ML19284F127
| ML19284F127 | |
| Person / Time | |
|---|---|
| Issue date: | 06/25/1985 |
| From: | Chandrasekaran Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19284F128 | List: |
| References | |
| NUDOCS 8507080096 | |
| Download: ML19284F127 (21) | |
Text
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TASK ACTION PLAN STEAM BINDING OF THE AUXILIARY FEEDWATER PUMPS GENERIC ISSUE NO. 93 Lead Organization:
Division of Systems Integration (DSI)
Auxiliary Systems Branch (ASB)
Task Manager:
T. Chandrasekaran Lead Supervisor:
Jared S. Wermiel, Section Leader, ASB NRR Principal Reviewers:
T. Chandrasekaran Auxiliary Systems Branch Division of Systems Integration Applicability:
Project Completion:
May 1986 (if p' ant specific)
April 1987 (if generic) 85070B0096 850625 CF SUBJ RD-7-2B CF
I.
Description Of Problem A.
Statement Of Issue Generic Issue No. 93, " Steam Binding of the Auxiliary Feedwater Pumps" deals with the potential problem of steam binding of the Auxiliary feedwater (AFW) pump (s) in PWRs due to possible backleakage of hot main feedwater (MFW) or steam from the steam conversion system (steam generator and/or MFW system) to the AFW system via remotely-operated valves and/or check valves which isolate the AFW system from the steam conversion system.
This backleakage can occur while the AFW system is idle and the steam conversion system is operational.
The concern expressed in this generic issue is applicable to all PWRs for the following reasons:
1.
Even though backleakage must occur through multiple valves in series to cause steem binding of a single AFW pump, once it occurs, the potential could exist for common mode failure of the AFW system because the AFW pumps are generally connected by common piping (discharge header and/or recirculation piping) in most designs with usually a single check valve to prevent backleakage to a second or third AFW pump.
2.
A study of operating PWRs in this regard did not identify any explicit regulatory requirements or uniform plant practices to reduce the likelihood of steam binding of the AFW pumps and common mode failure of the AFW system.
3.
The steam binding problem has major safety significance because
- 1) loss of a single AFW train due to steam binding is presently an undetectable failure that jeopardizes the capability of the AFW system to meet the single failure criterion i.e., common mode failure and 2) the unavailability of the AFW system due to steam binding contributes significantly to the risk of core melt in PWRs.
2 4.
A study of operating history of PWRs during the prior 1981-1983 showed that the steam binding of the AFW pump (s) due to backleakages into the AFW systems occurred in a number of PWRs.
B.
Backcround Some effort relating to this potential protlem has already been com-pleted by the staff and industry. The major efforts in this regard are listed below:
1.
DST has completed a prioritization evaluation of this potential problem. The evaluation has assigned a high priority for resolu-tion of this potential problem.
2.
IE issued an information notice on January 25, 1984, by which all PWR applicants and licensees were informed of this potential problem in the AFW systems at their f acilities.
IE has additionally prepared Tenporary Instruction 2515/67, Survey of Licensee's Response to Selected Safety Issues (April 22,1985),
which instructs resident inspectors on information to be gathered indicating how their respective licensee has dealt with the con-cerns raised by AFW check valve backleakage and determine how they have implemented the recommendations in INP0 SOER 84-3.
The results of this survey were received from IE in June 1985.
3.
The Institute for Nuclear Power Operation (INPO) prepared a Significant Operating Experience Repo-t (50ER) 84-3 dated April 17, 1984 which was given limited distribution. Besides listing sone of the events of backleakage into the AFW system that occurred in 1963, the report included recommendations for improving the pro-tection against steam binding of the AFW pumps.
4.
Cc 'nents on this issue were received by memorandum to R. Bernero
.su J. Sniezet dated November 2, 1984
3 5.
AE0D prepared a case study report entitled " Steam Binding of Auxiliary Feedwater Pumps" in July 1984 The report provided sn "in-depth" baciground of this potential problem and also included recommendations for reducing the likelihood of steam binding of the AFW pumps and the potential for common mode failure of the AFW system due to steam binding.
The AE00 study reported the following major findings:
a.
During the period 1981-1983, 22 events of backleakage into the AFW system at six operating PWRs in the US (five Westinghouse designs and one Babcock and Wilcox design) and one foreign PWR (KP,5K0 Nuclear Project, Yugoslavia) were reported. Most of these events resulted in at least one AFW train being declared inoperable.
Few of these events affected more than one AFW train. Of these reported events, 14 occurred in 1983, indicating an increasing trend of the reported events over the previous years.
D.
The reported events may not accurately reflect either the number or the frequency of steam binding events or the number of the AFW pumps that are simM t:,,ieously affected in lay single plant by backleakag. This is true because currently, backleakage into the AFW tystem is not by itself a reportable occurrence unless it
.esults in an event which is otherwise reportable by plant Technical Specifications.
c.
On the basis of the reported events, the AFW system at Westinghouse designed PWRs appeared more sasceptib.e 'o backleakages and steam binding of the AFW pumps, presumably because the remotely-operated valve which is in series with multiple check valves (that isolate the AFW system from the MFW system) is normally open in the Westinghouse designed PWR.
It should, however, be noted that B&W PWRs (except Davis Besse, Oconee and Arkansas) and one Combustion
4 Engineering (CE) PWR (Calvert Cliffs) that have norma.y open or partially open (for Calvert Cliffs) remotely-op= rated v0 ves in series with multiple check valves (that isolate the AFW system from the steam conversien system) have not reported events involving backleakage into the AFW system.
The exception to this is Crystal River, Unit 3, a B&W plant, where an AFW train was declared inoperable possibly due to steam binding caused by back-leakage, though the licensee did not identify this as the reason.
Also, Robinson, Unit 2, a Westinghouse PWR reported quite a few events involving backleakages into the AFW system, even though it has normally closed remotely-operated valves.
d.
Even thcugh the AFW designs at CE and B&L operating PWRs are very similar to the AFW designs at operating Westinghouse PWRs, steam binding of the AFW pumps due to backleakage has not been generally reported at these plants (except for Crystal River, Unit 3, where it is inferred to have occurred).
It is not clear whether the absence of reported events involving backleakages at these reactors is due to plant-specific features, e.
The reported events involved the misoperation or failure of about 60 check valves. Operational experience shows that check valves, in general, have a history of leakage problems in a variety of systems including the AFW system where they fail open or leak at times. A review of the AFW system designs for the three types of PWRs (Westinghouse, CE and B&W) indicated that the potential for backleakage is generic to all the AFW designs, because the check valves isolate the AFW system from the steam conversion system in most designs. The analysis of the causes for the reported check valve leakage into the AFW system did not identi#y any pattern or single major ceuse of the failures of the check valves. The causes differed between plants and involved different valve designs and manufacturers.
Furthermore, in most cases, the check valves experienced recurring leakage even af ter repair and/or replacement.
5 f.
Backleakage must occur through multiple valves in series before steam binding can occur at any single AFW pump.
If backleakage through a che u valve arises due to improper seating of the valve, multiple check valves in series may not provide added protection against backleakage.
This is so because the multiple check valves would have to close simultaneously in order to fully seat properly.
Such a situatiot, appears unlikely to occur.
In such cases, only one check valve may be effectively preventing backleakage due to the differential pressure available to seat valves in series (reported events involving backleakages into the AFW system at Surry, Unit 2 tend to support the above conclusion).
g.
The potential for common mode failure of the AFW system is present whenever one AFW pump is steam bound because the AFW pumps are generally connected by common piping (discharge header and/or recirculation piping) with usually a single check valve to prevent backleakage into a second or third AFW pump.
For example, at Surry, Unit 2, where all the AFW pumps share a common discharge header, two AFW pumps were simultaneously steam bound in November 1983.
h.
Current regulatory requirements do not require leak testing of any of the valves isolating the AFW system from the steam conversion system as part of the containment laak rate testing or inservice testing programs to ensure the isolation function of these valves.
Furthermore, existing Technical Specifications for operating PWRs do not contain surveillance requirements relating to monitoring or detecting leakage into the AFW system. Also, a study of operating PWRs did not identify any uniform plant practices to reouce the likelihood of steam binding of the AFW pump (s) ard common mode failure of the AFW system.
6 The AEOD report included a summary of the backleakage events into the AFW system during the period 1981-83. The summary is given below:
SUMMARY
OF BACKLEAKAGE EVENTS (1981-83)
Plant Date No. of Valves Leaking Comments Cook 2 7/12/81 Two Check Valves Turbine-driten AFW pump 10/29/81 (TDAFWP) casing hot.
Pump isolated and the train declared inoper-eble.
Cook 2 1/16/83 Two Check Vah es TDAFWP casing hot.
Plant in operational mode not requiring pumps to be operable.
Crystal 12/20/82 One Check Valve Train declared iroper-River 3(1) 10/03/82 able.
Backleakage caused AFW flow sensor to fail.
Robinson 2 6/11/81 Two Check Valves and Motor-driven AFW pump One Motor-Operated (MDAFWP) tripped during Valve plant startup.
Robinson 2 6/16/81 Two Check Valves and MDAFWP tripped after One Motor-Operated recctor trip.
Valve (1) The AFW system at Crystal River, a B&W 'lant, is connected to both the steam generators and the MFW system. The AFW systems at other B&W operating plants are connected only to the steam generate s.
7 Plant Date No. Of Valves Leakira Comments Robinson 2 6/19/81 Unknown MDAFWP tripped on low discharge pressure after reactor trip. TDAFWP out of service.
Pump trip believed to be caused by improper dis-charge valve throttle setting. Same pump tripped on 6/16/81 due to steam binding.,
Robinson 2 4/19/83 Two Check Valves and MDr.FWP tripped af ter One Motor-Operated Valve reactor trip.
Steam vented from pump casing.
Robir. son 2 t./20/83 Four Check Valves and Eoth MDAFWP casings hot.
Two Motor-Operated Leakage path for hot Valves or Three Check water to the second Valves and One Motor-pump not identified.
Operated Valve Leakage to the second pump believed to be through either the common disctarge header or the recirculation piping through a single check valve.
Robinson 2 7/21/83 One Chect Valve and TDAFWP casing hot.
One Motor-0perated Steam vented # rom the Val v.e casing. Train inoperable.
8 Plant Date No. Of Valves Leaking Comments Surry 2 11/18/83 Four Check Valves MDAFWP steam bour.d.
12/6/83 Feiled to develop flow (11/18/83). Train declared inoperable (12/06/83).
Surry 2 11/20/83 Eight Check Ve.lves MDAFWP and TDAFWP s i.mam bound. Trains inoperable.
Farley 1&2 Ongoing Four-Twelve Check MDAFWP and TDAFWP since mid-Valves per urdt casings hot, sometimes 83(2) simultaneously.
Pumps run to reduce tempera-ture.
No pump declared inoperable by litersee.
KRSK0 7/81 Four Check Valves Gross backhekage from the steam gt'lerators to the AFW pumps during hot functional testing.
Waterharrers occurred when AFWP scarted (Pugs not required to be operable).
(2) A minimum of six events are assumed to have occurred at both Farley units although each train has been affE ted Do"e than one time since 198:.
9 Plant Dag No. Of Valves Leaking Comments McGuire 1 8/25/81 Two Check Valves Slow closing of LVs caused the AFW pump suction piping to be overpressurized causing gross back-leakage.
The AEOD study also included the corrective measures undertaken at the various facilities where these backleakage events caused steam binding of the AFW pump (s) and consequent incoerability of the AFW train (s).
Besides repairing and/or replacing the involved valves, other corrective measures were also undertaken at these facilities only. The chief corrective n;easures are listed:
1.
At Robinson 2, procedural changes involving venting of the AFW pumps each shift and delaying closing of the motor operated valves until check valves have had time to seat properly were adopted in July 1983.
Ever since, no AFW pump tH ps or backleakages into the system have been reported.
2.
At Surry 2, procedural changes requiring frequent (during operator rounds) checking of the AFW system for elevated temperatures by using a hand held pyrometer and leak testing of the valves during refueling outages were adcpted.
3.
Farley 1 & 2 modified the AFW check valves by adding additional weight to the backside of the check valve discs to ensure proper seating of the discs against the backpressure in the system.
In addition, Farley proposes to install temperature monitoring of the AFW system with annunciators locally and in the control room.
10 4.
At Crystal River 3, upon receiving erratic indication from the AFW flow instrument, the AFW pump is run to put cool water into the AFW piping.
5.
Ad hoc procedures have been adopted in a few operating plants (primarily in those plants which experienced backleakage problems) which require the operator to detect elevated tempera-tures in the AFW systems during routine shift rounds by touching the system piping and the AFW pump casings. While this procedure has been usually effective at the affected plants, an AFW pump at Robinson 2 became steam bound even though it was checked once every four hours.
As mentioned above, the study recommended periodic leak testing of the AFW system isolation valves as part of the operability require-means for the system, monitoring the system fluid temperature, and revising plant procedures to spell out corrective actions to be taken in case a high temperature condition is detected in the system.
C.
Purpose The purpose of this task action plan is to evaluate the adequacy of plant specific informatica obtained in response to IE Temporary Instruction 2515/67 in the area of 1) improving the reliability of the AFW system isolation valves for preventing in-leakage into the system,
- 2) periodically monitoring the fluid conditions in the AFW system, and
- 3) taking appropriate corrective actions for relieving steam binding should it occur. The need for additional and/or alternative generic or plant specific requirements will be identified based on the above evaluation.
11 II. Plan For Problem Resolution A.
Approach In developing generic or plant specific requirements for resolution of this generic issue, the following approach will be adopted:
1.
The findings and recommendations given in the July 1984 AE0D case study and INP0 SOER 84-3 will be utilized as the starting point.
2.
Information gathered from the staff review of plant specific informa-tion gathered from Temporary Instruction 2515/67 mentioned above, and suggestions and recommendations by interested interagency staff such as resident inspectors, ORAB staff, MEB staff, etc., and industry groups will be utilized in determining whether plants have adtquately dealt with the concerns raised in this issue.
If it is concluded that they have been inadequately considered, then additional and/or alter-native generic or plant specific requirements will be identified.
B.
Tasks For Resolution See the iten, " Problem / Resolution" and the specific tasks described in the enclosed GIMICS schedule for this generic issue.
12 GENERIC ISSUE MANAGEMENT CONTROL SYSTEM Issue Issue Task Number Type Level Office /Div/Br Manager TAC No.
93 Safety /
L1 NRR/DSI/ASB T. Chandrasekaran 56291 High litle-----------------------Steam Binding of Auxiliar' Feedwater Pumps Work Authorization----------Memorandum to R. M. Bernero from H. R. Denton dated October 19, 1984 Contract Title--------------None Contractor Name/ FIN No.-----None Work Scope------------------Preventive maintenance measures to ensure the intended function of the AFW system isolation valves, surveillance programs for monitoring the AFW system fluid conditions, and needed corrective actions if surveillance indicates occurrence of backleakage into the AFW system will be determined. These determinations will be based on the 1) findings, summary of reported backleakage events, and recommendations given in the AEOD study and INP0 SOER 84-3, 2) staff review of the plant specif;c responses to IE Temporary Instruction 2515/67 and 3) suggestions by interested interagency staff such as resident inspectors, ORAB staff, MEB staff, etc., and
13 industry groups.
Specifically, the determination may include the periodicity of preventive mainte-nance leak tests for the AFW system isolation valves if it is concluded that such tests are needed. Also, it will include the periodicity and methodology for monitoring the fluid condition in the AFW system. The final generic or plant specific determination will involve any one of the following determinations as appropriate fc -
resolving the identified generic concerns in this regard:
- 1) concluding that the licensee's or applicant's proposed procedures are acceptable or
- 2) proposing additional and/or alternative pro-cedures generically or for some plants as necessary. Additionally, the work scope may include proposing follow-up revisions to plant Technical Specifications (TS) to implement pro-cedures if it is concluded that such revisions are warranted.
It is expected that these plant specific procedural changes and their implementa-tion will reduce the likelihood of steam binding of the AFW pump (s) and possible common mode failure of the AFW system by ensuring that the AFW system isolation valves perform their intended function.
Affected Documents----------Plant TS for certain PWRs may need revision to include 1) preventive maintenance tests for the AFW system isolation valves, 2) surveillance of the AFW system fluid conditions, and 3) identifi-cation of corrective operator actions when needed.
The need for these TS revisions will be determined generically or on a case by case basis.
Standard
14 Review Plan 10.4.9 acceptance criteria relating to the AFW system is considered to be adequate, how-ever revision to areas of review may be required.
Status----------------------Some stcff and industry effort relating to the potential problem of steam binding of the AFW pumps has alreac'y been completed.
Previous work on this problem is listed below:
1.
Based on AE0D's Engineering Evaluation Report pertaining to the steam binding of an AFW pump on April 19, 1983 at Robinson, Unit 2, I&E issued an information notice on January 25, 1984.
PWR applicants and licensees were informed through this notice about the poten-tial for the loss of AFW capability due to backleakage and consequent steam formation in the AFW systems at their facilities.
2.
Significant Operating Experience Report (50ER) 84-3 dated April 17, 1984 was prepared by the Institute of Nuclear Power Operation (INPO) and the report had limited distribution. This repo-t catalogued some of the backleakage (into the AFW system) events that occurred in 1983.
The report also included INP0's recommendations pertaining to procedures, training, maintenance, design, and surveillance measures for improving protection against steam binding of the AFW pumps.
15 3.
AE0D completed a case study entitled
" Steam Binding of the Auxiliary Feedwater Pumps" in July 1984, wherein they presented their findings and recommendations for solving the identified concerns in this regard.
4.
I&E has issued Temporary Instruction 2515-67 relating to this problem in April 1985.
This instruction solicits information from all PWR licensees to identify the actions they have taken to deal with the problem of backleakage into the AFW system.
The results of this survey were received from IE in June 1985.
Work on this generic issue will commence in accordance with this GIMCS.
Problem / Resolution----------Determine the generic or plant specific maintenance measures necessary to provide greater assurance that the API system isolation vaives perform their intended function, method of performing needed periodic surveillance of the AFW system fluid conditions, and corrective actions required to be taken should surveillance indicate backleakage into the AFW system.
Plant specific response and suggestions from industry groups and the NRC staff, particularly, the resident inspectors will be utilized in this regard.
16 Determine generic or plant specific hardware modi-fications that may be required to implement the chosen procedures for preventive maintenance, surveillance of the AFW system fluid conditions, and corrective actions when they are needed.
If hardware modifications are needed, determine the acceptable interim measures to be adopted for the plant until the modifications are completed.
Technical Resolution--------After the above mentioned determinations are completed, suggest appropriate revisions to the plant TS as necessary.
Task No.
Title / Milestones Starting /
Completion Date 1
Development of Guidelines Solicit recom Start-August 1985 mendations from interested interagency Complete-October staff such as resident inspectors, ORAB 1985 staff, MEB staff, etc. for resolving the identified concerns in this regard.
Develop guidelines based on the above recommendations, surmary of reported backleakage events into the AFW system, findings, and recommendations given in the AEOD study, and recommendations given in the INP0 50ER for resolving this generic issue.
17 Task No.
Title / Milestones Starting /
Completion Date 2
Evaluation of Plant-Specific Responses Start-November 1985 Using the guidelines developed in Task Complete-January 1986 No.1, evaluate plant specific informa-tion obtained from IE Temporarf Instruc-tion 2515-67 concerning actions taken by individual licensees relating to preven-tive maintenance measures, surveillance programs for monitoring the AFW system fluid conditions, and performance of corrective operator actions when needed.
3 Development of Plant-Specific Requirements Start-February 1986 Based on the plant specific review identi Complete-April 1986 fied in Task No. 2, develop additional and/
or alternative generic or plant specific modifications, and revisions to plant TS as necessary. Additionally, develop interim measures as necessary to be adopted for the applicable plants until the proposed backfits are completed.
4 Prepare Regulatory Requirements Package Start-May 1986 Complete-April 1987
18 Milestones Original Current Actual Issue assigned to DSI 10/84 Prepare Draft Task Action 1/85 Plan (TAP)
Draft TAP approved by DSI 1/85 1/22/85 Director Incorporate comments by 3/85 6/85 various divisions Revise and reissue approved 7/85 TA0 Task 1 - Development of 8/85 guidelines for resolving the identified concerns relating to this generic issue Task 2 - Evaluation of plant 11/85 specific information for adequacy of procedures and actions dealing with this concern using the guidelines developed in Task No. 1
19 Milestones Original Current Actual Task 3 - Development of Generic 2/86 or Plant Specific Requirements Generic or plant specific preven-tive maintenance measures, survei;-
lance requirements and corrective actions including cost-effective backfits and TS revisions when needed determined based on evalua-tion of plant specific information referred to in Task No. 2.
Task 4 - Regulatory Requirements Package If generic action required:
Value Impact Statement 5/86 prepared Final report prepared, CRGR 7/86 package approved by Director, DSI. Sent to DST, DL and others for comment Comments from other 9/86 Division Directors incor-porated. Package sent to Director, NRR
20 Milestones Original Current Actual Package sent to CRGR 10/86 CRGR review 11/86 EDO approval.
FR Notice 11/86 issued for public comment.
Public comments incorporated.
1/87 OMB clearance, if neeced.
Final CRGR package to 2/87 Director, NRR.
Review package to CRGR.
3/87 CRGR review.
EDO approval.
4/87 Regulatory requirements issued.
If plant specific action required:
Inform respective project 5/86 managers of the actions required including the interim measures if any that are needed for the affected individual plant