ML20155D649
| ML20155D649 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 03/13/1986 |
| From: | Delgeorge L COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 1399K, NUDOCS 8604170388 | |
| Download: ML20155D649 (14) | |
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Commonwealth Edison t
) One First Nitionit Plaza Chictgo Ilhnois f
- 7 Address R: ply to: Post Offics Box 767 j Chicago. Illinois 60690 March 13, 1986 v1 Mr. James G. Keppler Regional Administrator U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL 60137 l
Subject:
Zion Nuclear Power Station Units 1 and 2 Response to Inspection Report Nos.
50-295/85-42 and 50-304/85-43 NRC Docket Nos. 50-295 and 50-304
Reference:
February 10, 1986 letter from C. E. Norelius to Cordell Reed.
Dear Mr. Keppler:
This letter concerns the routine safety inspection of activities at Zion Station conducted on November 19, 1985 through January 3, 1986 by M. M.
Holzmer, L. E. Kanter, J. N. Kish, M. McCormick-Barger, and A. Dunlop. The referenced letter indicated that certain activities appeared to be in noncom-pliance with NRC requirements.
Specifically, two Level IV violations were included in a Notice of Violation. Commonwealth Edison Company's response to the Notice of Violation is provided in Attachments 1 and 2 to this letter.
The referenced letter also expressed concern regarding the apparent difficulty with Comonwealth Edison's corrective action system to prevent this event from recurring. Comonwealth Edison shares this concern. acknowledges that the corrective action review following the March, 1983 loss of RHR event should have been more comprehensive. However, the Company also wishes-to dispel any impression that the broader issue of Zion's decay heat removal reliability has been treated lightly in the past.
As discussed in Attachment 3, substantial review and modification effort has been expended since 1983. This effort included independent reviews of the AEOD and NSAC reports. While some of the recommendations, had they been implemented, may have prevented the December 14, 1985 event, the overall level of Commonwealth Edison's effort has been substantial.
l Thus, Commonwealth Edison views the corrective actions discussed in Attachments 1 and 2 as a necessary alteration to an ongoing effort rather than the response to a single event.
8604170388 860313 PDR ADOCK 05000295
, MAR 171986 G
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F J. G. Keppler March 13, 1986 The referenced letter requested that a number of specific concerns be addressed. These responses are contained in Attachment 4.
A one day extension for this response was obtained from W. Hehl by telecon on March 12, 1986. We look forward to discussing these items with you in more detail at the meeting requested by your staff. Arrangements for that meeting can be coordinated through Commonwealth Edison Company's Nuclear Licensing Department.
Very truly ycurs, 4 b.D Louis O. DelGeorge Assistant Vice-President im Attachments cc: NRC Resident Inspector - Zion 1399K
c-9 ATTACHMENT 1 ZION NUCLEAR POWER STATION UNITS 1 AND 2 RESPONSE TO NOTICE OF VIOLATION NO. 1 ITEM OF NONCOMPLIANCE As a result of the inspection conducted on November 19, 1985, through January 3, 1986, and in accordance with the " General Policy and Procedures for NRC Enforcement Actions," 10 CFR Part 2 Appendix C (1985),
the following violation was identified:
10 CFR 50, Appendix B. Criterion XVI, states in part, " Measures shall be established to assure that conditions adverse to quality.
. are promptly identified and corrected. In the case of significant conditions adverse to quality, the measures shall assure that the cause of the condition is determined and corrective action taken to preclude repetition."
Contrary to the above, on March 14, 1983, a condition adverse to quality, a loss of decay heat removal event, occurred on Unit 2, and the licensee failed to assure that corrective action was taken to preclude repetition, as indicated by a similar event on Unit 2 on December 14, 1985.
Corrective Action Taken and Results Achieved:
Investigative methods have been improved within the last year Which better identify the root cause and adequacy of corrective actions for plant events. These improvements include:
Providing checklists for Deviation Report (DVR) event investigators and reviewers which guide the content development and review process.
Use of a root cause diagnostic flow chart and form for each LER.
Providing a member of the on-site Regulatory Assurance Group with root cause assessment training (MORT).
Conducting multi-discipline event review meetings on-site to review reportable events during the investigation phase.
Enhanced modification design review by the on-site modification review committee.
A review of the importance of thorough root cause investigation and corrective action was held last year with the station reviewers and technical staff engineers.
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. These actions have resulted in higher quality investigations producing more accurate and comprehensive root cause analyses and more appropriate corrective actions. These controls were not in place at the time of the March 1983 event and would have resulted in a more comprehensive set of corrective actions in 1983.
Corrective Action To Be Taken To Avoid Further Violation:
Zion will continue to apply the above improved administrative actions.
Date When Full Compliance Will Be Achieved Zion Station is in full compliance at this time.
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e ATTACHNENT 2 ZION NUCLEAR POWER STATION UNITS 1 AND 2 RESPONSE TO NOTICE OF VIOLATION NO. 2 ITEM OF NONCOMPLIANCE As a result of the inspection conducted on November 19, 1985, through January 3, 1986, and in accordance with the "Ceneral Policy and Procedures for NRC Enforcement Actions," 10 CFR Part 2, Appendix C (1985),
the following violation was identified:
10 CFR 50, Appendix B, Criterion V, states in part, " Activities affecting quality shall be prescribed by documented instructions, procedures, or drawings, of a type appropriate to the circumstances...
Instructions, procedures, or drawings shall include appropriate quantitative or qualitative acceptance criteria for determining that important activities have been satisfactorily accomplished."
Contrary to the above:
Procedure MI-6, " Filling and Draining the Refueling Cavity and Fuel a.
Transfer Canal" was inappropriate to the circumstances in that it failed to provide periodic checks between reactor vessel level indicating system recorders and tygon level indication while the reactor coolent system loop was in the partially drained condition.
b.
Procedure MI-6, step 6.34, failed to include appropriate quantitative or qualitative acceptance criteria for determining that the comparison between reactor vessel level indicating system recorders and tygon level was satisfactorily accomplished.
Procedure MI-6 was inappropriate to the circumstances in that it failed c.
to contain a caution stating that the refueling vessel level recorders will not indicate below 584' 5", and that tygon level indication should be used exclusively if level is to be held at or below 584' 5".
Corrective Action Taken and Results Achieved:
As a result of the loss of Residual Heat Removal (RHR) incident, Standing Order #280 was written. This order explained the minimum level that the presently installed level system could monitor. The minimum level that the recorder could indicate was specified. The following policies were established as interim measures.
n
. 1.
Reactor Coolant System (RCS) level is not to be changed unless directed by an operating engineer. At that period in time all outage work was completed so 588' 6" was specified as the RCS level to be maintained.
2.
If the RCS level indication changes by more than 6",
a tygon reading is to be logged in the Nuclear Station Operator (NS0) los along with the remote reading.
3.
If the level drops to 585' 6", a continuous tygon watch will be established.
Tyson level will be verified shiftly and compared to remote 4.
readings and logged in the unit NSO log.
5.
If a difference of 9" exists between tygon and remote readings, the IM's will vent and calibrate the remote level system and the shift will look for the sources of error in the tygon system.
Corrective Action To Be Taken To Avoid Purther Violation:
A review of the Maintenance Instructions (MI's) and the Abnormal Operating Procedure (AOP) for LOSS OF RHR is being conducted with the lessons learned from the December 14, 1985 incident. This review will insure that MI-6 will contain caution statements that are consistant with other MI's.
Changes will be completed before the start of the next refueling outage (Unit 1) or before an outage that requires draining into the RCS loops. Training on the revised MI's and the revised AOP on loss of RHR will be conducted for shif t personnel before the use of the procedures.
A modification to use a loop drain line as the lower tap for a tygon level system will be installed during the next refueling outage for each unit.
This will provide positive indication for any RCS level existing in the loop piping. The use of this system will be incorporated into procedures and training. The long term solution will be to install a remote level system capable of measuring to the bottom of the loop piping and containing redundant transmitters recording in the control room with level alans functions that will be monitored by the Unit NSO.
Date When Full Compliance Will Be Completed Standing order #280 is already in place. The changes to the MI's and the AOP will be in place before the start of the Unit 1 outage (6/26/86) or earlier if needed for RCS draindown into the loops. The loop drain tygon level system will be installed before the end of the next refueling outage for both units. The final level system will be installed during the 1987 Unit 1 & Unit 2 refueling outages.
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r ATTACIGIENT 3 RECENT HISTORY OF CECO'S DECAY HEAT REMOVAL REVIEWS Comunonwealth Edison Company has initiated a number of actions which were directed at improving the overall reliability of Zion's decay heat removal system. These actions included; 1.
Procedure changes 2.
Review of the Zion Nuclear Power Plant RHR PRA-NSAC 84 3.
Review of the AEOD' case study 4.
Initiation of an RHR low suction pressure alatin 5.
Continuing efforts to improve the Refueling Reactor Water Level System These actions will be discussed separately below.
PROCEDURES
- 1) Zion Electrical Distribution Procedures (ZED).
May 15, 1980 These procedures address the plant's response following the de-energization of individual circuits.
Included in these were the conditions that resulted in the closure of the RHR pump suction valves..
(RH-8701, 8702).
Instrument Maintenance Procedures for Pressure Transmitters PT-403 and 2) 405.
June 21, 1983 This change required RH-8701 and 8702 to be de-energized while the pressure transmitters are being calibrated. This precludes inadvertent closure.
- 3) RHR Check Valve Verification Tests - TSS - 15.6.85.
March 22, 1984 This change required the closure of either 8701 or 8702, but not both, for this test. This reduced the probability of a loss of decay heat removal due to the valves failing to open.
- 4) Filling and Draining the Refueling Cavity and Fuel Transfer Canal -
Maintenance Instruction No. 6.
March 22, 1984 Thfs change was implemented in order to prevent the automatic closure of RH-8701 and 8702 due to a spurious signal by de-energizing the valves.
In general, MI6 was intended to better control the ectivities while draining and filling the refueling cavity.
m.
- 5) Loss of RHR Shutdown Cooling - Abnormal procedure No. 20.
February 4, 1985 The procedure was created to clarify the required actions following a loss of RHR shutdown cooling.
- 6) Safety Injection and Residual Heat Removal Systems Valve Interlock Check
- pT-2C.
November 22, 1985 This change minimized the stroking of RH-8701 and 8702 to reduce wear on these valves.
Review of the Zion RHR PRA-MSAC 84 As early as January, 1984, Conunonwealth Edison personnel participated in a review of the draft of NSAC-84.
Actions taken at that time included some of the procedural changes discussed above and the initiation of a modification to further improve the reactor vessel level indication system.
The Zion specific RHR PRA was issued in July of 1985. Corporate-Engineering began an evaluation of the specific recommendations for improve-ment to Zion's Decay Heat Removal System. In October of 1985, the Station Nuclear Engineering Department (SNED) requested initiation of a modification to the RNR system. This modification was intended to alert the operators of a loss of cooling during a partially drained condition. This modification will be discussed in more detail below.
Review of AEOD Case Study The NRC's Office for Analysis and Evaluation of Operational Data (AROD) issued a case study in December of 1985. SNED reviewed that document and produced the following six actions; (1) Zion Station was requested to review the planning coordination, procedures, and personnel training regarding the residual heat removal system.
(2) The status of the Company's efforts to install an improved refueling reactor water level indication system was reviewed.
This project will be discussed in more detail below.
(3) The need to improve the man-machine interface was reviewed. The Detailed Control Room Design Review (DCRDR) was determined to encompass this concern.
. (4) The. addition of a RHR suction bypass line is being reviewed for its applicability to Zion Station. This bypass line would provide for an additional flow path to enable decay heat removal to continue in the event that the normal path was unavailable. A cost benefit study has been initiated to study this potential modification.
(5) The removal of the suction valve auto closure interlocks was reviewed. These valves are de-energized during critical time periods as discussed above in the procedure change section. Thus, i
no additional action was required.
(6) Zion Station was requested to review the Technical Specifications to ascertain that RHR redundancy exists during Mode 4 and the early stages of Mode 5.
Residual Heat Removal System Low Suction pressure Alarm Commonwealth Edison's review of NSAC-84 resulted in the initiation of a modification to the residual heat removal system. This modification will provide a audible alarm in the control room to indicate low RHR flow.
Work on this modification was initiated in October of 1985.
i The modification was further defined in January of 1986. At that time it was decided that the indication would take the form of a low suction pressure alarm in the main control room. The concept was formally presented to the Zion Station modification approval committee in February of 1986.
That committee approved the formal initiation of this modification.
Refuelina Reactor Water Level Indication System Zion Station initiated a modification to upgrade the Refueling Reactor Water Level System (RRWLS) in January of 1984. Work was delayed on this modification during the summer of 1984 while discussions were held on t
potential design changes.
Work on this upgrade was re-initiated in February of 1985 with j
design drawings being released for comment in June of that year. Design work continued with construction drawings being issued in October of 1985.
l The final installation of this modification was deferred in October of 1985 due to scheduling conflicts with the on-going Unit 2 refueling outage. The loss of RHR suction event of December 14, 1985, caused the scope and design of the proposed modification to be carefully reviewed.
The modification was split into two phases during January of 1986.
The first phase will consist largely of the replacement of temporary tygon tube with permanent hard pipe runs. This will reduce the potential for the existence of loop seals.
m a
. The second segment involves the design and installation of a improved permanent RRWLS. The major design decision to be made is to choose between two possible locations for the critical lower tap.
They are currently:
(1) a reactor coolant loop; and (2) and incore thimble sleeve.
In addition,10 specific design objectives have been identified as being pertinent to the design of this system. These objectives are listed below. Phase 2 of this modification is anticipated to be installed during the 1987 refueling outages.
1.
Be capable of providing level indication in all refueling modes.
2.
Be operable with Loop Stop Isolation Valves closed.
3.
Be capable of monitoring level past 584'-0" (bottom of reactor coolant loop).
(It is desirable to make Elevation 584'-0" as near mid range of the sensing device as possible.)
4.
Have the sensing line in a position which would be unaffected by the dynamic affects of RHR pump operation.
5.
Have the instruments vented to the pressurizer air space for compensated les of transmitters.
(Allow use during drain down.)
6.
Have alarms for High Level Lo-Level, and Lo-Lo-Level.
7.
Possible change-out of recorder for improved indication and a larger scale (wide range and narrow range).
8.
Provide computer point ID's which are not tied to safeguards.
9.
Must accommodate the installation of bladder in RC line.
10.
Make the tap for this segment separate from the tap for the sight glass portion.
(Phase I segment)
The above discussion provides the historical background of Commonwealth Edison Company's efforts to improve the overall decay heat removal capability at Zion Station. It should be noted that this effort has been on-going and represents a considerable commitment of manpower and time.
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ATTACIBIENT 4 RESPONSE TO CONCERNS HIGHLIGHTED IN PARAGRAPH 3 1.s i:
The tap for ILT RC22A and B is at elevation 584'.
Modifications M-22-1(2)-81-31 show the tap at 584' 6", as does the instrument maintenance (IM) procedure for calibrating these level transmitters. The elevation of the tap for RCS vessel level was measured following the December 14, 1985 event.
It is not yet clear whether this condition contributed to the event.
Response: The tap elevation for ILT RC22A and B was not physically measured during the previous RHR event, therefore the location was listed incorrectly as 584' 6".
The tap has been measured and verified to be at 584' 0".
The instrument maintenance (IM) procedure did use 584' 0" as the bottom of the calibration.
1.a 11:
Modifications M-22-1(2)-81-11 & 31, while showing the level tap (and therefore the minimum possible level which could be indicated) as 584' 6", were implemented using a strip chart which used 584' 0" as the minimum possible level which could be sensed by the instrument. This is an example of poor human factors considerations.
Response: The proposed control room indication to the RHR Level measuring system will have a human factors review.
1.s ill:
The tap at 584' 6" was selected even though operating procedures Maintenance Instructions (MI's) already specified the use of 584' 6" as a point at which operators controlled level for certain maintenance activities. This is another example of poor human factors considerations, which left no margin for observing levels below 584' 6".
As noted above, it was fortuitously possible to read levels as low as 564' 0".
Response: The tap for the proposed modifications will allow measurement below the operating range.
1.a iv:
The tap selected is in close proximity to the RHR system return line, which may result in turbulence at half pipe conditions.
I I
The effects of this condition on level indication are not yet known. There may have been considerable turbulence at the level tap when at half pipe conditions.
n
.. Response: Segment 2 of the modification to provide a new RHR Level system will use a tap that will not be subject to velocity effects from the RHR return line.
1.a v:
The tygon tube indication system is a temporary hookup which has a high point at 583' which has occasionally formed loop seals, resulting in false level indications.
Response: 'The tygon level system for the next outages is being designed not to have any loop seals.
1.a vi:
There was a level deviation between the RCS vessel level indication system and tygon observed immediately following the event which persisted to varying degrees until the RCS was filled and vented. At least one SRO recalled that in the past, the recorder would not indicate levels below 584' 5", and procedural changes were written by him to a MI which permitted operating at 584' -0" to +4".
He stated that the reason for selecting this leval was that the vessel level indicating system would not indicate below this level, which was based on his personal experience and observation. The reason for the difference between vessel level indicators and tygon is not known, but is under investigation.- Calibration sheets for the vessel level instruments have been reviewed by the station and by the NRC resident inspectors, and no abnonmalities were noted with either the procedure or the results. It appeared possible that the vessel level recorders were indicating the actual level in the B RCS Loop at the time of the event.
Response: The tygon vessel level recorders were in fact indicating the correct level at the time of the event.
1.b 1:
Of approximately nine operators or senior operators interviewed after the event, all but one felt that the chart recorder would indicate properly over the full span. While their comments appear to be consistent with the equipment design, they conflict with both the elevation of the level tap in the modification packages and the IM calibration procedure, and appear to fail to reflect the previous experience with level not going below 584' 5" as described in (a)(vi) above.
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. Response: The range that the level system was capable of measuring was the same as the chart recorder was capable of indicating. Training that will be conducted before the use of RMR lower than 589' level will insure that all operators have the correct information about the currently installed level system.
1.b 11:
No operators were aware of the 6" offset described in (a)(1) above. This condition was detecnined during the licensee's review of the event in question. This does not appear to have contributed to the event.
Response: Training on the new permanent level system will discuss design features and limitations.
2.a 1:
Station procedures did not require cross checking control board indication with tygon indication while in this condition.
Several supervisors indicated that the non-licensed operators generally check the tygon about once per shift on an informal basis. These checks, if performed, were not logged. The procedure in use at the time of the event, MI-6, " Filling and Draining the Refueling Cavity and Fuel Transfer Canal", required tygon level to be verified to agree with the vessel level recorder at step 6.34, the step at which the tygon indication was put in service, but no other checks were specified.
Response
Station procedures will require crosn checking of the control board indication with tygon indication at specified intervals.
2.a 11:
MI-6, step 6.34 required verifying tygon to agree with vessel level recorder, but no tolerance was specified.
Response: A tolerance between the tygon and the vessel level recorder will be specified.
2.a 111:
MI-6 contained no caution as to the minimum value which the RCS vessel level indication system could indicate. Other MI's did contain this type of caution (MI-1 MI-1B, and MI-1F) stating that the " refueling vessel level recorders will not indicate below 584' 5".
Tyson level indication should be used exclusively if level is to be held at or below 584' 5"."
These cautions were established due to operating experience or erroneous understanding of the elevation of the vessel level tap, or both.
Response: MI-6 will be reviewed alon5 with the other MI's for consistancy and correctness of cautions.
9-1e +
, 2.b i:
Deviation Report (DVR) 22-2-83-36, dated March 14, 1983, reports a loss of RHR event which was attributed to the inability of the vessel level recorders to indicate below 584' 5",
and to the formation of a loop seal at the 587' elevation in the tygon indicating system. The DVR states that the " operators were informed that the temporary vessel level indicator would not read below 584' 5"."
This correction was inadequate, since operators generally felt that the vessel level indication system would provide valid indication down to the 584' level as described in a(1)(b)(i) above.
. Response: Classroom training will be conducted on the new level system and associated procedures. This should avoid operators not knowing the correct levels.
2.b 11:
In their response to IgB 80-12, the licensee stated, " Zion Station has analyzed its procedures for adequacy of responding to RHR Loss events. This review identified areas needing further clarification of modification.
As a result of this review, the necessary procedure changes have been initiated and will be implemented by September 12, 1980."
It appears that this action was not completed until after the September 14, 1984 loss of RHR event, when AOP-20 was written.
It does not appear that this condition contributed significantly to the event on December 14, 1985.
Response: -AOP-20 was written in response to the September 14, 1984 losslof RHR event. The corrective actions taken in response to IgB 80-12 were considered adequate at the time of the response and were implemented by September 12, 1980.
2.b 111:
'In LER 84-31-01, which documents the September 14, 1984, loss of RHR event, the licensee states, "A modification will be considered for a completely hard piped system relieving to the pRT."
This modification to the tygon level indicating system has yet to be installed.
Response: After the Unit 2 loss of RHR event in 1983, the mod as referenced in DVR No. 22-2-83-36 was pursued until after discussions indica-ted that compensating the low level leg of transmitters RC 22A &
B would not guarantee reliable indication. The concern was the potential for water to condense in the leg. Thus a modification was initiated in 1984 (M22-1(2)-84-13) to compensate the tygon to the pressurizer instead. There had been problems in the past with the formations of loop seals in the tygon due to kinking.
This modification was to run pipe in place of tygon except for the length where level is indicated.
Since that time the scope of this modification has changed due to the recent incident.
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