Information Notice 2005-26, Additional Results of Chemical Effects Tests in a Simulated PWR Sump Pool Environment
| ML060170102 | |
| Person / Time | |
|---|---|
| Issue date: | 01/20/2006 |
| From: | Charemagne Grimes NRC/NRR/ADRA/DPR |
| To: | |
| Paul Klein, NRR, 301-415-4030 | |
| Shared Package | |
| ML060170076 | List: |
| References | |
| BL-03-001, GL-04-002, GSI-191 IN-06-026, Suppl 1 | |
| Download: ML060170102 (6) | |
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
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
IN 2005-26, Sup 1 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 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
CONTACT
S
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
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)
Package - ML060170076, IN - ML060170102 OFFICE
OES:IREB:DIRS
TECH EDITOR
CSGB
CSGB
DCI
NAME
ICJung
HChang
PAKlein
AHiser EMurphy for
WHBateman
JNHannon
DATE
01/19/2006
01/18/2006
01/19/2006
01/18/2006
01/19/2006
01/19/2006 OFFICE
PGCB:LA
PGCB:DPR
BC:PGCB:DPR
D:DPR
NAME
RTregoning
CHawes
DBeaulieu
CJackson
CGrimes for
CGrimes
DATE
01/19/2006
01/19/2006
01/20/2006
01 /20 /2006
01 /20 /2006