BLOCK 1: GENERAL CONTROL DATA

Note: In Sections 5.3 to 5.6, examples of the input blocks are given at the end of each Section.

The title card of this block starts with 'ST%' or with 'ST*'. The remainder of the card may be filled with arbitrary text. For formatted input (title card starts with “ST%”) the first card of the block is read with format (8A1,2X,6E10.0). The eight CHARACTER-Variables are used to initialise the following LOGICAL control variables, which are predefined with. TRUE..

They will be changed to .FALSE. only if a “F” (capital!) is read in; for any other input they remain .TRUE.. The meaning of the control variables for .TRUE. is listed in Table 3.

Table 3: Control Flag Interpretations for Input Block 1

No. Control Variable

Default

Value Description

1 NUKL .T. The nuclear programme module is called.

2 MOFU .T. The calculations for the moderator and fuel temperatures are performed.

The boundary conditions in calculating the moderator and fuel

No. Control Variable

Default

Value Description

5 SGAS .T.

The gas flow is calculated. The .FALSE. option may only be used in a restart case or together with TGAS =.FALSE, but convergence cannot be guaranteed.

6 TGAS .T. The gas temperature is calculated.

7 TBEK .T.

The calculation of the fuel element temperature is repeated during the global solid temperature calculation. The .FALSE option means that the heterogeneous temperature calculation is not repeated; instead the heat source is taken from the

calculation of the fuel and moderator temperatures. (A .FALSE.

value for this option makes sense only in equilibrium

calculations: during transients it produces the heat source at the end of the time interval instead of the average).

8 TFST .T. The solid temperature is calculated. The option of .FALSE. here means that the initial temperature values (TVOR) for the solids remains unchanged.

Even if the title card starts with “ST*”, these 8 CHARACTER-variables are read in formatted format.

Examples:

1. The input flags for the pure neutronics Dodd’s benchmark are: TTTTTTFF.

2. The input flags for a pure TH conduction problem are: FFFTTTTT

3. The same pure TH problem can also be run with any convective heat calculations:

FFFTTFFT

The format-free reading in this case starts from column 11 of the first card and is performed separately for each of the other cards; omitted items will not start reading of the next card but the corresponding parameters will be interpreted as zeros (i.e. the default values will be used). The following six variables (with the default values in brackets) are indicated in Table 4.

Table 4: First Card Variables of Input Block 1

No. Variable Default Value

and Unit Description

1 STATPW 1.0

The total nuclear power of the reactor [MW] (without any 'imposed' power assigned to certain materials like the (negative) power of a steam generator region, or the decay heat power in the discharge tube).

2 FXSKF 1.0E-10

[fissions/s] See next parameter.

3 FXSOR 0.0

[neutrons/cm³s]

The fixed external neutron source, which stabilises the neutron flux at a certain (low) level in case of reactor shut-down. This is necessary to avoid numerical problems and to allow a reactor restart at any time. The source is assumed to be homogeneously distributed all over the core. The total strength is either FXSKF times the total nuclear fission rate or (if FXSOR ≠ 0) equal to FXSOR.

4 DLTFT 2.0 K See next parameter.

No. Variable Default Value

and Unit Description

6 DLTON 0.05

This factor is the limit for the maximum relative power change per time step. It is used to define the nuclear time step length, to test the actual power change in the nuclear time step (if necessary with recalculation of the neutronics using a smaller time step), and to control the endpoint of the temperature interval if a desired power change is reached.

Note that omitted input values or zeros results in the old (default or restart) values. This holds true for the second card as well (Table 5), where accuracy limits are read in format (7E10.0).

Table 5: Second Card Variables of Input Block 1

No. Variable Default Value

and Unit Description

1 EPSNI 2E-5

The relative convergence of the nuclear calculation with given temperature boundary conditions (transient calculations).

User Hints:

1. If in DLOFC calculations re-criticality is expected a value of about 1E-9 should be given here. This will lead to a much more stable transient with smooth re-criticality oscillations. However, this tight criterion might lead to instabilities in other transients.

2. Tighter values for this parameter (and the next one EPSNO) can be used to improve stability and convergence for large input models, e.g. changing from 2E-5 to 1E-6..

2 EPSNO lE-4 The relative (outer) convergence of the equilibrium nuclear calculation (steady state calculations).

3 EPSFT 0.2 K The solid temperature relative convergence.

4 EPSBT 0.2 K The fuel element temperature relative convergence (for the convergence test of the solid/fuel element iteration the value EPSBT /16 is used).

5 EPSGT 0.2 K The gas temperature relative convergence.

The third card may be blank, if the cooling gas is pure helium and the standard control for the gas properties shall be used. This card is structured the same way as card 1 (8Al,2X,I10.0) and starts again with eight CHARACTER-variables, where an input “F” changes the .TRUE.

predefined data to .FALSE. The items are indicated in Table 6.

Table 6: Third Card Variables of Input Block 1

No. Variable Default

Value Description

1 RGAS .T. The real-gas correction factor according to Redlich and Kwong is applied to the general gas equation.

2 STKO .T. The gas viscosity is calculated by applying the Stockmeier correction to the Lenard-Jones potentials.

The viscosity and heat conductivity of gas mixtures interaction

No. Variable Default

Value Description

4 WEMA .T.

Gas diffusion coefficients are calculated according to

Weissman and Mason (.F. calculates according to Chapman and Enskog) .

5 DIFU .T. Diffusion is accounted for in the calculation of the intermixture of different gases.

6 REAG .T. Chemical reactions in the gas phase are calculated.

7 REAC .T. Chemical reactions in the solid phase are calculated.

8 DFFE .T. Variable presently not used.

After these control parameters the item MGAS (default value = 1) is read. This integer defines the dimension of fields related to the gas concentrations. Each gas type under consideration has a fixed place in these fields, as follows:

1. Helium 2. Nitrogen 3. Oxygen

4. Carbon-Monoxide 5. Carbon-Dioxide 6. Steam (H₂O) 7. Hydrogen

8. Fluid water (droplets or condensed; option not yet working properly!).

MGAS may have values from 1 to 8. For MGAS = n the gases from 1 to n are considered in the calculation. The gases from (n+1) to n = 8 must not be given as sources, nor be the results of chemical reactions or condensation. On the other hand, the gases from 1 to n may exist individually or as mixture; they may be mixed and may react chemically. MGAS should be kept as small as possible to avoid large memory demands.

EXAMPLE

An example of the ST* input block is indicated below.

ST* Project A; Dose=18FPY, Excore power=TINTE, CRheight from VSOP-data TTTTTTTT 400.0 0 0 2. 5. .5 .00002 .0001 .1 .1 .1

TTTTTFFT 7