COMPUTER CODES IN NUCLEAR ENGINEERING

Nuclear data refer to all the physical constants characterising nuclear fuel behaviour and that of the other materials under the effect of radiation so as to assess their contribution to the nuclear reaction. Likewise, computer programs and codes are the mathematical tools used for solving these problems through computer simulation of the operation of an installation or piece of equipment, which offers great potential for plant design, technical and economic optimisation and safety studies. More systematic analyses can be conducted and there is often no further need to undertake expensive trials using large-scale equipment.

However, these concerns are leading to increasingly complex computer programs which require more and more powerful computers. On the other hand, in order to explore these possibilities computer codes must be adjusted, tested and, above all, homogeneous approaches must be found to ensure mutual compatibility of the codes and to maintain exchange opportunities among scientists. This is the purpose of the co-operation undertaken in large benchmark centres. The concept of a scientific data centre was at its origin very similar to that of a specialised library: it should collect and compile computer codes and numerical data, carry out limited verification and supply the information selectively in response to user requests. Furthermore, data centres play an important role in coordinating national efforts and in helping to avoid unnecessary duplication of work.

Computer codes are distributed internationally by a network of three data centres: Energy, Science and Technology Software Centre (Oak Ridge, USA); Radiation Shielding Information Centre (Oak Ridge, USA); NEA Data Bank (serves OECD countries except US and Canada, also serves non-OECD countries on behalf of IAEA). Countries providing copies of nuclear energy software prefer to retain control of its distribution: the above three centres provide users with the assurance of a well-defined version of each code and originators with the assurance that their wishes will be respected.

The OECD Nuclear Energy Agency Data Bank (NEADB) provides, in collaboration with the code centres in the United States, a service to its Member Countries, offering computer programs covering the full chain of computation needed for performance prediction and assessment of nuclear facilities. It also has service arrangements with IAEA. The Data Bank serves about 430 accredited institutions in the participating countries. The current collection of tested codes amounts to about 1500 packages, which is refreshed by the addition of about 100 new codes -or new version- each year; they fall into several categories of particular interest to nuclear engineers and physicists. Over the last few years, between 1500 and 1700 code requests have been answered each year, by sending both the source code and ample documentation. A recent development is the availability of versions of many of the most frequently requested codes for mainframe computers, adapted for personal computers. There exist several electronic ways to access the NEA Data Bank Services: by e-mail, by anonymous ftp, by telnet and by WWW.