The Rietvlei Water Treatment Plant was extended with a granular activated carbon (GAC) filtration system after an exhaustive series of tests, which were started in 1994. Upon commissioning towards the middle of 1999, a year of close monitoring followed to measure the GAC performance at full-scale. After verification that the GAC does indeed ensure a high quality product under all conditions, the emphasis shifted to the optimisation of the GAC handling and regeneration system. Frequently moving the entire GAC inventory from the filters to an off-site regeneration plant and back requires significant operational effort and contributes a major part of the total cost of the GAC system. A number of systematic investigations were carried out in response to a number of practical questions that arose at Rietvlei. The first part of the study was directed towards tracking and quantifying the GAC on and off site. The main findings were that 10.0% of the GAC is lost from the filter during backwashing (0.3%) and removal of GAC from the filter for regeneration (9.7%). The sump does not trap all this GAC and 2.3% of the total inventory is lost to the river. Inserting a sieve at the outlet of the sump can eliminate this loss. A further 80.3% of the GAC in a filter is removed for regeneration, of which 18.7% is lost during the regeneration process. The minimising of this loss can only be achieved through the optimisation of the regeneration process, which falls within the domain of the regeneration contractor. The second part of the study was directed at the behaviour of the GAC whilst within the filter bed. The porosity and sphericity were determined by laboratory tests and calculations. The porosity was found to be 0.69 for the 12 x 40 size carbon and 0.66 for the 8 x 30 size carbon. By using a calibrated bed expansion model, bed expansion could be calculated at 9°C and 23°C for the two carbon gradings; the maximum temperature range experienced at Rietvlei. The main finding of this part of the study was that the average available freeboard is 650 mm for the 12 x 40 grading and 430 mm for the 8 x 30 grading, and therefore no GAC should wash over the weir at all during backwashing. The third part of the study measured the physical changes of the GAC found at different points in the GAC cycle. The main findings were that the small fraction of GAC washed out of the bed during backwashing and removal has a finer grading, higher apparent density and lower adsorption capacity than the GAC in the filter bed. There seems to be no marked attrition of the carbon or generation of fines during the removal and transport of the GAC to the regeneration plant. After regeneration, there was a 7.0% decrease in apparent density and a 30.0% increase in adsorption capacity.The final part of the study correlated the adsorption capacity of the GAC with its time in use as well as UV254 removal. After regeneration, UV254 removal begins at approximately 20.0% and declines to 14.0% after 400 d of operation, and to 10.0% after 600 d. After regeneration, the...

August 24. 1994 c WHC-5 D-TP-0 RR-0 03 Rev. 0-I pR1A RFVIFW I IST e Design cask per ASME B&PV Code, Section Vlll or 111, as required by NRC Reguiatory Guides. (4.2) The NRF TRIGA Cask classification by the Packaging Review Guide and NUREGlCR3854 is a Category 111 package (7 A2's). The PDC required the design and analysis per ASME B&PV Code, Section VlI1, based on this category. Category 111 requires, as a minimum, ASME B&PV Code, Section V111, Division I , for fabrication and Division 2 for design and analysis. ASME B&PV Code, Section VI11 and Section 111, were used for the design and analysis of this cask. AI1 materials (pipeltubing, cap screws, lead, and plate) are either ASME or ASTM materials. All welds shall be sufficiently rounded and smooth to enable easy decontamination. (4.2.2) All welds shall be rounded or machined fiush. The abiiity to decontaminate was kept in mind during t h e design. 2-43 PDC CRITERIA REVIEW LIST (con't) Inspect all welds per t h e ASME requirements. (4.2.2) AI1 containment boundary welds can be radiographed and all other welds can be inspected as required by ASME B&PV code Section V111. The inner container shall be less than 16-in. in diameter and the outer container shall be less than 30-in. (4.2.3) The inner container OD is 10.5 in. and the outer container OD is I 6 in. c WHC-SD-TP-DRR-003 Rev. 0 August 24, 1994 PDC CRITERIA REVIEW LIST (con'tl AI1 cask components shall be of materials that assure that there will be no significant chemical, galvanic, or other reaction among The packaging components or between packaging components and contents. (5.1 A.2) a All cask components are stainless steel, lnconel, or coated to prevent chemical, gaivanic or other reactions. Criticality control shall be such that the two casks transported shall have a K, < 0.95 f WHC-SD-TP-DRR-003 Rev. 0 August 24. 1994 c described above) seal. 12 ASTM F-837, Type 410 cap screws, t o a torque specification o f a t l e a s t that necessary t o properly seat the metallic spring-energized seal. The 1 id assembly i s secured t o the cask vessel with 4. 2 ACCEPTANCE OF PACKAGING FOR USAGE 4.2.1 New Packaging used t o transport radioactive materials. performed within 12 months prior t o shipment o f radioactive materials. 4.2.1.1 Acceptance Requirements. The new NRF TRIGA Packagings shall be inspected p r i o r t o f i r s t use a s described in Section 4.2.1.2. Each inspection shall be documented as stated in Section 4.2.1.4. The inspections shall be performed t o ensure t h a t the packaging has maintained the original fabricated conf i gurat i o n .

Close observation at a number of South African water treatment plants has shown that media losses during backwashing are excessive-much higher than anticipated. The only likely reasons for this phenomenon are either that insufficient freeboard was provided by the designer or that the mechanical behaviour of the media gradually changes after being placed in the filters. A number of media tests confirmed that the biological fraction of the specific deposit on the filter media (after backwashing) is relatively high-about 50% of the total specific deposit. This led to the hypothesis that the combination of high nutrient concentrations in surface waters, coupled with elevated water temperatures, stimulate biofilm formation on the media grains. These films, in turn, somehow affect the mechanical behaviour of the media bed expansion and backwash. This paper reviews the Dharmarajah bed expansion model (as the most advanced model for media expansion to date) and presents evidence that it predicts the expansion of clean, ovendried media reasonably well. It further shows that media from filters which have been in operation for a while, expand significantly more than predicted by the Dharmarajah model. This finding has major implications for filter design, and suggestions are made on how to adapt design procedures for what is now believed to be the formation of biofilm on media grains.

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A l l changes a r e w i t h i n t h e scope o f t h e o n s i t e r i s k acceptance c r i t e r i a and t h e m a j o r i t y a r e a d m i n i s t r a t i v e i n c o n t e n t based upon p r o j e c t d e c i s i o n s s i n c e t h e r e l e a s e o f t h e o r i g i n a l Packaging Design C r i t e r i a .