ML20056C267
| ML20056C267 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 05/09/1993 |
| From: | Stratman R CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CAL-RIII-93-07, CAL-RIII-93-7, PY-CEI-OIE-0402, PY-CEI-OIE-402, NUDOCS 9305120326 | |
| Download: ML20056C267 (16) | |
Text
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.L CENTERCOR Q
ENERGY l
PERRY NUCLEAR POWER PLANT Mail Address:
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P.O. BOX 97 10 CENTER '40AD PERRY. OHIO 44081 PERRY, OHIO 44081 VICE PRESIDENT - NUCLEAR l
(216) 259-3737
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May 9, 1993 PY-CEI/0IE-0402 L U. S. Nuclear Regulatory Commission Document Control Desk
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Vashington, D. C.
20555 t
Perry Nuclear Power Plant Docket No. 50-440 Response to Confirmatory Action Letter Gentlemen:
This letter is submitted as a partial response to Confirmatory Action Letter (CAL) RIII-93-07, dated April 16, 1993, which details actions requested by the l
NRC regarding the performance of ECCS Suction Strainers at the Perry Plant.
Following initial evaluations of the strainer degradation, an_ Incident Response j
Team (IRT) was formed at Perry, in accordance with site Corrective Actions procedures. This IRT has been fully dedicated to the determination of the reasons for the degradation, the adequacy of strainer design, the impact on i
plant safety and operation, and the appropriate corrective action. The IRT will continue to pursue all necessary activities until the issue is adequately resolved.
Your Corrective Action Letter specifically identified the-following five r
actions which the Perry Plant had committed to perform in response to the strainer issue:
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Conduct an investigation to determine the cause of the reduced ~
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capability of the RHR pump strainers located in the suppression pool. _
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Include in the evaluation consideration of design adequacy, reasons for fouling, and reasons for any deformation.
2.
Maintain documentary evidence of the investigation effort and make this available to the NRC.
3.
Prior to startup, provide Regio.' III vith the basis for considering the t
ECCS suppression pool strainers is '.se capable of performing their required design function.
4.
Prior to startup, provide Region III with plans and a commitment to ensure that the suppression pool is maintained at an acceptable level of cleanliness, including any surveillances planned to be performed.
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Provide within 30 days to Region III a documented evaluation of the above issues including any additional corrective actions taken or planned. In the report, describe the basis for considering the RHR'
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system to be capable of performing its safety function during past operation, particularly in light of the problems identified-in RF03.
It is currently anticipated that all necessary modifications to the ECCS l
strainers, all improvements to Containment, Dryvell, and Suppression Pool
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conditions, and all program and procedure modifications for the sustained enhancement of those conditions vill be completed as necessary to support a plant startup prior to your receipt of the full response to the CAL.
l Accordingly, because items 3. and 4. of the above list require notification of Region III prior to startup, the Attachment to this letter is provided in advance. The complete response to the Confirmatory Action Letter will be provided by the date specified.
The excellent communication between the NRC and Perry Plant staff regarding this j
issue has allowed us to direct our resources toward all important aspects of
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this event. Ve have and vill continue to keep the NRC, as vell as other BVRs l
vith similar design, fully aware of our activities and findings. Your review of this information is greatly appreciated.
Sincerely, j
Y7 fay Robe'rt A.' Stratman i
RAS:HLH
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Attachment cc: NRC Project Manager f
NRC Resident Inspector Office l
USNRC Region III i
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RESPONSE TO CONFIRMATORY ACTION LETTER (CAL) RIII-93-007 CAL Item 3 Prior to startup, provide Region III with your basis for considering the ECCS suppression pool strainers to be capable of performing their required design function.
Response to CAL Item 3 l
All six suppression pool strainers (RHR "A",
RHR "B",
RHR "C",
LPCS,-
HPCS, and RCIC) will be capable of performing their required design I
function prior to startup.
This is based upon:
1.
Strainer Design.
- 2. Containment Design and Construction.
- 3. Suppression Pool, Containment, and Drywell Cleanliness Levels.
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- 4. Suppression Pool, Containment, and Drywell Cleanliness Methodology.
A discussion of each of these bases follows.
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- 1. The new strainer designs meets applicable established design criteria.
The design approach for this change is based upon minimizing the potential for strainer fouling, increasing the strainer's tolerance for accumulating debris and ensuring structural integrity for all operating and accident loads.
Fouling of suppression pool strainers is a complex issue which is a function of a number of variables,.for example: the amount of fibrous material inside containment and drywell; the 7
migration of insulation from drywell to suppression pool; flow patterns in the suppression pool; cleanliness of drywell, containment, and the suppression pool; and strainer performance variables.
This design change optimizes strainer performance variables to minimize i
i susceptibility to fouling and maximize the tolerance for accumulated debris on the strainers.
These factors were considered under the restraint of minimizing the resultant change to containment penetration loads.
A Design Change Package (DCP) is being implemented to replace the existing suppression Pool ECCS/RCIC strainers (lE12E0001A/B/C,;
1E21E0001, lE22E0001 and lE51E0001), with a new strainer design.
The strainers are located inside containment, in the suppression pool at the 578' elevation.
The new ECCS strainer design is-a truncated cone featuring larger diameter holes, increased total surface area, a larger l
flow area, and increased capacity for external pressure loading l
compared to the original design.
The new design has also been reviewed for capability of back-flush.
As the result of strainer fouling problems documented in Condition Reports numbered 93-022 and 93-085, l
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the maximum operating differential pressure of the strainers has been increased from 1 to 4 psid.
The surface area of the RCIC strainer was not increased by this change, however this evaluation will show that the resultant design is enhanced overall.
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A comparison of the strainer designs is presented below:
1 Original Design Replacement Design j
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surface Area, sq ft 20.0 7.3 42.2 7.2 a
I Flow Area, sq ft 7.3 2.7 17.7
'2.9 Perf. Diameter, in 0.070 0.070 0.094 0.094 Flow velocity,ft/s 2.37 0.58 0.98 0.54 (through strainer)
Approach velocity, 0.87 0.22 0.42 0.22 l
ft/s j
Maximum AP, psid 7
25 32 32 l
(forward flow)
Backflush GPM N/A N/A 3200 (RHR)
N/A r
It should be noted that the approach velocity in this Table is based on stagnant suppression pool conditions.
i Design documents reviewed for the strainer design included the USAR, the ASME Design Specification for each system (E12, E21, E22, E51) and the associated General Electric Design Specifications. ' Applicable codes and standards for the new strainers including compliance-with i
existing USAR loading requirements will be evidenced in the Piping / Equipment Analysis element final interface evaluation for this-DCP.
ASME B&PV Code Section II materials and ASME B&PV Code Section l
IX welding was utilized for strainer fabrication.
All welds'are Liquid Penetrant tested.
The American Institute of Steel Construction (AISC) j standards were utilized for the structural design of the strainers.
1 The strainers are not "N"
stamped, as.they are not pressure vessels.
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The replacement strainers are qualified using analytical methods in lieu of the testing as described in USAR Section 3.9.2.2.3, for the
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loads caused by seismic and hydrodynamic forces.
The results of these analyses demonstrate the capability of the strainers to perform as described and evaluated in the USAR.
Analytical methods are considered to be more representative to demonstrate qualification.
These.results will be reflected in the interface evaluation for the Piping /
Equipment Analysis element, as part.of the documentation for this DCP.
Design verification of these analyses will be completed and approved prior to changing to Operational Condition 2.
It should be noted that maximum differential pressure loads and strainer backflush AP loads are not superimposed on accident loads for these analyses, as.these events are considered as infrequent plant operating occurrences /conditiens.
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. Regulatory Guide 1.82, revision 1 was reviewed for design guidance during the process of establishing the replacement strainer design parameters, even though this guide was not part of the PNPP licensing basis.
The recommendations of Appendix A of the guide were reviewed for BWR suppression pool pump suctions.
The replacement strainer design complies with the geometric design envelope guidelines.
t Quantification of post LOCA migration of insulation from the drywell i
into the suppression pool is addressed in the USAR section 6.2.2.2.
l The approach velocity of the original and replacement strainers exceeds l
the 0.2 ft/sec recommendation provided in RG 1.82.
The approach 1
velocity is based on the the flow rate divided by the strainer's total surface area.
The 0.2 ft/sec velocity recommendation is premised on the theory that suspended solids will fall to the bottom of the pool at i
lower flow velocities.
Perry's suppression pool design is such that j
RHR test return and pool cooling operations impart a velocity to the j
entire pool well above 0.2 ft/see to preclude thermal stratification.
Hence the 0.2 ft/sec velocity guideline is not practical to implement, l
due to other design considerations.
The original strainer design for ECCS is shown to have an approach velocity of 0.87 ft/sec, and the-replacement design has a velocity of 0.42 ft/sec, at 7800 gpm.
At the
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RHR system design flow rate of 7100 gpm, this velocity is further
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reduced to 0.375 ft/sec.
This reduced approach velocity provides a l
reduced tendency to attract and hold debris onto the strainer screen.
Section 6.2.2.2 of the USAR describes the potential for suppression f
pool strainer fouling.
This section is being revised substantially tc
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describe the new strainer design.
Generally, the replacement design i
strainer is less susceptible to fouling as it has a lower approach velocity and larger strainer holes.
This design is more tolerant of l
' fouling because the total surface area is greater, such that the same volume of debris collected on the original strainer design will result 1
in a thinner accumulated " mat" on the new strainer, and likely a resultant lower differential pressure.
Conversely, a greater volume of debris is required in order to accumulate to the same " mat" thickness and the same differential pressure.
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Since this strainer is structurally designed to withstand substantially 1
higher differential pressures (AP's), it's theoretical " clean" AP is l'
slightly higher than the existing strainer design.
However, empirical results indicate similar 6P's.
Although the 6P across the new strainer perforated plate is slightly reduced, the internal stiffener network
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constitutes an increased flow restriction.
The Net Positive Suction Head (NPSH) available for each of the ECCS pumps and the RCIC pump was l
evaluated to be not affected by this minor increase.
The increase in i
accumulated AP capacity of the strainer provides for increased
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component / system availability during upset conditions.
Furthermore, l
strainer's designed capability to be backflushed adds another option-beyond system design bases to ensure that suppression pool and RHR "A" and "B"
availability is maximized.
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- The original strainer design featured external protection bars.
- j According to a discussion with the manufacturer, the bars existed to j
protect the strainer screen from deformation as the result of impact from objects.
The new strainer design does not have these protection i
bars, as the internal ring stiffener network provides sufficient j
stiffness to the strainer screen to resist deformation from such impacts.
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NPSH has been verified as acceptable with the new AP/ fouling limit j
according to RG 1.1 as shown below.
21 ft. required, 23 ft. available (ref. calc. E51-ll)
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=
RHR A,B,C =
4 ft. required, 6 ft. available (ref. calc. E12-1) l 4 ft. required, 6.9 ft. available (ref. calc. E21-2) l LPCS
=
4 ft. required, 5.3 ft. available.(ref. calc. E22-1) 1 HPCS
=
i The change to the maximum operating differential pressure of the strainers is demonstrated by the above calculations to have no effect on the flow capacity of the associated pumps / systems. This change of j
the maximum operating strainer AP, increasing from 1 to 4 psid, is a 2
measure to ensure that strainer cleanliness is maintained at a level S
which will not threaten the integrity of the strainer or the function of the respective systems.
The value of 1 psid was very close to the AP observed for a " clean" original design strainer, and is not j
considered as a condition warranting corrective action.
A 4 psid limit has been evaluated to not impact NPSH requirements per RG 1.1 for all of the ECCS pumps and RCIC.
The 4 psid limit constitutes a fouled strainer.
As~such, this change maintains the original design requirements, and establishes an expanded operating limit to ensure
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that corrective actions will be implemented before ECCS/RCIC system I
function is degraded.
The strainers have been analyzed to withstand a 4
AP much higher than this 4 psid limit.
As such, operation at this limit poses no threat to the reliability of the strainers or their l
associated systems.
The strainer hole size is increased with this change, but remains in
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conformance to the original General Electric (GE) design specification
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requirements.
The GE design specification sets the maximum particle size to minimize potential for: degradation of the associated ECCS pump f
seals, fouling of various spray headers, or negative effects from particulates in the reactor water.
The change from 0.070" diameter j
strainer holes up to the limit of 0.094" diameter (including l
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manufacturer's standard tolerances) represents no change from the original design requirements.
t In accordance with engineering procedures, other design interfaces were j
i evaluated:
i This design change was evaluated from the perspective of containment j
vessel isolation design basis, and was found to have no effect on the isolation capability of any containment isolation valves.
The I
strainer design change will be evaluated for its effects on the i
associated containment penetrations, and the results will show the
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. penetrations to perform as evaluated previously.
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u PY-CEI/OIE-0402L-i Page 5 of 14 This strainer design change was evaluated to have no impact on the j
hydrogen control program and equipment.
The replacement of these
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strainers within the suppression pool are being evaluated for loading from SRV discharge, LorA pool swell, high energy pipe break,-
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and moderate energy pipe break, and will be demonstrated to perform as described / evaluated in the USAR.
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t This design change was evaluated from an ALARA design perspective I
and was found to have no impact to offsite doses.
Although the strainer replacement activities will result in radiation exposure to the divers during installation, the replacement will have no effect on doses to plant personnel during operations.
b A procedure has been developed to provide capability to backflush the E12 A/B suppression pool suction strainers, and has been incorporated into the RHR system operating instruction.
This instruction utilizes the Suppression Pool Cleanup System (SPCU) pump to provide a motive force of water through the strainer in a reverse flow direction.
The flow path utilizes suppression pool water from the High Pressure Core Spray suction line, through the SPCU pump into the Fuel Pool Cooling.
The water is then directed into the RHR suction piping via the l
E12 Fuel Pool Cooling Assist suction valve, then flows back through the l
RHR suppression pool suction valve and subsequently through the
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strainer.
The flow rate will be approximately 1500-2000 gpm.
It is anticipated that this procedure would only be exercised during emergency response, and not during normal-plant operations.
The more appropriate action to a fouled strainer would be cleaning versus backflushing.
The suppression pool was determined to be the source of flush water because it will not add inventory to the suppression pool.
This will prevent the suppression pool from exceeding it maximum Technical i
Specification Limit, and permit the flush to continue for an extended q
period of time, if necessary, to allow the flushing water to remove any-debris.
For'RHR Loops A and B, other sources of flush-water are available, and other systems are available to provide a method of strainer i
backflushing in the event of SPCU unavailability.or HPCS suppression pool suction unavailability.
These include using Condensate Storage Tank as the SPCU suction source, or using Condensate Transfer System l
via-the RHR Shutdown Cooling suction line.
Other methods may exist, i
f and will be determined during reviews performed as part of implementation of these various flush alternatives into the Plant Emergency Instructiocs.
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-2. Containment and drywell are designed and constructed to not introduce debris, that would adversely affect strainer operation, into i
the suppression pool in the event of an accident.
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Containment and drywell design review were an important part of the
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A Incident Response Team's approach to addressing the strainer fouling issue.
The containment and drywell are designed and constructed to
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mitigate the effects of introducing debris into the suppression pool l
as a result of an accident.
Discussion of this can be found in USAR Section 6.2.2.2.
This section of the USAR describes the various types of insulation used for piping and equipment inside containment and i
drywell.
It also provides an evaluation on the safety significance of l
insulation being introduced into the pool with emphasis on the design
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features of the containment /drywell.
However, in light of recent experiences, a review of design /
construction features and operational / maintenance activities was in j
order.
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Insulation A review was performed to re-examine the types and locations of insulation in containment and drywell.
This consisted of a documentation review supplemented by actual plant walkdowns.
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The Containment Vessel Cooling System (Mll), located throughout
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I containment, is insulated with two (2) inch thick fiberglass board and wrapped with an aluminum jacket and banded in accordence with j
manufacturer requirements.
This installation is acceptable for j
accident conditions inside containment above the pool swell region.
The review discovered that some of this metal-jacketed fiberglass board i
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insulation was installed in the pool swell' area.
This was determined to be an unacceptable condition and the insulation was subsequently removed by a design change.
The issue of the use of NUKON insulation on piping in the drywell was also revisited.
A physical inspection of the drywell was performed by an Incident Response Team member to confirm that NUKON was the only
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type of insulation used on piping in the drywell.
Based on the results of the testing performed in the Owent-Corning Topical Report (OCF-1),
the NRC's evaluation of this report, and the Perry plant specific evaluation described in Section 6.2.2.2. of the USAR, it was concluded that the use of NUKON in the Drywell was acceptable.
In addition,.a
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review of the plant specific USAR's for Grand Gulf, River Bend, and i
Clinton nuclear power plants indicated similar analyses and conclusions f
were obtained with regards to drywell insulation.
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However, the event at the Barseback plant indicates that a more detailed review is warranted.
Due to the generic implications of this issue, it is Perry's intention to contact other members of.the GE BWR Owner's Group in the near future for a unified approach to the issue of migration of NUKON from the drywell to the suppression pool post LOCA, with supporting plant specific analyses such that this potential is more thoroughly understood.
This approach will enhance the assurance of the adequacy of ECCS strainer design for all GE BWR's.
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The inside of the drywell cooling (M13) air handling units have owens-Corning Type 703 fiberglass insulation with FRK-25 foil facing as an anti-sweat agent.
The insulation is held in place with glue and j
weld pins.
All joints, weld pins and exposed edges were coated with i
sealer.
According to discussions with Owens-Corning technical staff, the insulation will not degrade if it is exposed to water for an extended period of time, and this installation will maintain insulation integrity when exposed to water.
However, the insulation facing could
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degrade over a period of time since it is a paper base.
Once the drywell is flooded, the water in the area of the lower M13 cooler internal surfaces is expected to be in a stagnant condition which would permit any degraded paper facing to sink to the bottom of the M13 cooler.
Therefore, it was determined that this insulation is not a i
source of debris that could be transported to the suction strainers l
post-LOCA. and the insulation inside the M13 air handling units will remain installed.
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The 3M Interam E-50 Series material was used in various areas of i
containment, including pool swell area, to provide a " radiant energy shield" between a fire involving safe shutdown equipment and circuits and the redundant train.
To obtain a fire resistance rating, the E-50 flexible wrap system was tested per ASTM 119, which included direct impingement of a solid fire hose stream after fire exposure. It was i
also subjected to environmental tests which included immersion in water l
for 90 days with no loss of exothermic properties.
With the physical j
attachment provided by the stainless steel banding and the aluminum facing and tape over the seams to protect the material from water, it is not probable that the radiant energy shields would become dislodged or deposit any fibrous material in the suppression pool during pool swell or normal operations. As fire barriers, the integrity of the wrap assembly is inspected on an 18 month cycle as part of PTI P54-P054 Fire Barrier visual Inspection for any tears or holes..
Thereforc, it was j
determined that this material is acceptable for use in all areas of f
containment.
t The Containment Chilled Water System (P50), also located in various areas of the containment vessel, is insulated with closed' cell polyethylene type insulation.
Less than ten (10) linear feet of this insulation is Jocated in the pool swell region.
The acceptability of.
l this amount of material in addition to the entire P50 system insulation l
throughout ecstainment is based upon the negligible water absorption capacity and a material density of tvo (2) pounds per cubic foot.
Ventilation System Filters i
The filter material for the Drywell Air Cooler (M13) has been identified as the major contributor to the recent RHR "B"
suppression
. pool suction strainer fouling event.
The purpose of the roughing filter is to help maintain the Air Handling Unit (AHU) cooling coils-clean from dust created as a result of maintenance or construction activity.
This filter material is not required to be installed during power operation.
A Design Change Notice will have the filter material removed prior to startup.
The repetitive tasks for installing and removing the roughing filters will have material accountability i
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PY-CEI/OIE-0402L Page 8 of 14 i
i controls incorporated to ensure the material is properly installed (during outages) and removed from containment prior to startup.
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containment vesse] Cooling System (Mll) roughing filters were evaluated j
and found to be a minor contributor to the recent strainer fouling I
condition.
These roughing filter will be removed prior to startup.
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These are 20"X20"X2" cardboard encased, corrugated, woven cotton on wire filter elements (36 total).
The use of filters in the Containment' Vessel and Drywell Purge System (M14) supply plenum was evaluated and not considered to be a. potential problem.
The M14 supply plenums are located outside of Containment and hence, the process of changing out these filters can not introduce filter media into the suppression pool.
Also, the plenum utilizes an American Air Filter "Varicel" type (or equivalent) roughing filter.
These filters are built to be rugged with all metal sides and contain a i
much better quality filter media than that in the Mll and M13. systems.
i Because of the quality of these filters, together with the low velocity of air flow across them, and the limited run times of the M14 system, j
it is extremely unlikely that filter fines would get carried into l
containment and hence into the suppression pool.
This is evident by the lack of M14 filter media in the strainer debris sample.
Thus, no l
corrective action is deemed necessary for the M14 filters.
-i A physical inspection of the containment /drywell determined that there j
are no other installed filters made of fibrous materials in those areas.
f Sources of Other Fibrous Materials Fibers from grifolyn and herculite (sheeting material used to cover.
grating and the suppression pool during outage activities) were-found in the samples removed from the RHR "B"
suction strainer; however, i
these fibers were not considered to be major contributors to the fouling.
The Radiation Protection Section is evaluating options concerning these and other materials for use in covering the suppression pool in future outages, including the option of not
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covering-the suppression pool.
other sources of fibrous material such as portable filters, tape, i
paper, and packaging materials are used in containment /drywell during L
activities in all Operational conditions. -The'use of these materials-
-and their potential introduction to the suppression pool can best be addressed by material accountability (PAP-0204 Zone III requirements) i in Operational Conditions 1,-2, and 3, and by suppression pool, containment, and drywell inspections prior to commencing power operations.
In addition, fibrous type material usage _will be placed under tighter scrutiny, and-prompt action will be taken if this. type of material is identified to be in the suppression pool.
i Paint Chipping and Strippable Coatings L
Strippable coating used'for contamination control.and prevention was.
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l found on several items stored on the refueling floor.
These coatings l
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attachment 1 Page 9 of 14 l
have, by design, very poor adhesion to facilitate removal.
As a result, they are not capable of withstanding the immersion-type environment that would exist during activation of the containment spray l
rings.
This material will be removed or otherwise contained to prevent i
possible transport to the suppression pool prior to plant start-up.
i Numerous areas of epoxy paint delamination inside the Drywell and i
containment were also noted.
These were found primarily on the i
containment vessel wall and the drywell liner plate, but were also noted to a lesser extent on structural steel.
Most of the Reactor Building steel was painted with an inorganic zinc primer / epoxy topcoat l
system, which is susceptible to this type of delamination when the j
topcoat is applied too thick, or the primer is not properly cured.
j Other failure areas occurred at touch-up or repair areas at support l
attachments and are most likely the result of poor surface preparation.
l A Nonconformance Report was dispositioned to remove loose coating
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in accessible areas prior to plant start-up, and to rework them in j
accordance with SP-2350, " Nuclear Grade Coatings", prior to the end of-RFO-6.
The remaining quantity of loose coatings was evaluated to be l
sufficiently small over separate areas such that it was determined not l
to represent a threat of strainer fouling.
All of these non-conforming areas are relatively small in size, and no j
general failures were noted.
Additionally, there were no traces of l
either epoxy coating or strippable coating found in the samples taken j
from the fouled RHR "B"
strainer.
Other Sources of Suppression Pool Debris
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i A review of the Containment piping penetration schedule for piping which communicates with the suppression pool indicates that all of the process piping is fabricated from SA-106, carbon steel.
Although the suppression pool is fabricated from stainless steel, system test and operation activities subject the suppression pool to the introduction f
of normal particulate iron oxide corrosion products.
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- 3. Having obtained acceptable cleanliness levels in the suppression i
pool, containment, and drywell.
j Acceptable cleanliness levels for the suppression pool, containment, and drywell will be obtained prior to startup.
Standards for the containment and drywell were developed and are being implemented through a major cleanup effort.
These standards are:
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-Ensure no accumulations of loose dirt or dust exist under floor j
gratings, top of angle irons, top of components, and piping. (NOTE:
A flash light is necessary to perform this inspection.)
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-Ensure no debris (e.g. loose tape, metal tags, or fibrous material) i is present.
-Ensure tools, hoses, materials, equipment, etc. are either removed, l
seismically restrained, or properly evaluated as a mechanical foreign item in accordance with plant procedures.
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-Ensure no accumulation of loose corrosion or paint chipping exists.
.1 All areas of containment and drywell are being methodically cleaned and l
inspected to the established criteria, and the inspections are being signed off by Incident Response Team members as the areas meet the criteria.
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As the cleaning effort progressed from top to bottom, and the cleanup activities reached the pool swell area of containment, the Suppression Pool Cleanup system was run in conjunction with RHR "B"
in suppression pool to suppression pool mode to " catch" dirt and particles that were j
in suspension.
Additionally, the floor of the suppression pool was.
" lanced" where dirt had accumulated (both inside and outside drywell) l to put the dirt in suspension and allow it to be removed by the cleanup i
system.
The suppression pool area in the containment was recently cleaned in the Mid-Cycle Outage in February, 1993, and based on current l
inspection results, only the immediate areas at and around the strainers required vacuuming, which has been completed.
The entire suppression pool area in the containment was inspected, and a rigorous inspection is being performed for 100 percent of the i
suppression pool area inside the drywell.
All accessible sections (approximately 70 percent) of the suppression pool floor inside the drywell are being vacuumed, and non-accessible sections are being lanced to facilitate inspections.
Any objects or debris found that
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could potentially foul the strainers are being removed.
Divers also e
completed inspections of the 120 horizontal vents between the drywell l
and containment and removed the objects that they found.
Essentially, the material left in the pool will consist of a light film of material on the walls and piping and a small layer on the bottom of l
the vent holes.
This material is what has been analyzed to be potentially introduced into the pool during normal operation via
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corrosion and dirt settling.
Due to concerns about the particle size
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of this material, samples of the pool walls and material removed from the strainer were analyzed.
The largest particle removed from the wall measured approximately 0.009' inches in diameter.
All materidl removed from the strainer passed through a 0.033 inch sieve.
Both samples are well below that of the strainer hole size (0.094 inch) and thus capable of passing through the strainers.
This material is also-found to be magnetic, indicating the presence of iron.
A gamma spectroscopy-analysis shows the presence of Mn-54, Co-60, and Zn-65 which are i
isotopes that are indicative of normal corrosion products.
Since this j
material alone has not caused fouling problems in the past, it was j
determined to not present a concern to strainer performance.
Other corrective actions being pursued by the Incident Response Team, j
including periodic cleaning, will ensure that this material does not accumulate into a significant amount over time.
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'The drywell, containment, and the suppression pool will be inspected to f
the established cleanliness criteria as part of drywell/ containment i
closecut and mode change requirement activities prior to startup.
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r PY-CEZ/OIE-0402L Page 11 of 14
- 4. Having developed and implemented methodology to ensure and maintain acceptable suppression pool, containment, and drywell cleanliness levels before and during plant operation.
1 This methodology will be discussed in the response to CAL Item 4.
CAL Item 4 Prior to startup, provide Region III with your plans and a commitment to ensure that the suppression pool is maintained at an acceptable level of cleanliness, including any surveillances you inNend to perform.
Response to CAL Item 4
-An integral part of suppression pool strainer design is the condition that the suppression pool, containment, and drywell are maintained'at acceptable levels of cleanliness.
In addition, increased awareness of i
plant personnel on the importance of containment /drywell and suppression cleanliness and its potential impact on ECCS strainer performance is essential.
From previous experience, it has become apparent that past inspection and sampling methodologies have not been effective in detecting cleanliness degradation.
The suppression Pool 7
Cleanup System (G42) maintains suppression pool chemistry and clarity 2_
by demineralization.
However, the G42 system takes a suction from the suppression pool through the HPCS (E22) strainer which has tLe same perforation size as the other ECCS strainers.
Hence, the G42 system cannot filter any debris capable of accumulating on the other strainers at a lower velocity.
Hence, it can only remove suspended particles which can pass through the strainer perforations.
Therefore, improved inspection standards and surveillance techniques are being developed and will be implemented prior to.startup to provide-more appropriate indications of suppression pool cleanliness.
Suppression pool condition will be monitored during Technical
!l Specification Surveillance runs of ECCS pumps, in suppression pool to suppression pool mode, by monitoring pump suction pressures before, at the start of, at the end of, and after the runs.
The surveillances to be revised prior to startup include SVI-E12-T2001 (RHR "A"),
SVI-E12-T2002 (RHR "B"), SVI-E12-T2003 (RHR "C"),
SVI-E21-T2001.(LPCS),
i and SVI-E22-T2001 (HPCS). -These surveillances are performed on a quarterly frequency.
The pump suction pressure data will be compared against pre-established criteria.
These criteria include an Alert level, an Action level, and a differential.
The Alert level suction pressure will correspond to a strainer differential pressure that
~i represents a specified departure from the baseline data for a clean strainer.
The Action level suction pressure will correspond to a strainer differential pressure that approaches the strainer maximum operating differential pressure.
The differential criteria is based on an observed change in suction pressure during an individual pump run, or between pump runs as determined by evaluation of trend data.
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PY-CEI/OIE-0402L l
l Page 12 of le l
l If suction pressure drops below an Alert level, the strainer will be visually inspected and a determination of the appropriate actions (may i
include cleaning) will be made.
If comparison of suction pressures between the start and the end of the pump run indicate a drop in run pressure greater than a pre-established differential, the strainer will be visually inspected and a determination of appropriate actions will 4
be made.
Additionally, previous performances will be compared against the most recent pressure drops.
If a trend of pump suction' pressures between pump runs indicates a degrading suction pressure, a visual inspection of the strainer will be performed and a determination of appropriate actions will be made.
If the suction pressure drops to the Action level, the strainer will be visually inspected and an operability determination will be conducted.
Based on the results of l
the inspection and the operability determination, appropriate actions will be initiated.
At the end of each surveillance-pump run, the applicable strainer will be visually inspected.
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The System Operating Instruction (SOI-E12) " Residual Heat Removal
-System will also be revised to include monitoring of suction pressure-i during suppression pool to suppression pool modes of operation for RHR
'l "A" and "B".
Initial and maximum suction pressure drop will be j
recorded and evaluated with inspections and determinations to be made j
4 if preset levels are exceeded.
To prevent the introduction of fibrous or plastic-type material into the containment /drywell as a result of design modification activities, l
Nuclear Engineering Instruction (NEI-0330) " Interface Reviews and Evaluation" is being revised to include a required interface for design modifications to ensure appropriate consideration of the use of such materials.
This revision will be in effect prior to startup.
1 Plant Administrative Procedure (PAP-1102) " Plant Chemistry Control Program" is being revised to add an analysis parameter to the Suppression Pool Chemistry Log which will provide an indication of corrosion product buildup and the presence of fibrous material.
This l
sampling and testing is performed weekly.
To ensure that degradation of pool cleanliness is-limited over time, a
repetitive-task is in place to inspect and clean the suppression pool as necessary every refueling outage.
It is being revised to ensure that all portions of the suppression pool (including the drywell and the 120 horizontal vents between the drywell and containment) are-inspected and that no debris or objects capable of fouling the strainers are left in the pool.
i Until the recent'RHR strainer fouling events, the importance of containment and drywell cleanliness was not fully realized.
j Previously, Plant Administrative Procedure (PAP-0204) j
" Housekeeping / Cleanliness' Control Program" had established Containment /Drywell as a Zone IV housekeeping area (No use of tobacco-or eating); however, our understanding of the impact of debris-in the areas affected by pool swell and containment spray scenarios has-made i
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PY-CEI/OIE-0402L
' Attachment 1 Page 13 of-14 it imperative that the Containment /Drywell be maintained under Zone III housekeeping requirements during Operational Conditions 1,2, and 3.-The Zone III requirements include:
- 1) All personnel entrances into the area shall be posted as zone III.
- 2) A written record of the entry and exit of all personnel and material shall be established and maintained.
- 3) No use of tobacco or eating.
A special section of PAP-0204 is being added to detail the cleanliness.
t requirements for the already prescribed weekly inspections of 1
accessible areas of containment and drywell.
Details for.this inspection include the following:
j (NOTE) l To prevent the ECCS suction strainers from fouling-during a pool swell or containment spray event, this inspection needs to focus on any debris that may enter the pool.
Personnel performing this inspection'shall be trained to the circumstances surrounding Condition Reports93-022 and 93-085.
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-Ensure no accumulations of loose dirt or dust exist under floor gratings, top of angle irons, top of components, and piping. (NOTE:
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A flash light is necessary to perform this inspection.)
-Ensure no debris (e.g. loose tape, metal tags, or fibrous material) is present.
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-Ensure tools, hoses, materials, equipment, etc. are either removed,.
seismically restrained, or properly evaluated as a mechanical foreign item in accordance with plant procedures.
-Ensure no accumulation of loose corrosion or paint chipping exists.
i If violations of this inspection criteria are discovered during power operation and are not immediately rectified, the contrcl room shall be-notified immediately so the appropriate actions can be' determined and implemented.
In addition, Integrated Operations-InstructionsL(IOI-1) 4
" Cold Startup" and'(IOI-2) " Hot Startup" are including this same l
criteria for containment and drywell inspections'to be performed by.the I
-shift Supervisor (or higher) prior to changing to operational Condition l
2..
I Under certain circumstances, the Operations. Manager can authorize the relaxation of Zone III housekeeping requirements for specific areas ~of containment /drywell.
If Zone III_ requirements-for containment /drywell are relaxed, it will be mandatory to perform a visual inspection of the containment side of the suppression pool ~ (and drywell-side-ifLthe drywell was accessed)-using a high powered light, after Lone III requirements are re-instituted.
An assessment of pool cocdition will be made after the inspection and objects _with a potential'for causing f
strainer fouling that are found in the pool will be: evaluatet and removed as required.
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Page 14 of 14 i
To-increase plant personnel awareness, a plant communication f
identifying the importance of eliminating foreign material in the suppression pool and maintenance cleanliness conditions within the l
containment will be distributed to PNPP employees This communication will also provide for a non-disciplinary reporting process in situations where items are dropped into the suppression pool.
Training will also be provided as part of Radiological Controls Training (RCT) to further indoctrinate personnel to the necessity of maintaining i
containment /drywell and suppression pool cleanliness.
Inspection prior to power operation, monitoring of pump suction pressures and visual inspections during Technical Specification surveillances, and periodic cleaning, in conjunction with higher housekeeping and inspection standards for containment and drywell.will ensure that an acceptable level of suppression pool cleanliness is maintained.
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