ML20198P836
| ML20198P836 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 01/09/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20198P834 | List: |
| References | |
| NUDOCS 9801220265 | |
| Download: ML20198P836 (7) | |
Text
-
fwou y+
t UNITED STATES
'j NUCLEAR RECULATORY C3MMISSION s*
t WASHWOToN D.C. 3000H001 L-s...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE CONDITION AND QUALIFICATION OF PROTECTIVE COATINGE USED INSIDE THE CONTAINMENT STRUCTURES AT THE ZION NUCLEAR POWER STATION. UNITS 1 AND,2 DOCKET NOS. 50-295 AND 50-304
1.0 INTRODUCTION
Following the shutdown of Zion Nuclear Power Station, Unit 2, for refueling outage Z2R14, problems were found with the safety related coatings inside the containment.
In a conference call on January 7,1997, the staff requested that the licensee submit documentation related to the protective coatings issue. This information consisted of: (1) calculations of the containment sump zones of influence for coatings (Commonwealth Edisore Company (Comed) Zion Station Calculation No. 22S-B-040M-002, Revision 1), (2) calculations of residual heat removal (RHR) pump available net positive suction head (NPSH) during the recirculation phase of a loss of coolant accident (LOCA) (Comed Zion Station Calculation No.
22S B-008M-092, Revision 2), and (3) Comed Report M-00282-97, ' System Materials Analysis Department Report on the Evaluation of Level I Coatings in Zion Station Unit 2 Containment",
dated January 22,1997. This information wcs submitted by Comed in its letter dated February 5,1997.
In a letter dated May 23,1997, the staff requested additional information from Comed on the protective coatings concems. The licensee responded by letter dated September 5,1997.
2.0 BACKGROUND
The Zion Station, Unit 1 and 2, reactors are Westinghouse four loop pressurized water reactors (PWRs) w%h large, dry containments.
During refueling outage Z2R14 for Zion Station, Unit 2, concems were identified regarding the qualification and condition of protective coatings in the containment. The qualification and condition of protective coatings inside the containment is important to safety since failure of these coatings during a LOCA end the subsequent transport of the coating pieces to the emergency core cooling system (ECCS) containment recirculation sump could potentially degrade the ability of the ECCS and the safety-related containment spray system to deliver sufficient flow to successfully perform their safety functions following depletion of the refueling water storage tank (RWST) inventory.
Comed performed calculations of the zones of influence of the various cowlings in the Zion containment. These calculations were used as a guide to the extent to which unqualified and undocumented coatings had to be removed. The calculations are discussed below.
Comed also performed calculations o' evallable net positive suction head (NPSH) to determine how much of the emergency recirculation sump screen could be blocked without reducing the 9001220265 990109 PDR ADOCK 05000295 P
4,
I 2
+
?
avallable NPSH to the point that the ECCS pumps could not perform their safety func. A in j
addition, Comed performed tests to demonstrate the margin available between the eies of the emergoney recirculation sump screen that would probably be blocked by paint chips and the area i
of the emergency recirculation sump screen that could ! e blocked without adversely affecting the l
1 residual heat rerwval (RHR) pumps. Finally, Comed evaluated the adhesive integrWy of the protective costings to provide assurance they would not delsminate during a design basis acoloont. The colouest6ons and tests are discussed below.
l 1
j 3.0 EVALUATION The staff has tviewed the Comed calculations used to determine the aorw td influence. The calculations appear reasona'ule for this applicat:en. However, recent problems with coatings in
.l containments identined at Zion and other commercial nuclear power plants have prompted the j
staff to reexamine the topic of protective coatings inside conteinment. The staff has begun t
discussions with the industry and is considering performing confirmatory research to assess the l
safety significance of the issue. It is expected that this work will result in the ded-pM of i
improved methods of analy:Ing the effects of protective coatings on LOCA mitigation. Until this work has progressed farther, the staff does wi6h to endorse any methodology for broad use.
This safety evaluatio deals specifically with the restart and operation of Zion Nuclear Power j
Station UnNs 1 and 2. Following the formulation of the staff's positien concoming the containment coatings issue in containments of pressurized water rs dors. the staff may elect to oopen this issue for Zion Station.
3.1 Zone of influence calculation i
The zone of influence of a containment recirculation sump hump) can be defined as the volume surrounding the sump of such a magnitude that a specified material will be transported to the i
sump screen if H enters the vclume. According to this definition, any of this material outside the l
zone of influence will not reach the sump screen. The material can be transported in several l
ways, ehher 6uspended in and carried by the water or moved by the flow of water along the i
contalsment floor. The Comed definition of the zone of influence, while not identical to this, is l
equh" it, in sov past applications, the zone of influence has been used to define the quantity of materia. /hich can reach the sump screen. This estimate of material has then been used to I
calculate a reduction in the available NPSH of the ECCS pumps due to the increase in tne head loss across the sump screens. If this estimate of the reduction in the availab'e NPSH did not render the pump inoperable, the condition of the containment coatings was considered 1
satisfactory, and no paint was removed. Comed used the ::one of influence in a different way.
(The st/f's request for additional information dated May 23, igg 7, contained a numbered list of questions. The question numbers in the subsequent paragraphs refer to those nubered j
questions.) The responses to Questions 1 and 2 in Comed's September 5,19g7, submittal 4
describe the use of the results of the zone of influence calculatione. Unqualified coatings were j
t removed if they were inside their zone of influence with three exceptions. In two cases,- the flow paths for these coatings were judged to be such that it was not likely that the coating particles would reach the sump. In the third case, the amount of coating was relatively small, approximately 1 ft', and the coating was left in placec Ur"locumente) coatings with a zone of influence of lens than 20 feet worw either removed or were confirmed to be located outside their
~ particular zone of influence. The 20 foot distance was based ten initial calculations by the lloonsee.4 Table 1 in Calculat!on 228-B-040M-002 shows that no undocumented coatings had l
}
l~
_., _ S._ um._ _ _ _
.2... -
.4
1 3
j
. sones o n luence grea er than 20 feet.- The staff considers this approach to be acceptable since fi f t
undocumented and unquellflod coatings were removed out to, and in some cases, beyond the calculated zone of influence.
l 1
The terma "unqualifler and *undocumenter coatings will be used throughout this safety l
l evaluation, "Unqualiller coatings fallinto one of two categories.
the coatings are known not to have been tested in accordance with the radiation and adhesion gr54r, test methods in NRC endorsed s'andards (e.g., ANSI Standard No, j
N101.2 (1972), " Protective coatings for Light Water Nuclear Reaclor Contairwnent j
Facilities," ANSI Standard No. N5.12 (1974),
- Protective Coatings for the Nuclear i
industry," ANSI Standard No. N5.9 (1969), " Protective Coatings for the Nuclear industry").
i on coatings, or H is known that the coatings have nut met the pooeptance artteria of these qualification test methods, or, 1
H is determined that a coating was not property applied in accordance with NRC endorsed l
+
coating standards or with plant specific quality assurance proce:Iures for coating applications, and H cannot be determined that the coating w:t sithstand the conditiens j
resulting from a postulated design basis "cident at the platit.
'Undocumenter costings are ones for which it is suspected that the coatings have been tested
\\
to and have mot the acceptance criteria in sp4cific radiation and adhesion qualification test methods detailed in NRC endorsed standards on coatings (e.g., ANSI Standard No. N101.2 (1972)," Protective Coatings for Light Water Nuclear Reactor Conta,nment Facilities," ANSI i
Standard No. N5.12 (1g74), " Protective Coatings for the Nuclear indu try," ANSI Blandard No.
N5.9 (1969), " Protective Coatings for the Nuclear Industry"), but the quality assurance records of i
the tests performed on the coatings bre lacking or deficient.
l 1
Comed modeled the failed paint chips as equalin size to the outer sump screen mesh opening l
i.
which is 0.5 inches. Dati on the actual size distribution of paint particles produced by paint failure under LOCA conditions are not available. Comed stated that the assumption ef a paint particle equal in slae to the outer sump scr9en opening of 0.5 inch is conservative since a j
smaller particle would past. through the sump screen and a larger particle would have a smaller tone of influence. However, the licensee's calcul1tions do not consider the effect of turbulence.
i Turbulence would decrease the settling rate of paint particles and could allow larger paint particles to be transported to the sump. The effect of turbulence on the size of the paint particles i
F which could reach the sump screen has not been experimentally determined, and in this case, is mitigated to some extent by the fact that Comed removed the unqualified and undocumeented paints within their zones of influence. Therefore, the staff finds the licensee's assumption of a i
U.5 inch paint chip to be acceptable.-
The calculations assume a flow equal to the runout flow of both RHR pumps, which is 9000 ppm.
Using the maximum flow is conservative for transport calculations.
- The zone'of influence for each coating type is calculated in two steps. F!rst, the maximum y
distance from the conter of the sump enclosure to the lochon at which the flow of water will i
i
. provide er.ough force to move the particle along the floor and reach the sump is calculated. The second step is to calculate the horizontal distance a particle could move Os it travels from the radius of the zone of influence if the containment floor had no obstacles to the flow path, in surface of the water to the containment floor. The sum of these two distances would be the some cases, however, the calculated radius of the zone of influence is greater than the distance
-. from the sump to the missile barrier, in this case, the assumption of a cylindrically uniform N
u O
1
..~..u
-.n.....-
~.
_._..__.__.~,.,,_--.---.~...w,__.J_-,,,._-.-._,w,._-.
4 velocity field is no longer valid and a correction is included in the calculations to move the zone of influence away from the missile barrier toward the conter of the reactor building to maintain a constant Jurface area for water flow. This adjustment is reasonable.
l The basic modes of transport of the paint particles are sim ar to those developed by the NRC u
staff during the resolution of Unresolved Safety issue A-41, " Containment Emergency Sump Performance," as described in NUREG/CR 2791, " Methodology for Evaluation of insulation Debris Effects." These include the sliding of the particle along the floor, and the settling of the particle at its terminal velocity while it is being trar sported by the water flow to the sump screen.
NUREG/CR-2791 used a flow network to determins the flow velocities and transport of debris.
The Comed calculations determined an average horizontal velocity by making the assumption that the volumetric flow rate is preserved at all radil from the center of the pump. This is a reasonable approach.
There are several approaches to determining the zone of influence for transport of debris to the ECCS containment recirculation sump. While the details vary, the basic assu.7)ptions are the anme. However, there are no experimental data available to verify these calculations. Thus, calculations of paint particle transoort should be performed using conservative assumptions.
Comed's calculations for Zion contain several conservatisms. These include:
(1)
The shape of the coating particle when calculatin; 'is vertical toe. mal velocity is a circular disk parallel to the floor. This minimizes in vertical tem..aal velocity and maximizes the zone of influence.
(2)
The pr.rticle size is assumed to be the minimum that will not pass through the sump mesh screen. This maximizes the zone of influence.
(3)
The maximum RHR flow is assumed.
(4)
A conservatively low temperature (which maximizes density and minimizes the velocity required to initiate particle sliding and minimizes the vertical terminal velocity) is used.
The staff finds the zones of influence calculated by Comed to be acceptable for this application for the reasons given above.
3.2 Net Positive Suction Head (NPSH) Calculation Comed also calculated the amount of blockage of the containment recircu'ation sump screens which would stillp)rovide adequate NPSH for the RHR pumps. This blockage be 69% (11.56 ft of the sump screen area.
The NPSH calculation was not required to determine the zone of influence. Therefore, the staff has not made a finding as to the acceptability of this calculation.
The NPSH calculation is not used directly by Comed. In response to a staff question, Comed stated thet while the NPSH calculation demonstrated that 11.56 ft' could be blocked before NPSH was adversely affected, the estimated quantity of paint capable of reaching the sump screen, based on the removal of degraded paint in containment, is 1 ft'. Thus, the NPSH calculation provides an indication of the margin ava..c
.v.
m-
j I
e$e
(
3.3 ExperimentalWork At the request of the staff, in its letter dated September 5,1997. Comed provided a report on experimental work done on behalf of Comed titled," Evaluation of Paint Chip Head Loss on l
Vertically Oriented Zion Station Strainer Screen: July igg 7 Test Phasa " The primary objective stated in the report was "to determine the head loss across the strainer sump screen as a result of the buildup of paint chips."
j One comer of a full scale 7, ion containment recirculation sump screen was setup in a istge basin.
\\
An approach flow velodly M 0,72 ft/sec was used since this is the value of approach fiow calculated for thu *?lon sump at runout conditions of the RHR pumps. Various quaintities of paint a
chips were addeu. The experiments demonstrated that at a flow blockage of 65% of the scroon area, the head loss was only 3/16 inch water gage. The 65% is close to the calculated blockage t
of Sp% at which the loss in NPSH was calculated to have an adverse effect on the RHR pumps.
{
These experiments add some confidence to the margin between the available and required l
NPSH during a LOCA, considering the effects of detached paint.
3.4 Coatina intenrity it is important fron, a safety perspective for licensees to monitor for the adhesive integrity of protective coatings applied inside the containment structures of their plants to provide assurance that the protective coatings will not block the containment recirculation sump and precluds operation of containment spray and emergency core cooling systems rfu+g a design basis l
sccident. With this in mind, the staff assumes that protective coating 6 t;a d in Pfety related
[
applecations ve uncontrolled and will lose adherence to their substrate surfaces e,i a design basis accident if any of the following conditions exist with respect to the application of the coatings.
l lt is determined that a coating is losing adherence to its substrate surfaces either by peeling, flaking, delsminating or blistering from the applied surfaces, or It is determined that the coating is unqualified, or lt 16 determined that the coating is undocumented.
Comed has removed all of the qualified coatings inside containment which were determined to be peeling, flaking, delsminating or excessively blistering from the applied surfaces. In regard to the amount of qualified coatings remaining inside the Unit 2 containment structure, in its letter dated February 6, igg 7, Comed provided the quality assurance record summaries for the quality assurance tests performed on widely used coating systems supplied by two vendors for application inside the containment structures, The quality assurance tests were performed by two independent testing laboratories in socordance with acceptable industry standards for coatings applications (ANSI Standard No. N101.2 (1972), 'ProtectNo Coatings for Light Water Nuclear Reactor containment Facilities" and ANSI Standard No, N5.12 (1974), " Protective Coatings for the Nuclear Industry") The tests included, as a minimum, LOCA environmental tests, chemical resistance tests, and radiation / design basis accident exposure tests.- These i
quality assurance records included both the vendor's quality record summaries of the results of
'3 the tests and the quality records from nuclear steam supply system (NSSS) vendors, nuclear l-component vendors or architectural engineering firms which were contracted to supply nucleat grade components for the Zion plant design and which used the coatings to protect the surfaces l-of the components procured for the plants. The staff has reviewed these quality assurance records and has determined that the records are acceptable.
o i
. ca.
.. _ _ _ ~ _ _ _ _. _. - _ _, -. _ _ _. _ _ - _ _._, _ _. _ _, _ _ _ _ ;
1 t
in addNion, Comed performed addhional in shu adhesion testing of the quahfled contings j
remaining inside the Zion, Unit 2, containment struar re in accordance with the test methods and i
u l
acceptance orHerla described nr N Standard N6.12.ig74. With the exception of one adhesion j
test performed on a quak6ed om... Aich was not property applied to its surface, all adhesion tests indicated that the costings had suf6cient adhesive strength to justify leaving them intact for l
further service. The coating on the component whloh did not meet the ortleria of the adhesion i
lost was removed from the component. Together, the resuus of the additional adhesion tests, l
when evaluated in oorQunction with the quality records for the costings, provide suf6cient evidonoe that the quali6ed coatings remaining inside the containment will maintain their integrWy during the environmental conditions that are postulated to result during a design basis sooident, j
and provide a sufficient basis for leaving these coatings intact for further servios at the facility.
Comed h'es also removed all of the unqualified or undocumented coatings within the zone of influence of the Zion, Unit 2, containment roolroulation sump (i.e., within 20 feet of the centerline of the sumph Currently Comed estimates that approximately 3100 ft' of unqualified or undocumented protective coatings are stillin place, outside the zone of influence of the Zion,
' Unit 2, contair.mont recirculation sump. This estimate is conservative based on a rs betion of the confidence level to 80% Of the 3100 ft: of unqualified or undocumented coating, remaining l
outside the Unit 2 mone of infk once, Comed estimates that only 1 ft' will reach the Zion, Unit 2, containment recirculation sump screen during a design basis accident. This is less than the 11.66 ft' of soceptable screen blocitage calculated by ComEss Not Positive Suction Head calculations.
The stLN has accepted ComEss zone of in9uence calculations for the Zion, UnN 2, containment.
Therefore, the staff concludes that the licensee's corrective actions provide assurance that the unqualified or undocumented coatings remaining outside the Unit 2 zone of influence will not result in an unacceptable amount of clogging of the containment recirculation sump screen during a design basis accident.
Prior to restart of the unit, Comed has completed or will enmplete recoating of the Unit 2 containment structure in the following areas:
1.
An area outside the missile barrier bounded by the containment wall and the missile l
barrier wall at the 568 ft Elevation between Azimuth Z22 and Z23, floor to oeiling. This area is approximately 25 feet long. The coating effort will include the coating of concrole walls and floors, containment liner, and structural steel.
2.
An area inside the missile barrier at the 568 ft Elevation centered at Azimuth Z22. This arem is approximately 32 feet by 12 feet and will include the concrete floor and adjacent
- walls to a height of approximately 10 feet.
3.
_ Components which had undocumented coatings removed within 20 feet measured radially from any edge of the sump.
In addition, an overall plan for the long term inspection and maintenance of containment costings is under development. This plan will be completed by the end of the second quarter of calendar year 1998. Comets recoating efforts during the Z2R14 outage were or will be performed in -
accordance with the NRC approved standards and regulations (ANSI Standard No. N5.12 (1g74),
" Protective Coatings for the Nuclear Industry," ANSI Standard No. N5,9 (1g69), " Protective
- Coatings for the Nuclear industry," ANSI N101,4 (1g72), " Quality Assurance for Protective Costings Applied to Nuclear Facilities,' ANSI N45.2," Quality Assurance Program Requirements (Design and Construction)," Appendix 8 to Part 50 of Title 10, Code of FederaIRegulations, 1
l i
,,.+.a-~,w.,,'
,,,.n.,
. nn
~.i n.
...~._n-..._.,____,,,.._.;_~n,
_.,.. a ---..-.. _.,.
C 7
l
" Quality Assurance Cettens for Nuclear Power Plants and Fuel Reprocessing Plants").- Testing of
~
the newty applied coating system consists of dry film thickness measurements and visual l
examination of the completed application. This testing will be performed by certdied coating j
inspection personnel. These activhies are designated to be pedormed in accordance with plant spoolfic quality work spoolfications and procedures to ensure that the fleid application meets installation requirements such that the quellfloation of the coating remains valid. These activities l
will provide assurance that the newly applied qualified coatings will maintain their integrity dunng a design basis accident, and justify the new costings for future servios at the facility.
1 Comed has taken numerous steps to improve the condition of protective coatings applied inside l
the containment structure of Zion, UnN 2. Comets activhies include removal of all detected pooling, flaking, delsminating, or excessively blistering coatings from the surfaces inside the j
UnN 2 containment structure, removal of all unqualified or undocumented costings within a i
j 20 foot zone of influence of the containment roeirculation sump, recosting the accessible portions of the containment surfaces that were designated in the body of this report, and submittal of the quality assurance records of qualified conings that have been widely used inside the Zion, Unit 2 i
containment structure. Comed is also in the process of developing a quality monitoring program for protective coatings used for applications inside the containment structures of Zion, Units 1 j
and 2. Comed has indicated that this program is expected 13 be completed by the end of the j
second quarter of 1998. The staff has reviewed the quality assurance records submitted by
+
Comed, and Comets transport modeling of free falling coatings and debris that is postulated to occur during a design basis accident. The staff, therefore, concludes that the additional actions i
taken by Comed to ensure coating integrity provide added assurance that the protective coatings applied inside the containment structure of the Zion, Unit 2, facility will not preclude the operation j
of safety-related containment spray and emergency core cooling systems during a design basis
+
accident.
j i
4.0 Conclusion j
i The staff has concluded that Comets analysis described in its February 5,1997, letter and Comets actions in removing unqualified and undocumented paint within the zone of influence t
are acceptable for Zion, Unit 2. Furthermore, the staff concluded that the same analysis and g
L similar actions to ensure the coating integrity of containment coatings in Zion, UnN 1, would also result in coatogs that are acceptable for restart and operation of Unit 1.
l It should be noted that the staff has raised this issue generically in Information Notice 9713 and lasued a draft Generic Letter for comment on May 13,1997 (62 FR 26331). As a result of further information that is acquired, the staff's position on this issue concoming Zion could change and l
. require additional information or work on the part of Comed. The staff is still in the process of formulating its position on the generic issue, and may choose to reopen the issue for Zion Nuclear Power Station at some future date.
Principal contributors: R. Lobel
{
J, Medoff Date:
January 9, 1998 l
l I
i
?
. i t,
, w5
-sr~
d d. mmw,.m m~.~r+
.,-,w-+U-~.w..-~
...;-.4...
w.-,.-m~e.~a-emm-.~/.m...
-, ~ --