BLOCK 5: MATERIAL ASSIGNMENT TO THE MESH GRID FOR NUCLEAR

Third Part: If GFAKO <0, the final two cards of the KG* block contain information on the emissivity of the fuel pebble material. n the first of these cards a series, (TEPS(I), I=1,IE(≤10)), consisting of up to 10 positive, monotonic increasing temperatures in ^oC, is read, while the last card gives the corresponding emissivities for the material under consideration (EPS(I), I=1,IE).

EXAMPLE

An example of the KG* block is indicated below. The structure of the block shows 11 columns for the 11 fixed temperatures, and 5 rows for the 5 fixed doses in lines 2-6. Line 7 shows the modified pebble bed parameters (discussed in Table 11), where the -1.0 value of GFAKO results in the last two lines being read in for the emissivities of the fuel pebbles.

KG* Lambda for 11 Temp and 5 fixed doses, Rule No.52 negative!

.4940,.4460,.4115,.3790,.3555,.3300,.3100,.2875,.2740,.2625,.1486, .3100,.3060,.2900,.2740,.2635,.2525,.2445,.2335,.2260,.2190,.1486, .2025,.2160,.2170,.2135,.2090,.2015,.1945,.1895,.1845,.1815,.1414, .1510,.1660,.1710,.1740,.1735,.1725,.1720,.1715,.1710,.1705,.1364, .1211,.1359,.1465,.1500,.1506,.1486,.1472,.1423,.1415,.1408,.1296 6 0.61 87.0 0.0165 -1.0

100, 200, 300, 400, 500, 600, 700, 800, 900, 2500 0.85, .85, .85, .85, .85, .85, .85, .85, .85, .85

If MGAS = 1 has been given on the third card of the ST Block (see below Table 6) a blank card follows to indicate the end of the TM block. Otherwise the equilibrium case gas-mixture is read in here. Either format-free (TM*) or with format (8E10.0) (TM%), the relative molar fractions for the constituents are given. The normalisation is performed internally.

EXAMPLE

An example of the last line of the TM block is indicated below.

1. 0. 0. 0. 0. 0.

3.7 BLOCK 5: MATERIAL ASSIGNMENT TO THE MESH GRID FOR NUCLEAR

done. The dimensions of the rows (MNR) and the columns (MNZ) of the NZ block is calculated from the data in the GM* input block, where the meshes are defined as nuclear meshes (see Section 5.4). If a mismatch inn dimensioning occurs between the GM* and the NZ* input sets, the TINTE calculation will stop. Also note that the “nuclear material” numbers used in the NZ* block are independent from those defined for thermal calculations (i.e. in the TZ* block). The definition of layers is done similar to that in section 5.4 by MNZ times reading of MNR positive or negative numbers, either (NZ%) in format (18I4), or unlimited format-free (NZ*) as follows: (LNRZ(J ,1), J=1,MNR), where identification numbers of materials for the nuclear calculations are read in along a row I (I=1, MNZ), each I starting on a new record.

The positive numbers in LNRZ refer to sets of nuclear cross-sections, defined in the next (NQ%) block, while the negative material numbers are reserved for nuclear materials that consist of a mixture of sets of cross sections.

There is a correspondence between the cross-section set numbers here and in the .tn4 file.

Each set number given here has to be found in the .tn4 file, but there may be set numbers in the .tn4 file not used here. However, the highest number found in the .tn4 file has to be part of the NZ block.

EXAMPLE

An example showing a section of a NZ* input block is indicated below.

NZ*

240 214 214 214 214 214 214 214 214 214 214 214 -1 214 240 241 241 241 241 241 241 241 241 241 241 241 -2 241 242 243 243 243 243 243 243 243 243 243 243 243 -2 243 171 274 282 15 39 63 87 111 135 159 296 304 -18 -28 171 274 282 16 40 64 88 112 136 160 296 304 -19 313 171 260 278 290 290 290 290 290 290 290 300 300 212 317 171 260 278 290 290 290 290 290 290 290 300 300 212 317 171 221 223 224 224 224 224 224 224 224 225 225 211 226 -1 209 1. 183

-2 209 1. 184 -3 209 1. 185 -4 209 1. 186 -5 209 1. 187 -6 209 1. 188

Among the materials with negative numbers the one with the largest absolute value (e.g. -28 in the block above) has a special meaning: when evaluating the transient neutron flux it is assumed that at this location a flux detector is located. This is the reason why at least one negative number has to be present in the NZ* block.

For defining the dimensions of the NZ* block the largest (MMM) and the absolute value of the smallest (MVH) material number are extracted first. These two numbers define the total number of materials with fixed cross-sections, and the number of materials in which cross sections may be mixed and/or changed.

For materials with varying cross section compositions (negative material numbers), the basic cross section sets and the sets for superposing are defined with the following series of numbers:

(-I, LCNC(I,0), (CONC(I,J,1), LCNC(I,J), J = 1, jmax)),

LCNC(I,J) = one of the “overlay cross section sets”

CONC(I,J,1) = the fractional part of concentration of the corresponding cross section set.

EXAMPLE

-1 209 1. 183

-2 209 0.6 184 0.2 185

This example shows that basic cross section set for nuclear material -1 is nuclear material

#209 (as defined in the next NQ% data block). This basic cross section set is overlaid (or superimposed) with the cross section set from nuclear material #183. The fraction of overlay is 1.0, i.e. the cross section data for nuclear material -1 is completely obtained from nuclear material #183. This overlay fraction can be changed during transient events (see Section 8).

The second line shows that the basic cross section set for nuclear material -2 is also nuclear material #209, but here the basic cross section set is overlaid with 60% of the cross section set from nuclear material #184, and 20% of the cross section set from nuclear material #185.

The cross section data for material -2 therefore consists of 20% #209 data, 20% #185 data and 60% of #184 data. (Also note that there is no open line/card between this section of the input, and the “map” of the NQ* block- see the previous example).

For each negative material number appearing in the block LNRZ, up to 6 sets of data per card can be read in an arbitrary sequence, either in format (8F7.0,I2) (for NZ%) or format-free (for NZ*). Zeros at the end of the cards are added, if necessary. Cross sections are determined from the adjusted fractions (as indicated above), but this is not possible for the average burn-up. This factor is determined with the basic cross section composition, which fixes the precursor-concentrations after the equilibrium calculation. The sum of the overlay parts has to be identical to 1, therefore for J = jmax down to 1, the CON(I, J, 1) are corrected by

and additionally CON(I, 0,1) is adjusted according to

.

jmax is defined by reading LCNC(I,jmax) > 0 and LCNC(I,jmax + 1) = 0. Therefore, when jmax = 7 then one card is needed, when jmax = 15 a second card becomes necessary, and so on. For defining the dimension limits, the largest J has to be found, for which LCNC(I, J) is different from zero.

This overlay input is finished, when LCNC(..., 0) = 0 (blank card). In regions with variable compositions, additional previously unused cross section sets might appear. Now the maximum MLL of cross section sets to be read is determined as the maximum of MMM and the largest number of the LCNC.

3.7.1 Final Input Data

The final NZ* input (and the final input for the .tn3 file) is used to group material meshes into leakage iteration meshes (see /1/ Section 3.4.) for memory saving reasons. The data is read

zero. The length of the series determines the number of iteration columns MRI and rows MZI.

The items of these series are (ND(J), J=1, MRI resp. MZI), meaning ND(J) material meshes will be grouped into leakage iteration mesh J.

The leakage iteration calculation is then performed using the leakage rates from the newly defined “coarse mesh” rows and columns, instead of those from the original “finer” material mesh. This course mesh procedure has been proven to work well for nuclear calculations, as opposed to the temperature calculations (where this approach is not followed). Care has to be taken in applying this method in the core regions, as the accuracy of the heat production (needed in material meshes) is degraded.

EXAMPLE

The example below indicates the grouping of the 1-D iteration meshes. Note that the core region is not divided into coarser meshes (i.e. the 14 radial and 25 axial core regions are kept as single 1-D iteration meshes), and the 0 to end the input cards. This block of input is separated by a single open (empty) line from the NZ* block, but technically still forms part of the NZ* block.

14*1 2 1 2 3 0 3 3 25*1 3 2 2 0

USER NOTE:

As indicated above, the two lines shown in the example are also the last input lines in the .tn3 file. The .tn3 file should be closed off with two open (empty) lines after the final input data, or run-time problems will occur.