UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

January 20, 2006

NRC INFORMATION NOTICE 2005-26, SUPPLEMENT 1: ADDITIONAL RESULTS OF

CHEMICAL EFFECTS TESTS IN A

SIMULATED PWR SUMP POOL

ENVIRONMENT

ADDRESSEES

All holders of operating licenses for pressurized-water reactors (PWRs), except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform

addressees about recent NRC-sponsored research results related to chemical effects in a

simulated PWR sump pool environment. This supplement specifically provides additional

information regarding test results related to chemical effects in environments containing

dissolved phosphate, (e.g., from trisodium phosphate (TSP)), and dissolved calcium. NRC

anticipates that recipients will review the information for applicability to their facilities and

consider taking actions, as appropriate, to avoid similar issues. However, no specific action or

written response is required.

DESCRIPTION OF CIRCUMSTANCES

NRC opened Generic Safety Issue 191 (GSI-191), "Assessment of Debris Accumulation on

Pressurized-Water Reactor (PWR) Sump Performance," because debris accumulation on PWR

sump screens may affect the emergency core cooling system pump net positive suction head

margin. To address GSI-191, NRC issued Bulletin 2003-01, "Potential Impact of Debris

Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors," and Generic

Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During

Design Basis Accidents at Pressurized-Water Reactors." GL 2004-02 requests, in part, that

licensees evaluate the maximum head loss postulated from debris accumulation (including

chemical effects) on the submerged sump screen. Chemical effects are corrosion products,

gelatinous material, or other chemical reaction products that form as a result of interaction

between the PWR containment environment and containment materials after a loss-of-coolant

accident (LOCA). NRC and the nuclear industry jointly developed an integrated chemical

effects test (ICET) program to determine if chemical reaction products can form in

representative PWR post-LOCA containment pool environments. These tests were conducted

by Los Alamos National Laboratory at the University of New Mexico. The ICET series involved

five tests, each representing a different post-LOCA environment, that are broadly

representative of existing PWR plant conditions. Although chemical products were

ML060170102
IN 2005-26, Sup 1

Page 2 of 4

observed in all of the ICET environments, evaluating the head loss associated with these

products was outside the scope of the ICET program. NRC initiated additional testing to obtain

insights on the head loss associated with some chemical products that may form in PWR

containment pools. Initial results from head loss testing performed at the Argonne National

Laboratory (ANL) were provided in NRC IN 2005-26, dated September 16, 2005. ANL

performed these tests in a simulated containment pool environment that was buffered with TSP

and contained calcium silicate insulation (cal-sil). These tests were intended to recreate

calcium phosphate precipitates observed in the ICET 3 environment and measure the head loss

effect. Testing at ANL was conducted in a closed, unpressurized vertical test loop with NUKON

fiberglass and cal-sil particulate first deposited on a test screen. Subsequently, dissolved

calcium was introduced to react with the TSP buffer to create calcium phosphate. In these

initial tests, calcium phosphate precipitate led to significant head loss for the conditions

evaluated.

Subsequent to the issuance of IN 2005-26, three additional sets of tests were conducted at

ANL: (1) head loss tests in a borated solution containing TSP, NUKON fiberglass, and varying

concentrations of either dissolved calcium or cal-sil, (2) calcium phosphate settling tests

performed in a static water column, and (3) dissolution tests to determine the dissolved calcium

concentrations produced by various cal-sil amounts and the effect of TSP addition rate on 

 cal-sil dissolution. Details from these tests are contained in an attachment, "Chemical Effects

Head Loss Testing, Quick Look Report Tests ICET 3-4 to 3-11," (ML060190709) dated January

20, 2006.

DISCUSSION

As part of the mechanistic evaluation discussed in GL 2004-02, licensees are required to

evaluate the sump screen head loss consequences of any chemical effects in an integrated

manner with other postulated post-LOCA conditions. The most recent research results confirm

that a simulated containment pool environment containing phosphate and dissolved calcium

can rapidly produce calcium phosphate precipitate that can significantly increase head loss if

transported to a fiber bed covered screen. Highlights from the attached report include the

following:

• Initial testing with a debris bed of 0.33 kilograms per square meter (kg/m2) NUKON

fiberglass and 1.19 kg/m2 cal-sil (0.2 grams per liter (g/L) cal-sil concentration) resulted

in a significant pressure drop across the test screen in both a baseline test without

chemical products and when TSP was present to form calcium phosphate precipitate. 

Therefore, subsequent head loss tests were performed with lower cal-sil concentrations

to more clearly evaluate chemical effects related to calcium phosphate formation.

• Test results with a debris mixture consisting of 0.71 kg/m2 of NUKON fiberglass and

either 0.71 kg/m2 of cal-sil (0.13 g/L cal-sil concentration) or an equivalent dissolved

calcium concentration from calcium chloride showed a significant increase in pressure

drop across the test screen attributed to the formation of calcium phosphate precipitate.

• Test parameters (e.g., amount of cal-sil dissolution prior to debris bed formation, TSP

addition rates) were varied to investigate how the relative timing of calcium phosphate

formation and the arrival sequence with respect to other debris affected head loss. 

Significant head loss occurred most quickly for tests that represented the maximum
IN 2005-26, Sup 1

Page 3 of 4

cal-sil dissolution rates (i.e., instantaneous through calcium chloride addition) and had

the greatest amount of calcium phosphate present initially. Although the head loss

increased less rapidly in tests with less initial calcium phosphate precipitate, the head

loss eventually approached the steady state values of the tests with maximum initial

calcium phosphate.

• Tests performed with incremental calcium chloride addition suggest a strong nonlinear

relationship between the amount of calcium phosphate precipitate and the pressure

drop. For the ANL test loop configuration and test conditions (e.g., TSP concentration,

debris loadings, etc.) dissolved calcium concentrations equal to or greater than 25 parts

per million (ppm) caused a rapid and significant pressure drop increase.

• Settling tests were performed to assess the settling rate of calcium phosphate

precipitate under conditions with no bulk directional flow. Precipitate agglomeration was

observed at higher concentrations (300 ppm) of calcium phosphate and approximately

50 percent of the precipitate settled more rapidly (3.8 cm/min) at these concentrations. 

At lower concentrations (75 ppm) precipitate agglomeration was not observed and the

settling velocity was estimated to be 0.8 cm/min.

• The dissolution of cal-sil was slowed by instantaneous TSP dissolution at higher

(1.5 g/L) cal-sil concentrations. However, the cal-sil dissolution rate (for the

concentrations evaluated) is not strongly dependent on the TSP dissolution rate within

the range of complete TSP addition between one and four hours. Although complete

dissolution of the cal-sil took up to 4 or more days under some test conditions, the

equivalent dissolved calcium concentrations reached 75 ppm within a few hours for

cal-sil concentrations down to 0.5 g/L.

The information provided in the attachments to IN 2005-26 and this supplement are relevant to

plants containing phosphate (e.g., plants using TSP as a containment pool buffering agent) and

calcium containing materials (e.g., insulations, concrete) that could dissolve within the

post-LOCA containment pool to form calcium phosphate precipitate. These test results confirm

that substantial head loss can occur if sufficient calcium phosphate is produced in a

containment pool and is transported to a sump screen along with fibrous insulation debris.

Although NRC observed significant increases in head loss because of chemical effects, it is

important to note that these head loss results were obtained in a recirculating test loop in which

virtually all chemical products were transported to the test screen. These tests were not

intended to be prototypical of a PWR plant containment. In similar plant containment pool

environments, chemical product formation, transport, and subsequent head loss will be a

function of several variables including: the cal-sil (or other calcium containing materials) debris

concentration within the pool, the calcium dissolution rate, the TSP dissolution rate, the

containment pool velocity profiles and fluid approach velocity at the sump screen, the LOCA

break location, the containment fluid recirculation time, the containment pool temperature

history, the containment floor layout and location of TSP baskets, the sump screen debris

loading, and the sump screen design.

The NRC is continuing head loss testing in simulated PWR containment pool environments that

use other chemicals to buffer pH.
IN 2005-26, Sup 1

Page 4 of 4

CONTACTS

This information notice does not require any specific action or written response. Please direct

any questions about this matter to the technical contacts listed below or the appropriate Office

of Nuclear Reactor Regulation (NRR) project manager. 

 

Christopher I. Grimes, Director /RA/

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: Paul Klein, NRR Robert Tregoning, RES 

301-415-4030 301-415-6657

E-mail: pak@nrc.gov E-mail: rlt@nrc.gov

Attachment: 

Chemical Effects/Head-Loss Testing Quick Look

 Report, Tests 1 and 2 (ML060190709)
Chemical Effects/Head–Loss Testing 

Quick Look Report, Tests ICET-3-4 to 11 

January 20, 2006 

J. Oras, J.H. Park, K. Kasza, K. Natesan, and W. J. Shack 

Argonne National Laboratory 

Abstract 

This summary report describes the continuation of studies conducted at Argonne National 

Laboratory on the potential contributions of chemical effects to head loss across sump screens in 

environments where trisodium phosphate (TSP) buffering is used to control pH and calcium silicate 

(CaSiO3) insulation (cal–sil) debris may be present. Head loss testing, settling rate testing of calcium 

phosphate precipitates and cal–sil dissolution testing in TSP solutions are described. The objective of the 

head loss tests was to assess the pressure drop across debris beds created by various mixtures of cal–sil, 

fibrous insulation, and calcium phosphate precipitates. The effects of both the degree of cal–sil 

dissolution that will occur before the formation of the debris bed and the relative arrival time of the 

precipitates and insulation debris at the screen were specifically evaluated. The debris loadings and test 

temperature were chosen to be reasonably representative of those expected in limiting design basis 

analyses for plants with updated sump screen configurations. Other variables were then selected with the 

intent to encompass the variability in head loss due to the effect of TSP dissolution rates, debris residence 

time in the containment pool prior to accumulation at a sump screen, and other variables that could affect 

the amounts and homogeneity of calcium phosphate precipitates in the debris bed. 

Settling tests were conducted to measure the settling rates of calcium phosphate precipitates 

(formed by adding dissolved Ca to boric acid and TSP solutions) in water columns having no bulk 

directional flow. The dissolution tests were intended to identify important environmental variables 

governing both calcium dissolution and subsequent calcium phosphate formation over a range of 

simulated containment pool conditions. The results from this testing were used to inform and interpret 

both the head loss and settling test series. 

 The results of the head loss tests demonstrate that chemical products (calcium phosphate 

precipitates) associated with TSP-buffered containment environments can contribute significantly to head 

loss across simulated sump screen debris beds. The head losses associated with pure physical debris beds 

of NUKONTM (a trademarked fiberglass blanket insulation, referred to hereafter as NUKON) and cal–sil 

can be much smaller than those that occur across debris beds in which some of the cal–sil has been 

replaced with a corresponding amount of calcium phosphate precipitates. The cal–sil dissolution rate for 

concentrations less than 1.5 g/L is not strongly dependent on the TSP dissolution rate over the range of 

TSP dissolution rates that are likely to be relevant. For cal–sil concentrations as low as 0.5 g/L, the 

equivalent dissolved Ca could be high enough after a few hours to potentially produce significant 

increases on head loss even for instantaneous TSP dissolution. 

Background 

Integrated Chemical Effects Tests (ICET) 

The ICET project is a joint effort by the U.S. Nuclear Regulatory Commission (NRC) and the 

nuclear utility industry; undertaken through a memorandum of understanding between the NRC and the 

Electric Power Research Institute (EPRI).1 The ICET tests simulate the chemical environment present 

inside a containment water pool after a loss-of-coolant accident. The chemical systems were monitored 
2 

for an extended time to identify the presence, composition, and physical characteristics of any chemical 

products that form during the test. The ICET tests were conducted by Los Alamos National Laboratory 

(LANL) at the University of New Mexico (UNM). 

The containment pool environments selected for study were based on input from the Westinghouse 

Electric Company, the NRC and EPRI. The specific conditions, material types, and parameters in the 

ICET test series are intended to be broadly representative of all domestic PWRs. The Westinghouse 

Owners Group and the Babcock & Wilcox Owners Group aided in soliciting information. To obtain the 

necessary details of plant-specific conditions within containment (materials present, containment pool 

conditions, etc.), Westinghouse reviewed plant-specific documents, (such as Post-LOCA Hydrogen 

Generation Evaluations), other available plant documents (e.g., updated final safety analysis reports), and 

submitted survey questions to plant personnel. The plant survey responses formed the primary source of 

data for determining the parameters used to define the ICET test conditions.2 

Post-LOCA Environment 

After a loss-of-coolant accident (LOCA), physical debris will reside in the containment pool for 

some period of time before the initiation of emergency core cooling system recirculation. During this 

time, the sump pool environment will be changing as TSP dissolves. After recirculation starts, debris will 

begin arriving at the sump screen to form a debris bed. If both NUKON and cal–sil debris are present, the 

sump screen debris bed will consist of some mix of plant debris, including cal–sil, NUKON, and calcium 

phosphate precipitates. The relative amounts of cal–sil and calcium phosphate precipitates in the debris 

bed as it initially forms will vary depending on the residence time in the containment pool prior to the 

onset of recirculation, the transport time to the sump screen, the initial containment pool pH, the 

containment pool temperature, and the TSP dissolution rate. 

For some conditions, e.g., long residence times, a large fraction of the cal–sil may have dissolved 

before the debris actually reaches the sump screen. In such cases, the debris bed will primarily contain a 

mix of NUKON fibers and calcium phosphate precipitates. In other cases, e.g., short residence times, 

little cal–sil dissolution may have occurred before the debris reaches the sump screen, and the bed that is 

initially formed will consist predominantly of a mix of NUKON fibers and cal–sil particulates. In this 

case, with time, the cal–sil within the bed can continue to dissolve, and any dissolved calcium (Ca) that is 

released will react with the available phosphate to form additional calcium phosphate precipitates. 

Prior ANL Head Loss Testing 

An initial Quick Look report by ANL3 describes the results of preliminary tests to determine the 

potential for chemical products observed in the third Integrated Chemical Effects Test (ICET–3) to 

increase the head loss associated with sump screen debris beds. The first head loss test, identified as 

ICET-3-1, was intended to simulate the calcium phosphate precipitate concentration created by the initial 

burst of dissolved calcium that formed within the first 30 minutes of the ICET-3 test, prior to metering 

TSP into the test chamber. The initial dissolved calcium concentration in ICET-3-1 (200 ppm) was 

determined through dissolution testing of the corresponding ICET-3 cal–sil loading (19 g/L submerged 

cal–sil), but did not represent the total amount of calcium phosphate that could ultimately be created from 

the cal–sil and other calcium sources (e.g., concrete) within the ICET-3 test.4 The second test (ICET-3-2) 

was parametric and intended to determine the effect of a range of chemical product loadings on head loss. 

In both tests, a pre-existing physical debris bed approximately 16 mm (5/8 in) thick consisting of 

equal amounts (15 g) of NUKON fiber and cal–sil insulation was formed. Then, dissolved calcium was 

added to the test loop, which contained TSP-buffered borated water, to form calcium phosphate 

precipitates. The added head loss due to the chemical product was then measured. A large increase in 

head loss was observed in ICET-3-1 with the chemical product loading (200 ppm of dissolved Ca) 
3 

intended to simulate initial calcium phosphate formation during ICET–3. In the parametric test (ICET-3-

2), increases in head loss were observed when the chemical product loading was one-twentieth of that 

used in ICET-3-1 (10 ppm of dissolved Ca). A detailed description of the ICET-3-1 and ICET-3-2 results 

and a detailed description of the ANL test loop are given in the first ANL Quick Look Report Tests 1 & 

2.3 

Approach 

ANL performed a series of follow-up tests (ICET-3-4 to ICET-3-11) that evaluated the potential for 

head loss due to chemical effects in a TSP-buffered environment. The tests were designed to explore 

conditions corresponding to a range of debris amounts, containment pool residence times, and TSP 

dissolution times. The two basic physical parameters that are affected by these variables are the degree of 

cal–sil dissolution that will occur before the formation of the debris bed and the interaction between the 

chemical products and the physical debris during bed formation. For instance, some fraction of chemical 

precipitates and the debris will arrive at the sump screen together and some fraction of precipitates will 

form due to cal–sil dissolution within the debris bed after the bed has initially formed. 

The NUKON and cal–sil mass loading per unit screen area utilized in these tests are reasonably 

representative of those plants that currently have, or will have after sump modifications, relatively low 

debris mass loading (i.e., less than 2 kg/m2). Because the Argonne test loop has a fixed ratio of screen 

area to fluid volume ratio, it is impossible in most cases to simultaneously match both the debris loading 

per unit screen area and the debris loading per unit volume of fluid that would be encountered in an actual 

sump configuration. In assessing the head loss, the screen loading per unit area is the critical scaling 

parameter. The cal–sil dissolution rate, however, can be a function of the debris loading per unit volume. 

The current plant estimates of the cal–sil loading per unit volume of the containment pool are less 

than 1.5 g/L. The small scale dissolution data presented later in this report show that the cal–sil 

dissolution rate at these low concentrations is not too strongly dependent on the concentration. Therefore, 

it is not too important to match the plant debris loading per unit volume within the test loop. 

 The NUKON fiberglass insulation and the cal–sil insulation used in the tests were prepared from 

materials obtained from obtained from Performance Contracting Inc. (PCI), Lenexa, Kansas. The 

NUKON was originally produced in the form of insulating blankets. The blankets were rough shredded 

to get a collection of loose fibers and clumps of fibers ranging in size from 1–2 cm in diameter. The 

shredded fiberglass is then mixed with water (≈ 1 g/65 mL water) in a blender for a short time (≈10 s) to 

produce a relatively smooth slurry. The cal–sil was originally produced in the form of molded blocks. 

The material is friable and was first broken up by hand–crushing with a mortar and pestle. The crushed 

material was mixed with water (≈ 1 g/65 mL water) in a blender for about a minute to produce a smooth 

slurry. In the present tests, the two slurries were then mixed together. The preparation of the slurry is 

done just prior to the performance of the head loss tests. 

To simulate the dissolution of the cal–sil that occurs during the residence time in the containment 

pool prior to the onset of recirculation, the cal–sil and NUKON slurry was presoaked at temperature 

(60o

C) in the baseline boric acid, lithium hydroxide (LiOH) solution for 30 minutes, and then added as a 

slurry to the loop. Since only 2.5 liters of solution were used for the presoak, the cal–sil concentration is 

much higher than it would be in the loop or in an actual sump. At high cal–sil concentrations (≥ 6 g/L), 

the total amount of cal–sil dissolution is limited by the solubility of calcium silicate (CaSiO3).3 

Regardless of the initial pH or the rate of addition of TSP, the pH of solution rises to about 7, primarily 

because cal–sil contains sodium silicate as an impurity. The sodium silicate is very soluble, and as it 

dissolves, the dissolved sodium (Na) causes the pH of the initial boric acid/LiOH solution to increase. At 

these high concentrations, the dissolved Ca level rises quickly to a saturation value of ≈200 ppm.3 In 

highly concentrated solutions, addition of TSP increases the amount of cal–sil that will eventually 
4 

dissolve, because the phosphate combines with the dissolved Ca and forms calcium phosphate 

precipitates, lowering the dissolved Ca level, and permitting further dissolution of the cal–sil. Thus, the 

highly concentrated presoak slurry is expected to form lower initial dissolved Ca concentrations than are 

realistically expected. In contrast, as subsequent dissolution data presented in this report show, at lower 

cal–sil concentrations, the increase in pH due to the dissolution of the sodium silicate impurity is much 

smaller, and rapid addition of TSP can decrease the cal–sil dissolution rate. Thus, because of the increase 

in pH, the highly concentrated presoak slurry, even with TSP additions, is expected to form lower initial 

dissolved Ca concentrations than would occur under prototypical conditions. 

The tests were performed under isothermal conditions at 60°C (140°F). The debris in all the tests 

was introduced into the loop with the flow velocity in the loop at 0.1 ft/s. The intent in these tests was to 

maintain a constant velocity through the test until a stable bed configuration steady-state head loss was 

reached and then to cycle the velocity to examine the effect on head loss. However, in most the tests, the 

head losses were too large to maintain a constant flow of 0.1 ft/s. [The maximum head loss that currently 

can be maintained in the loop is about 6 psi (≈13.8 ft of water).] Because a flow velocity of 0.1 ft/s is 

higher than expected at the sump screen in most planned modified sump configuration, the head loss 

measurements are conservative with respect to this variable. 

The test conditions used in this series of tests are summarized in Table 1. The judgments expressed 

in the Table 1 comment section that the test conditions represent “minimal”, “maximum”, or “typical” test 

values for the amount of cal–sil dissolution during the initial debris bed formation is based on the results 

of the cal–sil dissolution tests reported in the previous Quick Look Report3, the new dissolution tests 

described in this report, and expected plant TSP dissolution times.5 

Each head loss test utilized a slightly different procedure for simulating specific chemical product 

formation rates and debris arrival sequences depending on the test objective. While the general test 

procedures are similar to those described in [3], the unique procedures associated with each test were 

varied to obtain the conditions described in Table 1. Descriptions of the unique procedures associated 

with each test are subsequently presented along with a summary of the results. 
5 

Table 1. ICET-3 Environment Head Loss Tests 

Test No. 

NUKON 

(g)a

cal–sil 

(g) 

30 min 

Presoak TSPb

Additional 

dissolved 

Ca (ppm) Comment 

ICET-3-1 15 15 No Initially in 

loop 

200 Simulates initial conditions in 

ICET-3; precipitates arrive 

after bed forms 

ICET-3-2 15 15 No Initially in 

loop 

10, 25, 50 

ppm Cad Parametric test starting with 

1/20th dissolved Ca of ICET3: precipitates arrive after bed 

forms 

ICET-3-4 7 25 Yes 1/8th 

initially in 

loop; 7/8th 

metered in 

None Minimal cal–sil dissolution 

prior to initial bed formation; 

continued dissolution as test 

continues 

ICET-3-5 7 25 Yes None None Baseline physical debris only 

ICET-3-6 15 15 Yes 1/8th 

initially in 

loop; 7/8th 

metered in 

None Minimal cal–sil dissolution 

prior to initial bed formation 

ICET-3-7 15 15 Yes None None Baseline physical debris only 

ICET-3-8 15 0 No Initially in 

loop 

43.5c

 CaCl2 & NUKON added 

simultaneously; Maximum 

cal–sil dissolution prior to 

bed formation 

ICET-3-9 15 0 No Initially in 

loop 

9, 18, 27 

ppm Cad 

CaCl2 added after NUKON 

bed stabilizes maximizes 

arrival time of precipitates to 

bed; Maximum cal–sil 

dissolution prior to arrival at 

the bed 

ICET-3-10 15 15 Yes 1/2 in 

metered 

during 

presoak; 1/2 

metered in 

None Intended to represent a 

“typical” degree of cal–sil 

dissolution prior to bed 

formation 

ICET-3-11 15 15 Yes None None Baseline physical debris only 

(Replicates ICET-3-7) 

a1 g of debris corresponds to a screen loading of 47.6 g/m2

bThe total amount of TSP in each test where TSP was added was always 3.4 g/L. Some fraction was 

either dissolved initially in the test loop or metered in during the presoak period. The remaining fraction 

was metered in during a 30-60 minute period after the debris was added to the loop. 

cCa equivalent to full dissolution of 15 g cal–sil. 

dCa additions added incrementally to sequentially reach values of dissolved Ca listed. 
6 

ICET-3-4 Test Procedure: 

The physical debris in ICET-3-4 consisted of 25 g (1.19 kg/m2; 0.2 g/L) of cal–sil and 7 g of 

NUKON (0.33 kg/m2; 0.06 g/L). The amount of cal–sil per unit area of the screen in this test was 

intended to bound the values expected after plants have installed their modified screen designs.5 The cal–

sil and NUKON were heated outside the test loop for 30 minutes at 140oF in borated water (2800 ppm B 

and 0.7 ppm Li) to simulate the cal–sil/NUKON dissolution that occurs in the period between the LOCA 

and the onset of recirculation. Because no TSP was added during the presoak phase, the dissolution 

testing results for high concentrations of cal–sil (> 6 g/L)3 show the concentration of dissolved Ca in the 

2.5 L of presoak solution will saturate at ≈200 ppm. This gives an effective inventory of dissolved Ca in 

the loop of ≈ 4 ppm when the 2.5 L of presoak solution is added to the loop, which has a volume of ≈120 

L. One eighth of the desired TSP concentration was premixed in the loop before the addition of the debris 

to simulate the TSP dissolution that occurs prior to the start for recirculation. The remaining TSP was to 

be metered into the loop over an hour to simulate the dissolution of the remaining TSP after the start of 

recirculation. Although there is uncertainty in how long it will take for the TSP to dissolve, even one 

eighth of the TSP inventory is sufficient, on a stoichiometric basis, to convert to calcium phosphates the 

dissolved Ca level equivalent to full dissolution of 0.2 g/L of cal–sil. Thus, the amount of precipitate that 

is formed as the debris slurry is added to the loop is limited by the dissolved Ca available. 

This test was intended to be a lower bound (for this cal–sil loading) for the amount of calcium 

phosphate precipitate arriving at the screen as the initial debris bed is formed. However, additional cal–sil 

dissolution and calcium phosphate formation was expected to occur after the initial formation of the bed. 

Therefore, it was planned that the test would proceed until either all the calcium phosphate had formed 

(based on stabilized dissolved phosphorus levels in the loop mixture), or the head loss reached steady 

state. It was anticipated that the test could last up to three days. 

ICET-3-4 Results: 

The test started at 7:45 am and terminated at 12:07 pm on November 15, 2005. Figure 1 shows the 

bed approach velocity and differential pressure across the screen, as a function of time during the test. 

Figure 2 shows an expanded view of the velocity and pressure during the first 15 minutes of the test. 

After the introduction of the debris, the pressure drop across the bed increased very rapidly to 6.5 psi, 

before any additional TSP could be metered into the loop. The pump started to ingest air so the flow 

velocity was reduced to 0.03 ft/s. However, after operating for several minutes at that velocity it became 

apparent that large amounts of air had accumulated under the test screen and the test was terminated. 
7 

Figure 1. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-4. 

Figure 2. Expanded view of bed approach velocity and differential pressure across the screen during 

the initial 15 minutes of test ICET-3-4. 

ICET-3-5 Test Procedure: 

The type and amount of physical debris for this test was identical to that for test ICET-3-4. This 

was a baseline test to determine the effects of the debris alone with no calcium phosphate precipitates. 

The cal–sil and NUKON were again heated outside the test loop for 30 minutes at 140oF in borated water 

(2800 ppm B and 0.7 ppm Li), but no TSP was added either to the presoak or to the loop during this test. 

ICET-3-5 Results: 

This test again resulted in high head loss. Figure 3 shows the bed approach velocity and differential 

pressure across the screen, as a function of time during the test. After the debris was added to the loop, 
8 

the pressure drop increased very rapidly. When the pressure drop across the bed increased to about 3 psi, 

jetting through the debris bed was observed at 25 minutes and the test was terminated at 35 minutes. It is 

not clear whether the difference in the peak values of ∆p attained between this test (3 psi) and ICET-3-4 

(6 psi) reflects simple scatter in when jetting can occur or whether the presence of the chemical product 

helps prevent jetting by more effectively plugging weak spots in the bed. Figure 4 shows an expanded 

view of the velocity and pressure during the first 10 minutes of tests ICET-3-4 & 5. Head loss for the 

debris loading in these tests was substantial and occurred within the first six minutes (or after 

approximately one test loop recirculation) after introducing debris. Other than the maximum pressure 

reached during the test, the presence of calcium phosphate did not clearly alter the observed accumulation 

of head loss during these tests. 

Figure 3. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-5. 

Figure 4. Expanded view of bed approach velocity and differential pressure across the screen during 

the initial 10 minutes of tests ICET-3-4 & 5. 
9 

ICET-3-6 Test Procedure: 

Due to the high head losses observed with the debris bed loading used in the previous tests, the 

debris loading in ICET-3-6 was changed to 15 g of cal–sil and 15 g of NUKON. The intent of this test 

was identical to that of test ICET-3-4, i.e., to minimize the amount of initial calcium phosphate precipitate 

arriving at the screen as the debris bed is formed for a given cal–sil loading. The motivation for 

decreasing the loading was to attempt to more clearly understand the head loss contribution that could be 

attributed to calcium phosphate formation. This debris loading had been previously used in ICET-3-1 & 

2 and exhibited only modest increases in head loss in the absence of chemical effects. The 15 g cal–sil 

loading (0.13 g/L) is also representative for some plants containing TSP and cal–sil.5 

ICET-3-6 Results: 

Figure 5 shows the bed approach velocity and differential pressure across the screen, as a function 

of time during the test. Figure 6 compares the head loss in this test during the first 45 minutes after 

introducing NUKON and cal–sil to the test loop with the earlier ICET 3-1 & 2 tests. Tests ICET-3-1 & 2 

had similar amounts of debris loading as ICET-3-6, although the NUKON and cal–sil in ICET-3-6 came 

from different batches of materials. Additionally, the debris materials were not presoaked in ICET-3-1 & 

2 to create an initial dissolved Ca inventory, thus less calcium phosphate would be expected initially in 

tests ICET-3-1 & 2. However, the initial amount of dissolved Ca in ICET-3-6 is minimized because no 

TSP was added during the 30 minute presoak. It is therefore not surprising that the difference in head loss 

between test ICET-3-6 and tests ICET-1 & 2 within the first 30 minutes is not too large. However, 

compared with ICET-1 & 2, the head loss in ICET-3-6 continues to increase as the test proceeds, more 

cal–sil dissolves, and more calcium phosphate is subsequently formed. 

Figure 5. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-6. 
10 

Figure 6. Expanded view of bed approach velocity and differential pressure across the screen during 

the initial 45 minutes of tests ICET-3-1, 2 & 6. 

ICET-3-7 Test Procedure: 

Test ICET-3-7 was a baseline test with a debris loading of 15 g of cal–sil and 15 g of NUKON and 

no TSP in the loop or in the presoak at any time. Therefore, no calcium phosphate precipitate is present to 

contribute to head loss. The cal–sil and NUKON were again heated outside the test loop for 30 minutes at 

140oF in borated water (2800 ppm B and 0.7 ppm Li) and then added to the loop. 

ICET-3-7 Results: 

Figure 7 shows the bed approach velocity and differential pressure across the screen, as a function 

of time during the test. The pressure drop across the bed increased rapidly (within 25 minutes) to about 

2.8 psi and then stabilized. It was suspected that, at this point, the bed had perforated and jetting was 

occurring even though the bed appeared smooth and uniform. However, a considerable layer of air had 

developed underneath the bed and this precluded the actual identification of any jet. To determine if 

jetting was occurring, the inlet tee, which is normally left open, was filled to the top with about one liter 

of demineralized water and sealed with a closure flange. The loop was then pressurized to 13 psi using 

demineralized water 46 minutes after the debris was added. Under pressure, the air layer under the bed 

was greatly reduced and it became possible to confirm that jetting was occurring and to identify jet 

locations in the bed, although the bed still exhibited no observable defects. 

 The pressure drop across the debris bed increased very rapidly compared to the corresponding 

pressure drops observed in ICET-3-1, 2, & 6 which had similar debris loadings. Because no TSP was 

introduced at any time during the test, no calcium phosphate precipitates were expected to form. 

Chemical analysis of grab samples taken periodically through the test confirmed that P levels were very 

low, as expected. Because the magnitude and rapidity of the pressure drop increase in this test are much 

greater than observed in both earlier tests with similar debris loading and in subsequent replicate tests 

under the same nominal conditions, the results of this test are believed to be anomalous. 

During this test, some release of noncondensible gases was observed as the pressure drop across the 

bed increased to about 1.4 psi. This led to a re-evaluation of the procedure for deaerating the loop. In this 

test and in previous tests, the loop had been deaerated on the day prior to the test day by heating the water 
11 

to 71°C (160°F) and circulating the test loop fluid at fairly high speeds (2 ft/s) for several hours. The loop 

was then allowed to cool overnight. This procedure had been chosen to avoid running the pump 

overnight unattended. However, as the test loop fluid cooled, additional gases were re-entrained in the 

fluid and thus, were available to be released at relatively low pressures. Exploratory tests had shown that 

heating of the water induced sufficient natural circulation to maintain a uniform temperature in the loop 

without the pump. The deaeration procedure for subsequent tests was modified to never let the loop cool 

down after the initial heat–up in order to minimize the noncondensible gases in the fluid. Natural 

circulation was used to maintain a uniform temperature without the need to run the pump unattended 

overnight. 

Figure 7. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-7. 

ICET-3-8 Test Procedure: 

ICET-3-8 was intended to represent the limiting case when the cal–sil debris is largely dissolved 

prior to the formation of the debris bed. In this test, the boric acid, lithium hydroxide and all of the TSP 

were added to the loop water and heated to 60°C prior to adding the physical debris. The physical debris 

consisted of 15 g NUKON which has been presoaked for 1⁄2 hour at 60°C. The NUKON slurry was then 

combined with 14.3 g of CaCl2, which gives an amount of dissolved Ca level equivalent to complete 

stoichiometric dissolution of 15 g cal–sil. The NUKON/CaCl2 mixture (about 2.5 L) was then added to 

the loop. The addition was done in about 30 seconds. Because the reaction of the dissolved Ca with the 

phosphate is very rapid, the test screen debris bed was formed with a simultaneous mix of NUKON and 

calcium phosphate precipitates. 

ICET-3-8 Results: 

Figure 8 shows the bed approach velocity and differential pressure across the screen as a function 

of time. After adding the NUKON and CaCl2 mixture, the pressure drop across the bed increased very 

rapidly and it was not possible to maintain the loop flow velocity at 0.1 ft/s through the pump. After ≈8 

minutes, the flow rate was decreased to 0.03 ft/s, and the pressure drop stabilized at ≈5 psi. The debris 

bed appeared to be uniform with a thickness between 8 – 10 mm early in the test before the pressure drop 

got too large. The bed compressed to a thickness of approximately 6 mm at the end of the test. The loop 

water quickly cleared indicating rapid debris bed filtration. No jetting through the bed was observed. 
12 

Figure 9 shows the photographs of the debris bed from this test after removal from the loop and at 

the end of the test with the loop almost drained. The debris bed height (see Figure 9b) has increased 

slightly compared with thickness at the end of the test. Additionally, the debris bed is comprised of two 

distinct layers (Figure 9b). The bottom layer is mixed NUKON and calcium phosphate precipitate while 

the top layer is predominantly calcium phosphate precipitate. 

Figure 8. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-8. 

(a) (b)

Figure 9. (a) Debris bed from ICET-3-8 after removal from the loop: (b) Debris bed in the loop at the 

end of the test with the loop almost drained. The bed has two distinct layers. (Readers of the 

electronic version may wish to zoom to 500% to see the layers more distinctly.) 

ICET-3-9 Test Procedure: 

ICET-3-9 was intended to evaluate the head loss from chemical phosphate precipitate arriving at 

the test screen after the NUKON bed had formed. This test objective and procedure is similar to previous 

ICET-3-1 & 2 tests. The physical debris bed consisted of 15 g of NUKON and was formed before the 

addition of any CaCl2, i.e., before the formation of any calcium phosphate precipitate. The loop initially 

contained a base solution with 2800 ppm B, 0.7 ppm Li, and TSP (3.4 g/L). A total of 14.3 g of CaCl2
13 

was chosen to give a dissolved Ca inventory equivalent to a complete stoichiometric dissolution of 15 g 

cal–sil. The CaCl2 solution was planned to be added in 5 steps (1/5 of the total amount at each step) with 

the pressure drop allowed to reach steady state between each step. Only 3 of the 5 CaCl2 additions were 

completed before the test was terminated. 

ICET-3-9 Results: 

The pressure drop across the screen prior to the addition of the NUKON was 0.07±0.02 psi at an 

approach velocity of 0.1 ft/s. [The pressures are recorded approximately every 5 sec by the data 

acquisition system. When the pressure data are presented as a running average over a minute, the 

standard deviation of the running average is much smaller, ±0.005.] The pressure drop across the 

NUKON bed before the addition of any CaCl2 is shown in Fig. 10. The steady state drop across the bed 

at this stage of the test was 0.14±0.02 psi and the debris bed was about 14 mm thick. A relatively stable 

value of the pressure drop was reached after one pass around the loop (≈4 min). 

Eighteen minutes after the NUKON was introduced, 200 ml of CaCl2 solution was added. This 

addition represents the stoichiometric dissolved Ca equivalent (≈9 ppm) of 3 g of cal–sil. The pressure 

drop increased to 0.242 psi (Fig. 11) and the bed compressed to 12 mm. Twenty–eight minutes after the 

NUKON was introduced, a second 200 ml CaCl2 addition was made. The pressure drop increased to 1.2 

psi and the bed compressed to 9 mm. It appears from the data (Figure 11) that this value may not quite 

represent the steady state head loss for this condition. Forty–one minutes after the NUKON was 

introduced, the third 200 ml CaCl2 addition was made. After this addition, the pressure drop increased 

dramatically and the approach velocity could not be maintained at 0.1 ft/s. The flow rate decreased to 

0.02 ft/s 43 minutes after the initial NUKON addition, and could no longer be controlled because the 

pump inlet pressure was at 0 psi. The flow rate continued to slowly decrease slowly while the pressure 

drop continued to rise gradually during the remainder of the test. The pressure drop asymptotically 

increased to ≈5.2 psi, as the velocity decreased. The bed thickness decreased to 7 mm at the highest 

pressure. Figure 11 shows the bed approach velocity and differential pressure across the screen as a 

function of time for entire duration of the test. 

Figure 10. Pressure drop across the NUKON bed in test ICET-3-9 at an approach velocity of 0.1 ft/sec. 
14 

Figure 11. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-9. 

ICET-3-10 Test Procedure: 

ICET-3-10 also used a debris loading of 15 g NUKON and 15 g cal–sil. The debris was presoaked 

for 30 minutes at 60°C, prior to introduction into the loop. One half of the total TSP addition was added 

to the debris slurry during the 30 minute presoak period, starting five minutes after the introduction of the 

debris and then continuing at a nominally uniform rate over the remaining 25 minutes. The remaining 

half of the TSP was metered directly into the loop over 30 minutes at a nominally uniform rate after the 

introduction of the debris. This TSP addition sequence was intended to represent a plant where TSP 

begins to dissolve 5 minutes after the start of a LOCA, and complete dissolution has occurred one hour 

after a LOCA. The conditions in this test were intended to represent a “typical” degree of dissolution of 

cal–sil prior to formation of the bed. However, because of the rapid rise in pH in the presoaking solution 

due to the high concentration of cal–sil, the presoaking probably leads to somewhat less cal–sil 

dissolution than would occur at more realistic concentrations for the same TSP history. 

ICET-3-10 Results: 

The bed approach velocity and differential pressure across the screen as a function of time for test 

ICET-3-10 is shown in Fig.12. This test resulted in a rapid buildup of head loss. After 10 minutes, the 

flow velocity could not be maintained at 0.1 ft/s and the flow velocity gradually decreased. At the end of 

test, the pressure drop across the bed was 4.7 psi (±0.9%) at a bed approach velocity of 0.06 ft/s (±0.8%). 
15 

Figure 12. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-10. 

ICET-3-11 Test Procedure: 

ICET-3-11 was a repeat of the baseline test, ICET-3-7, with a debris loading of 15 g NUKON and 

15 g cal–sil. No TSP was introduced in the test during either the presoak or in the loop. 

ICET-3-11 Results: 

The bed approach velocity and differential pressure across the screen as a function of time for test 

ICET-3-11 is shown in Fig. 13. At 0.1 ft/s, the pressure drop stabilized at around 1.4±0.03 psi. After 210 

minutes (≈52 recirculations) at a loop velocity of 0.1 ft/s, the loop velocity was cycled from 0.1 ft/s to 

0.01 ft/s to 0.14 ft/s and back to 0.1 ft/s. Figure 14 shows the variation of the pressure drop across the bed 

as the velocity is cycled. Comparison with Fig. 10 shows that it takes much longer for a NUKON/cal–sil 

bed to reach a stable pressure drop than it does for a pure NUKON bed. 

Test ICET-3-11 was a repeat of ICET-3-7. However, the pressure drop across the bed is very 

different for the two tests as shown in Fig. 15. No reason for this difference in behavior has been 

determined. The behavior illustrated in ICET-3-11 is consistent with the behavior observed in other tests 

without TSP while the ICET-3-7 results are substantially different and appear to be anomalous. This 

point is illustrated in Fig. 16, which shows a comparison of bed approach velocities and differential 

pressures across the screen as a function of time for tests ICET-3-1, 2, & 11. Therefore, ICET-3-11 

results have been used as the baseline for comparisons with tests in which precipitates are present. 
16 

0

0.05

0.1

0.15

0.2

0.25

0

1

2

3

4

5

0 40 80 120 160 200 240 280 320

Velocity

∆p

Approach Velocity (ft/s)

Pressure Drop (psi)

Time (min)

NUKON & CalSil

added at t=0

ICET-3-11

NUKON 15 g

CalSil 15 g 

No TSP

Figure 13. Bed approach velocity and differential pressure across the screen as a function of time for 

test ICET-3-11. 

Figure 14. 

Change in pressure drop across the bed 

as the velocity is cycled from 0.1 ft/s to 

0.01 ft/s to 0.14 ft/s and back to 0.1 ft/s. 
17 

Figure 15. Bed approach velocities and differential pressures across the screen as a function of time for 

tests ICET-3-7 & 11. 

Figure 16. Bed approach velocities and differential pressures across the screen as a function of time for 

test ICET-3-1, 2, & 11. 

Discussion of the loop test results 

The pressure drops across the bed for tests with physical debris of 15 g NUKON/15 g cal–sil and 

TSP present (ICET-3-6 and ICET-3-10) are compared with the baseline test ICET-3-11, which had 15 g 

NUKON/15 g cal–sil but no TSP, in Figs. 17a and b, respectively. In ICET-3-6, no TSP was added to the 

presoak in order to limit the possible dissolution of the cal–sil. This scenario was intended to give a 

lower bound for the amount of calcium phosphate precipitate arriving as the debris bed is formed. As 

expected, the initial pressure drop behavior in ICET-3-6 is very similar to the baseline case ICET-3-11 in 

which no chemical precipitates are present (Figure 17a). However, a comparison of the maximum 

pressure drops reached in ICET-3-6 and -11 (Figs. 5 and 13) show that the difference in the pressure drop 
18 

increases with time. The increase of the pressure drop with time in ICET–3-6 is attributed to the 

continuing dissolution of cal–sil and additional formation of calcium phosphate precipitates. 

Test ICET-3-10 was intended to give the “typical” amount of calcium phosphate precipitate 

arriving as the bed is formed in design basis analyses. As noted previously, at the end of the presoak 

period, a much larger amount of CaSiO3 will have dissolved, and much larger amount of calcium 

phosphates precipitates will have formed compared to the ICET-3-6 case. This results in a much more 

rapid increase in head loss than in ICET-3-6 (Figure 17b), although the pressure drop in ICET-3-6 

eventually approaches the steady state value obtained in ICET-3-10. Although this argument qualitatively 

explains the differences between ICET-3-6 and 10, the “lag” in the pressure drop is greater than the 30 

minutes that would be expected due to differences in the amounts of cal–sil dissolved during the presoak. 

A comparison of the pressure drops in ICET-3-8 and ICET-3-9, shown in Fig. 18, suggests a 

strongly nonlinear relationship between the amount of the calcium phosphate precipitate and the pressure 

drop. The first two additions of CaCl2 in ICET-3-9 produced relatively small increases in pressure drop. 

The third addition resulted in a very rapid increase in pressure drop. The total inventory of dissolved Ca 

added in ICET-3-9 is equivalent to complete dissolution of 9 g of cal–sil. The pressure drop observed in 

ICET-3-8 after addition of 43.5 ppm of dissolved Ca as CaCl2 is almost as the same as that observed in 

the ICET-3-2 test (see Reference 3) in which 50 ppm Ca as CaCl2 was added to the loop. However, this 

comparison may be confounded by the difference in precipitate distribution through the bed. The bed in 

ICET-3-8 was formed from the simultaneous arrival of fiber and precipitate. In ICET-3-9, the precipitate 

was deposited on a preformed fibrous bed. Since precipitate can presumably move through and into the 

bed, the difference in the way the beds were formed may not completely define the actual structure. The 

beds from the two tests can be examined to compare the precipitate distribution, but this has not yet been 

done. An additional test would be required to directly compare the effects of either simultaneous or 

sequential arrival of the chemical precipitate associated with the complete dissolution of 9 g of cal–sil. 

The pressure drop increases with time occur because more debris is trapped during each pass 

through the debris bed during recirculation and because of continued cal–sil dissolution and formation of 

additional precipitates. In ICET-3-10, which represents a “typical” amount of cal–sil dissolution before 

the formation of the bed, it takes about 3 recirculations (or approximately 12 minutes) of the test loop 

fluid to build to the maximum pressure drop. In ICET-3-8, which represents the maximum cal–sil 

dissolution before the formation of the bed, the maximum pressure drop is reached after 1 test loop 

recirculation. The head loss due to chemical products in both of these cases is dominated by the 

precipitates that formed due to dissolution prior to the initial bed formation, and the pressure drop 

increases as more of these precipitates are trapped during recirculation. The effect of continued 

dissolution could not be determined because the pressure drop quickly reached the capability of the loop. 

However, in ICET-3-6, which represents the minimum cal–sil dissolution that would occur before the 

formation of the bed, it takes about 15 passes test loop recirculations to approach the maximum pressure 

drop. In this case the pressure increase is probably dominated by the time needed for additional cal–sil 

dissolution. 

The degree of dissolution that would occur before the debris reached the sump screen in a 

prototypical situation would presumably be bounded by the ICET-3-6 and ICET-3-8 limiting cases, and 

may be most similar to the ICET-3-10 case. The amount of head loss for a plant specific case is 

dependent on factors such as the sump screen debris loading, uniformity of the screen debris loading, 

propensity for flow bypass (i.e., jetting) through the debris bed, debris bed screen approach velocity, and 

transport of chemical precipitate. However, the ICET-3-6, 8, and 10 results indicate the variability of 

head loss behavior that could be encountered for a specific loading because of differences in the onset of 

recirculation, debris transport time, initial containment pool pH, and TSP dissolution rate. 
19 

(a) 

(b) 

Figure 17. (a) Bed approach velocities and differential pressures across the screen as a function of time 

for test ICET-3-6 & 11; (b) Bed approach velocities and differential pressures across the 

screen as a function of time for test ICET-3-10 & 11. 

In the tests with 15 g NUKON/15 g cal–sil, the strong effect of the chemical precipitates on 

pressure drop is readily evident. Such an effect is less evident in the comparison of the tests with 7 g 

NUKON/25 g cal–sil. The pressure drops in ICET-3-4, in which some precipitation of calcium phosphate 

would occur, and ICET-3-5, in which no precipitation would occur are compared in Fig. 19. Since no 

TSP was added to the presoak, the cal–sil dissolution in ICET-3-4 was limited similarly to ICET-3-6, so 

that a strong chemical effect would not be expected until there was time for additional dissolution in the 

loop. However, with this cal–sil loading, even without the effect of calcium phosphate precipitates, the 

head loss increases very rapidly to a high level. 
20 

Figure 18. Bed approach velocities and differential pressures across the screen as a function of time for 

test ICET-3-8 & 9. 

Figure 19. Bed approach velocities and differential pressures across the screen as a function of time for 

test ICET-3-4 & 5. 

Calcium Phosphate Settling Tests 

In the head loss loop tests, virtually all the calcium phosphate precipitates that form are transported 

to the bed. In an actual sump, there is a potential for the precipitates to settle before they reach the sump 

screen. Settling tests were performed to determine settling rates for calcium phosphate under conditions 

with no bulk directional flow. Tests were performed in a settling tower with an effective height of 71.5 

cm. The tower was filled with a solution containing LiOH (0.7 ppm Li) and boric acid (2800 ppm B) and 

TSP (3.4 g/L). CaCl2 solution was then added to the tower. The dissolved Ca reacts with the TSP in the 

solution to form calcium phosphate precipitate. The solution is stirred to get a uniform mixture and then 

the precipitates are allowed to settle. Two different CaCl2 concentrations were tested. One produced a 
21 

dissolved Ca inventory equivalent to 300 ppm and the other an inventory equivalent to 75 ppm. The 300 

ppm inventory is roughly equivalent to full stoichiometric dissolution of a 1 g/L concentration of cal–sil; 

the 75 ppm inventory is roughly equivalent to full stoichiometric dissolution of a 0.25 g/L concentration 

of cal–sil. In both cases, the solutions are phosphate-rich for a TSP concentration of 3.4 g/L, i.e., the 

formation of calcium phosphate precipitates is limited by the amount of Ca available. Replicate settling 

tests were conducted for each concentration. 

In the 300 ppm tests, there was more of a tendency for precipitate particles to agglomerate and a 

visible settling front was observed, as shown in Fig. 20. Grab samples taken before and after the front 

passed suggest that about half the precipitate was removed as the front passed. The mixture behind the 

front looked relatively uniform and gradually became less cloudy. In the 75 ppm tests, a front was not 

visible. The mixture looked relatively uniform throughout most of the tower and gradually became less 

cloudy. There was a more noticeable mix of upward and downward moving individual particles. 

The time histories of the settling front in the 300 ppm dissolved Ca tests were estimated by taking a 

sequence of pictures of the front at intervals and noting the location of the front relative to a scale 

mounted on the settling cylinder. As shown in Fig. 21, the front velocity is relatively constant until it 

approaches the bottom of the settling tower. The average velocity of the front in the 300 ppm tests is 

3.8 cm/min. Settling of remaining particulate after the front passed occurred much more slowly and the 

settling velocities are likely more consistent with those measured in the 75 ppm tests. 

In the 75 ppm dissolved Ca tests where no front was evident, the settling velocities were estimated 

by taking three grab samples at intervals from the top of the settling column and noting the relative 

decrease in the amount of precipitate in the samples with increasing time. The decay in the amount of 

precipitate in the samples can be modeled as exponential as shown in Fig. 22. The time constant for the 

decay is approximately 87.5 minutes. This corresponds to a settling velocity of 0.8 cm/min. This is more 

representative of the settling characteristics of the calcium phosphate precipitates at the concentrations of 

most interest. 
22 

Figure 20. 

Settling front in test with 300 ppm Cl 

(a) (b)

Figure 21. Time history of the motion of the settling front in the two 300 ppm dissolved Ca settling tests. 

Figure 22. 

Assumed exponential decay of volume of 

suspended precipitate in 75 ppm dissolved Ca test. 
23 

Small Scale Dissolution Testing 

The objective of the small scale dissolution testing is to identify important environmental variables 

governing both dissolution of cal–sil and the subsequent formation of calcium phosphate precipitates over 

a range of simulated sump pool conditions. The variables considered in the results reported herein are the 

effect of the rate of TSP addition to the cal–sil solutions for various cal–sil concentrations. 

Three different histories of TSP addition were studied. These histories are intended to encompass 

the range of histories of TSP dissolution expected within an actual containment pool: 

1. Add TSP before cal–sil addition (instantaneous dissolution of TSP). 

2. Titrate TSP over 1 hr period into solution after cal–sil addition (nominal case). 

3. Titrate TSP over 4 hr period into solution after cal–sil addition (very slow addition of TSP). 

The test temperature was 60°C. The base solution consisted of 2800-ppm-B and 0.7-ppm Li. The TSP 

concentration was 3.4 g/L which results in a nominal pH value of 7.1 in the buffered solution. The cal–sil 

concentrations for the tests were 0.5 and 1.5 g/L. The 0.5 g/L cal–sil concentration is generally 

representative of current plant design basis concentrations based on a survey of plants that utilize TSP 

buffering and expect cal–sil to be present in the containment pool.5 The 1.5 g/L concentration is greater 

than current plant concentrations. At these concentrations, the formation of calcium phosphate 

precipitates is expected to be Ca limited, since Ca3(PO4)2 [tricalcium phosphate] or Ca10(PO4)6(OH)2

[hydroxylapatite] are the two most likely forms for the calcium phosphate precipitates at this pH.6 

The results from small scale dissolution tests performed at 60°C to date are summarized in Table 2. 

Time, in these tables, represents the elapsed time after the cal–sil was added to the base solution. 

However, grab samples were taken only after the TSP additions were completed in each test. The values 

for Ca, P, Si, and Na in the tables were determined by inductively coupled plasma (ICP) measurements on 

the grab samples. ICP measures the total amount of elements present in a sample whether they are 

present as solutes or solid species. However, the samples were filtered prior to ICP analysis and the ICP 

results are expected to represent only species in solution. 

Since the Ca which is released (as the cal–sil dissolves) and quickly combines with the available 

dissolved phosphate to form a solid calcium phosphate precipitate, the ICP measurements of Ca in the 

filtered supernate are not representative of the amount of Ca that has actually dissolved. The 

measurements of dissolved P have been used to estimate the amount of Ca that has been precipitated. If 

all the P that was added as TSP remained in solution, the P concentration would be 277 mg/L. The 

measured P concentrations are always less than this concentration. It is assumed that the missing P has all 

combined with Ca to form solid calcium phosphate precipitates. There are a variety of calcium phosphate 

species having different stoichiometries. The least soluble species at the pH values of interest are 

Ca3(PO4)2 [tricalcium phosphate] and Ca10(PO4)6(OH)2 [hydroxylapatite].6 Values of the amount of Ca 

residing in calcium phosphate precipitate have been calculated for each of these assumed species based on 

the missing P in solution. This information is summarized in the last two columns of Table 2. The total 

dissolved Ca can be estimated by adding the measured Ca (column 4 in Table 2) with the Ca from either 

of the last two columns in Table 2. 

The dissolved Ca that has combined to form calcium phosphate can be estimated based on the 

assumption that the precipitates are primarily hydroxylapatite. These values are shown in Figs. 23a and 

23b. In these graphs, the time, once again, is measured from the time that the cal–sil is added to the 

solution. The data legend indicates if the TSP dissolution was instantaneous (“instant”), completed in 1 

hour (“nominal”), or completed in 4 hours (“slow”). While there is variability in the data, it appears that 
24 

the TSP dissolution history has a larger effect at the higher cal–sil loading (1.5 g/L) than it does at 0.5 

g/L. It appears from the data in Table 2, that it takes substantial time (approximately 4 days) to achieve 

full dissolution for the 1.5 g/L cal–sil concentration while the 0.5 g/L concentration appears to be 

completed within approximately 1 - 3 days. For both cal–sil concentrations, substantial Ca dissolution 

(> 75 mg/L) has occurred within a few hours regardless of the TSP addition rate. 

 These data are replotted in normalized form in Fig. 24. In this figure, the total dissolved Ca at each 

point in time is normalized by the Ca concentration corresponding to complete stoichiometric dissolution 

of the total amount of cal–sil present. The figure shows that for the case of instantaneous TSP 

dissolution, the fractional amounts of dissolved Ca are significantly different for the two different cal–sil 

loadings. For the more realistic 1 hour TSP dissolution history and the bounding 4 h TSP dissolution 

history, the normalized Ca values are close for the two loadings, i.e., the amount of dissolved Ca just 

scales with concentration. Even for the case of instantaneous TSP dissolution, the normalized dissolution 

rate of the 0.5 g/L cal–sil loading is similar to that observed for the 1 and 4h TSP addition rates for the 0.5 

and 1.5 g/L loadings. This supports the assumption stated earlier that the cal–sil dissolution rate is not too 

strongly dependent on the concentration for these low cal–sil concentrations. Thus, the screen loading per 

unit area is the most important scaling parameter for head loss tests with calcium phosphate precipitates. 

(a) (b) 

Figure 23. (a) Dissolution of cal–sil at a loading of 1.5 g/L for three different histories of TSP addition; (b) 

Dissolution of cal–sil at a loading of 0.5 g/L for three different histories of TSP addition. 
25 

Figure 24. Normalized dissolution data, dissolved Ca/Ca for full dissolution for loadings of 1.5 g/L and 

0.5 g/L for three different histories of TSP addition. 

Summary of Important Findings 

Chemical products (calcium precipitates) associated with the ICET-3 sump environment have a 

significant effect on head loss across simulated sump screen debris beds. The head losses associated with 

pure physical debris beds of NUKON and cal–sil are typically much smaller than those that occur across 

debris beds in which some of the cal–sil has been replaced with a corresponding amount of calcium 

phosphate precipitates. 

The relative importance of chemical effects depends strongly on the debris loading at the screen. 

For a screen loading corresponding to 1.19 kg/m2 of cal–sil and 0.33 kg/m2 of NUKON (25 g and 7 g 

respectively in the ANL loop), the pressure drop associated with the physical debris bed is sufficiently 

large that the additional contributions related solely to chemical products could not be determined in the 

current test loop. Debris loadings of this magnitude produced significant pressure drop in the test loop 

even without consideration of chemical product effects. However, for a screen loading corresponding to 

0.71 kg/m2 (15 g each) of cal–sil and NUKON, the pressure drop across the physical debris bed in 

benchmark testing is approximately 1.4 psi at an approach velocity of 0.1 ft/s. With TSP, and thus 

calcium phosphate precipitates present, the same debris loading caused the pressure drop across the bed to 

be greater than 5 psi for the same approach velocity. Because the conversion of cal–sil into calcium 

phosphate significantly increased the head loss, the relative importance of chemical effects is greater for 

this NUKON and cal–sil debris mixture than for the higher cal–sil concentration. 

Complete dissolution of the cal–sil could take one to four days or more depending on the TSP 

dissolution rate and the cal–sil concentration. Dissolution of 1.5 g/L cal–sil concentrations is retarded by 

instantaneous TSP dissolution. However, the cal–sil dissolution rate (for the concentrations studied) is 

not strongly dependent on the TSP dissolution rate over the range of slower, more realistic TSP 

dissolution rates studied. Regardless of TSP dissolution rate, the equivalent dissolved Ca exceeded 75 

mg/L in a few hours for cal–sil concentrations as low as 0.5 g/L. Such an equivalent dissolved Ca 

concentration was shown to produce pressure drops on the order of 5 psi at an approach velocity of 0.1 

ft/s across a 0.71 kg/cm2 NUKON debris bed. 
26 

In the loop tests, all the calcium phosphate that is formed is transported to the screen. Settling tests 

were performed to determine settling rates for calcium phosphate under conditions with no bulk 

directional flow. At higher dissolved calcium concentrations (300 ppm), the precipitates can agglomerate. 

The agglomerated precipitates settle more quickly, but approximately one half of the total precipitate 

settles more slowly than the agglomerated precipitate. At a lower dissolved calcium concentration (75 

ppm), which is expected to be more representative of plant conditions, the estimated settling velocity is 

0.8 cm/min. 

References 

1. For more information on the ICET program see: http://www.nrc.gov/reactors/operating/opsexperience/pwr-sump-performance/tech-references.html

2. Test Plan: Characterization of Chemical and Corrosion Effects Potentially Occurring Inside a PWR 

Containment Following a LOCA, Prepared by Timothy S. Andreychek, Westinghouse Electric 

Company (ADAMS ML052100426). 

3. ANL Quick Look Report Tests 1 & 2, September 16, 2005 (ADAMS ML052590238) 

4. Integrated Chemical Effects Test Project: Test #3 Data Report (ADAMS ML053040479) 

5. MEMORANDUM on "Summary of Meeting on September 30, 2005, to Discuss GSI-191 Chemical 

Effects Head Loss Information," dated November 2, 2005, ADAMS Accession Number 

ML053060359, http://www.nrc.gov/reactors/operating/ops-experience/pwr-sumpperformance/public-mtgs/2005/index.html 

6. Solubility of Calcium Phosphates, http://www.azom.com/details.asp?ArticleID=2140. 
27 

Table 2 Summary of Current Results for the Small Scale Dissolution Tests at T= 60°C. 

Test Series Time (h) pH (RT) Ca 

(mg/L)

P 

(mg/L)

Si 

(mg/L)

Na 

(mg/L)

cal–sil 

(g/L)

Ca equiv 

(mg/L) 

(Ca3(PO4)2 )

Ca equiv 

(mg/L) 

Ca10(PO4) 

6(OH)2

0.08 7.04 39 263 23 536 1.5 28 31

0.50 7.17 25 252 24 554 1.5 49 55

2.67 7.38 16 232 36 549 1.5 88 98

24.50 7.24 8 165 60 534 1.5 217 242

71.25 7.33 4 135 67 557 1.5 276 306

I 

TSP is added 

before the cal–

sil is 

introduced

119.00 7.48 3 132 68 567 1.5 281 313

1.08 6.83 58 65 21 159 1.5 412 458

1.5 6.79 54 66 22 168 1.5 409 454

3.67 7.1 11 131 25 357 1.5 283 315

25.5 7.1 5 103 46 382 1.5 337 375

72.25 7.15 3 67 62 405 1.5 407 452

II 

TSP metered 

over an hour 

after the cal–sil 

is added

120 7.26 3 57 65 395 1.5 427 474

4.08 7.12 19 102 26 289 1.5 339 377

4.5 6.85 14 104 28 295 1.5 336 373

6.67 6.92 6 95 30 297 1.5 353 392

28.5 6.99 5 67 42 292 1.5 408 453

75.25 7.1 3 36 60 327 1.5 467 519

III 

TSP metered 

over a 4 hour 

period.

123 7.25 3 22 65 331 1.5 494 549

0.08 7.13 9 250 7 598 0.5 54 59

0.50 7.29 9 241 9 585 0.5 70 78

2.67 7.4 10 223 20 594 0.5 105 117

24.00 7.37 4 208 36 600 0.5 134 149

72.00 7.26 3 198 42 579 0.5 154 171

IV 

TSP is added 

before the cal–

sil is 

introduced

120.00 7.26 3 199 42 577 0.5 152 168

1.08 7.2 14 211 9 512 0.5 128 142

1.5 7.25 14 249 12 618 0.5 55 61

3.67 7.26 13 237 20 620 0.5 78 87

25.5 7.32 7 222 37 627 0.5 108 120

72.25 7.23 4 216 45 631 0.5 118 131

V 

TSP metered 

over an hour 

after the cal–sil 

is added

120 7.2 4 225 47 642 0.5 101 112

4.08 7.24 21 230 22 585 0.5 91 102

4.5 7.24 18 229 24 600 0.5 93 104

6.67 7.26 7 212 28 582 0.5 126 140

28.5 7.35 4 201 37 583 0.5 148 164

75.25 7.24 3 206 44 600 0.5 139 154

VI 

TSP metered 

over a 4 hour 

period.

123 7.24 4 203 46 601 0.5 143 159