Current status of neutron spectrum unfolding

275 Pages·14.322 MB·English

IAEA-TECDOC-221
CURRENT STATUS
OF NEUTRON SPECTRUM
UNFOLDING
PROCEEDINGA FSO
TECHNICAL COMMUEE MEETING ON
CURRENT STATU FSON EUTRON SPECTRUM UNFOLDING
ORGANIZEHET YDB
INTERNATIONAL ATOMIC ENERGY AGENCY
HELD IN OAK RIDGE, 10-12 OCTOBER 1977
A TECHNICAL DOCUMENT ISSUED BY THE
INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1979
CT3REENT STATP UONSE UTRON SPECTRUM UNFOLDING
IAEA, VIENNA, 1979
Printed by the IAEA in Austria
August 1979
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FOREWORD
Accore dhrti enoctg ommendae thIti noftone rnational Working Grounop
Reactor Radiation Measurements (IWGRRM) and within the frame of the IAEA pro-
gramm noes tandardizatio fonr eactor radiation measuremente shtt, echnical
committee meeting on "Current Status of Neutron Spectrum Unfolding" was held
by the IAEA. The meeting took place at Oak Ridge, Tennessee, USA, from 10 to
12 October 1977k ,aR Oih doeghsett yeNbd ational Laboratory, with Bett.Py
Maskewitz, Radiation Shielding Information Center,s a general chairmadnna
.KK a.mB ,. FOperations Divisions ta, echnical programme chairme ahmnTe. eting
s aawtten 7d2pe yadb rticipants from5 countries.
e dheTve emhluotlp tmfieopnl te foil neutron activation technsiaquh e
allowed detailed spectrum information to be obtained for the whole energy range
important for reactor technology. Jhe importance of accurate and well-documented
unfolding procedures is widely recognized. The overall objective of the meeting
was to permit a number of experts to discuss recent advances in the field of
neutron spectrum unfoldind gnta,h o etsn ummarie hzctue rrent state-of-the-art
e ht ni form fo recommendationsy b esu rof researcherse ht ot dna Agency's future
programme in the field.
e phaTrticipants consid ddenirasece dufhsolstle odwing aspects:
- Gross—cciction data libraries; qua dlanivata yilability
- Methods for evaluation of computed st>ectra
- Selection of suitable foil sets
The proceedings include4 d1 papers submitted ndad iscusse hetm tdea eting
in Oak Ridge, summary of this meeting, conclusions having
been proposed by the participants. It is hoped that these proceedings will not
a u seeofnubll y refet rweuinlcble ,alr sa mopoo o rfissene taravd evanced
work in the field.
e hATgency wish oetes xpre stsaips precie ahattui toothn of rops apers,
to the authorities in the host country who helped to arrange the meeting.
. V .CV hernyshev
Scientific Secretary
of the IWGRRM
CONTESTS
Comparisonf o neutron spectrum unfolding codes .....................1
W.L. Zijp, J.H. Board, H.J. Nolthenius
Reviewf o unfolding methods ue shetU ndi .Sd n.ta heir
standardization for dosimetry ................................... 29
C.A. Oster
Cross section library DOSCROSS-77 (in the SAHD-II format) .......... 45
H.J. Holthenius, W»L Zijp, N.J.C.M. -van der Borg
ffi
Shielding effect of foil covers .................................... 133
W.L. Zijp, H.J. Hblthenius, U.J.C.Mr ed n.av Borg
Spectrum unfolding in the high neutron energy rangej comparison
of detector se duntans folding procedures ....................9.31..
L.J.M. Kuijpers
The modifying factor in unfolding .................................. 151
W.L. Zijp, H.C. Hieffle
The certainty parameter in unfolding ............................... 161
W.L. Zijp, H.C. Eieffle
Errn odirasm age function analysis .........................7..6.1.....
E.R. Burrus
The quadruple technique ...................o......................96.1.
W.L. Zijp, H.J* Holthenius, N re.BdJ.o Cnrag.vI.
Window function and bounds in multiple foil dosimetry .............. 179
F.M. Stallmann, F.B„K. Kam
Application des méthodes de la programmation linéaire au
dépouillement des résultats de mesures par activation ........... 183
J. Dorlet
Spectrum unfolding fey the least square method ...................... 195
P,G. Perey
Progrese shI ArtEe Apn ooarct tivn nioteyu tj?on spectra
unfoldingy b activation technique ...............................732
C. Erte. BkC, ro .MsVsl, asov
Preparation of cross section files and corrections in
neutron spectrum unfolding ...................................... 259
M. Matzke
Summary and Conclusions ............................................. 269
Lf ioPst articipants ..........................................5.7.2...
PAPERS PBESEITTED
COMPARISONF O NEUTRON SPECTRUM UNFOLDING CODES
W»L Zijp, J.H. Board, H.J» Nolthenius
9
Netherlands Energy Research. Foundation EOT
Fetten, Netherlands
Abstract:
This report presents results obtaineda ni comparisonf o three promising
neutron spectrum unfolding proce eCdhRuYrtSeTs A nLb aoBsAe LdL, RFSP-JÜL
and SAND-II computer programs.
The calculations have been performed for three neutron spectra i.e.
CFRMF, IT, and STEK.
Two cross section data sets were considered based on a recent SAND-II
library and the ENDF/B-IV dosimetry file.
The codes give comparable results when good input spectrum information
is given. When in particular energy regions (e.g. between 1 keV and 1 MeV)
there is no or poor detector response, then the three codes give there
different output spectra,
RFSP-JÜL modifies the input spectrum only in those regions where there
is appreciable detector response. CRYSTAL BALL and SAND-II extend the
modifications alo stro egions r woli iottnh tle response hesT.m oothest
modification curvs ei obtained with CRYSTAL BALL.
1. INTRODUCTION
At present three computer programs (CRYSTAL BALL, RFSP-JÜL and SAND-II)
e bms oeosettm proe hmdtie strieonrfgm inatif oonn eutron flux density
spectra, starting from experimental reaction ratesn i irradiated activa
tion and fission detectors.
e f fheooqtl ul aottwfieioonsng s aty pes:a nphIr iencniopl e
= ia ai(E).<j>E(E).dE (for i=l...n)
o
where:
a£ = the experimentally obtained reaction rate per target nucleus
( nfaaocr tivation detector this corree shsptao tnoudtrs a-
tion activity) per target nucleus;
e ehnetr g=y )deEp(ae indent activation cross section;
e fhlut<xJ >r Ed=(u eEenn)ispti t eynergy interval;
e htn =u mn berf o detection reaction.
The unfolding programs studied have a number of energy groups larger than
the number of detectors. They require à priori knowledge in the form of
an input spectrum, which represee nahttvas ilable neutron spectrum infor-
mation from physics experiments or reactor physics calculations.
The approaches and algorithms of the three unfolding programs have been
reviewed elsewhere 1|.
This report describes results of an intercomparison of the three programs
mentn isoienle edcted illustrative exae miphnlvTees s.tigation comprised:
- three unfolding codes: CRYSTAL BALL J2J, RFSP-JÜL |3J and SAND-II
(|4|d na |5|);
- three fast neutron flux density spectra, from the facilities CFRMF at
Idaho 6|, ZE at Mol |?| and STEK at Petten |s|;
- two cross section libraries, a recent SAND-II library (denoted here as
SAND/L) J9| and the ENDF/B-IV dosimetry file J10|.
The input activities and the input spectra were taken from literature
|11| and |12 | .
Preliminary results obtainedr of this intercomparison were presentedni
two progress reports |13| and |14|. A shortened version of |13 is given
. |1 5 i1n
This report prese enhstte us hpmtrm eafvroiy ous results (|l3J, 14|,|l5|)
together with some wen information.
The intercomparison was performed in such a way that as much as possible
the same input data wee rtheht rae perp olcifoed des.
e hTcomputer programs which have been e hutcs areolfd culations wt?nrie
most cases somewhat modified without influencing the actual spectrum cal-
culation algorithm.
The modification referred mainly to the output procedures and to the cal-
culation of the improvement ratio |16|.
The SAND-II program was extended with a procedure which calculates an
estimate of the uncertainty for each of the 620 group flux density values
oe hfts olution spectra.
This procedure is based on the Monte Carlo procedure described by Oster
et al. |l7[. While Oster performs the Monte Carlo procedure on the cal-
culated activities using the output spectrum, the procedure followed in
this o stmt ousde diihiy ftny put activities use ihintng put spectrum
for each Monte Carlo run. This SAND-II extension can also take into account
modifications in cross section values and in input spectrum.
2. SPECTRUM CALCULATIONS
2.1. Rof loie nput data
e ahcWttiit vhity vae lchuoetnsv e rpdgreennsan ce netita 1ebc ldr eite-
ria given in table 2, solution spectra were calculated.
The calculations were performed with cross section values obtained from
either an updated SAND-II library (coded SAND/L) or the ENDF/B-IV dosi-
metry file.
Durie hnctga lculatiot nits urnt uetodh n aist ome case hectsa lculated
activity values devi omaotutec dh efehrxtop merimental input activities.
e haTctivity values which weree rhdeter a lostdehofntin aes d deletion
are indicated in table 1. It will be clear that sometimes more than one
reason holdr osfd eletion.
e thhrteee dsnhfhieaToupmte r sone hse pvTrei n csaft.iiirb g1al uer e
line gives the SAND-II solution and the two outer lines are plotted at
o dswittsatn adfnacroed s deviationse ShfArtNoD m-II solutions.
e hT plotse ht ta lefte ra obtained with variations eht fo input activi-
ties. The variation of these activity values was based on the experimen-
tal measurement error (table 1).
The plots at the right are obtained with variations of activity values
e chrtos sf aoss e cwsteail oln values.
The solution spectra were calculated with the updated SAND-II library
(SAND/L). The influence of the cross section library on the solution
is relatee htd ort esponsee ht sraof pplied reactions.
ehre Tehtsthpr oerneosf ens euo twcrtroo nse shs tps eedccnttari aon
libraries are shown in figure 2. Comparison of the corresponding respon-
ses shows that there is a clear difference in these two libraries.
e hcTonsequenf cote hese different res ephCotFn RrsoMefFs useihntg
o lwn ittbIe hrn s ia rthfsrieohia.iwrghe 3 enuster e prdognraam s
e e pd rf rfrhaioientnouagstiptaueou prn stu etted. These results show
thae thtE NDF/B-IV dosimetry file givesn a important correctiont a about
e ht1s n3io V0ue ution spectra,and thae httS AND/L file gives a more
pronounced contributit oaabn O oMJuet V.
2.2. Ra ftoo diu otinpnaup utt spectra
The right part of figure 3 and the plots of figure 4 show the ratios of
solution spectra (i.e. accepted output spectra)d na input spectra.
These solution spece trrcaaa lculae thdtea dtf aow difiterahho tm
ENDF/B-IV dosimetry file. From these plots the following observations can
be made: