UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

September 16, 2005

NRC INFORMATION NOTICE 2005-26: RESULTS OF CHEMICAL EFFECTS HEAD LOSS

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 is issuing this information notice to inform

addressees about recent NRC-sponsored research results related to head loss from chemical

effects in a simulated PWR sump pool environment. The 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

Generic Safety Issue (GSI) 191 addresses the potential for debris accumulation on PWR sump

screens to affect emergency core cooling system (ECCS) pump net positive suction head

margin. The NRC has 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,” related to the GSI-191 resolution. 

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 sump 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 subset of expected post-LOCA

environments within existing PWR plants. Although chemical products were observed in all of 

ML052570220
 IN 2005-26

Page 2 of 3

the ICET environments, the head loss associated with these products was not evaluated as it

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

insights on the head loss associated with chemical products that may form in PWR sump pools. 

Head loss testing is being performed at the Argonne National Laboratory. Initial testing has

been done in a piping loop containing a simulated sump pool environment intended to represent

the ICET Test 3 conditions. ICET Test 3 was performed in a borated water environment

containing trisodium phosphate (TSP), various metallic and non-metallic sample coupons

representative of containment materials, and a mixture of insulation (80% calcium silicate, 20%

fiberglass) samples. This environment was selected for initial head loss testing based on the

early formation of chemical product during ICET Test 3 and the characteristics of this product

observed during and after this test (NRC ADAMS Package Accession Number ML052140490). 

During initial testing to simulate these observed products, significant head loss was measured

across a test screen containing a preexisting fiber bed. The Argonne tests and initial test

results are described in detail in the attachment, “Chemical Effects/Head Loss Testing Quick

Look Report, Tests 1 and 2,” dated September 16, 2005. 

DISCUSSION

As part of the GL 2004-02 response, licensees are required to evaluate the sump screen head

loss consequences of any chemical effects in an integrated manner with other postulated postLOCA conditions. These recent research results indicate that a simulated sump pool

environment containing phosphate and dissolved calcium can rapidly produce a calcium

phosphate precipitate that, if transported to a fiber bed covered screen, produces significant

head loss. The attachment report contains several interesting observations:

• Significant head loss was observed in tests combining TSP with a higher concentration

of dissolved calcium (simulating the ICET Test 3 environment) and in tests with TSP and

lower dissolved calcium concentrations (i.e., less than the ICET 3 environment). 

• Small-scale leaching tests were done with calcium silicate insulation. The amount of

calcium that will dissolve appears to depend more on the initial pH of the solution than

on the amount of calcium-silicate insulation placed into solution. Lower initial pH

solutions produced greater amounts of dissolved calcium. 

• The amount of calcium phosphate precipitant in an ICET Test 3 type environment may

be limited by the amount of phosphate available from the TSP. 

This information is relevant to plants containing phosphate (e.g., plants using TSP as a sump

pool buffering agent) and calcium sources (e.g., insulation, concrete) that may dissolve within

the post-LOCA containment pool with sufficient concentrations to form calcium phosphate

precipitate. These test results indicate that substantial head loss can occur if sufficient calcium

phosphate is produced in a sump pool and transported to a preexisting fiber bed on the sump

screen.

Although significant increases in head loss were observed due to chemical effects in these

tests, it is important to note that these head loss results were obtained in a recirculating test 
IN 2005-26

Page 3 of 3

loop not intended to be prototypical of a PWR plant containment. For example, the calcium 

phosphate precipitant was formed by introducing calcium chloride into a TSP buffered solution 

immediately upstream and at a higher elevation than a screen with a preestablished fiber bed. 

The test loop orientation and method of calcium introduction result in transport of virtually all

chemical products to the fiber bed covered screen. Parameters that may influence head loss in

these tests include screen approach velocity, fiber bed thickness, relative arrival times for

debris and chemical precipitates, and loop fluid recirculation time. Applicability of these results

to plant specific environments may also be affected by these and other variables (e.g.,

insulation materials, break location, and sump design).

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

other chemical species to buffer pH.

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. 

 /RA/

Patrick L. Hiland, Chief

Reactor Operations Branch

Division of Inspection Program Management

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
Chemical Effects/Head–Loss Testing

Quick Look Report, Tests 1 & 2 

September 16, 2005 

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

Argonne National Laboratory
Abstract 

This report 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 test was intended to simulate the conditions in ICET–3. The second 

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

loss. With a pre-existing physical debris bed approximately 16 mm (5/8 in) thick consisting of equal 

weights of NUKON fiber and CalSil insulation, a large increase in head loss was observed for the 

chemical product loading intended to simulate ICET–3 conditions. In the parametric test with a similar 

physical debris bed, increases in head–loss were observed for a chemical product loading one-twentieth of 

the simulated ICET–3 conditions. 

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 for an 

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

that form during the test. The ICET test series was 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

The third ICET test, ICET–3, investigated the chemical behavior of boric acid/LiOH solutions containing 

80% calcium silicate/20%fiberglass insulation with a trisodium phosphate (TSP) buffering agent to obtain 

a target pH of 7. The steam generator is the largest plant component that may have fiberglass or calcium 

silicate insulation and that might be affected by a postulated large break LOCA. Based on the dimensions 

of a representative steam generator and accounting for a conservatively–large zone–of–influence (ZOI) 

volume, Westinghouse estimated that the volume of fiberglass or calcium silicate insulation debris that 

could be generated is 141.6 m3

 (5,000 cubic feet). The smallest containment pool volume, based on the 

survey information, is about 36,500 ft3 so a conservative estimate of the insulation debris per volume of 

containment pool fluid is 0.137 ft3/ft3. For insulation with 80% CalSil, this gives about 25 g/l of CalSil if 

all the CalSil debris is assumed to be immersed in the sump fluid. 

The ICET–3 test was performed by first adding boric acid (2800 ppm) and LiOH (3 ppm) to water in the 

ICET tank. HCl was also added to simulate degradation of electrical insulation. The resultant pH of this 

solution was 4.2. CalSil corresponding to about 20 g/l was placed in the submerged portion of the ICET 

tank; the remainder of the CalSil was only wetted by the sprays during the initial 4 hours of testing. The 

circulation pump was then turned on and the solution was allowed to circulate for about 5 hours. At this 

time, a solution containing dissolved TSP was metered into the test chamber solution over the next four 
hours. Within 20 minutes after the beginning of metering TSP into solution, a white flocculent precipitate 

was observed in the tank. The precipitate appeared to be neutrally buoyant. The precipitate was 

presumed to be calcium phosphate. Subsequent analysis showed that substantial amounts of calcium

phosphate are present in the precipitates, although other products could also be present. It has also not yet 

been determined which specific varieties of calcium phosphates are present in the ICET-3 products. 

Hereafter in this report, this ICET-3 product is generically referred to as Ca3(PO4)2, tricalcium phosphate, 

for convenience. 

Small Scale Dissolution Test Results 

No measurements were made of the dissolved calcium levels in ICET–3 at times prior to the addition of 

the TSP through the sprays. Therefore, small scale dissolution experiments were performed using 

additions of CalSil to solutions containing 2800 ppm boric acid and 3 ppm LiOH to estimate the dissolved 

Ca level initially present in ICET-3. In some cases, small amounts of HCl (to simulate breakdown of 

electrical cables) were added since these were included in the ICET–3. 

Small scale dissolution tests were performed for a range of CalSil concentrations that encompassed the 

ICET–3 conditions for durations ranging from 35 minutes to 24 hours. The results of these tests are 

summarized in Table 1. The Ca concentration values in this table are the dissolved Ca levels at the end of 

the leaching period. The “initial pH” values given in the table are the initial starting pH of the solution 

before the CalSil addition while the “final pH” values represent the pH at test termination. The CalSil 

dissolution raises the pH of initially acidic solutions to near pH 7 due to the hydrolysis of potassium and 

sodium released from the CalSil. However, the pH of the solutions already buffered with either NaOH or 

LiOH did not vary much upon CalSil dissolution. The amount of dissolved Ca most strongly depends on 

the initial pH of the solution as seen in Fig. 1 while the initial CalSil loading has very little effect for the 

loadings examined in this study. 

Dissolution of the CalSil is more rapid in initially acidic solutions, but will occur even in near neutral and 

buffered solutions as seen in Table 1. In ICET–3, in which the initial solution was acidic, the phosphate 

was exhausted by the end of the second day. Thus in ICET-3, the amount of calcium phosphate formed is 

ultimately limited by the amount of TSP available. Assuming the product is Ca3(PO4)2, 1 mole of TSP 

can consume 1.5 moles of CaSiO3. Because CalSil is mostly CaSiO3, this implies that the formation of 

precipitate will be phosphate limited for CalSil loadings down to about 2 g/l (for TSP additions of 4 g/l),

but this could vary somewhat depending on the actual calcium phosphate species that form. 

Based on the small scale test results, the dissolved Ca level in the ICET–3 tests before the start of the TSP 

injection is estimated to be about 200 ppm. Because not all the phosphate is consumed by this amount of 

dissolved Ca, only the initial “burst” of Ca3(PO4)2 formation (within the first four hours of the ICET 

simulated post-LOCA environment) is associated with this inventory of dissolved Ca. As noted 

previously, additional Ca3(PO4)2 likely continued to form in the ICET-3 test until all the phosphate was 

depleted. 

2 
Table 1. Small Scale Dissolution Tests on CalSil

Test Conditions 

No. Initial 

pH (RT) T(C) Time

CalSil 

g/l 

Final 

pH (RT) 

Dissolved

Ca 

(ppm)

Notes 

1 4.0 60 35 min 6 7.5 176

2 4.0 60 35 min 15 6.9 256

3 4.0 60 35-min 25 6.7 244

4 4.0 60 35-min 166 6.5 228

5 4.0 60 4-h 6 6.7 196

6 4.0 60 4-h 15 6.9 195

7 4.0 60 4-h 25 7.1 195

8 4.0 60 4-h 166 7.7 168

Solution pH = 4.0 made 

from B(OH)3 + Li(OH) + 

HCl 

9 4.5 60 4-h 6 6.7 156

10 4.5 60 4-h 15 6.9 169

11 4.5 60 4-h 25 7.1 184

12 4.5 60 4-h 166 8.0 127

Solution pH = 4.5 made 

from B(OH)3 + Li(OH) + 

HCl 

13 7.0 62 4-h 2 7.1 45

14 7.0 62 4-h 6 7.4 88

15 7.0 62 4-h 25 7.2 69

16 7.0 62 24-h 2 7.2 73

17 7.0 62 24-h 6 7.3 108

18 7.0 62 24-h 25 7.4 102

Solution pH =7 made 

by B(OH)3 + Li(OH) + 

HCl + NaOH addition (No 

TSP added) 

19 10.1 60 3.5-h 6 10.0 17

20 10.1 60 3.5-h 15 10.0 18

21 10.1 60 3.5-h 25 10.0 20

22 10.1 60 3.5-h 166 9.7 23

Solution pH = 10.0 made 

by B(OH)3 + Li(OH) + 

HCl + LiOH excess 

addition (No TSP added) 

3 
Figure 1. Dependence of dissolved Ca level on initial solution pH 

ANL Test Facility 

A schematic of the ANL test loop is shown in Fig. 2. The test screen has an effective diameter of 6 in. 

The fluid volume in the loop is 4.2 ft3. At 0.1 ft/s, the transit time around the loop is about 4 minutes. 

For these tests, a perforated plate with a 51% flow area and staggered 3/16 in. holes was installed in the 

test–section. The test screen is shown in Fig. 3. In scaling results from the ANL test facility, the mass of 

chemical product per unit area of screen must be considered. The amount of chemical product produced 

scales with fluid volume while the screen area per fluid volume determines the product mass per unit 

screen area. 

4 
Figure 2. Schematic of the test loop 

Figure 3. Perforated plate test screen

5 
Head Loss Test #1 Results 

The initial tests in the Argonne National Laboratory (ANL) chemical effects/head–loss testing program

were intended to investigate the potential head loss associated with the chemical products observed in the 

third Integrated Chemical Effects Test (ICET–3). 

In the ICET–3 tests, the TSP was added to the CalSil solution through the sprays. In the ANL tests, the 

loop is filled with a solution containing boric acid, LiOH, and TSP. The concentration of TSP 

corresponds to that metered into the test solution over 4 hours in ICET–3 (about 4 g/l). Calcium chloride 

(CaCl2) solution is then added to supply the desired inventory of dissolved Ca. In the first head loss test, 

the Ca inventory was taken to be that corresponding to the estimated Ca concentration in the ICET 

solution at the start of the TSP spray, which, as discussed previously, has been estimated to be about 

200 ppm. As noted previously, this will result in the formation of an amount of Ca3(PO4)2 per volume of 

solution comparable to that observed in the initial stages of ICET–3. 

The loop was filled with deionized water and heated to 130°F. Boric acid in powder form was slowly

added to the loop and circulated until it was dissolved. The LiOH and TSP were added as solutions. The 

concentrations of these chemicals in the loop were also chosen to match those in ICET–3. The test 

temperature was lower than that in ICET–3 (140°F), because the test loop was not fully insulated. 

Because of the retrograde solubility of Ca3(PO4)2, the lower temperature results in the formation of 

slightly less precipitate. 

After the chemical solution was prepared, the physical debris bed was built by adding a slurry containing 

15 g NUKON/15 g CalSil to the loop with the loop flow at 0.1 ft/s. The bed was about 3/4 in thick. The 

NUKON bed formed essentially in the first pass of the debris past the test screen. The pressure drop 

across the bed slowly increased as the test loop solution recirculated, presumably due to increasingly

effective filtration of fine CalSil particles. After recirculating for about 45 minutes, the flow rate was 

then increased to 0.2 ft/s. At this flow rate, the bed compressed to about 5/8 in thick. The flow rate was 

then reduced back to 0.1 ft/s. The pressure drop and flow velocity at each stage of the debris bed 

formation is shown in Fig. 4. The physical debris bed at this point in the test is shown in Fig. 5. 

Figure 4. Flow rate and pressure drop as a function of time in Test 1. 

6 
Figure 5. NUKON/CalSil bed before formation of the Ca3(PO4)3 precipitate 

The CaCl2 was then added to the vertical part of the test loop just above the clear test section. A total of 

400 ml of CaCl2 solution was added over a 4 minute period (the transit time around the loop at 0.1 ft/s) to 

obtain the 200 ppm dissolved Ca inventory. A fine, milky precipitate was observed as shown in Figure 6 

just after the introduction of the CaCl2. The pressure drop across the bed increased from 1.7 psi to greater 

than 7.0 psi within 10 minutes of introducing the CaCl2. An accurate pressure drop measurement could 

not be obtained beyond this point, because the loop was running unpressurized, and the pump started to 

cavitate as the precipitate continued to accumulate on the bed. The flow rate and pressure drop as a 

function of time after CaCl2 addition are also shown in Fig. 4. As discussed previously, the 200 ppm Ca

inventory is likely not sufficient to produce the full amount of Ca3(PO4)2 formed during ICET–3. 

However, no additional Ca was added to simulate the depletion of all the available phosphate as in ICET–

3, since the pressure drop across the bed had already caused the pump to cavitate. Figure 7 shows the 

accumulation of the precipitate on the debris bed just before the pump was shut off. 

7 
Figure 6.

Ca3(PO4)2 forming after addition of CaCl2 and 

approaching the debris bed.

Figure 7. 

Precipitate buildup on the fiber debris

bed just after the pump was turned off. 

8 
Head Loss Test #2 Results 

The initial procedure for the second test was similar to the first test. The loop was filled with deionized 

water and heated to 130°F. Boric acid in powder form was slowly added to the loop and circulated until it 

was dissolved. The LiOH and TSP were added as solutions. 

The physical debris bed was again built from 15 g of NUKON and 15 g of CalSil. The bed was built at 

0.1 ft/s and the flow rate was not increased above this value in contrast to the previous test. The debris 

bed was somewhat thinner than the initial debris bed for Test #1 at 0.1 ft/s (5/8 in for Test #2 and 3/4 in

for Test #1). The pressure drop across the bed was also slightly smaller at this flow rate (0.4 psi in Test 

#2 and about 0.6 psi for Test #1). 

For this test, the CaCl2 additions were made in stepwise fashion starting with an initial addition 

equivalent to 10 ppm (one-twentieth of the simulated ICET-3 inventory) of dissolved Ca. Then amounts 

were added incrementally corresponding to total dissolved Ca inventories of 25 ppm, and 50 ppm. Each 

addition was metered in over a 4 minute period as in the first test. 

When CaCl2 equivalent to an inventory of 10 ppm dissolved Ca in the loop volume was added, the 

pressure drop at a flow rate of 0.1 ft/s increased from 0.4 psi to 1.4 psi. The Ca3(PO4)2 precipitate was 

again visible, but the cloud was much fainter than the previous test which had a 200 ppm Ca inventory.

Additional CaCl2 was then added to simulate a 25 ppm inventory. The pressure drop increased from

1.4 psi to 6.4 psi and the pump again started to cavitate, since the test loop was unpressurized. The 

velocity was then decreased to 0.01 ft/s at which point the pressure drop decreased to 0.5 psi. A final 

increment of CaCl2 was added to simulate a 50 ppm inventory of total dissolved Ca. At a flow rate of 

0.01 ft/s, the pressure drop increased from 0.5 psi to 1.0 psi within 4 minutes. Under continuing operation 

for another 12 minutes, the pressure drop increased to 5.2 psi, but the velocity could not be maintained as 

the suction pressure on the pump dropped. The flow rate and pressure drop as a function of time in Test 2 

are shown in Fig. 8. 

An interesting qualitative difference was noted between the CaCl2 additions at flow rates of 0.1 ft/s and 

those at 0.01 ft/s. At 0.1 ft/s, the precipitate was a finely dispersed milky cloud. At 0.01 ft/s, these 

particles seemed to agglomerate into light, flocculent assemblies up to perhaps 0.25 in. in diameter as 

shown in Fig. 9. These larger assemblies appear similar to the material observed in the ICET–3 tank 

where velocities are likely lower than 0.1 ft/s. 

9 
Figure 8. Flow rate and pressure drop as a function of time in Test 2. 

Figure 9. 

Flocculent precipitates observed at 0.01 ft/s in 

Test 2 

References 

1. For more information on the ICET program see: 

http://www.nrc.gov/reactors/operating/ops-experience/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). 

10