ML20247K847
| ML20247K847 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 05/24/1989 |
| From: | Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20247K842 | List: |
| References | |
| EA-88-266, NUDOCS 8906020039 | |
| Download: ML20247K847 (3) | |
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NOTICE OF VIOLATION AND PROPOSED IMPOSITION OF CIVIL PENALTY Commonwealth Edison Company Docket No. 50-454 Byron Station Unit 1 License No. NPF-37 EA 88-266 As a result of an inspection conducted during the period September 19 through 28, 1988, a violation of NRC requirements was identified. In accordance with the
" General Statement of Policy and Procedure for NRC Enforcement Actions," 10 CFR Part 2, Appendix C 53 Fed. Reg. 40019 (October 13,1988), the Nuclear Regulatory i Connission proposes to impose a civil penalty pursuant to Section 234 of the Atomic Energy Act of 1954, as amended (Act), 42 U.S.C. 2282, and 10 CFR 2.205.
The particular violation and associated civil penalty are set forth below:
10 CFR Part 50, Appendix B, Criterion V, as implemented by Connonwealth Edison Company's Quality Assurance Manual, Quality Requir'ement 5.0, requires that activities affecting quality be prescribed by documented procedures of a type appropriate to the circumstances.
Contrary to the above, on September 19, 1988, it was determined that activities affecting quality were not adequately prescribed by documented procedures of a type appropriate to the circumstances, as noted by the following examples:
(1) Byron Operating Procedure B0P RH-9, Revision 51A, " Pump Down of the Reactor Cavity to the RWST," was inadequate in that it did not specifically require the use of any means of Reactor Coolant System (RCS) level indication during draining of the reactor cavity below the reactor vessel flange. While the procedure specified that the operator " ENSURE that the tygon hose connection, for RCS level indication, is in place," it did not require that the tygon hose, or any other means of level indication, be utilized during the drain down process.
(2) Byron Operating Procedure B0P RC-4a, Revision 51, " Reactor Coolant System Drain," which contains instructions for the installation of the tygon hose level indication system, was inadequate in that it did not provide appro-priate guidance for ensuring that the tygon hose was an accurate indication of RCS level, such as verifying that the hose was installed vertically, that there were no loop seals, or that the elevation markings were accurate.
This is a Severity Level III violation (Supplement I). (454/88019-01(DRP)) l Civil Penalty - $50,000.
Pursuant to the provisions of 10 CFR 2.201, Commonwealth Edison Company, is hereby required to submit a written statement or explanation to the Director, Office of Enforcement, U.S. Nuclear Regulatory Commission, within 30 days of the date of this Notice. This reply should be clearly marked as a " Reply to a Notice of Violation" and should include for each alleged violation:
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Notice of Violation 2 l t
s (1) admission or denial of the alleged violation; (2) the reasons for the violation if admitted; (3) the corrective actions that have been taken and the results achieved; (4) the corrective actions that will be taken to avoid further violations; and (5) the date when full compliance will be achieved. If an adequate reply is not received within the time specified in this Notice, an Order may be issued to show cause why the license should not be modified, suspended, or revoked or why such other action as may be proper should not be taken. Consideration may be given to extending the response time for good cause shown. Under the authority of Section 182 of the Act, 42 U.S.C. 2232, this response shall be submitted under oath or affirmation.
Within the same time as provided for the response required under 10 CFR 2.201 1 the Licensee may pay the civil penalty by letter to the Director, Office of Enforcement, U.S. Nuclear Regulatory Commission, with a check, draft, or money order payable to the Treasurer of the United States in the amount of the civil penalty proposed above, or may protest imposition of the civil penalty in whole or in part by a written answer addressed to the Director, Office of ,
Enforcement, U.S. Nuclear Regulatory Commission.
Should the Licensee fail to answer within the time specified, an Order imposing the civil penalty will be issued. Should the Licensee elect to file an answer in accordance with 10 CFR 2.205 protesting the civil penalty, in whole or in part, such answer should be clearly marked as an " Answer to a Notice of Violation" and may: (1) deny the violations listed in this Notice in whole or in part; (2) demonstrate extenuating circumstances; (3) show error in this Notice; or (4) show other reasons why the penalty should not be imposed. In addition to protesting the civil penalty, in whole or in part, such answer may request remission or mitigation of the penal ty.
In requesting mitigation of the proposed penalty, the factors addressed in Section V.B of 10 CFR Part 2, Appendix C,. should be addressed. Any written answer in accordance with 10 CFR 2.205 should be set forth separately from the statement or explanation in reply pursuant to 10 CFR 2.201, but may incorporate parts of the 10 CFR 2.201 reply by specific reference (e.g.,
citing page and paragraph numbers) to avoid repetition. The attention of the licensee is directed to the other provisions of 10 CFR 2.205, regarding the procedure f0r imposing a civil penalty.
Upon failure to pay any civil pena'lty due which subsequently has been determined in accordance with the applicable provision of 10 CFR 2.205, this matter may be referred to the Attorney General, and the penalty, unless compromised, remitted, or mitigated, may be collected by civil action pursuant to Sec' ion 234c of the Act, 42 U.S.C. 2282c.
The responses to the Director, Office of Enforcement, noted above (Reply to a Notice of Violation, letter with payment of civil penalty, and Answer to a Notice of Violation) should be addressed to: Director, Office of Enforcement, t
e,
' Notice of Violation 3 U.S. Nuclear Regulatory Commission, ATTH: Document Control. Desk, Washington, D.C. 20555, with a copy to,the Regional Administrator, Region III, U.S. Nuclear Regulatory Commission, 799 Roosevelt Road, Glen Ellyn, Illinois 60137 and a copy to the NRC Inspector at Byron.
FOR THE NUCLEAR REGULATORY COMMISSION M
A. Bert-Davis Regional Administrator Dated t Glen Ellyn, Illinois
-this day of May 1989
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L 4 Ut S. NUCLEAR REGULATORY COMMISSION' REGION III w
-Report No. 50454/.88019(DRP)l Docket No; 50-454 License No. NPF-37
-Licensee: LCommonweal th. Edison ' Company '
Post Office Box 767 Chicago; ILL60690-Fasility. Name: ' Byr,on- Station, Unit 1 J Inspection At: . Byron . Station, Byron,. IL Inspection Conducted: September 19 - 28, 1988
' Inspectors: P. G.'Brochman
'N. V..Gilles 1 L L~ . .
Approved B : J.; . Hinds, JrMi t o . r2 88 o ctor Projects Section 1A I) ate Inspection-Sunmary 3 1
. Inspection from September 19'- 28, 1988-(Report No. 50-454/88019(DRP)1 1 Areas Inspected: .Special, reactive safety inspection by the resident
. inspectors to review the events surrounding the loss of one train of the
' residual heat removal (RHR) system while the water level in the reactor Jcoolant system was being . lowered on September 19, 1988.
-Results: Two' examples of one-apparent violation were identified (procedures inadequately directed installation and use of tygon tubing for reactor coolant system level indication - paragraph .7).1This apparent violation is of safety significance due to the potentiel for the loss of both trains of RHR when reactor vessel. level is at-the mid-plane of the hot leg nozzles and
'both trains of RHR are in operation. However, this event did not affect the
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public's' health and safety due to the prompt actions by the control room operator to prevent the loss of the RHR system.
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? , n@n j0, o DETAILSL
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1.s Persons Contacted-
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. Commonwealth Edison Company-
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1R. Pleniewicz,: Station Manager l*T. Joyce, Production Superintendent
- R. Ward,; Services Superintendent' y..;
- D. Winchester, Quality. Assurance Superintendent' p~ T. ' Tulon, Assistant? Superintendent, Operating -
- f. '*G.1 Schwartz, Assistant Superintendent, Maintenance
- *L.- Sues,' Assistant Superintendent, Technical Services
- D. St.-' Clair.PAssistant. Superintendent,LWork Planning
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J.?Schrock, Operating Engineer, Unit 1
- D.LBrindle,;0perating Engineer, Unit 2 .
- M. Snow, Regulatory- Assurance _ Supervisor-o ,
_*W.1Pirnat, Regulatory Assurance Staff L*E. Zittle,LRegulatoryl Assurance'S.taff; 1*B.;Jacobs, Acting Unit 1 Operating Engineer
.'X *L'. Bunner, Lead _0perations' Instructor l'
- D. Bump,1 Quality Assurance: Inspector
,, : *A. ' Chernick, Training: Supervisor
- D.; Berg,; Nuclear Safety.
'*R. Polek, Regulatory Assurance The insper m also contacted and : interviewed other licensee and -
- g. contractor / personnel- during the course of this . inspection..
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- Denotes those present'during the exit interview on September 28,
, . 1988;
'2. . Purpose (93702) d This inspection was con'ucted to review the circumstances surroundinthe system after air was ingested into the RHR system as a vortex formed while operators were lowering the water level.in the refueling cavity to support maintenance activities on September 19, 1988.
- f 3. Description of'the Event l
The licensee entered the second refueling outage for Unit 1 on l
September 3,1988. On-the. morning of September 19,1988, with the l' reactor vessel (RV)~ head removed, repairs hw Dr n made to the refueling hS cavity. boot seal.' The .1A RHR train was ope stis ) in the shutdown cooling .
mode'at a flowrate' of approximately 3200 gpm. dperators had just
- completed fillingLthe refueling cavity to the 402 foot elevation to check the boot seal- repairs when. they noticed that' a vessel stud hole ,
i plug had come free and was floating on the surface of the water. At L
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l 4:38 a.m., operators started the 18 RHR pump in order to lower reactor coolant system (RCS)/ refueling cavity water level to below the RV flange so that maintenance personnel could replace the stud hole plug.
At 4:48 a.m., operators shut down the IB RHR pump with RCS level at 398 feet 8 inches, according to the temporary tygon hose level instrumentation (the RV flange is at the 400 foot elevation). Between approximately 6:00 a.m. and 7:00 a.m. , a shift change was occurring for the operating shift. At approximately 7:30 a.m., an equipment attendant (EA) assigned the duty of " tube watch" relieved the EA from the previous shift ared told the control room that the tygon hose was reading approxi-mately 401 feet. The control room attributed the difference from the l earlier indication to the fact that the tygon hose had been acting l erratically on_ previous shifts. At 9:57 a.m., with level approximately 3 inches above the RV flange according to visual observation, the Unit 1 Reactor 0perator (RO) started the IB RHR pump to lower RCS level further to allow reinstallation of the stud hole plug. At this time the EA and a mechanical maintenance foreman were at the refueling cavity and in communication with the control room. At 10:05 a.m., the R0 shut down the IB RHR pump when told that level had dropped below the RV flange.
The EA had checked the tygon hose and told the R0 that level had dropped approximately 1 foot. At approximately 10:45 a.m., the Unit 1 R0 was relieved by an extra RO on shift due to increased activity because of the outage. l At about the same time, the mechanical maintenance fereman sent a man into the refueling cavity to check the water level and subsequently informed the control room that there was still water standing above the RV flange / stud holes. The foreman then asked to have level in the refueling cavity lowered further to allow dewatering of the stud hole and replacement of the plug. At 10:52 a.m., the Unit 1 R0 started the IB RHR pump again to lower refueling cavity level. At 10:59 a.m. , just as the maintenance foreman told the R0 that level had dropped far enough, the R0 noticed the 1A RHR pump ammeter oscillating (30 - 50 amps) and letdown flow fluctuating. The R0 isolated letdown flow and shut down the 1B RHR pump, to stop the draining. At 11:00 a.m., the R0 shut down the 1A RHR pump, with amps now fluctuating between 20 and 60 amps. The R0 then entered Byron Abnormal Operating Procedure 80A Refuel-4, " Loss of RH During Refueling," and action statement a. of Technical Specification 3.9.8.2 for the loss of one RHR pump in Mode 6 with water level less than 23 feet above the RV flange. At 11:02 a.m., the RO began a gravity fill of the RV/ refueling cavity from the refueling water storage tank (RWST) using the 1B RHR train. The IB RHR pump was then started several minutes later, after the R0 was certain that there was sufficient level in the RV to prevent cavitation of the pump. By this time operators had checked the containment radiation monitors and noted no changes in radiation level. At 11:09 a.m., the R0 shut down the IB RHR pump with the refueling cavity level approximately 6 inches above the RV flange. The R0 realigned the IB RHR train for shutdown cooling and started the IB RHR pump at 11:14 a.m. Procedure BOA Refuel-4 was exited. Operations department management directed operators to fill and vent the 1A RHR train. An air and air / water mixture was vented from a 3/4-inch sample line for 3
( 1 approximately 20 to 40 seconds, with its valve 1/4 turn open. At 1:39 p.m., operators began a gravity fill of the refueling cavity from the RWST using the 1A RHR train and shortly thereafter started the 1A RHR pump. An EA at the pump indicated that everything looked and sounded normal. Control room indications appeared normal. Based on these observations, the licensee declared the 1A RHR pump operable at 1:46 p.m.
and exited the Limiting Condition for Operation Action Requirement. At 3:33 p.m., the 1A RHR pump was shut down with the refueling cavity filled to 24 feet 6 inches above the RV flange.
- 4. Chronology of Events i All of the events described below occurred on September 19, 1988, and utilize the 24-hour clock. The times are approximate.
0430 Gravity fill of refueling cavity to 402 foot level to check the effectiveness of the RV boot seal repairs.
0435 Boot repairs appeared satisfactory; however, an RV stud hole plug came free.
0438 Started IB RHR pump to lower refueling cavity level to below RV flange to replace the stud hole plug.
0448 Shut down IB RHR pump. RV level at 398 feet 8 inches per tygon hoseindication(corrected).
0730 Equipment Attendant (EA) checked level in the tygon hose, which read approximately 401 feet. The control room attributed the difference between this reading and the reading at 0448 to the fact that the tygon hose indication had been acting erratically.
0957 Started IB RHR pump to lower RCS level further to allow maintenance to reinstall the stud hole plug. Level now approximately 3 inches above RV flange by visual observation.
1005 Shut down 18 RHR pump. Level lowered approximately 1 foot per tygon level indication.
1045 Unit 1 R0 relieved by extra R0.
1052 Started IB RHR pump again. Maintenance requested slightly lower level. Maintenance Foreman monitoring level at RV cavity, and individual at flange.
1059 Isolated letdown and shut down IB RHR pump due to fluctuating indications of letdown flow and amps on 1A RHR pump (IA RHR aligned for shutdown cooling at approximately 3200 gpm).
1100 Shut down 1A RHR pump. Amps still fluctuating from 20 to 60 amps. Entered Byron Abnonnal Operating Procedure 80A Refuel-4,
" Loss of RH During Refueling." Entered action statement a. of Technical Specification 3.9.8.2 on loss of one RHR pump during refueling with water level less than 23 feet above RV flange.
1102 Aligned IB RHR train to gravity fill refueling cavity from the RWST.
1108 Started the IB RHR pump. No change in containment low or high range area radiation monitors.
1109 Shut down IB RHR pump. RCS level approximately 6 inches above RV flange.
1114 Started IB RHR pump to provide for shutdown cooling. Exited B0A Refuel-4.
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1153 Checked a 3/4" sample line at IA RHR pump discharge.- Vented air and air / water mixture for 20 to 40 seconds with valve 1/4 turn open.
1339 Started gravity fill of refueling cavity from RWST using 1A RHR train.
1342 Started 1A RHR pump. Pump observed locally. Control room indicators checked and no problems indicated. 1 1346 Exited Limiting Condition for Operation Action Requirement on 1A J RHR pump.
1533 Filled refueling cavity to 24 feet 6 inches above reactor flange. !
Shutdown IA RHR pump and aligned 1A RHR train for shutdown .j cooling. l l
S. Evaluation of the Event {
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Based on the inspectors' analyses of the event, it appears that water i level in the refueling' cavity remained above the flange while the actual ;
level inside the RV. dropped to approximately one inch below the center-line of the hot leg nozzles. This phenomenon was caused by the hydraulic resistance of the small flow holes on the edge of the top hat, which restricted the rate at which water could drain from the refueling cavity into the RV while, simultaneously, the RHR pump was rapidly removing water from inside the RV, as the control rod guide stub tubes provided ,
sufficient venting to allow for easy drainage. The uncoupling of water !
levels inside and outside of the RV was compounded by the operators believing that water level indication inside the RV could be observed visually with the upper internals installed. As a result, RCS level was unintentionally. lowered to approximately one inch below the centerline of the RV hot leg nozzles. This allowed a vortex to develop in the suction line of the 1A RHR pump and air was entrained into the system, thereby making it inoperable.
The procedure being used to drain the refueling cavity was 80P RH-9, Revision SIA, " Pump Down of the Refueling Cavity to the RWST."
Prerequisite C.14 states, " ENSURE that the tygon hose connection, for RCS level indication, is in place ... prior to lowering the water level below the Reactor Vessel Flange (EL = 400'0")." i Subsequent to the event, the tygon hose was walked down by one of the licensee's engineers. The engineer removed several loop seals from the hose and restructured the tygon hose to establish vertical installation in all places. He also corrected a 2 foot level discrepancy with the elevation markings for the tygon hose, which had existed since its installation.
Based on interviews and discussions with licensee personnel and a review of records, the inspectors have developed the following observations regarding this event:
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- There appeared to be a widely held, incorrect perception by the i licensed operators that water level inside the RV could be visually observed with the upper internals installed. No training was l
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.a provided to the R0s or SR0s to either reinforce nor discredit this idea. Licensed operator training discusses all of the approved ,
methods of RCS level indication however, no mention of visual level indication is made.
- The EAs had not received training which would allow them to relate an elevation number to a physical point in the plant, e.g., the RV flange is at the 400 foot elevation. Consequently, when the EA reported that level was 398 feet 8 inches and then went up to the refueling deck and observed level above the RV flange, he did not recognize the disparity between these two observations and, conse-quently, did not identify this fact to the-control room.
- Licensee panagement believes that the control room operators followed procedure 80P RH-9 and that direct visual observation is an acceptable method for determining refueling cavity water level.
Management believes that the 80P does not require that the tygon hose be used and implies that visual observation is acceptable when draining the refueling cavity to the RV flange. Management stated
-that this had been done before, with no problems having occurred.
The inspectors have reviewed the B0P in detail and agree that there is no explicit statement to utilize the tygon hose during evolutions which lower water level below the RV flange. In fact, there is no explicit statement in the 80P to utilize any means of level indication while lowering RCS level.
However, the inspectors note that prerequisite C.14 requires the I operators to ENSURE (emphasis original) that the tygon hose connection is in place, prior to lowering water level below the RV flange. Consequently, the inspectors believe that it is the clear intent of this prerequisite to require that the tygon hose be utilized to determine water level for any draining evolution which will' lower water level below the RV flange, as the licensee planned-to do. The inspectors agree that visual observation can be useful, but believe that it should be used in addition to, rather than in place of the tygon hose.
- The licensee did not intend to lower water level to mid-loop, only several inches below the RV flange. The licensee does not normally use 80P RH-9 to drain down to mid-loop operation (below the RV i flange). However, the B0P does not have any restriction concerning l lowering RCS water level below the RV flange, other than not to go j below mid-plane of the hot legs. The inspectors believe that several of the conservatism utilized in B0P RC-4a, " Draining the RCS" could be effectively utilized in 80P RH-9, such as reducing the flow rate of the pump supplying shutdown cooling from 3000 gpm to 1000 gpm, draining via the letdown system (120 gpm) verses via RH8735 I l (RHR to Safety Injection pump isolation valve) to the RWST (750 - l 1000 gpm), suspending draining operations if level indication is unreliable, and resolving discrepancies in level indication before ;
resuming draining activities.
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'* The acceptance by control room personnel that the tygon hose was inaccurate (be it level error or slow response) while continuing to perform draining operations, even if using another " acceptable" method of level indication, does not appear to the inspectors to be the most conservative method of operation.
- The response of the control room operators, once they had received indication of problems with the 1A RHR train, was prompt and effective and prevented the potential for both trains to become air-bound and inoperable.
. The licensee has provided substantial training to the operators on the hazards of mid-loop operation. The licensee believes that because the operators continuously monitor the performance of the RHR pumps while draining the RCS they would not allow the level to drop to the point where both trains would become air-bound without the R0 initiating action to stop the evolution. The licensee noted that even though the R0 believed that RCS level was in the vicinity of the flange, the R0 followed the conflicting indications of RHR pump performance he was receiving and then stopped the IB RHR pump to secure the draining and initiated ,
corrective actions to recover level to a known elevation. )
The licensee believes that the safety significance of this event is mitigated by the ability of the RWST to gravity fill the refueling cavity at 1500 gpm per train. In addition, the high and intermediate head emergency core- cooling system pumps could have been returned to service and then utilized to inject water into the RV had both RHR pumps become inoperable.
Technical Specification 3.9.8.2 requires that two RHR loops shall be operable and at least one loop shall be in operation with the unit in Mode 6 and water level less than 23 feet above the RV flange. With less than two loops operable, action a requires that corrective actions be initiated immediately to return the affected loop to an operable status or that water level be established at greater than 23 feet above the RV flange. The inspectors have reviewed the licensee's actions and believe that they comply with Technical Specification 3.9.8.2.
- 6. Corrective Actions Initiated by the Licensee Subsequent to the event the following corrective actions were implemented by the licensee:
- a. The licensee issued a Daily Order prohibiting draining of the refueling cavity below the " top hat" of the RV upper internals.
On September 22, 1988, after further evaluation of the event, the licensee issued a second Daily Order prohibiting draining of the refueling cavity below the tops of the control rod guide tube assemblies when the upper internals are installed. This is to prevent the condition where flow into the RV plenum area is only via the 32 small head bypass flow holes.
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- b. The licensee conducted training sessions for all o'perating shifts; i to discuss this event and the lessons learned. 1
- c. The licensee has revised B0P RH-9 which now requires that two methods of level indication must.be utilized and functional prior to any draining operations more than 2 inches below the-top of the control rod drive shaft support housings. The procedure also ,
contains a caution that visual indication of RV level at or below j the " top hat" area of the upper internals is not reliable or ;
acceptable for one of the two methods for level indication while i draining tFe RV. In addition, the procedure also requires that !
draining below the 403 foot elevation (top of the control rod drive. i shaft support housing) be done at a slow draining rate, such as the ]
minimum 1,ndicated flow rate on the RHR pump, and in any case, less q than'1000 gpm. Draining below the RV flange (400 feet) is required to be done using letdown, which allows a maximum flow rate of 120 gpm RHR to letdown, compared to a 500-1000 gpm flow rate when RHR to RWST is used.
- d. New instructions for the tygon hose level indicator installation are being developed which will utilize an installation checklist.
An SR0 walkdown of the tygon hose after installation will be ;
required prior to its use.
- e. The licensee has developed an operator aid which relates gallons of l water removed per foot of level change for both the reactor vessel and the refueling cavity.
- f. The Westinghouse Owners Group is evaluating a Technical-Specifica-tion change which would utilize an RHR flow vs. time vs. level l
concept for requirements on RHR in Mode 6.
The licensee has deferred development of further long term corrective actions until after the NRC issues the generic letter on mid-loop i operations, to ensure that no conflicts exist. This generic letter provides significant new requirements for licensees on mid-loop operations.
- 7. Conclusion 10 CFR 50, Appendix B, Criterion V, as implemented by Commonwealth Edison Company's Quality Assurance Manual, Quality Requirement 5.0, requires that activities affecting quality shall be prescribed by documented procedures of a type appropriate to the circumstances. Byron Operating '
l Procedure BOP RH-9, Revision 51A, " Pump Down of the Reactor Cavity to the RWST," paragraph C.14, requires that the operator " ENSURE that the tygon hose connection, for RCS level indication, is in place or LI-RYO46 Reactor Vessel Level Instrumentation operable prior to lowering the water level below the Reactor Vessel Flange (EL-400'0")." However, nowhere in the procedure does it specifically require that the tygon hose, or any other means of RCS level indication, be utilized during the drain down j process. The failure of 80P RH-9 to specify the use of an appropriate i
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f means of RCS level indication while draining the refueling cavity to a level below the RV flange is an apparent violation of 10 CFR 50, Appendix B, Criterion V (454/88019-01a(DRP)).
Additionally, 80P RC-4a, " Reactor Coolant System Drain," which contains instructions for installation of the tygon hose level indication system, provides no guidance for ensuring that the tygon hose was properly installed to accurately reflect RCS level. For example, the procedure did not require verification that the tygon hose was installed vertically, that there were no loop seals, or that the elevation markings were accura te. The failure of 80P RC-4a to provide adequate guidance for installing the tygon hose is an example of an apparent violation of 10 CFR 50, Appendix B, Criterion V (454/88019-01b(DRP)).
The failure of"80P RH-9 to require the use of the tygon hose for RCS level indication during draining of the refueling cavity led the control room operators to utilize a method of level indication which was ineffective when level was below the control rod drive shaft support housings. The consequence of this action was to unintentionally drain the RCS to an estimated 1 inch below the center line of the reactor vessel hot leg nozzles, thereby allowing a vortex to develop and air to be entrained into the 1A RHR system, rendering one train of RHR inoperable.
During his follow-up of this event, the inspector identified a concern reloting to the human factors design of the RHR flow indicators in .
the main control room. The flow meter scale is non-linear and very compressed at the lower end, with only 1 graduation between 0 and 1000 gpm. Consequently, the licensee is requested to evaluate the <
desirability of rescaling the RHR flow meter or other options such as !
providing a second, lower-range meter, to improve the ability of the R0s to accurately monitor low RHR flow rates. This concern will be tracked as an open item (454/88019-02(DRP)). j l
- 8. Open Items Open items are matters which have been discussed with the licensee, which will be reviewed further by the inspector, and which involve some action on the part of the NRC or licensee or both. An open item disclosed during the inspection is discussed in paragraph 7.
- 9. Exit Interview (30703)
The inspectors met with the licensee representatives denoted in paragraph 1 at the conclusion of the inspection on September 28, 1988. The inspectors summarized the purpose and scope of the inspection and the I findings. The inspectors also discussed the likely informational content !
of the inspection report, with regard to documents or processes reviewed by the inspectors during the inspection. The licensee did not identify I any such documents or processes as proprietary.
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