Digesting to Make Simulant Based Slurries

The simulant decomposition test slurries were prepared from the two sludge simulants characterized in Table 6.

First, each sludge was thrice sequentially digested using either 1 or 2.5 wt% oxalic acid solution, with the wt% oxalic acid solution(s) determined based on which of the simulant tests were being performed. The analyses are considered to support the following determinations:

Section 4.5. Is UV Light Required?

Section 4.6. Differing Role of Metal Catalysts During Ozonation.

Section 4.7. Using pH to Confirm Completion of Oxalate Decomposition.

Section 4.8. Is Decomposition Hydroxyl Radical Driven?

Specifics of the digestion process used to make the slurries, are as follows.

Sludge Digestion Procedure: Approximately 61 litres of oxalic acid solution were added to a standard 114-litre capacity 304 stainless steel drum that had previously been loaded with sludge simulant.

Based on the expected digestion capacity of the oxalic acid solution of 3 gram/litre cation digestion, conservatively assuming iron, aluminium and nickel contribution only, and the cation content of each simulant, the equivalent of approximately 2.0 kg dry weight of Fe-rich simulant and 3.3 kg dry weight of H-Area simulant were the minimum required amounts of simulant to ensure sufficient loading was available for digestion. The moisture was determined using a moisture analyser (Mettler Toledo, Hal Moisture Analyser HE53). The equivalent dry simulant sludge loadings used for the sequential digestions are shown in Table 7.

Table 7. Dry sludge simulant loadings used to support three sequential digestions. Simulant decomposition test slurries1 Initial wet simulant (kg) Measured average wt% moisture Eq. dry simulant (kg) 1-Fe-x.no 5.20 61.06 2.03 1-Fe-x. clean 5.05 59.91 2.03 1-Fe-x. fouled 4.80 57.67 2.03 1-Al/Mn-no 10.40 66.51 3.47 1-Al/Mn-clean 11.09 68.79 3.46 1-Al/Mn-fouled 10.95 68.31 3.47 2.5-Fe-x-no 12.68 60.01 5.07 2.5-Fe-x-clean 12.09 57.89 5.09 2.5-Fe-x-fouled 12.36 58.32 5.15 2.5-Al/Mn-x.no 20.86 58.41 8.68 2.5-Al/Mn-clean 20.29 57.61 8.60 2.5-Al/Mn-fouled 20.60 58.01 8.65

Note: 1_{the nomenclature used to identify the simulants is provided in Table 8.}

Maintaining the drum temperature at 70±5ºC, the acid digests the sludge for approximately 24 hours, with mild agitation applied for roughly the first three and last three hours (i.e. using an approximate 19 litres/minute Titan electric drum pump for recirculation). Better agitation was not supplied, in attempt to roughly emulate the limitations associated with slurrying the HLW tank (i.e. the goal of this mixing was not to ensure a well-mixed tank that would maximise digestion, but instead mimic the limited mixing in a HLW tank). The pH was monitored throughout digestion, with the digestion assumed to have gone to completion once the pH value stabilised in the pH range 1.5 to 2.5. Using the electric transfer pump, approximately 61 litres of the simulant decomposition test slurry were transferred out of the drum, of which ~1 litre was placed in a sample vial for metals characterisation by Atomic Absorption Spectroscopy (AA). The bulk of the slurry was transferred to the Simulant Decomposition Test Apparatus

After transferring the simulant decomposition test slurry out of the “digestion” drum, the drum

was replenished with approximately 61 litres of fresh oxalic acid of the same original concentration (i.e. 1 or 2.5 wt% depending on the specific testing). The above procedure was then performed again, digesting the sludge simulant sequentially two additional times, resulting in 3 slurries, ~61 litres each, of simulant decomposition test slurry. All of the steps were then repeated for the other sludge simulant, thus creating a total of six simulant decomposition test slurries for the specific acid strength. Depending on the test(s) to be performed (i.e. with the four tests and analyses detailed in Chapter 4.5, Chapter 4.6, Chapter 4.7, or Chapter 4.8), the procedure was repeated using the appropriate UV light testing protocols, as well as the appropriate oxalic acid concentration.

Derived from the acid concentration and HLW sludge simulant digestion matrix used for making the simulant decomposition test slurries, the nomenclature applied for naming (i.e. identifying) the slurries are shown by Table 8.

Table 8. Acid/sludge simulant digestion matrix and resultant simulant decomposition test slurry nomenclature.

Acid concentration used for sludge

digestion

Type of sludge digested

Fe-rich simulant Al/Mn-rich simulant

NAME OF SIMULANT DECOMPOSITION TEST SLURRY

1 wt% oxalic acid

1 wt% oxalic acid applied to Fe-rich simulant, named 1-Fe-x.y

1 wt% oxalic acid applied to Al/Mn-rich simulant,

named 1-Al/Mn-x.y

2.5 wt% oxalic acid

2.5 wt% oxalic acid applied to Fe-rich simulant, named 2.5-Fe-x.y

2.5 wt% oxalic acid applied to Al/Mn-rich simulant, named 2.5-Al/Mn-x.y

Where:

 “x” refers to the digestion sequence of the sludge simulant by the addition of oxalic

acid, either “1,” 2, or “3.” (i.e. the number of times the subject sludge simulant was treated with acid to create the specific simulant decomposition test slurry).

 “y” refers to one of the three UV light protocols used during testing. That is, “no”

refers to no UV light (i.e. without UV) added during ozonation. “Clean” refers to the UV lamp energised with the UV lamp sheath maintained clean (i.e. cleaned with 5 wt% oxalic acids after the oxalate decomposition of each simulant decomposition test slurry) as the result of ozonation. “Fouled” refers to the UV lamp being energised, with the UV lamp sheath only cleaned before the beginning the decomposition of the 1st sequentially created simulant decomposition test slurry.

In addition to “no,” “clean,” and “fouled” UV light protocols, the “clean” and “fouled” are largely limited to the tests performed as part of Section 4.5 - Is UV Light Required? With the other three simulant tests (Section 4.6 through 4.8) done only under the “no” UV light protocol.

Since solids are formed throughout the decomposition of the oxalate, application in actual HLW use would prohibit the use of a filter because of operational/personnel exposure concerns. Therefore, no filter was used in simulant decomposition test apparatus.