ML20198P057
| ML20198P057 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 09/03/1998 |
| From: | NORTHERN STATES POWER CO. |
| To: | |
| Shared Package | |
| ML20198P046 | List: |
| References | |
| 95T047, 95T047-R01, 95T47, 95T47-R1, NUDOCS 9901060288 | |
| Download: ML20198P057 (9) | |
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Safety Evaluation 95T047, Revision 1 Back-up Compressed Air Supply for Cooling Water Strainer Backwash Valve Actuator l
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9901060288 981222 PDR ADOCK O 2 2{u G
l * " PINGP 279, R v.15 l '.P:ga 1 of 2 (FRONT)
R;t:ntion: Life of Plant /LSFS l
Document Type: 3.240/3.241 SAFETY EVALUATION (NON-MODIFICATION)
SE No. %764 7 co. I Addendum Page 1 of A l
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All Safety Evaluations for changes, tests and experiments required by 10CFR50.59 and 10CFR72.48 (except those done under the Modification Process - SACD 6.1 series) SHALL be submitted using this form.
TITLE:
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1.
DES.CRIPTIQN (The description should answer the seven questions in Table 2 of SAWI 3.3.2, and be attached to this cover form.)
2s TECHNICAL SPECIFICATION / LICENSE AMENDMENT OR UNREVIEWED SAFETY QUESTIONS YES l
1 (NRC approval is required prior to implementation for conditions identified in section 6.2.2 of 5AWI 3.3.2.)
A.
Amendment Request Transmittal DATE:
B.
NRC Approval Received DATE:
C.
1'0CFR72 ISFSI related i
IYES NO
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NAD ANALYSIS AFFECTED (See 5AWI 3.3.2, Table 3) l I YES fL7 l NO PREPARED BY:_M DATE: B//4/99; REVIEWED BY.
DATE: ?/24/99 EVIE i
DATE: 7' NN I (SYSTEM ENGINEER LRnbrI Oole/
M DATE: 9e2O-98
/ I-/5-f9 l
DE51dfN REVIEW DESIGN STANDARD 6 REVIEW
(
(Design & standards review are "NA* for Procedural changes)
OPERATIONS COMMITTEE REVIEW:
DATE: kNM DATE:
98 APPROVED BY:
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GEN SUPT ENGINEERING (PLANT)
COPY TO:
Manager, Power Supply Training - Nuclear (PITC)
DATE:
I COPY TO:
Licensing & Management issues @ PI DATE:
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l SAFETY AUDIT COMMITTEE REVIEW DATE:
v (For Technical Specification / License Amendments or unreviewed Safety Questions, the SAC SHALL review l
the change prior to implementation.)
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', - PINGP 279, Rev.15 H
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Paga c of 2 (BACK).
l SE No. 957047 m1 Addendum 7.,q.
7 Page 2 of A
INDEX TO FUTURE NEEDS l
YES NO:
'l X
l 1.
Computer File (File Name: SE###A#) Copied Into L W Sub-Directory J:\\EVERYONE\\SE
'X 2.
Analysis of Record index....................... PINGP 1075 y
3.
Drawing Revision Request..................... DRR g
4.
New Drawing Request........................ NDR
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y.,
5.
Drawing Deletion Request..................... DDR
- 6. - Construction File Submittal.................... CFS
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g 7.
Technical Manual Addition..................... TAF l
8.
Technical Manual Deletion..................... TDF y
9.
Technical Manual Revision.................... TRF
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- 10. New or Revised Specfications.................. SPEC
- 11. TechnicalSpecifications/ License Changes....... Amndmnt x
- 12.. USAR/FSAR/ISFSI SAR Changes.............. Submitted q
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- 13. 10CFR50.59 or 10CFR72.48 Report Summary... Submitted y
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- 14. Fire Hazards Analysis......................... Submitted q
- 15. Safe Shutdown Analysis....................... Submitted j
y
- 16. Appendix R Submittals................. /...... Submitted +
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- 17. NRC Submittal Review........................ Submitted
- 18. Operating Procedures or Changes............... Updated -
- MlHs-N/#. #
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- 19. Surveillance Procedures...................... SP.
- - # Pc2 som em2.
- 20. Maintenance Procedures...................... PM
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- 21. ASME Section XI Program (ISI/IST)...<....r.
Submitted._ _ m ---
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- 22. Data Files................................... CFN
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- 23. Modification Training Request.................. Submitted
- 9/S/9s
- 24. Installation Procedures........................ WR/WRA
- 92417e se -
- 25. Pre-Op Procedures........................... WR/WRA
- 95b4Z78 y
- 26. - Operational Tcst Procedures................... WR/WRA.
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- 27. Purchase Orders............................. PO
- fW%873/PFh84 V
- 28. Spare Parts..................................- Ordered
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- 29. HOLDS y
- 30. Other Organizations (Name below)............. Contacted l
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I I OTHER Future Needs:
_ scc 7-mo r.ce-sceu.eco ew c <:. / cera.c urec <
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The Operations Committee Recommends Completion of items by the Following Date:
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The above applicable Future Needs have been completed and/or submitted.
- R3sponsible Engineer Date:
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SE#95T047 Rsvision 1 l
PURPOSE The Sentice Water Operational Performance Inspection Self Assessment identified a potential operability concem regarding the performance of the Cooling Water (CL) j l
system with a failure of instrument air; a loss of air pressure to the CL strainer j
backwash valves would result in all four valves moving to their full open position.
This would divert some CL water away fiom the supported heat loads and potentially prevent safeguards components from performing their safeguards i
function (also see NCR19981620).
l As a compensatory measure to enhance the capability of the CL system, Temporary l
Modification 95T047 was installed to provide a backup source of air pressure to the cooling water backwash strainer valves. The purpose of this Safety Evaluation is l
to determine whether the compensatory action impacts other aspects of the facility as described in the SAR (REF: 5AWI 3.15.5);
5AWI 3.15.5: If an interim compensatory action is taken to address the condition and involves a.. temporary modification, a 10CFR50.59 review l
should be conducted and may result in a safety evaluation. The intent is to determine whether the compensatory action itself(not the degraded condition) impacts other aspects of the facility descnbed in the SAR.
l Describe the Change, including possible Safety Concerns l
Loss of the instrument air header pressure will cause all four CL strainer backwash l-valves to fail to their full open position. This would divert some CL water away from the supported heat loads and potentially prevent saf.eguards components from perfarming their safeguards function (also see NCR19981620).
l Installation of the backup compressed air system ensures control of the valves will be maintained during loss of instrument air scenarios. This T-Mod does not alter the operation of the CL strainer backwash valve control system. The backup l
compressed air system will provide pressurized air to operate the strainer backwash l
valves, via the normal control system, in case of instrument air failure. The backup l
compressed air system consists of a single bottle of compressed air, a pressure i
regulator, tubing and check valves required to make the connections to the four CL strainer backwash valves pneumatic tubing. Control of the backwash function will continue to be provided by the automatic backwash features and master controller.
The bottle, regulator and tubing are situated in locations which will not impact equipment access. In addition, the bottle contains compressed air, thereby ensuring that a bottle leak will not result in an unsafe room environment or compromise the CL diesel combustion air. To eliminate the potential for seismic missile concems, the support of the bottle and tubing conforms to the plant seismic requirements.
August 14,1998 Page 3 of 8 i
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SE#95T047 Ravision 1 1
4 System and Components affected The existing automatic backwash system is provided to backwash the strainers at a predetermined differential pressure (indicating debris loading on the strainer). When any one strainer reaches the set point, the master control begins a backwash cycle.
l The backwash cycle consists of backwash of one strainer at a time, sequencing through all four strainers. The master controller also performs the backwash cycle at predetermined time intesvals (i.e. daily), regardless of differential pressure.
The motive force for the four strainer backwash valves is provided by the instrument air header via local regulators and a solenoid valve used to control the air flow to the
. actuator assembly. Air pressure maintains the valves closed; venting the air from the actuator allows a spring to open the valve. This T-Mod provides a backup air supply to all four CL strainer backwash control valves; CV-31652 11 CL STRAINER BACKWASH CV CV-31653 12 CL STRAINER BACKWASH CV CV-31654 21 CL STRAINER BACKWASH CV CV-31655 22 CL STRAINER BACKWASH CV 1
4 Design Basis Accidents Reviewed The SAR was reviewed for discussion of the CL strainer backwash system. It was determ!ned that the backwash system is referenced only once: Table 10.4-1 Cooling Water (flow) Requirements for Single Unit Operation in GPM. This table identifies the required flow for the filter water system, strainer backwash and screen 3.j' backwash as 250 gpm; this Temporary Modification ioes not affect the required i
4 flows.
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In addition, the Design Basis Accidents were reviewe'd for possible impact. It was identified that, while the backwash system is not credited with mitigation of any of the Design Basis Accidents, the CL header is required to support several safeguards components and their associated functions. However, the probability of L
needing to backwash is considered to be highly remote, and the need would occur only under very extraordinary conditions; therefore; the backwash capability is not considered to affect equipment important to safety.
' Potential Failure Modes of the T-Mod The pressure regulator used on the backup air system is a two-stage Smith Mod.
- H1408-346 (or equal) that has a 0-125 psig output range. The regulator is equipped with a factory installed safety relief valve set at 300 psig. The relief valve
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protects against first stage, high pressure regulator failure. In a second stege failure i
situation, the regulator is limited by the first stage outlet pressure of 250 psig.
Ultimately, the tubing system could be exposed to 250 psig. This pressure could potentially cause CV pneumatic pressure boundary failure, or result in a condition where the SVs can not operate (i.e. pneumatic system pressure exceeds SV maximum operating differential pressure of 125 psig).
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SE#95T047 RIvision 1 l
Pneumatic pressure boundary failure will result in the valves falling to the open position; this is consistent with the existing design; i.e. loss of the existing l
non-safety related instrument air system results in the valves failing open. This j
condition will be detected by the existing BACKWASH VALVE Fall TO CLOSE alarm which is received in the control room if any valve is full open longer than 3.5 l
minutes. Therefore this does not introduce any new failure mode or result in an l-unsafe condition.
l Regulator failure may result in the backwash valves becoming " blocked" in the closed position; th;s is consistent with the existing design; i.e. malfunction of the non-safety related master controller or differential pressure switches may result in the valves becoming " blocked" closed. However, several methods exist for l
detecting this conditions (1) strainer DPs are checked and logged twice per shift (2)
L the compressed air bottles outlet pressure is checked and logged daily (3) If high j
debris loading is present, failure to backwash will be automatically detected by the COOLING WATER STRAINER HIGH DP alarm which is received in the control
, om if any strainer DP exceeds 8 psid (backwash is initiated at 4 psid). Therefore uis does not introduce any new failure mode or result in an unsafe condition.
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Tech Spec Change -
l This T-Mod does not affect any Tech Specs, or require any changes to Tech Specs.
Unreviewed Safety Questions l
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May The proposed activity increase the consequences of an accident 1
previously evaluated in the SAR or in a pending SAR submittal?
NO. The backup air supply system is installed as a compensatory measure to enhance the capability of the CL system; by providing a backup air source, the T-Mod enhances the capability of the CL system to provide adequate water flow to j
safeguards components by ensuring that flow is not directed out the backwash valves during a loss of instrument air scenario. There is no credible means for the backup air system to prevent the CL header from performing its safeguards function.
Therefore, the backup air system does not increase the consequences of an l
accident.
2.
May the proposed activity increase the probability of occurrence of and accident previously evaluated in the SAR or in a pending SAR submittal?
The CL strainers, including backwash system, are not a precursor to any accidents described in the SAR, therefore the probability of occurrence of an accident is not changed.
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SE#95T047 l
R: vision 1 i
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May the proposed activity increase the probability of occurrence of a malfunction of equipment important to safety previously evaluated in the SAR or in a pending SAR submittal?
l Although specific malfunctions of the backwash system are not discussed in the SAR, potential malfunctions could impact the CL header. Two potential backwash il malfunctions are evaluated-(1) failure of the pneumatic pressure boundary (backwash valves fail OPEN) is not increased by installation of the backup air supply..
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Common mode failure of the pneumatic pressure boundary is possible due to
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j potential malfunction of the backup air regulator or loss of the existing j
instrument air system. Malfunction of the backup regulator could result in air at pressures between 0-250 psig being supplied to the SV and CV. These pressures could result in pneumatic pressure boundary failure at the CV O-Rings (structural valve damage is not anticipated due to the valve design and j
pressure relief provided by the O-Rings).
To ensure that the probability of this malfunction.is no higher than the probability p
of the original common mode instrument air system malfunction, the backup air i;
supply system is treated as Safety Related Design Class 1. The existing lA l
supply is QA/ Design Class Ill, non-seismic; therefore it is not relied upon in an accident and the backwash valves would fail open in every design basis event.
Therefore the probability of pneumatic pressure boundary failure is not increased by installation of the backup air supply.
j; (2) failure of the SV to operate when required (backwash valves failed CLOSED) l
. does not affect equipment important to safety.
Common mode failure of the solenoid valves to operate is possible due to potential malfunction of the backup air regulator or the existing control system.
i Malfunction of the backup air supply regulator could result in 250 psig lined up to the SV and CV. Assuming the CV pneumatic pressure boundary would not fall, the SV operation would be blocked by the high differential pressure (>125 psig).
i This type of malfunction could result in all four backwash valves being blocked closed.
However, the probability of needing to backwash is not considered a credible.
event, and the need would occur only under very extraordinary conditions, e.g.,
canal dredging. Thus, the strainer backwash valves provides no specific reactor shutdown to cold shutdown, or accident mitigation function (REF: H10.1 Section 6.12.1). Therefore, this malfunction does not affect equipment important to safety.
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May the proposed activity increase the consequences of a malfunction of equipment important to safety previously evaluated in the SAR on in a pending SAR submittal.
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Although specific malfunctions of the backwash system are not discussed in the SAR, potential malfunctions could impact the CL header. Two potential backwash i
malfunctions are evaluated; (1) failure of the pneumatic pressure boundary; i.e.
a backwash valves fail OPEN. (2) failure of the SV to operate when required; i.e.
i backwash valves failed CLOSED. There is NO credible mechanism for the passive i
backup air system to affect the consequences of these malfunctions.
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May the proposed activity create the possibility of an accident of a different type than previously evaluated in the SAR or in a pending SAR j
submittal?
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NO. The CL header and backwash system are not a precursor to any accidents evaluated in the SAR. The installation of the backup air system affects only the CL header and the CL strainer backwash system and does not introduce any credible i
methods to initiate an accident. To prevent the backup air system and components j'
from becoming a seismic hazard, the bottle and tubing are seismically restrained.
To ensure a safe room environment, and ensure combustion air for the diesels, the
. bottles are charged with compressed air. No accidents of a different type are j
identified.
l 6.
May the proposed activity create the possibility of a different type of malfunction of equipment important to safety than any previously evaluated in the SAR or in a pending SAR submittal.
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Although specific malfunctions of the backwash system are not discussed in the l
SAR, potential malfunctions of the backup air system could impact the CL header.
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The backwash system does support the CL Header by providing backwash i
capabilities on strainer Dp and maintaining the backwash valves normally closed (with backwash sequenced by the master controller to limit backwash to one strainer at a time).
i Existing backwash system malfunctions which may affect equipment important to safety:
As originally designed, the backwash Control Valve and associated SV were supplied only from the non-safety related instrument air system. Failure of the upstream pneumatic pressure boundary could result in a common mode failure (loss of instrument air) which causes all backwash valves to fail open. This type of malfunction would reduce the CL flow available to the header.
As originally designed, the possibility existed for mechanical malfunction of the individual solenoid valves, or malfunction of the master controller, resulting in a common mode failure which causes all four solenoid valves, and therefore all four CVs to fail to operate. This type of - iunction could result in all four backwash valves being blocked closed, or multiple valves being blocked open.
With the valves blocked closed, potentiai strainer fouling (without backwash)
August 14,1998 Page 7 of 8
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SE#95T047 R vision 1 could reduce the CL flow available to the header. However, the probability of needing to backwash is not considered a credible event, and the need would occur only under very extraordinary conditions. Therefore, the loss of backwash capability is not considered to affect equipment important to safety.
Backup air system malfunctions which may affect equipment important to safety:
Common mode failure of the pneumatic pressure boundary is possible due to potential malfunction of the backup air regulator. Malfunction of the backup regulator could result in air at pressures between 0-250 psig being supplied to the SV and CV. These pressures could result in pneumatic pressure boundary failure at the CV O-Rings (structural valve damage is not anticipated due to the valve design and pressure relief provided by the O-Rings). This failure mechanism is consistent with the loss of pneumatic pressure boundary discussed for the existing backwash system.
Common mode failure of the solenoid valves to operate is possible due to potential malfunction of the backup air regulator. Malfunction of the backup air supply regulator could result in 250 psig lined up to the SV and CV. Assuming the CV pneumatic pressure boundary would not fail, the SV operation would be blocked by the high differential pressure (>125 psig). This type of malfunction could result in all four backwash valves being blocked closed. This failure mechanism is consistent with solenoid valve and master controller failures discussed for the existing backwash system.
Based on the preceding evaluation, installation of the backup air systems does not create any different malfunctions of equipment important to safety.
9 7.
Does the proposed activity reduce the margin of safety as defined in the basis for any Technical Specification.
No margins of safety are discussed in the Tech Specs regarding the function of the CL strainers or backwash system The backup compressed air system will increase margins associated with the strainers and backwash system by providing a redundant method of operating the backwash control valves.
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