1. NAME AND TITLE

SYVAC-D/2: Code System For Risk Assessment From Underground Radioactive Waste Disposal In the United Kingdom.
 

2. CONTRIBUTORS

UK Department of Environment (DOE), London, England through the NEA Data Bank, Issy-les-Moulineaux, France.
 

3. CODING LANGUAGE AND COMPUTER

Fortran 77; Dec Vax (C00690D0VAX00).
 

4. NATURE OF PROBLEM SOLVED

The SYVAC D/2 program simulates the ground water mediated movement of radionuclides from underground facilities for the disposal of low and intermediate level wastes to the accessible environment, and provides an estimate of the subsequent radiological risk to man. The simulated timescales are usually within the range 1.0E+03 to 1.0E+07 years. SYVAC is capable of modelling both shallow disposal facilities (located in argillaceous media and overlaying an aquifer) and deep disposal facilities (in a saturated environment). The software was developed for use within the UK Department of the Environment (DOE) Radioactive Waste Management Programme, as one tool in the DOE Assessment Methodology.

The acronym SYVAC (System Variability Analysis Code for deep and shallow burial of radioactive waste) comes from the name of an assessment code originally obtained from the Atomic Energy of Canada (AECL) in 1982, which was found to be inappropriate for geological conditions in the UK. The development of the previous version, SYVAC A/C, was undertaken by the following private installations under UK Department of the Environment (DOE) contracts: Atkins Research & Development, Epsom, Surrey, England; Associated Nuclear Services, Epsom, Surrey, England; CAP Scientific, London, England; Electrowatt Engineering Services, Horsham, West Sussex, England; and Scicon Limited, Wavendon, Milton Kenes, England.
 

5. METHOD OF SOLUTION

A simplistic description of the physical model simulated by SYVAC is given below. Low and intermediate level radioactive waste is stored in a repository or "vault". For shallow disposals, the "vault" is an engineered trench at depths of 20-30m; for deep disposals, it is a modified mine or purpose-built structure at depths of 150-300m. Over a long period of time, groundwater penetrates the vault structure; and the canisters containing the waste corrode. The radionuclides migrate in the groundwater flow through the vault structure into the ground - the "geosphere" - surrounding the vault. The processes are represented in the code by a set of modules known as the Vault submodel. The radionuclides from the vault migrate through the geosphere to the surface and into the "biosphere" where they become accessible to man, through drinking water, crops, etc. The migration takes place through the groundwater flows in aquifer structure for both the shallow and deep disposal sites. For the shallow sites, the radionuclides can also migrate directly to the surface; and, where appropriate, this latter process is simulated in SYVAC as part of the Vault submodel. The process of migration through the Geosphere (with the exception of the shallow site direct path) is represented in the code by the set of modules known as the Geosphere submodel.

The Vault and Geosphere submodels are principally concerned with the numerical calculations needed to simulate radionuclide migration from the vault through the geosphere into the biosphere. The final output from the Geosphere submodel is in the form of a radionuclide flux over time. To estimate the subsequent radiological risk to man from this flux, the SYVAC program applies a series of dose conversion factors (these are different for each nuclide). The dose rate is calculated by multiplying the nuclide flux by the dose conversion factors. These dose conversion factors are supplied to SYVAC as input data, in the form of biosphere data files. The files are currently produced from a structurally separate biosphere model called ECOS.
 

6. RESTRICTIONS OR LIMITATIONS

It is not suitable for considering high level wastes as it does not allow for the heat produced by such wastes. See the documentation for details on restrictions within the submodels.
 

7. TYPICAL RUNNING TIME

The running time for SYVAC depends on the number of runs, the number of nuclides in each run, and the number of nuclides in each chain. The system was implemented by NEADB on a VAX 8810 computer. The sample case for LAND 2 required 35 seconds, and the case for LAND 3 required 127 seconds of execution time.
 

8. COMPUTER HARDWARE REQUIREMENTS

NEA-DB executed the test cases on a VAX 8810 computer, and the code has also been run on DEC Micro VAX computers. It was not tested at RSICC. A printer is needed for producing physical output. SYVAC allows a case study to be restarted to increase the number of runs. This is necessary to test for convergence of results and also to work within the limitations on storage, by deleting unwanted files. Typically 18,000 blocks are needed for 600 simulation runs. A system clock is needed to continue case studies in this way. A clock is also needed for the analysis of CPU usage that is carried out by the program.
 

9. COMPUTER SOFTWARE REQUIREMENTS

SYVAC runs under VMS version 4.3 and uses the VAX standard mathematical library but also requires the NAG (Numerical Algorithms Group) library or an equivalent for certain numerical routines not provided in standard FORTRAN libraries. The changes required to run SYVAC on another machine would be any that resulted from differences in the implementation of FORTRAN 77 on the two systems. Converting SYVAC to run in another programming language would be a major undertaking and is unlikely to be effective. It would be preferable to start with the design documents, if it was intended to modify SYVAC in this manner.
 

10. REFERENCES

Distributed in electronic (PDF) format in the DOC subdirectory on the CD:

S. Carr and G.Rowling, "Documentation Introduction. SYVAC-D/2 Overview, Volume 1" (April 1988).

S. Carr, M. Fisher and G. Rowling, "Documentation Index. SYVAC-D/2 Overview, Volume 2" (April 1988).

S. Carr, "Glossary. SYVAC-D/2 Overview, Volume 3" (April 1988).

S. Carr, G. Rowling and F. Taylor, "System Overview/SYVAC-D/2 Overview, Volume 4" (April 1988).

S. Carr and G. Rowling, "Input and Execution. SYVAC-D/2 User Guide, Volume 1" (February 1988).

J. Falconer and G. Rowling, "Output and Error Messages. SYVAC-D/2 User Guide, Volume 2" (February 1988).

S. Carr, G. Rowling and F. Taylor, "Installation Instructions. SYVAC-D/2 User Guide, Volume 3" (February 1988).

J. Falconer, G. Rowling and F. Taylor, "Analysis Programs. SYVAC-D/2 User Guide, Volume 4" (February 1988).

S. Carr, G. Rowling and F. Taylor, "Program Structure. SYVAC-D/2 Programmers' Guide, Volume 1" (February 1988).

J. Falconer, and G. Rowling, "File Descriptions. SYVAC-D/2 Programmers' Guide, Volume 2" (February 1988).

S. Carr, J. Falconer and G. Rowling, "Data Transfer. SYVAC-D/2 Programmers' Guide, Volume 3" (February 1988).

J. Falconer, G. Rowling and P. Saul, "Data Dictionary. SYVAC-D/2 Programmers' Guide, Volume 4" (February 1988).

S. Carr, J. Falconer and G. Rowling, "Executive Modules. SYVAC-D/2 Programmers' Guide, Volume 5" (February 1988).

S. Carr, J. Falconer and G. Rowling, "Vault Modules. SYVAC-D/2 Programmers' Guide, Volume 6" (February 1988).

S. Carr, J. Falconer and G. Rowling, "Geosphere Modules. SYVAC-D/2 Programmers' Guide, Volume 7" (February 1988).

A. Saltelli, E. Sartori, T.H. Andres, B.W. Goodwin and S.G. Carlyle, "PSACOIN Level 0 Intercomparison An International Code Intercomparison Exercise on a Hypothetical Safety Assessment Case Study for Radioactive Waste Disposal Systems," (OECD/NEA) (November 1987).
 

11. CONTENTS OF CODE PACKAGE

The package is transmitted on a CD in which the source, command files, test cases and electronic documentation (PDF) are written in DOS self-extracting, compressed files.
 

12. DATE OF ABSTRACT

April 2000.
 

KEYWORDS: HYDRODYNAMICS; RISK ASSESSMENT