Sump water

As part of program control, all cooling systems should employ certain items of fixed equipment, for example, coarse and fine screens, in cooling tower sump water boxes and recirculating pump suction intake areas. 

Once the contaminated materials were placed inside the storage facility, the treated sludge rapidly dewatered to the three sumps. Water was pumped from the sumps in the storage facility as the dewatering occurred. This process will continue until no water remains in the sumps. Any water pumped from the facility is treated, analyzed and discharged to the municipal sewer system. 

The production of the key reactant, the hydroxyl radical ( OH), increases with increases in the radiation dose rate to the water. The dose rate to the water depends, of course, on the total amount of fission products and other radionuclides that escape the core and enter the containment. Dose rates to sump waters will vary depending on the type of reactor, the type of accident and with time following an accident. Typical values will be in the range of 1 to 20 kGy hr. ... 

The purpose of this question was to find out whether any additional iodine mitigation measures have been planned or already implemented other than using additives in the spray and containment sump water and using controlled containment venting with a filter. Other than these measures, if already implemented, there are no other mitigation measures reported by the participating organizations. 

Flow capacity (Injection phase/recirculatlon phase), chemical additive (if yes, what, concentration) BWRs contain UOH to maintain pH at 8-8.5, this will act as a chemical additive tc the sump water. PWRs trisodlumphosphate is added during the recirculation phase to increase pH and increase absorption of iodine... 

In PWR plants equipped with both a cold-leg and a hot-leg injection of the emergency coolant, a fraction of the fission products released from the failed fuel rods will be washed down by the downward water flow. Thus, it will be transported back to the water phase inside the reactor pressure vessel and, finally, to the containment sump water. Since the extent of this type of retention of fission products depends strongly on the contact time between the steam flow and the downward flow of the liquid emergency coolant, it is only difficult to quantify. It can be assumed that Csl (and other iodides) will be trapped almost completely in the water phase for this reason, a 90% retention of the halogens and alkalis and a 99% retention of the so-called solid fission products has been assumed in the German Storfall-Berechnungsgrundlagen . For the h fraction in the steam flow a similar degree of washout can be expected experiments performed under conditions similar to those in the relevant LOCA period have yielded h washout fractions of about 92% at 25 C and about 96% at 85 °C water temperature (Kabat, 1980). 

The total sump water volume in the containment is approximately 1500m depending on the design of the safety systems in the particular plant. 

The final partitioning of fission product iodine between the sump water and the atmosphere of the containment is determined by the equilibrium partition coefficient as will be discussed in more detail in Section 7.4.3.1., this figure depends on several parameters, such as iodine concentration and sump water pH and, to a lesser extent, temperature. As can be seen from Fig. 4.13., the iodine partition coefficient increases with decreasing iodine concentration in the solution this behavior is the consequence of the shift in the h hydrolysis reaction towards a lower I2 equilibrium fraction at lower total iodine concentration. Below a concentration of about 10" g/1, however, the partition coefficient remains virtually constant, an effect which has been attributed to the volatility of the hydrolysis product HOI (Lin, 1981). This constant value is about l(f at pH 7 and 25 °C it applies as well for the concentration range to be expected in a loss-of-coolant accident. Concerning the HOI partition coefficient at 100 °C, several measurements yielding quite different values have been reported. The lowest one is 240 given by Lin (1981) Lemire et al. (1981) reported values between 100 and 1(1, while Wren and Sanipelli (1984) measured values between 7 10 and 3 10. Since the HOI compound was... 

When calculating the h equilibrium concentration in the containment atmosphere from these data, one has to remember that the partition coefficients usually were determined using pure I2 solutions. The fission product iodine in the sump water, however, mainly consists of non-volatile iodide with smaller fractions of I2 on the order of 10% and less. The airborne fraction of I2, therefore, has to be calculated from the dissolved I2 concentration only. The excess 1 present in the solution will act to shift the I2 hydrolysis equilibrium towards a higher I2 fraction at the low total iodine concentrations present, however, this effect is not expected to result in a significant decrease in the total iodine partition coefficient. 

This estimation is a very simplified one and does not take into accoimt a possible oxidation of iodide to elemental iodine in the sump water. At the very low iodine concentrations present and at the temperatures under consideration, thermal oxidation caused by dissolved oxygen proceeds rather slowly, as far as it is not catalyzed by UV light or by traces of metals. According to the calculations reported by Bums and Marsh (1986), a fraction of only about 10 of the original iodide is thermally oxidized in the ten days following the accident. Since the extent of iodide oxidation in the sump water is determined by the redox potential of the liquid... 

Containment spray systems are used in some types of PWR plants, resulting not only in a condensation of steam but also in a washout of airborne radioiodine and other fission products from the containment atmosphere. Normtilly, an alkaline borate spray solution is used, resulting in a shift of the I2 disproportionation equilibrium to the iodate side and a suppression of revolatilization of iodine previously trapped by the spray droplets. In some cases, solutions containing sodium thiosulphate have been used to decompose volatile organic iodides present in the containment atmosphere, but because of its corrosivity this reagent has been largely abandoned. By the addition of boric acid to the spray solution, subcriticality of the reactor core is guaranteed when, after the injection phase, the sump water is recirculated for removal of decay heat from the core. 

In sum, the reactions that can occur on the way from the sump water to the containment free volume (and vice versa) are assumed to result in a significant reduction of the amount of airborne radionuclides, in particular of volatile iodine species. Ignoring these reactions, therefore, would lead to an overestimation of the amount of volatile radionuclides and, as a consequence, to a conservative assumption regarding a potential release. 

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