The US ENDF/B-VI nuclear data library was released to the international community in the early 1990s (Dunford, 1992). An initial point of note is the development over many years of an internationally-accepted data format (ENDF-6), including the potential to accommodate uncertainties in the form of covariance matrices. Specific aims included the production of a self-consistent set of evaluated neutron cross sections, updated decay-data files (extracted from the ENSDF files, and supplemented with new measurements and theory), and the addition of charged — particle and high-energy reaction files. Many of the neutron-reaction cross sections were completely re-evaluated, including U(n, f), Pu(n, f) and the resonance

parameters for 235,238U and 239,241Pu. Adjustments were also made to the neutron-

capture cross sections of 151,153Eu, 165Ho and 197Au (latter as standard). Both the decay-data and fission-yield files of ENDF/B-VI have been supplemented with the beta and gamma energies and Pn values of Rudstam et al (1990 and 1993) and the chain yields derived by Wahl (1988). This resulting data base was tested in a series of decay-heat calculations and shown to reproduce the experimental results in a satisfactory manner (Rudstam and England, 1990). ENDF/B-VI gamma-ray data for the short-lived fission products were also augmented by spectra calculated from the gross theory for beta-strength functions to form mixed files of discrete and theoretical decay data (Katakura and England, 1991).

The Joint Evaluated File (JEF) is a collaborative project between member states of the NEA-OECD to produce a nuclear data library for industrial applications and research (Nordborg et al, 1992; Nordborg and Salvatores, 1994). Various decay-data files have been assembled by staff at the NEA Data Bank from other sources (particularly ENSDF, UKPADD-2 (Nichols, 1993) and UKHEDD-2 (Nichols, 1991)). This JEF-2.2 library consists of a general purpose file, radioactive decay — data files and fission-yield files. A number of adjustments were made to the JEF-2.2 decay-data starter files:

(a) mean beta and gamma energies of 109 short-lived fission products measured by Rudstam et al (1990) were added to the files;

(b) theoretical data were based on the p-n QRPA model of Hirsch et al (1992): 16 half-lives, 101 mean beta and gamma energies, and 32 Pn values.

The contents of the JEF-2.2 files have been summarised in hardcopy, and represent a definitive data set for nuclear applications (NEA-OECD, 1994 and 2000).

Efforts are underway to amalgamate the NEA fission (JEF) and fusion (EAF) data libraries, and to improve and expand the contents of the resulting files (Finck et al, 1997; Jacqmin et al, 2001; Bersillon et al, 2001). A Joint Evaluated Fission and Fusion project has been formulated to combine JEF and EAF database activities. Other sources of updated decay-data for JEFF-3 include NUBASE, ENSDF, UKPADD and UKHEDD. Various studies are also underway or completed to improve the contents of specific decay data files judged to be inadequate for fission and fusion reactor applications (e. g., Backhouse and Nichols, 1998; Nichols et al, 1999a and 1999b).

Other libraries have been developed for nuclear power applications that contain decay-data files. Staff at the Chinese Nuclear Data Centre, have assembled files of basic nuclear data and model parameters (Su Zongdi et al, 1994 and 1997). This nuclear parameter library (CENPL) contains atomic masses and constants for ground states, nuclear level properties and gamma-ray data extracted from ENSDF.

The JNDC-FP (Japanese Nuclear Data Committee — Fission Product) library contains decay and fission yield data for 1087 unstable and 142 stable fission products, and neutron cross-section data for 166 nuclides (Tasaka et al, 1990; Katakura et al, 2001). Recommended decay data include half-lives, branching ratios, and total beta and gamma-ray energies released per decay of every radionuclide. Significant emphasis has been placed on producing a comprehensive set of fission-product decay data, with the introduction of theoretical half-lives and mean energies for over 500 radionuclides with no known discrete decay data.

The contents of the various national and international decay-data files are difficult to summarise with respect to their technical origins (i. e., discrete decay-data or mean beta-decay measurements; file supplemented with calculated decay data from gross theory of в decay, microscopic analyses or p-n QRPA). Table 14 focuses on the fission-product nuclides to be found in the US ENDF/B-VI, JENDL-FP and JEF-2.2 libraries.

“Estimated decay energies” refers to a combination of data that originate from Rudstam et al (1990), Hirsch et al (1992) and others. The inclusion of estimated and theoretical decay data is considerably more extensive in US ENDF/B-VI and JENDL-FP than in JEF-2.2 (latter includes more recommended data based on direct measurements (with the concomitant problem of pandemonium (Hardy et al, 1977)).