ML17209A945
| ML17209A945 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 02/26/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17209A944 | List: |
| References | |
| NUDOCS 8104150021 | |
| Download: ML17209A945 (8) | |
Text
Enclosure TOPICAL REPORT
".VALUATION REPORT TITLE:
REPORT NUMBER:
REPORT GATE:
ORIGINATING ORGAN IZATION:
REVIEWED BY:
DATE OF EVALUATION:
- FIESTA, A One Oia'ensional, Two Group Space-Time Kinetic Code for Calculating PMR Scram Reactivi ties CEN-122 (F )
- November, 1979 Combustion Engineering Core Performance Branch/Reactor Physics Section February 26, 1981 Summary of Topical Report This report describes the FIESTA space-t,ime kinetiics computer code which was developed by CE, for PVR scram reactivity calculations which account for he axial space-time variations in the neutron flux.
The one-dimensional two-group time dependent neutr on diffusion equation i s solved by a space-time factorization method which divides the neutron flux in o a time-dep ndent amplitude function times a time-dependent shape inc-.ion.
The flux amplitude is calculated by the point kinetics equations using very small time steps.
These time steps are automatically expanded or reduced by zhe code as needed in order to achieve a converged point Kinetics solution.
The point kinetics approximation is appropriate since the flux shape between relatively small time in.ervals may be assumed to be constant.
The flux shape, which varies more slowly.han
.he ampli.ude, is calculated by the shape equation using a much larger time step size which is specified by the user.
Therefore, al though the space-time actorization method introduces an additional variable and an addi ~ional equation (point kinetics equation),
an overall saving is realized since the shape
- equation, which is the most time consuming calcula.ion, may be evaluated less frequently than wi th norma'.
space-time cal culational procedures.
0
. r P
1
"=r'.-,',ca ion calculations have been performed and are summarized i~ this
. =port.
Both a subcritical and a supercritical
".. ansient'were anaTyzed f-o.-.: the Argonne Hational Laboratory report of benchmark problems (AHL-74161.
n addi tional compari son was made between FIESTA and the HRC approved
-i-re -dimensional neutron kinetics code HERMITE in calculating scram r=ac ".'vities.
S:r m re-ctivities for a typical cycle using space-time calculations are c".m"ared to static calculations in this report.
The impact of using the s:ace-tismie approach on the results of analyses of design basis transients
',=- also presented.
'. d scriotion of the code input is also included as an appendix.
S -.;.;.ary of Review
"=-:-ave reviewed the subject report, including ihe mathematical models and a ytical procedures and methods.
Although the;IESTA code incorporates a
- ~-1 hydraulic model and is capable o= anaiyzing a variety of transients w'".'r;he inclusion of feedback effects, the code description and verifica-
,'o;. calculations presented in this repor". were limited and intended only "al idate the use of FIESTA for scram reactivi ty cal culations without.
a=k effects.
Therefore, a detailed descript',on of the feedback
.-.="ales were not included in the topical
. eport and were not reviewed or a::roved by ihe staff.
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'I I
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.he FIESTA code is verified by comparison with two benchmark problems which have been dis.ributed by the Argonne Hational Laboratory Code Center in ANL-7416 Supplement I dated
- Oecember, 1972.
The first benchmark problem consists of a subcritical transient in a three region infinite slab reactor model where the thermal absorption cross section in one of the regions is linearly increased by three percent in one second.
The second benchmark
/
problem consists of a supercritical transient using the same geometry as he previous problem but with the hermal absorp
',on cross section decreased by one percent in one second.
The results of both benchmark problems obtained by FIESTA are in excellent agreement with the results obtained by four other widely used and acceptable space-time J<inetics codes;
- RAUNZEIT, MIGLE, QX1, and HERMITE.
This valida.ion procedure as well as the results obtained are acceptable.
Additional comparisons are perform d between FIESTA and the HERMITE code, which has been previously approved by the staff.
The analysis is representa-tive of a reactor scram in which control, rods are inserted into the core in three seconds.
The excellent agreement between the results obtained with the one-dimensional FIESTA code and the hree-dimensional HERMITE code con,irm to the staff that FIESTA is acceptable
-"or calculating scram reactivities.
Comparisons of soace-time (FIESTA) scram reactivities with static scram reactivities show the FIESTA calculations result in greater reactivity insertions at intermediat CEA positions.
This is due
.o the fact that in the space-time calculation, the delayed neutron precursors are distributed
'"."crding to the initial flux shape.
The neutron precursors provide a
Vs"'r"e of delayed neutrons which tends to tilt the neu ron flux shape
.cward the CEAs compared to static methods, leading to greater CEA reactivity w"rth at intermediate CEA positions.
At full CEA insertions both methods v ei d nearly he same reactivi ty.
Although
.he space-time results are less
- nservative than those of the previous static method of calculating scram r= c-',vi ties, they are more real istic since delayed neutron effects are ac"c.n.ed for and are, therefore, acceptable.
=" <<u=.ion'Procedure
-evi ew of topical report CEH-122(F) has b en conduc ed within the
-;ical'nes provided by the Standard Review Plan, Section 4.3, HUREG 75/087.
S'.ff'cient information is presented to permit a knowledgeable person to that the calculational procedures and techniques used in the
=::-S.A code are state-of-the-art and acceptable for the calculation of PMR
=-=-=-. reactivity worth.
This conclusion is reinforced by the fact thai
".."ari son of Fi STA results with r esults of other widely-used and acceptable a=ace-time kinetics codes for scram type calculations produce similar
~
~
resu:
. s ~
=-tino Position
=".e basis o,
our review of topical report CEH-i.22(F) we conclude that it
- a=ceptable for reference in licensing ac.-'.ons in regard to PMR scram
-=<<c-.ivi y calculations for various design basis events which require a
V
The thermal-hydraulic model -which is available in the FIESTA code was not included in the topical report because it is not used in the scram reactivity calculations.
The feedback.
modules in FIESTA have, therefore, not'been reviewed or approved.
lp ty~
~ 0 0
APR 1 8 1881