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5.5 BWR Fuel Assembly Calculation (PIJ)
As the last sample, an example to analyze a fuel assembly of BWR loaded with MOX by using
a geometry model (IGT=16) of PIJ. The assembly is shown in Fig.5.5-1 at the last of this section. A
series of calculations consists of the following 6 cases.
(1) A MOX fuel pin cell calculation (case name: UPIN)
A pin cell calculation by PIJ (IGT=4) with 107-group structure is solved for the MOX pin cell
with the model shown in Fig.5.5-2. The cross-sections are homogenized in the cell and collapsed into
39-group structure.
(2) A partial cell containing a UO 2 -Gd 2 O 3 pin (case name: GDPN)
A 3 × 3 rod cell calculation by PIJ (IGT=9) with 107-group structure is done by using the model
shown in Fig.5.5-3 to obtain the 39-group constants of UO 2 -Gd 2 O 3 rod under the condition that it is
surrounded by MOX pins. As the later assembly calculation treat UO 2 -Gd 2 O 3 rod heterogeneously, the
cross-sections of meat, cladding and moderator are separately collapsed by assigning different
X-Region number.
(3) A partial cell of control rod insertion (case name: CRIN)
Control blade is heterogeneously treated with the cell model shown in Fig.5.5-4. The
homogenized cross-sections of the control blade are obtained in 39-group structure by PIJ (IGT=16).
(4) A partial cell of control rod withdrawn (case name: CROT)
The same geometry as the previous case is treated while the materials inside control blade are
replaced by saturated water used in gap region.
(5) An assembly calculation with control rod insertion (case name: ASMI)
By using the 39-group constants obtained in (1), (2) and (3) cases, an eigenvalue problem is
solved by PIJ with 39-group structure for the assembly with control rod insertion. Fig.5.5-5 shows the
R-Region map (identical with T-Region map) used in the calculation where the thick water rod is
treated as homogeneous mixture because of the restriction of the model IGT=16.
(6) An assembly calculation with control rod withdrawal (case name: ASMO)
The same problem as the previous case is solved with the replacement of cross-sections for the
control blade obtained in (3) by those in (4).
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