisis, kW;

n is the number of balanced TVEL;

NKPIthe power allocated to the Fe (or Fe), which is the definition of crisis, kW;

m is the number of crisis TVEL, m≥ 1;

d - diameter of a fuel rod, mm

Define KTP on individual groups and / or individual fuel rods (fuel simulators)determine the reserves before the crisis, the heat transfer by comparing the obtained values of PTS and heat flows at the nominal operating parameters of the Assembly.

The achievement of the technical result consists in increasing the accuracy of stocks before the crisis, provided that KTP, certain of the proposed method obtained under conditions maximally close to real ones.

1. QFT on the fuel rods (fuel simulators) obtained modal parameters at the input and output assemblies, corresponding to the nominal (or beforehand set (emergency).

2. Heat flow on the fuel rods (fuel simulators that do not face the crisis (balanced)correspond to the nominal (or required by condition)

3. Conditions in the cross section of the Assembly correspond to real (non-uniform heat generation section, the height of the Assembly, the non-uniformity of cells and so on).

The method is as follows. Set mode parameters at the inlet and outlet RU (models RU)where it is necessary to determine the reserves before the crisis. Next on the Assembly with the simulated fuel elements, which is included in the composition of the experimental setup for pumping water through the Assembly and create the input conditions at the inlet (inlet water temperature, pressure, flow rate), set the desired conditions of the experiment, the power balance simulators and crisis simulations. As a result, the input and output Assembly required operational parameters and the density of the heat flux on the simulators. Further, by increasing the power crisis (crisis) simulators face the crisis. On balance simulators vary the power in order to keep the conditions at the exit of the Assembly. The obtained values of the critical heat flux are used to determine the reserves before the crisis for PN under given conditions at the inlet and outlet assemblies. Figure 1 shows an example of the definition of reserves before the crisis, the known and the proposed method. To simplify figure 1 considers the case when the fuel rods have a uniform heat along the length, and the proposed way is defined by one value KTP. Figure 1 shows the 1 - dependence of qkr=f(x) based on the values of KTP, obtained in a known manner (prototype); 2 - dependence of the heat flow from the steam content (heat balance). Uniform heat dissipation. Xo=XI+qMr.π dLn/Gr, Xo- mass steam quality at the outlet Assembly, XI- mass steam quality at the entrance to the Assembly, is defined as - XI=(II-In)/r, where II, In- enthalpy of water at the entrance to the Assembly and on the saturation line, respectively II=f(P, tI), kJ/kg is based on the tables of thermophysical properties of water R and tI- the water pressure in the Assembly (at the entrance) and the temperature of the water that enters the Assembly, In=f(P) - enthalpy of water at saturation line, kJ/kg, r=f(P), kJ/kg latent heat of vaporization is determined on the basis of tables of thermophysical properties of water, qMr.- nominal heat flux on the fuel elements (Fe) kW/m2i.e. the heat flow is taken as the source when determining the reserves before the crisis, L is the length of a fuel rod, m, n is the number of fuel elements, d is the diameter of a fuel rod, G is the flow rate of water pumped through the Assembly, kg/s 3 - stock before the crisis derived from the proposed method (values KTP obtained in a known manner (prototype)). 4 - the Value of KTP, obtained on the basis of the proposed method. 5 - the Stock until the crisis is, obtained by the proposed method (taken value KTP obtained by the proposed method).

As can be seen from figure 1, in this case the stock before the crisis turned out to be smaller, which is defined in a known manner. Apparently, there may be cases when the picture will be reversed.

As an example, consider the definition of reserves before the crisis in the Assembly, simulating the VVER and available in EREC. FA power up to 10 MW with imitators indirect heating (number of imitators 168). The power of one of the simulator corresponds to the average density of the heat flow WWER ~0.6 MW/m2there is a possibility on some rods to increase power to the crisis.

Figure 2 shows the cross-section of the Assembly, indicated fuel simulators, where it is possible to exit to the crisis (their number and placement of cross section Assembly can be changed). Suppose the output to a crisis will occur on four simulated fuel elements placed in the most characteristic places of Assembly (bordering the most characteristic cell Assembly). The values of KTP, when the parameters at the input and output corresponding to the nominal (outlet pressure -16,0 MPa, the water temperature at the inlet 290° C, water temperature at the outlet 320° C) is 2-2,2 MW/m2(depending where the fuel simulators). The average heat flux at the balanced terminals of 0.6 MW/m2. About the relative power change Assembly at the exit to the crisis in four simulators is Δ N=4· 3,14· 9,1· 10-3·3,5· 2· 106/10· 106=0,08, i.e. approximately 8% of the total capacity. Exit to the crisis on the same simulator changes the total power of approximately 2%. These changes in power and, therefore, the output conditions are corrected using balanced imitators. Thus, using the proposed method, obtaining a KTP and, accordingly, reserves before the crisis under conditions close to the real operating conditions of the Assembly.

Thus, the proposed solution allows to increase the accuracy of determination of reserves before the crisis in the channels NPP due to the fact that QFT defined by the proposed method obtained under conditions maximally close to real ones.

The method for determining the reserves before the crisis, the heat transfer in the channels of the NPP, which consists in the fact that the required operational parameters at the entrance of the fuel Assembly (FA), bring power to the fuel assemblies, change the power assemblies, measure the wall temperature of the fuel rods (fuel simulators), determine the time of onset of the crisis by comparing the temperatures of the walls at various capacities Assembly, determine the critical heat fluxes (KTP) at different parameters on the output Assembly, determine the reserves before the crisis, the heat transfer by comparing the obtained values of PTS and heat flows in batteries the x mode parameters of the Assembly, and for the crisis of the heat transfer taking first, compared with the normal mode of heat removal, disproportionate power change the temperature of the wall associated with the deterioration of heat transfer from the fuel rod, wherein the power down to the individual groups and (or) individual fuel rods (fuel simulators), change the power supplied to individual groups TVEL and (or) individual fuel rods, so that the conditions at the exit of the Assembly were equal beforehand set

where G is the rate of flow through the Assembly FA, kg/s;

io, iI- enthalpy fluid outlet and inlet Assembly, kJ/kg;

i- power allocated to balance the fuel rods (fuel simulators), which is not defined (does not occur) crisis, kW;

n is the number of balanced TVEL;

NKPIthe power allocated to the fuel rods, which is the definition of crisis, kW;

m is the number of crisis TVEL,

define KTP on individual groups and / or individual fuel rods (fuel simulators)determine the reserves before the crisis, the heat transfer by comparing the obtained values of PTS and heat flows at the nominal operating parameters of the Assembly.



 

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