Delay tank

Removal of Activity from Delay Tank Solutions Using an RO Unit.934... 

Composition of Fuel Pond and Delay Tank Solutions... 

Fuel Pond Water Delay Tank Water... 

The specifications of the membrane module, which was supplied by the Desalination Division of the BARC (Mumbai), are listed in Table 33.2. The RO setup installed at the delay tank site is shown in Figure 33.3. The delay tank water composition is given in Table 33.1. The module was operated at a pressure of 15 bar, which was adjusted by a throttle valve placed on the reject line. The experiments were performed both in once-through and recirculation modes. The alpha and beta activities, and nitrate and TDS levels were periodically monitored by sampling the feed, permeate, and reject solutions using standard analytical methods. 

FIGURE 33.3 RO setup installed at delay tank site in PREFRE plant, Tarapur. 

Typical Analytical Results of RO Pilot Plant Studies Conducted for Delay Tank Solution in Once-through Mode... 

The delay tank solution contains high alpha and beta activity. 

Pabby, AK. et al. Role of membrane technology to achieve ALARA concept in reprocessing plant Utilization of low pressure reverse osmosis for treatment of delay tank solutions at Theme meeting on Trends in Separation Science and Technology-SESTEC 2004 BARC, Mumbai, July 22-23, 2004. 

FLOW DELAY TANK FOR OZONE DECOMPOSITION AND CONVERSION OF SOLUBLE NONDEGRADABLE MATERIA15 TO BIODEGRADABLE COMPOUNDS... 

In the absorber tank, time for external desupersaturation is provided and fresh reagent is added to raise the pH and thereby promote desupersaturation of the spent reagent stream. The delay tank provides contact time for crystal growth and sulfite and sulfate salt precipitation. 

The feed limestone usually is fed into the delay tank. A sidestream of slurry is withdrawn from the tank or at a point just before the tank, the solids are separated and discarded, and the liquid phase is returned to the scrubber. Thus, the system is in a continuous dynamic state rather than at equilibrium. 

Lime scrubbing is quite similar to limestone scrubbing except that the pH in the delay tank is higher, about 8-10 as compared with 5.8-6.0 in limestone scrubbing. The pH apparently drops quickly when the slurry returns to the scrubber, caused by absorption of carbon dioxide and sulfur dioxide, so that the scrubber exit pH is about 5.4-5.8 no matter which absorbent is used. 

If the limestone is used as is, however, the dissolution rate of the dolomite fraction is so slow that the overall effectiveness appears to be decreased. It may be that with enough delay time the dolomite would react adequately in the delay tank with bisulfite species formed in the scrubber, but suitable data on this do not appear to be available. 

TABLE 26.4 Composition of Delay Tank Solutions Delay Tank Water pH TDS Gross alpha Gross beta/gamma activity 6-8 1700 ppm 2.8 X 10-5 mQ/L 3.5 X 10 mCi/L... 

Using the results presented in [17] we find that the optimal solution, i.e., the minimal capacity volume that gives g = 0.05, is a delay-tank with residence-time %d = 23 min combined with a caseaded mixing tank with residence time of Tg = 27 min. See also Fig. 7. In terms of volumes, accounting for flow rate sizes, this means that we reduce the required capacity volume by 40% compared to a traditional cascaded buffer. For lower g the reduction is even more significant, e.g., for g = 0.02 the optimal solution gives a required capacity volume which is only one third of the required cascaded buffer volume. 

Fig. 8 shows the scaled disturbance sensitivity from Aq to yo after the design modification, and as can be seen we have achieved g = 0.05. Fig. 9 shows the effect of the delay tank on the process sensitivity function Sp. As can be seen, the delay reduces the sensitivity Sp at g from 2 to 0.8, implying that the interactions effectively serves to dampen disturbances at g after the design modification. The resonances that appear at higher frequencies are dampened out by the low-pass properties of the process units, and do therefore not pose a problem as can be seen from Fig. 8. 

Fig. 7. Reactor-separator plant with plug-flow (delay) tank and mixed buffer tank.

Fig. 8. Scaled disturbance sensitivity of reactor-separator process before (dashed) and after (solid) addition of delay tank and mixed buffer. See also Figure 7.

Fig. 10. Filter effect of delay tank in recycle path (solid) and cascaded mixing tank of same size (dashed) for reactor-separator system.

For all operational states and DBAs, adequate provision shall be made in the design, on the basis of a consistent radiation protection programme and in accordance with the radiation protection objective (see para. 205 of Ref. [1], quoted in para. 2.2), for shielding, ventilation, filtration and decay systems for radioactive material (such as delay tanks), and for monitoring instrumentation for radiation and airborne radioactive material inside and outside the controlled area. 

Provisions for decay devices (e.g. use of delay tanks for or retention tanks) to minimize releases of radioactive material ... 

DESIGN CONSIDERATIONS EOR COLLECTION OR HOLDING (DELAY) TANKS EOR LIQUID RADIOACTIVE WASTE... 

The flow scheme of the Takahax process is quite similar to that of the Perox process, and, as in the Perox process, the oxidation of hydrosulfide to elemental sulfur in the absorber occurs almost instantaneously. Therefme, there is no need for a delay tank downstream of the absorber to complete the reaction. The process requires no steam and operates at ambient pressure. 

Absorber Configuration. The fundamental steps in the absorption process are the mass transfer of H2S from the gas to the liquid and the oxidation of the HS" to sulfur (Vancini and Lari, 1985). The absorption of hydrogen sulfide can take place in one or more contact stages, with the gas washed by the Stretford liquor either countercurrently or cocurrently. A subsequent delay tank allows enough residence time to convert major portions of the absorbed H2S to elemental sulfur. 

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