Point nuclear data

N. Accuracy of MONK Calculations Using Point Nuclear Data. ... 

Database/3 and the other data used in this paper consist entirely of zero-point-exclusive data, which allows for direct comparisons with calculated Bom-Oppenheimer potential energy surfaces, i.e., the sum of the electronic energies and nuclear repulsion. Although the G3X and CBS families of methods have standard geometry and frequency calculations associated with them, in this paper only the potential energy surfaces are required to compare with Database/3. The geometries used are optimized QCISD/MG3 geometries for all calculations in this paper. 

In the CANDU heavy-water reactor the dominant source of tritium is the deuterium activation reaction of Eq. (8.53). The data given in Prob. 3.3 for the Douglas Point Nuclear Power Station provide a basis for estimating the rate of production of tritium in the heavy-water moderator and coolant ... 

In the version of MONK which uses point data, the basic source of data is the UK nuclear data library 4, 5). In the data library, cross sections and energies are given in pairs such that linear interpK>lation on a log-log scale introduces acceptably small errors. MONK determines the interval in which the incident neutron energy lies and calculates the microscopic cross section from Eq. (2) ... 

Independent core calculations performed at the Nuclear Engineering Institute (lEN, Rio de Janeiro) pointed out to discrepancies -with respect to calculations done at lEAv- which were mainly attributed to the differences in nuclear data sets. 

An extensive survey was carried out to identify those uncertainties in nuclear data which were expected to be of significance from the point of view of fast reactor core design. This work was presented in papers by Greebler et al. 8-10) in this study, the discussion is restricted to the effects of only those changes in nuclear parameters which appear to be of greatest importance, and for which strong experimental evidence exists. 

The principal feature of MONK 6 is tire incorporation of a new point form nuclear data base. The FOND system of collision processing in MONK S has been replaced by the DICE mc ular coding package, which achieves enhanced accuracy via a histogram representation of all primary reaction cross sections using a fixed mesh. DICE is linked, via the program MOULD, with the UKNDF library, which contains up-to-date evaluations of differential cross sections. 

As with the nuclear data, the radioactive sources used for calibration must be suitable for their purpose. For energy and peak width calibration, it is sufficient that the energies of the gamma-rays (or X-rays) it emits be known to a satisfactory degree of accuracy but the source strength need not be known. For efficiency calibration, it is essential that nuclides are used for which the gamma-ray emission probabilities are known accurately and that a source of known activity is used. Whenever possible, sources that have been certified as to their radioactive content should be used. I will discuss traceability in a later chapter but it is worthwhile remarking at this point that the value of a calibration is much reduced unless the activities of the sources used can be traced back to standards with international credibility. 

For this section, I have omitted the older publications mentioned in the first edition. In view of the recent developments in the publication of nuclear data, there seems little point in referring to sources of data that are now out-of-date. At the end of this section are two relatively recent sources that I recommended in the first edition. I include them here only to point out that they can no longer be relied upon. 

Longworth, G. (Ed.), (1998). The Radiochemical Manual, AEA Technology pic, HMSO, London, UK. Incorporates the NPL RSA(EXT)53 data and other data taken from the UKHEDD database. Includes the TECDOC-619 nuclides but does not incorporate the TECDOC-619 data. Superseded by DDEP and no longer recommended as a source of nuclear data. That does not diminish the value of this manual from a general informative point of view. 

The melting points, optical rotations, and uv spectral data for selected prostanoids are provided in Table 1. Additional physical properties for the primary PGs have been summarized in the Hterature and the physical methods have been reviewed (47). The molecular conformations of PGE2 and PGA have been determined in the soHd state by x-ray diffraction, and special H and nuclear magnetic resonance (nmr) spectral studies of several PGs have been reported (11,48—53). Mass spectral data have also been compiled (54) (see Mass spectrometry Spectroscopy). 

Kalbitzer and his colleagues used the Si (p, y) resonant nuclear reaction to profile the range distribution of 10-MeV Si implanted into Ge. Figure 8 shows their experimental results (data points), along with theoretical predictions (curves) of what is expected. 

The neutron dose to graphite due to irradiation is commonly reported as a time integrated flux of neutrons per unit area (or fluence) referenced to a particular neutron energy. Neutron energies greater that 50 keV, 0.1 MeV, 0.18 MeV, and 1 MeV were adopted in the past and can be readily foimd in the literature. In the U.K., irradiation data are frequently reported in fluences referenced to a standard flux spectrum at a particular point in the DIDO reactor, for which the displacement rate was measured by the nickel activation [ Ni(np) t o] reaction [equivalent DIDO nickel (EDN)]. Early on, neutron irradiation doses to the graphite moderator were reported in terms of the bum-up (energy extracted) from imit mass of the adjacent nuclear fuel, i.e., MW days per adjacent tonne of fuel, or MWd/Ate. 

Loss of offsite power at nuclear power plants is addressed in EPRI NP-2301, 1982 giving data on the frequency of offsite power loss and subsequent recoveiy at nuclear power plants. Data analysis includes point estimate frequency with confidence limits, assuming a constant rate of occurrence. Recovery time is analyzed with a lognormal distribution for the time to recover. 

Table 4.3-3 from Joksimovich et al. (1983) presents the data sources used in preparing the Big Rock Point and Zion nuclear power plant PSAs. It is seen that both PSAs used plant records extensively. 

If the data quality was acceptable, they were then evaluated for their relevance and fit to the CCPS Taxonomy. The data in the SAIC data base were fitted to taxonomy levels that best correlated with nuclear plant equipment and operational environments. CPI resources were reread thoroughly to understand the equipment subtypes, operating modes, and process severities represented by the data points and to identify as many relevant taxonomy levels as possible. SAIC data analysts made preliminary judgments on the applicability of data points to taxonomy levels and on the quality of the data. The majority of the data applied to high taxonomy levels (x.x) and a smaller amount was applicable to lower levels (x.x.x.x). The data were assigned to the lowest level possible. 

Terms up to order 1/c are normally sufficient for explaining experimental data. There is one exception, however, namely the interaction of the nuclear quadrupole moment with the electric field gradient, which is of order 1/c. Although nuclei often are modelled as point charges in quantum chemistry, they do in fact have a finite size. The internal structure of the nucleus leads to a quadrupole moment for nuclei with spin larger than 1/2 (the dipole and octopole moments vanish by symmetry). As discussed in section 10.1.1, this leads to an interaction term which is the product of the quadrupole moment with the field gradient (F = VF) created by the electron distribution. 

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