sp-fispact2001 - ENEA AFS Cell

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4. Warnings 1. Not all the nuclides provided by MCNPX are included in the EAF2001 decay data library [9] (the missing nuclides are usually neutron-rich nuclides for low Z and neutron-deficient nuclides for high Z). This follows from the fact that residual nuclei are calculated by MCNPX by means of physics models while those included in EAF2001 are based on experimental evaluations. These nuclides are expunged by SP-FISPACT2001 and highlighted in the output of the collapse process (collapx.out). In the cases analysed they represent 20%-45% of the total number of nuclides and about 1%-25% of the total residual nuclei production. The greatest number of expunged nuclei are obtained for high energy fission on U 238 where many exotic nuclei are produced. Their contribution seems negligible in a first approximation for spallation processes (6%) but, depending on their decay modes, the activity could be more considerable. Since most of these data are publicly available (see [10]), the nuclide inventory in the EAF2001 decay data library could be increased for this purpose. 2. The production of gas nuclides (H 1 , H 2 , H 3 , He 3 , He 4 ) as a consequence of the nuclear interactions above 20MeV has not yet been implemented. 3. The production of daughter nuclides is proportional to the number of atoms of the parent nuclides (see equation (1) in APPENDIX B). Therefore, the decrease with time of the amount of atoms of the initial material causes a decrease in the production of residual nuclei above 20MeV (see the factor Nj(t)/Nj(0) in APPENDIX B). This should be treated as a burn-up effect but it is usually negligible even for long period of irradiation (Nj(t)/Nj(0) decreases by 0.5% in value for typical cases). The user should check and evaluate the effect for the problem under investigation. 4. Even if the material irradiated in MCNPX is composed of more than one isotope only a single isotope must be chosen in SP-FISPACT2001. This does not affect the residual nuclei production, but the decrease in time of the number of atoms of the initial material turns out to be approximated. As mentioned above, this effect is usually negligible (although in principle all the quantities involving the weight of the material irradiated, such as the DOSE RATE, are thus modified). 5. The pseudo cross-sections created in the file COLLAPX must have a value higher than ~10 -20 (see equation (3), APPENDIX B). Lower values (they should not occur with usual physical problems) give rise to errors due to the fact that the arrays are treated as single precision variables. The user is responsible for checking such values. 6. The activity and particle emission (�, �, �) due to the formation of the residual nuclei described by the physics models (such as residual deexcitation processes) is not included in the treatment; the duration in time of the whole nuclear interaction process has been neglected. 7. In the FISPACT main output the values „FLUX‟ and „FLUENCE‟ refer to the values under 20MeV provided by the user. The values „NUMBER OF FISSION‟ and „HEAT PRODUCTION‟ and the particle emissions do not include fissions over 20MeV. 8. All the code words concerning uncertainties (such as UNCERTAINTY) are not available. Also pathway analysis is not a possible option. 9. The highest value of the energy used by FISPACT is 19.64 MeV and the lowest neutron energy value considered in HTAPE3X is 20MeV. Thus the bin 19.64-20MeV is neglected. 14
10. Benchmarks of MCNPX (physics models at 1GeV) suggest to consider roughly the degree of accuracy in predicting residual nuclei as a factor of 2 for spallation events and as a factor of 10 for fission events [6]. This is a general trend, individual isotopes can be mispredicted even by 2 orders of magnitude. In the range ~20-100MeV the accuracy of the models is generally worse than above ~100 MeV. 11. FISPACT can treat only trace amounts of actinides that are able to fission because selfshielding and burn-up effects are not included (see [4], p.11) 15
Page 1: SP-FISPACT2001 A COMPUTER CODE FOR
Page 5: TABLE OF CONTENTS 1. Introduction .
Page 8 and 9: protons) in a 3-D geometry. Neutron
Page 10 and 11: output (with flux
Page 12 and 13: 3. Input the main nuclide which com
Page 16 and 17: 5. Conclusions SP-FISPACT2001 makes
Page 18 and 19: c Initialisation NUCLF=0 NUCLH=0 NM
Page 20 and 21: HISOT(IZM(I),INM(I))=HISOT(IZM(I),I
Page 22 and 23: The differences between the two fma
Page 24 and 25: COMMON /SPAL3/ NP2(15000),ND2(15000
Page 26 and 27: dNi ( t) �24 � �� ij N j (
Page 28: References [1] Laurie S. Waters, Ed

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