Prediction of the Total Decay Heat from Fast Neutron Fission of 235U and 239Pu

The analytical prediction of the decay heat results from the fast neutron fission of actinides was initiated under a project, 10-MAT1134-3, funded by king Abdulaziz City of Science and Technology (KASCT), Long-Term Comprehensive National Plan for Science, Technology and Innovations, managed by a team from King Abdulaziz University (KAU), Saudi Arabia, and supervised by Argonne National Laboratory (ANL) has collaborated with KAU's team to assist in the computational analysis. In this paper, the numerical solution of coupled linear differential equations that describe the decays and buildups of minor fission product actinides, MFA, has been used to predict the total decay heat and its components from the fast neutron fission of U and Pu. The reliability of the present approach is illustrated via systematic comparisons with the measurements reported by the University of Tokyo, in YAYOI reactor. Keywords—Decay heat, fast neutron fission, and Numerical Solution of Linear Differential Equations. I. INTRODUTION CCURATE prediction of total decay heat and its time dependence is required in studies of loss of coolant accidents, and also in connection with the transportation and storage of spent fuel. At short cooling times, the main component is due to the decay of the fission products and also to U and Np decay, which are important for cooling times up to 15 days. Many of the neutron-rich nuclei in question have also considerable current spectroscopic and astrophysical importance. In nuclear structure, a key issue of interest is the modification of shell structure in nuclides with large neutron excesses. In astrophysics, the challenge is to more clearly define the rate and trajectory of r-process nucleosynthesis in order to better delineate possible sites for this type of element production. Whatever the motivation, improved β-decay spectroscopy of neutron-rich fission fragments is needed. During the last 20 years enormous progress has been made in nuclear spectroscopy, especially in improving the sensitivity for “in-beam” gamma ray spectroscopy [1, 2]. The S. S. Nafee is with, King Abdulaziz University, Physics Department, Faculty of Science, Jeddah 21589, Saudi Arabia (Phone: +966565813180; fax: +966565812180;snafee@kau.edu.sa). He is also, with Alexandria University, Faculty of Science, Alexandria 21121, Egypt (sherif.nafee@sci.alex.edu.eg). S. A. Shaheen is King Abdulaziz University, Physics Department, Faculty of Science, Jeddah 21589, Saudi Arabia (sshaheen@kau.edu.sa) . A. K. Al-Ramady is with King Abdulaziz University, Deanship of Graduate Studies, Jeddah 21589, Saudi Arabia (aalramady@kau.edu.sa). production cross-sections required for detailed spectroscopy have fallen from millibarns to tens of nanobarns, an improvement of five orders of magnitude. With a few notable exceptions these advances have not been applied to β-decay spectroscopy studies. Some aspects of the new large gamma arrays, like Gammasphere, are not required for decay spectroscopy, (for example their very high angular granularity used for Doppler correction). Other aspects, like their high coincidence efficiency, and capability for total energy calorimetry, can be critical in resolving complicated decay patterns for nuclei far from the line of stability whose decay Q-values are significantly large. Combining data from modern multi-detector germanium arrays with high quality calorimetry from Total Absorption Gamma Spectrometers (TAGS) has already proven (in a few interesting cases) [3, 4] to be very powerful and complimentary in revealing both the gross decay features, like the total decay strength functions, and the details of the daughter nuclear structure. It is this path of research it is proposed to pursue at Argonne, using a TAG spectrometer for calorimetry. The experimental data are particularly scarce for short cooling times (less than 3000 s) where the decay of neutronrich FP dominates owing to the large β-decay Q values (~410 MeV) and the fact that β-decay feeding intensities into the high-energy region of the daughter nuclei are frequently missing (“pandemonium effect”) [5]. This is the case for almost half of all known FP involved in the fission process (~1200 nuclides). These missing intensities account for about 20-40 % loss in energy releases. In order to compensate for such a loss, due to paucity of experimental data, a gross betadecay modeling is frequently used in the decay data libraries [6, 7], and therefore these libraries become “contaminated” by theoretical predictions rather than been on a firm experimental footing. Attempts made in past to resolve data deficiencies using high-resolution γ−ray spectroscopy techniques were only partly successful, due to the low efficiency and sensitivity of the detector systems used in these measurements and the lack of pure, and intense sources. In the present work, following our approach that has been successfully used before in predicting the decay heat from Cm isotopes in the mixed oxide nuclear fuel, MOX, we continue reporting the data obtained in our project from the fast fission of U and Pu [8]. Prediction of the Total Decay Heat from Fast Neutron Fission of U and Pu Sherif. S. Nafee, Ameer. K. Al-Ramady, and Salem. A. Shaheen A World Academy of Science, Engineering and Technology International Journal of Physical and Mathematical Sciences Vol:6, No:11, 2012 1574 International Scholarly and Scientific Research & Innovation 6(11) 2012 ISNI:0000000091950263 O pe n Sc ie nc e In de x, P hy si ca l a nd M at he m at ic al S ci en ce s V ol :6 , N o: 11 , 2 01 2 pu bl ic at io ns . w as et . o rg /5 82 9/ pd f II. METHODOLOGY The algorithm of the present approach is divided into three steps. In the first step, the building the branching ratio, the decay constant and the independent fission yield matrices for the isotopes under consideration from the ENDF/B-VII.I database by applying the matrix form as follow;