NEA-1023 SYVAC.
SYVAC, Risk Assessment from Underground Radioactive Waste Disposal in UK
NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROGRAM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, UNUSUAL FEATURES OF THE PROGRAM, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHORS, MATERIAL, CATEGORIES
[ top ]
1. NAME OR DESIGNATION OF PROGRAM: SYVAC.
The simulation program SYVAC A/C (System Variability Analysis Code for deep (A) and shallow (C) burial of radioactive waste) has been developed by the UK Department of the Environment (DOE). The acronym SYVAC comes from the name of an assessment code originally obtained from Atomic Energy of Canada (AECL) in 1982. (The AECL code was found to be inappropriate for geological conditions in the UK).
The simulation program SYVAC A/C (System Variability Analysis Code for deep (A) and shallow (C) burial of radioactive waste) has been developed by the UK Department of the Environment (DOE). The acronym SYVAC comes from the name of an assessment code originally obtained from Atomic Energy of Canada (AECL) in 1982. (The AECL code was found to be inappropriate for geological conditions in the UK).
[ top ]
To submit a request, click below on the link of the version you wish to order.
Only liaison officers are authorised to submit online requests. Rules for requesters are
available here.
| Program name | Package id | Status | Status date |
|---|---|---|---|
| SYVAC-D/2 | NEA-1023/04 | Tested | 10-OCT-1991 |
Machines used:
| Package ID | Orig. computer | Test computer |
|---|---|---|
| NEA-1023/04 | DEC VAX 11/780 | DEC VAX 8810 |
[ top ]
3. DESCRIPTION OF PROGRAM OR FUNCTION
The SYVAC 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). It is not suitable for considering high level wastes as it does not allow for the heat produced by such wastes.
SYVAC has been developed for use within the DOE Radioactive Waste Management Programme, as one tool in the DOE Assessment Methodology.
The SYVAC 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). It is not suitable for considering high level wastes as it does not allow for the heat produced by such wastes.
SYVAC has been developed for use within the DOE Radioactive Waste Management Programme, as one tool in the DOE Assessment Methodology.
[ top ]
4. METHOD OF SOLUTION
4.1 The Physical System
-------------------
A simplistic description of the physical 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 20-30mm; for deep disposals 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 noted above for 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 controlled within the program by the Executive, a set of management modules. Generally, the Executive modules are concerned with data handling and data input/output to the submodels. 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, and applies to maximally exposed individuals.
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.
4.2 Probabilistic Parameter Sampling in Syvac
-----------------------------------------
The previous section has briefly described the simulation of radionuclide migration carried out by the Vault and Geosphere submodels. This simulation requires data to describe the physical structure and transport characteristics of the vault and geosphere.
The necessary data is supplied to SYVAC in the form of parameters that represent hydraulic conductivities, diffusion coefficients, porosities etc for the vault and geosphere. Thirteen basic vault parameters are used to model deep disposal sites, and fifteen for shallow disposals. For both types of site, an additional six parameters are needed for each geological layer modelled in the geosphere.
The values of some of the parameters are not precisely known, and will vary over the timescale of the transport to the biosphere. SYVAC allows for this with a probabilistic approach; the parameter values are sampled from distributions chosen to cover the expected range of values that may be encountred during the post-closure phase of a vault. For each parameter, SYVAC allows the user to select one of five distributions: constant, uniform, log uniform, normal and log normal. Usually, for each parameter, the user will select the distribution that best fits the observed parameter values.
The calculation of risk to man requires knowledge of both the dose from a particular run, and the probability of that run.
Clearly, the dose to man calculated for a particular simulation run will depend on the parameter values chosen for that run. The probability of a particular run - i.e. the probability of choosing a particular set of parameter values - also depends on the parameter value chosen, and can be calculated from the parameter distributions selected by the user when setting up the input data.
The probabilistic nature of these calculations means that to obtain statistically valid estimates of risk (etc), SYVAC must be run a large number of times with different parameter values. The user chooses the number of runs when setting up the input data. The user also chooses the type of sampling used to select the parameter values for each run. SYVAC stores the results of each run for later analysis.
Two different sampling methods can be chosen for SYVAC; Random Sampling and Deterministic Generator Sampling. Random Sampling chooses values (randomly) from the entire range of the distribution chosen for each parameter. Deterministic Generator sampling selects one of 11 possible (discrete) sample points for each parameter for a run; the method of sampling is such that all eleven points are chosen in the course of 11 consecutive runs. The eleven points span the range of the distribution chosen for each parameter.
4.3 Run Acceptance Level
--------------------
The calculations performed in the Vault and Geosphere submodels use most of the CPU time needed for a run. Consequently, to avoid unnecessary calculations, the program carries out a screening procedure to eliminate runs (i.e. sets of parameter values) that will produce no dose or are physically unrealistic. After the sampled parameter values have been generated, each SYVAC run is classified as being one of four run acceptance levels. The interpretation of run levels is as follows:
Level 0 : No dose expected within the time of study.
Level 1 : A non-zero dose expected. This is an accepted run. The actual dose of course may turn out to be zero.
Level 2 : Physically unreal data. An infeasible combination of sampled parameters has been selected.
Level 3 : The data is outside the validated range of one of the submodels and there is an expectation of a high dose. Note that the Vault and Geosphere submodel calculations are only performed for accepted (level 1) runs.
To arrive at the classification for a particular run a series of tests (of different levels of severity) is performed. Each test checks whether a sampled parameter value or value calculated from several parameters is within a specified range.
4.4 Executive Control
-----------------
The Executive is the framework that controls the simulation program as a whole, and specifically calls the Vault and Geosphere submodels.
The functions performed by the Executive are:
(i) Input and validation of user defined data.
(ii) Generation of sampled values for data defined by probability distributions.
(iii) Verification and classification of each complete set of sampled data.
(iv) Invocation and control of the submodels which represent the stages of the nuclide transportation process.
(v) Generation of reports and other output.
(vi) Case study control.
4.5 Vault Submodel
--------------
The Vault submodel simulates the release of radionuclides from non heat-producing radioactive waste placed within an engineered vault in either deep or shallow land disposal facilities. The model includes representations of the waste matrix, waste canister, vault liner, the vault backfill material and the region of host rock around the vault disturbed during construction.
This submodel consists of a hydrogeological model, representing the groundwater flow through the different engineered barriers, and a radionuclide migration model. In the hydrogeological model,the different structural features of the vault are represented by a series of compartments. The hydrogeological model uses an electrical resistance analogy to represent flow within each of these compartments.
The migration model includes the processes of solubility-limited or mass-limited leaching of radionuclides from the waste matrix, linear equilibrium sorption of radionuclides onto the barrier materials, radioactive chain decay, dispersion and advection. Migration of radionuclides in groundwaters is predicted using a numerical solution to the transport equation. The leaching of radionuclides from the waste matrix is simulated using a diffusion model and gives the source term for the transport equation. In solving the transport equation, the radionuclide concentration at the vault/geosphere interface is taken to be zero.
4.6 Geosphere Submodel
------------------
The Geosphere submodel is a 1-dimensional model that deals with the migration of radionuclides from the vault to the biosphere through the geosphere. This is through the calculation of a response function for each geosphere layer. The response function describes the output from each geosphere layer at a given time for unit input to the geosphere layer at a start time The convolution of this response function with the time-varying input to the layer gives the total output from the geosphere layer at any time. Up to five distinct layers can be modelled. This submodel includes the effects of linear equilibrium sorption (for porous or fractured media), linear dispersion and chain decay. Up to 8 member chains can be considered. A semi-finite analytical Laplace transform solution technique is used to solve the geosphere partial differential transport equation.
4.7 Biosphere Model - ECOS
----------------------
The biosphere code ECOS calculates the rate of accumulation of committed effective dose equivalent (dose) arising from the flux of radionuclides entering the biosphere. Dose to a maximally exposed individual and collective dose are calculated deterministically.
ECOS is an equilibrium-type compartmental model. The contents of parent and daughter radionuclides at equilibrium in nine activity reservoirs are computed by solving a set of linear simultaneous equations which represent the equilibrium solution of a general differential equation description.
The transfer processes modelled are: percolation and leaching in soils, erosion by wind and water, irrigation, cropping, water phase and sediment phase transport, sedimentation and resuspension in aquatic environments, equilibrium radionuclide sorption and radioactive decay. The dose pathways to man modelled are: drinking water, foodstuffs, external exposure and inhalation. Consumption of aquatic foodstuffs, terrestrial crops and animal products are included. For both drinking water and foodstuff pathways, intakes by man are reduced if the contaminated suply is insufficient to meet total annual needs. The model database includes parameters (e.g. foodchain parameters and sorption coefficients) for 53 radionuclides.
ECOS can be used in two different ways. It can be used in isolation, in order to investigate the relation between dose and biosphere state and in order to identify biosphere scenarios that should be considered in radiological assessment. It can also be used, as part of the overall SYVAC simulation, to produce dose conversion factors that are applied to the activity flux from the geosphere in order to estimate dose to man.
4.8 Nuclide Chemistry
-----------------
Chemical processes are incorporated in the Vault and Geosphere submodels, not in a separate chemistry submodel.
Chemical parameters are obtained from expert judgement, basic research and site data, together with the use of more detailed models to examine scenarios and hence estimate ranges of values. At present, probability distributions are obtained judgementally for most cases.
The detailed models include simulation of the near-field, which provides direct input to SYVAC in the form of limiting solubilities, and coupled geochemical transport programs which are intended to provide verification for SYVAC runs. The principal programs used are based on ion-association models and solve for mass balance and mass action iteratively using a form of the Newton-Raphson technique and/or a continued fraction approach.
4.1 The Physical System
-------------------
A simplistic description of the physical 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 20-30mm; for deep disposals 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 noted above for 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 controlled within the program by the Executive, a set of management modules. Generally, the Executive modules are concerned with data handling and data input/output to the submodels. 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, and applies to maximally exposed individuals.
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.
4.2 Probabilistic Parameter Sampling in Syvac
-----------------------------------------
The previous section has briefly described the simulation of radionuclide migration carried out by the Vault and Geosphere submodels. This simulation requires data to describe the physical structure and transport characteristics of the vault and geosphere.
The necessary data is supplied to SYVAC in the form of parameters that represent hydraulic conductivities, diffusion coefficients, porosities etc for the vault and geosphere. Thirteen basic vault parameters are used to model deep disposal sites, and fifteen for shallow disposals. For both types of site, an additional six parameters are needed for each geological layer modelled in the geosphere.
The values of some of the parameters are not precisely known, and will vary over the timescale of the transport to the biosphere. SYVAC allows for this with a probabilistic approach; the parameter values are sampled from distributions chosen to cover the expected range of values that may be encountred during the post-closure phase of a vault. For each parameter, SYVAC allows the user to select one of five distributions: constant, uniform, log uniform, normal and log normal. Usually, for each parameter, the user will select the distribution that best fits the observed parameter values.
The calculation of risk to man requires knowledge of both the dose from a particular run, and the probability of that run.
Clearly, the dose to man calculated for a particular simulation run will depend on the parameter values chosen for that run. The probability of a particular run - i.e. the probability of choosing a particular set of parameter values - also depends on the parameter value chosen, and can be calculated from the parameter distributions selected by the user when setting up the input data.
The probabilistic nature of these calculations means that to obtain statistically valid estimates of risk (etc), SYVAC must be run a large number of times with different parameter values. The user chooses the number of runs when setting up the input data. The user also chooses the type of sampling used to select the parameter values for each run. SYVAC stores the results of each run for later analysis.
Two different sampling methods can be chosen for SYVAC; Random Sampling and Deterministic Generator Sampling. Random Sampling chooses values (randomly) from the entire range of the distribution chosen for each parameter. Deterministic Generator sampling selects one of 11 possible (discrete) sample points for each parameter for a run; the method of sampling is such that all eleven points are chosen in the course of 11 consecutive runs. The eleven points span the range of the distribution chosen for each parameter.
4.3 Run Acceptance Level
--------------------
The calculations performed in the Vault and Geosphere submodels use most of the CPU time needed for a run. Consequently, to avoid unnecessary calculations, the program carries out a screening procedure to eliminate runs (i.e. sets of parameter values) that will produce no dose or are physically unrealistic. After the sampled parameter values have been generated, each SYVAC run is classified as being one of four run acceptance levels. The interpretation of run levels is as follows:
Level 0 : No dose expected within the time of study.
Level 1 : A non-zero dose expected. This is an accepted run. The actual dose of course may turn out to be zero.
Level 2 : Physically unreal data. An infeasible combination of sampled parameters has been selected.
Level 3 : The data is outside the validated range of one of the submodels and there is an expectation of a high dose. Note that the Vault and Geosphere submodel calculations are only performed for accepted (level 1) runs.
To arrive at the classification for a particular run a series of tests (of different levels of severity) is performed. Each test checks whether a sampled parameter value or value calculated from several parameters is within a specified range.
4.4 Executive Control
-----------------
The Executive is the framework that controls the simulation program as a whole, and specifically calls the Vault and Geosphere submodels.
The functions performed by the Executive are:
(i) Input and validation of user defined data.
(ii) Generation of sampled values for data defined by probability distributions.
(iii) Verification and classification of each complete set of sampled data.
(iv) Invocation and control of the submodels which represent the stages of the nuclide transportation process.
(v) Generation of reports and other output.
(vi) Case study control.
4.5 Vault Submodel
--------------
The Vault submodel simulates the release of radionuclides from non heat-producing radioactive waste placed within an engineered vault in either deep or shallow land disposal facilities. The model includes representations of the waste matrix, waste canister, vault liner, the vault backfill material and the region of host rock around the vault disturbed during construction.
This submodel consists of a hydrogeological model, representing the groundwater flow through the different engineered barriers, and a radionuclide migration model. In the hydrogeological model,the different structural features of the vault are represented by a series of compartments. The hydrogeological model uses an electrical resistance analogy to represent flow within each of these compartments.
The migration model includes the processes of solubility-limited or mass-limited leaching of radionuclides from the waste matrix, linear equilibrium sorption of radionuclides onto the barrier materials, radioactive chain decay, dispersion and advection. Migration of radionuclides in groundwaters is predicted using a numerical solution to the transport equation. The leaching of radionuclides from the waste matrix is simulated using a diffusion model and gives the source term for the transport equation. In solving the transport equation, the radionuclide concentration at the vault/geosphere interface is taken to be zero.
4.6 Geosphere Submodel
------------------
The Geosphere submodel is a 1-dimensional model that deals with the migration of radionuclides from the vault to the biosphere through the geosphere. This is through the calculation of a response function for each geosphere layer. The response function describes the output from each geosphere layer at a given time for unit input to the geosphere layer at a start time The convolution of this response function with the time-varying input to the layer gives the total output from the geosphere layer at any time. Up to five distinct layers can be modelled. This submodel includes the effects of linear equilibrium sorption (for porous or fractured media), linear dispersion and chain decay. Up to 8 member chains can be considered. A semi-finite analytical Laplace transform solution technique is used to solve the geosphere partial differential transport equation.
4.7 Biosphere Model - ECOS
----------------------
The biosphere code ECOS calculates the rate of accumulation of committed effective dose equivalent (dose) arising from the flux of radionuclides entering the biosphere. Dose to a maximally exposed individual and collective dose are calculated deterministically.
ECOS is an equilibrium-type compartmental model. The contents of parent and daughter radionuclides at equilibrium in nine activity reservoirs are computed by solving a set of linear simultaneous equations which represent the equilibrium solution of a general differential equation description.
The transfer processes modelled are: percolation and leaching in soils, erosion by wind and water, irrigation, cropping, water phase and sediment phase transport, sedimentation and resuspension in aquatic environments, equilibrium radionuclide sorption and radioactive decay. The dose pathways to man modelled are: drinking water, foodstuffs, external exposure and inhalation. Consumption of aquatic foodstuffs, terrestrial crops and animal products are included. For both drinking water and foodstuff pathways, intakes by man are reduced if the contaminated suply is insufficient to meet total annual needs. The model database includes parameters (e.g. foodchain parameters and sorption coefficients) for 53 radionuclides.
ECOS can be used in two different ways. It can be used in isolation, in order to investigate the relation between dose and biosphere state and in order to identify biosphere scenarios that should be considered in radiological assessment. It can also be used, as part of the overall SYVAC simulation, to produce dose conversion factors that are applied to the activity flux from the geosphere in order to estimate dose to man.
4.8 Nuclide Chemistry
-----------------
Chemical processes are incorporated in the Vault and Geosphere submodels, not in a separate chemistry submodel.
Chemical parameters are obtained from expert judgement, basic research and site data, together with the use of more detailed models to examine scenarios and hence estimate ranges of values. At present, probability distributions are obtained judgementally for most cases.
The detailed models include simulation of the near-field, which provides direct input to SYVAC in the form of limiting solubilities, and coupled geochemical transport programs which are intended to provide verification for SYVAC runs. The principal programs used are based on ion-association models and solve for mass balance and mass action iteratively using a form of the Newton-Raphson technique and/or a continued fraction approach.
[ top ]
5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM
5.1 Restrictions in the Vault Submodel
----------------------------------
(a) The vault submodel allows 5 "boxes" for the internal construction of the vault and 2 barriers (liner and clay). These cannot be changed by the user.
(b) The model includes representations of 2-dimensional diffusion, and 1-dimensional advection for shallow sites/2-dimensional advection for deep sites. The flow is approximated by Darcy's Law.
(c) Time invariant chemistry; elemental (not isotopic) solubilities; diffuse leaching; nuclide independent retardation. For the case of shallow land disposal, retardation in the damaged region around the Vault structure is incorporated for the direct pathway to the biosphere but not for the pathway through the biosphere.
(d) The equations for flow and transport are uncoupled. solubility, leaching, sorption, diffusion and permeability are all time independent.
(e) There is no allowance for man made or natural (e.g.) tree roots) intrusion into the Vault.
(f) The Vault structure is below the water table (saturated) after a certain period.
(g) There is no interaction between adjacent Vault structures if these were present.
(h) There are a number of limitations on number of canisters, nuclides per chain, etc built into the program.
5.2 Restrictions in the Geosphere Submodel
--------------------------------------
(a) The Geosphere submodel contains stated limitations on the parameter values. The range of allowed values corresponds to physically admissible values for the parameters.
(b) The timesteps in the model are of fixed duration, which limits the minimum pore water transit times across each geosphere layer.
(c) Although the number of nuclides in each chain is theoretically without limit, practical restrictions on CPU suggest that chains with more than 4 members use secular equilibrium for short lived members and chain truncationfor long lived members.
(d) SYVAC can model up to 5 geosphere layers but for practical computations it is advisable not to exceed 3.
(e) The physical approximations incorporated in the submodel are those normally used in one dimensional, continuum models of transport in homogeneous porous media.
5.3 Restrictions in the Biosphere Model
-----------------------------------
ECOS calculates estimates of activity and dose to man for a constant radionuclide flux into the biosphere. It cannot be used to estimate doses from rapidly changing input fluxes or "spike" inputs. The model does not simulate the production or transport of gaseous radionuclide species nor estimate the dose from such species. This may lead to inaccurate estimates (usually over- estimates) of doses from potentially gaseous radionuclides such as H-3, C-14, I-129. The model includes 53 radionuclides and up to 7 member chains. The allowed list has been found to be more than adequate in the studies to date.
5.1 Restrictions in the Vault Submodel
----------------------------------
(a) The vault submodel allows 5 "boxes" for the internal construction of the vault and 2 barriers (liner and clay). These cannot be changed by the user.
(b) The model includes representations of 2-dimensional diffusion, and 1-dimensional advection for shallow sites/2-dimensional advection for deep sites. The flow is approximated by Darcy's Law.
(c) Time invariant chemistry; elemental (not isotopic) solubilities; diffuse leaching; nuclide independent retardation. For the case of shallow land disposal, retardation in the damaged region around the Vault structure is incorporated for the direct pathway to the biosphere but not for the pathway through the biosphere.
(d) The equations for flow and transport are uncoupled. solubility, leaching, sorption, diffusion and permeability are all time independent.
(e) There is no allowance for man made or natural (e.g.) tree roots) intrusion into the Vault.
(f) The Vault structure is below the water table (saturated) after a certain period.
(g) There is no interaction between adjacent Vault structures if these were present.
(h) There are a number of limitations on number of canisters, nuclides per chain, etc built into the program.
5.2 Restrictions in the Geosphere Submodel
--------------------------------------
(a) The Geosphere submodel contains stated limitations on the parameter values. The range of allowed values corresponds to physically admissible values for the parameters.
(b) The timesteps in the model are of fixed duration, which limits the minimum pore water transit times across each geosphere layer.
(c) Although the number of nuclides in each chain is theoretically without limit, practical restrictions on CPU suggest that chains with more than 4 members use secular equilibrium for short lived members and chain truncationfor long lived members.
(d) SYVAC can model up to 5 geosphere layers but for practical computations it is advisable not to exceed 3.
(e) The physical approximations incorporated in the submodel are those normally used in one dimensional, continuum models of transport in homogeneous porous media.
5.3 Restrictions in the Biosphere Model
-----------------------------------
ECOS calculates estimates of activity and dose to man for a constant radionuclide flux into the biosphere. It cannot be used to estimate doses from rapidly changing input fluxes or "spike" inputs. The model does not simulate the production or transport of gaseous radionuclide species nor estimate the dose from such species. This may lead to inaccurate estimates (usually over- estimates) of doses from potentially gaseous radionuclides such as H-3, C-14, I-129. The model includes 53 radionuclides and up to 7 member chains. The allowed list has been found to be more than adequate in the studies to date.
[ top ]
6. TYPICAL RUNNING TIME
The running time for SYVAC depends on:
- the number of runs
- the number of nuclides in each run.
- the number of nuclides in each chain
Typical CPU times of a single run on a MicroVAX 1 are:
No. of Nuclides in Chain Time (CPU minutes)
1 0.6
2 2
3 4.4
4 11.1
Single run times on a MicroVAX 2 are approximately 1/5 of these figures. A representative example case study - say 1000 runs for the single member Iodine 129 chain - would need approximately (1000 x
0.6) x 0.2 CPU minutes (2 hours) to complete execution on the MicroVAX2.
The running time for SYVAC depends on:
- the number of runs
- the number of nuclides in each run.
- the number of nuclides in each chain
Typical CPU times of a single run on a MicroVAX 1 are:
No. of Nuclides in Chain Time (CPU minutes)
1 0.6
2 2
3 4.4
4 11.1
Single run times on a MicroVAX 2 are approximately 1/5 of these figures. A representative example case study - say 1000 runs for the single member Iodine 129 chain - would need approximately (1000 x
0.6) x 0.2 CPU minutes (2 hours) to complete execution on the MicroVAX2.
NEA-1023/04
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.[ top ]
[ top ]
8. RELATED AND AUXILIARY PROGRAMS
The biosphere model, ECOS, has already been described in Section 4. There are a number of other auxiliary programs concerned with graphical analysis and sensitivity analysis. They are not integral to SYVAC, and access the output data files created by SYVAC in the course of execution. These programs are discussed briefly for completeness.
These additional programs have been written to facilitate the analysis of the results in the output files. The programs examine:
- runs in dose or risk order
- dose at specified times
- high dose/risk runs
- risk over time with confidence limits
- the cumulative probability of dose occurrence
- the sensitivity of dose to parameter values
- the efficiency of sampling.
Importance sampling, a recent inclusion, uses the results of sensitivity analysis studies to significantly increase sampling efficiency. Several techniques have been investigated for quantifying expert judgement and also for incorporating measured data using a Bayesian approach.
The biosphere model, ECOS, has already been described in Section 4. There are a number of other auxiliary programs concerned with graphical analysis and sensitivity analysis. They are not integral to SYVAC, and access the output data files created by SYVAC in the course of execution. These programs are discussed briefly for completeness.
These additional programs have been written to facilitate the analysis of the results in the output files. The programs examine:
- runs in dose or risk order
- dose at specified times
- high dose/risk runs
- risk over time with confidence limits
- the cumulative probability of dose occurrence
- the sensitivity of dose to parameter values
- the efficiency of sampling.
Importance sampling, a recent inclusion, uses the results of sensitivity analysis studies to significantly increase sampling efficiency. Several techniques have been investigated for quantifying expert judgement and also for incorporating measured data using a Bayesian approach.
[ top ]
10. REFERENCES
At present, the SYVAC documentation (prepared by SCICON Limited) totals 13 volumes, with another 2 volumes in preparation. Additional volumes describing the submodels are currently being revised by the other contractors. The documentation available is listed below:
Part 1 : SYVAC A/C Overview : Volumes 1 - 3
Volume 1 - Documentation Introduction
Volume 2 - System Overview
Volume 3 - Glossary
Part 2 : SYVAC A/C User Guide : Volumes 1 - 3
Volume 1 - Input and Execution
Volume 2 - Output and Error Messages
Volume 3 - Installation Instructions
Part 3 : SYVAC A/C Programmers' Guide : Volumes 1 - 7
Volume 1 - Program Structure
Volume 2 - File Descriptions
Volume 3 - Data Dictionary
Volume 4 - Data Transfer
Volume 5 - Executive Modules
Volume 6 - Vault Modules
Volume 7 - Geosphere Modules
At present, the SYVAC documentation (prepared by SCICON Limited) totals 13 volumes, with another 2 volumes in preparation. Additional volumes describing the submodels are currently being revised by the other contractors. The documentation available is listed below:
Part 1 : SYVAC A/C Overview : Volumes 1 - 3
Volume 1 - Documentation Introduction
Volume 2 - System Overview
Volume 3 - Glossary
Part 2 : SYVAC A/C User Guide : Volumes 1 - 3
Volume 1 - Input and Execution
Volume 2 - Output and Error Messages
Volume 3 - Installation Instructions
Part 3 : SYVAC A/C Programmers' Guide : Volumes 1 - 7
Volume 1 - Program Structure
Volume 2 - File Descriptions
Volume 3 - Data Dictionary
Volume 4 - Data Transfer
Volume 5 - Executive Modules
Volume 6 - Vault Modules
Volume 7 - Geosphere Modules
NEA-1023/04, included references:
- 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)
[ top ]
11. MACHINE REQUIREMENTS
At present, case study work is carried out by SCICON Limited (Section 15) on a DEC MicroVAX 1 and a DEC MicroVAX 2. Short term storage is via 10MByte discs for the MicroVAX 1, and a 700MByte disc for the MicroVAX 2. Tapes are used for long term storage. A printer is needed for producing physical output.
SYVAC A/C 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 18000 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.
At present, case study work is carried out by SCICON Limited (Section 15) on a DEC MicroVAX 1 and a DEC MicroVAX 2. Short term storage is via 10MByte discs for the MicroVAX 1, and a 700MByte disc for the MicroVAX 2. Tapes are used for long term storage. A printer is needed for producing physical output.
SYVAC A/C 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 18000 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.
[ top ]
13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED
SYVAC is presently run under the DEC Micro VMS operating system, version 4.2. To run SYVAC A/C under version 4.2, it is necessary to have a
software modification from DEC to correct an error with double precision exponentials. The program runs under version 4.3 which does not need the modification. SYVAC 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.
SYVAC is presently run under the DEC Micro VMS operating system, version 4.2. To run SYVAC A/C under version 4.2, it is necessary to have a
software modification from DEC to correct an error with double precision exponentials. The program runs under version 4.3 which does not need the modification. SYVAC 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.
NEA-1023/04
NEA-DB executed the test cases included in this package on a VAX 8810 computer running under VMS 5.3[ top ]
14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS
The MicroVax 1 and 2 are virtual memory machines and so there is no overlaying or similar restrictions due to storage. The only changes required to run SYVAC on another machine (apart from the operating system) 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.
The MicroVax 1 and 2 are virtual memory machines and so there is no overlaying or similar restrictions due to storage. The only changes required to run SYVAC on another machine (apart from the operating system) 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.
[ top ]
15. NAME AND ESTABLISHMENT OF AUTHORS
The development of SYVAC has been undertaken by private contractors under DOE contracts.
Project Management
------------------
Dr. B.G.J. Thompson
Radioactive Waste (Professional) Division
Department of the Environment
Room A5.35, Romney House
43 Marsham Street
London SW1P 3PY, England
Contractors Areas of Responsibility
----------- -----------------------
Atkins Research and Models for the migration of
Development radionuclides through host rock.
Associated Nuclear Services Models for the biosphere and the
calculation of dose to man.
CAP Scientific Statistical techniques used for
sensitivity and uncertainty analysis
Electrowatt Engineering Models for the migration of
radionuclides from the vault.
Scicon Limited Software coordination, computing
services, system documentation.
Contractor Addresses
--------------------
1. Dr. T. Broyd, Atkins Research & Development, Woodcote Grove,
Ashley Road, Epsom, Surrey KT18 5BW, England.
2. Dr. T. Summerling, Associated Nuclear Services, Eastleigh House,
60 East Street, Epsom, Surrey KT17 1HB, England.
3. Dr. G. Dalrymple, CAP Scientific, 20 - 26 Lambs Conduit Street,
London WC1N 3LF, England.
4. Dr. A. Gralewski, Electrowatt Engineering Services, Grandford
House, 16 Carfax, Horsham, West Sussex RH12, England.
5. Dr. I.C. Rae, Scicon Limited, Wavendon Tower, Wavendon, Milton
Kenes MK17 8LX, England.
The development of SYVAC has been undertaken by private contractors under DOE contracts.
Project Management
------------------
Dr. B.G.J. Thompson
Radioactive Waste (Professional) Division
Department of the Environment
Room A5.35, Romney House
43 Marsham Street
London SW1P 3PY, England
Contractors Areas of Responsibility
----------- -----------------------
Atkins Research and Models for the migration of
Development radionuclides through host rock.
Associated Nuclear Services Models for the biosphere and the
calculation of dose to man.
CAP Scientific Statistical techniques used for
sensitivity and uncertainty analysis
Electrowatt Engineering Models for the migration of
radionuclides from the vault.
Scicon Limited Software coordination, computing
services, system documentation.
Contractor Addresses
--------------------
1. Dr. T. Broyd, Atkins Research & Development, Woodcote Grove,
Ashley Road, Epsom, Surrey KT18 5BW, England.
2. Dr. T. Summerling, Associated Nuclear Services, Eastleigh House,
60 East Street, Epsom, Surrey KT17 1HB, England.
3. Dr. G. Dalrymple, CAP Scientific, 20 - 26 Lambs Conduit Street,
London WC1N 3LF, England.
4. Dr. A. Gralewski, Electrowatt Engineering Services, Grandford
House, 16 Carfax, Horsham, West Sussex RH12, England.
5. Dr. I.C. Rae, Scicon Limited, Wavendon Tower, Wavendon, Milton
Kenes MK17 8LX, England.
[ top ]
NEA-1023/04
| File name | File description | Records |
|---|---|---|
| NEA1023_04.001 | Information file | 275 |
| NEA1023_04.002 | Command file to compile and link SYVAC-D/2 | 9 |
| NEA1023_04.003 | Command file to compile FORTRAN programs | 5 |
| NEA1023_04.004 | Command file to compile SYVAC-D/2 sources | 157 |
| NEA1023_04.005 | Command file to link SYVAC-D/2 (nondebug) | 4 |
| NEA1023_04.006 | Command file to link SYVAC-D/2 (debug) | 4 |
| NEA1023_04.007 | FORTRAN source ('Executive' modules) | 10873 |
| NEA1023_04.008 | FORTRAN source (Geosphere submodel modules) | 3165 |
| NEA1023_04.009 | FORTRAN source (Vault submodel modules) | 5617 |
| NEA1023_04.010 | FORTRAN source (included module) | 1 |
| NEA1023_04.011 | FORTRAN source (included module) | 474 |
| NEA1023_04.012 | FORTRAN source (included module) | 271 |
| NEA1023_04.013 | FORTRAN source (included module) | 19 |
| NEA1023_04.014 | FORTRAN source (included module) | 164 |
| NEA1023_04.015 | FORTRAN source (included module) | 79 |
| NEA1023_04.016 | FORTRAN source (included module) | 34 |
| NEA1023_04.017 | FORTRAN source (included module) | 43 |
| NEA1023_04.018 | FORTRAN source (NAG alternative) | 2870 |
| NEA1023_04.019 | SYVAC-D/2 executable image | 305 |
| NEA1023_04.020 | SYVAC-D/2 object module | 634 |
| NEA1023_04.021 | LAND 2 sample input data | 54 |
| NEA1023_04.022 | LAND 2 sample input data | 40 |
| NEA1023_04.023 | LAND 2 sample input data | 12 |
| NEA1023_04.024 | LAND 2 sample input data | 45 |
| NEA1023_04.025 | LAND 2 sample input data | 12 |
| NEA1023_04.026 | LAND 2 sample input data | 14 |
| NEA1023_04.027 | LAND 2 sample output | 62 |
| NEA1023_04.028 | LAND 2 sample output | 708 |
| NEA1023_04.029 | LAND 2 sample output | 810 |
| NEA1023_04.030 | LAND 2 sample output | 810 |
| NEA1023_04.031 | LAND 2 sample output (binary) | 7 |
| NEA1023_04.032 | LAND 3 sample input data | 50 |
| NEA1023_04.033 | LAND 3 sample input data | 38 |
| NEA1023_04.034 | LAND 3 sample input data | 12 |
| NEA1023_04.035 | LAND 3 sample input data | 54 |
| NEA1023_04.036 | LAND 3 sample input data | 6 |
| NEA1023_04.037 | LAND 3 sample input data | 15 |
| NEA1023_04.038 | LAND 3 sample output | 47 |
| NEA1023_04.039 | LAND 3 sample output | 696 |
| NEA1023_04.040 | LAND 3 sample output | 1012 |
| NEA1023_04.041 | LAND 3 sample output (binary) | 7 |
Keywords: geologic strata, ground water, radioactive waste storage, risk assessment, underground storage.