[en] In this paper we describe a modelling project to improve a nuclear waste management program in charge of the creation of a new system for the permanent disposal of nuclear waste. SADT (Structural Analysis and Design Technique) is used in order to provide a work-flow description of the functions to be performed by the waste management program. This description is then translated into a number of Coloured Petri Nets (CPN or CP-nets) corresponding to different program functions where additional behavioural inscriptions provide basis for simulation. Each of these CP-nets is simulated to produce timed event charts that are useful for understanding the behaviour of the program functions under different scenarios. Then all the CPN models are linked together to form a single stand-alone application that is useful for validating the interaction and cooperation between the different program functions. A technique for linking executable CPN models is developed for supporting large modelling projects and parallel development of independent CPN models. (au) 11 refs

[en] The NEA International Database of Features, Events and Processes (FEPs) relevant to the assessment of post-closure safety of radioactive waste repositories has been compiled by a working group within the Nuclear Energy Agency (NEA) of the OECD. The main parts of the database are a master list of 150 generalized FEPs and the original project-specific databases containing descriptions, comments and references on the FEPs. The first version of the database includes in total 1261 FEPs from seven national or international performance assessment projects. All project FEPs are mapped to one or more of the FEPs in the master list. The aim of the auditing was to discuss how the FEBs in the international database have been treated in the TVO-92 and TILA-96 safety assessments on spent fuel disposal (in Finland), where no formal methods were applied to develop scenarios. The auditing was made against all the 1261 projectspecific FEPs in the international database. The FEPs were discussed one by one and classified into categories according to their treatment in TVO-92 and TILA-96 or in the technical design of the disposal system

[en] This report documents the results of testing performed to determine the feasibility of using a pulsed-air mixing technology (equipment developed by Pulsair Systems, Inc., Bellevue, WA) to mix cementitious dry solids with supernatant and settled solids within a horizontal tank. The mixing technology is being considered to provide in situ stabilization of the open-quotes Vclose quotes tanks at the Idaho National Engineering and Environmental Laboratory (INEEL). The testing was performed in a vessel roughly 1/6 the scale of the INEEL tanks. The tests used a fine soil to simulate settled solids and water to simulate tank supernatants. The cementitious dry materials consisted of Portland cement and Aquaset-2H (a product of Fluid Tech Inc. consisting of clay and Portland cement). Two scoping tests were conducted to allow suitable mixing parameters to be selected. The scoping tests used only visual observations during grout disassembly to assess mixing performance. After the scoping tests indicated the approach may be feasible, an additional two mixing tests were conducted. In addition to visual observations during disassembly of the solidified grout, these tests included addition of chemical tracers and chemical analysis of samples to determine the degree of mixing uniformity achieved. The final two mixing tests demonstrated that the pulsed-air mixing technique is capable of producing slurries containing substantially more cementitious dry solids than indicated by the formulations suggested by INEEL staff. Including additional cement in the formulation may have benefits in terms of increasing mobilization of solids, reducing water separation during curing, and increasing the strength of the solidified product. During addition to the tank, the cementitious solids had a tendency to form clumps which broke down with continued mixing

[en] This paper discusses the corrosion of the aluminum-clad spent fuel and the improvements that have been made in the SRS basins since 1993 which have essentially mitigated new corrosion on the fuel. It presents the results of a metallographic examination of two Mk-31A target slugs stored in the L-Reactor basin for about 5 years and a summary of results from the corrosion surveillance programs through 1996

[en] This study is intended to analyze the requirements of buffer material that is one of the major components of the engineered barriers in a high-level waste repository. Based on the results, it is intended to suggest the quantitative functional criteria that is necessary to establish the preliminary concept for the domestic geological repository. The criteria are composed of seven major items, such as hydraulic conductivity, retardation capacity, swelling potential and swelling pressure, thermal conductivity, longevity, organic carbon content, and mechanical properties. (author). 87 refs., 12 tabs., 3 figs

[en] The basic requirements for the geological situation at a deep underground radioactive waste disposal site are highlighted, a survey of candidate host sites worldwide is presented, and the situation in the Czech Republic is analyzed. A 'General Project of Geological Activities Related to the Development of a Deep Underground Disposal Site for Radioactive Wastes and Spent Fuel in the Czech Republic' has been developed by the Nuclear Research Institute and approved and financed by the authorities. The Project encompasses the following stages: (i) preliminary study and research; (ii) examination of the seismicity, neotectonics, and geodynamics; (iii) search and critical assessment of archived geological information; (iv) non-destructive survey; and (v) destructive survey. The Project should take about 30 years and its scope will be updated from time to time. (P.A.)

[en] The retained gas volume can be estimated by several methods. All of these methods have significant uncertainties, but together they form a preponderance of evidence that describes the gas retention behavior of the tank. The methods are (1) an increase in nonconvective layer thickness; (2) a waste surface level rise (surface level effect [SLE] model); (3) the barometric pressure effect (BPE model); (4) direct void measurement; and (5) the consequences of the transfer process. The nonconvective layer thickness can be determined with sufficient accuracy to describe the overall waste configuration by means of temperature profiles or densitometer indications. However, the presence of a nonconvective layer does not necessarily indicate significant gas retention, and small changes in layer thickness that could quantify gas retention cannot be detected reliably with the methods available. The primary value of this measurement is in establishing the actual open-quotes fluffing factorclose quotes for thermal calculations. Surface level rise is not a useful measure of gas retention in Tank 241-C-106 (C-106) since the waste level fluctuates with regular makeup water additions. In Tank 241-AY-102 (AY-102) with the existing ventilation system it should be possible to determine the gas retention rate within 30-60% uncertainty from the surface level rise, should a significant rise be observed. The planned ventilation system upgrades in AY- 102 will greatly reduce the exhaust flow and the headspace humidity, and the evaporation rate should be significantly lower when transfers begin. This could reduce the uncertainty in gas retention rate estimates to around ± 10%

[en] The vertical ammonia concentration distributions determined by the retained gas sampler (RGS) apparatus were modeled for double-shell tanks (DSTs) AW-101, AN-103, AN-104, and AN-105 and single-shell tanks (SSTs) A-101, S-106, and U-103. One the vertical transport of ammonia in the tanks were used for the modeling. Transport in the non-convective settled solids and floating solids layers is assumed to occur primarily via some type of diffusion process, while transport in the convective liquid layers is incorporated into the model via mass transfer coefficients based on empirical correlations. Mass transfer between the top of the waste and the tank headspace and the effects of ventilation of the headspace are also included in the models. The resulting models contain a large number of parameters, but many of them can be determined from known properties of the waste configuration or can be estimated within reasonable bounds from data on the waste samples themselves. The models are used to extract effective diffusion coefficients for transport in the nonconvective layers based on the measured values of ammonia from the RGS apparatus. The modeling indicates that the higher concentrations of ammonia seen in bubbles trapped inside the waste relative to the ammonia concentrations in the tank headspace can be explained by a combination of slow transport of ammonia via diffusion in the nonconvective layers and ventilation of the tank headspace by either passive or active means. Slow transport by diffusion causes a higher concentration of ammonia to build up deep within the waste until the concentration gradients between the interior and top of the waste are sufficient to allow ammonia to escape at the same rate at which it is being generated in the waste

[en] One of the alternative systems for disposal of high-level radioactive nuclear waste being studied by SKB is the very deep hole (2000 - 4000 m) concept. As part of SKB's research programme a study has been carried out to increase the level of knowledge on the expected geological conditions in the depth interval 1000-5000 m in older crystalline rock. As a first step, existing data from relevant areas throughout the world have been compiled. The majority of the data come from deep boreholes, mines, and surface geophysical surveys. An attempt has been made to interpret these data in an integrated manner and to develop a conceptual geological model on the conditions in the Baltic Shield down to a depth of 5 km. One of the main features of the suggested model is that the upper 1 km of crust contains significantly more open fractures than the rock below. However, hydraulically conductive fractures and fracture zones may exist at great depth. In areas of low topography active groundwater circulation is primarily limited to the upper 1 km with the water below 1 km having high salinity. The high salinity reflects the near hydraulically stagnant conditions which exist relatively shallow in areas of low topography. In areas with greater topographic relief fresh water penetrates to great depth and near stagnant conditions are first encountered much deeper. The report also covers how the studied parameters which describe the geological conditions vary with depth. A number of recommendations are made on how the presented conceptual model can be tested and improved aside from obtaining data from new boreholes. These recommendations include the following geoscientific surveys and studies: Reflection and refraction seismics for mapping discrete sub-horizontal fracture zones and the upper more fractured part of the crust; Geoelectric methods for mapping the depth to saline water; Detailed hydrogeological measurements in existing deep boreholes; Isotope studies on fracture minerals from deep boreholes; Earthquake studies; Numerical modelling of large scale groundwater flow

[en] This evaluation examines the compatibility of coating Instacote with existing High-Level Waste facilities and safety practices. No significant incompatibilities are identified. The following actions need to be completed as indicated when applying Instacote on waste tank tops:(1) Prior to application in ITP facilities, the final product should be tested for chemical resistance to sodium tetraphenylborate solutions or sodium titanate slurries.(2) Any waste contaminated with Part A or B that can not be removed by the vendor such as for radiological contamination, HLW must hold the waste until HLW completes a formal assessment of the waste, disposal criteria, and impact.(3) Prior to the start of any application of the coating, each riser needs to be evaluated for masking and masking applied if needed.(4) At the conclusion of an application actual total weight of material applied to a waste tank needs to documented and sent to the tank top loading files for reference purposes.(5) Verify that the final product contains less than 250 ppm chloride