IR 05000271/1992025
| ML20128E001 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 01/25/1993 |
| From: | Della Greca A, Ruland W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20128D988 | List: |
| References | |
| 50-271-92-25, NUDOCS 9302100286 | |
| Download: ML20128E001 (10) | |
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U.S. NUCLEAR REGULATORY COMMISSION REGION 1 REPORT / DOCKET NO.
50-271/92-25 LICENSE NO.
DPR-28 LICENSEE:
Vermont Yankee Nuclear Power Corporation RD 5, Box 169 Brattleboro, VT 05301 FACILITY NAME:
Vermont Yankee Nuclear Power Station INSPECTION AT:
Vernon, Vermont INSPECTION DATES:
December 14-18, 1992 INSPECTOR:
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Electrical Section, EB[, DRSeMtor bngineer, Date L. Della Greca, Sr.
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APPROVED BY:
W. H. Rufand, Chief, Electrical Section,
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Date Engineering Branch, DRS Areas Inspected: Routine, announced inspection by regional personnel to review the status of several previously identined issues und to determine the adequacy of the licensee's actions to resolve these issues.
Results: The inspection concluded that the licensee satisfactorily resolved six of the nine open issues that were reviewed. The corrective actions pertaining to the environmental qualification of equipment not included in the Technical Specifications, to the surveillance of the service water system, and to the protection of the diesel fuel oil during extremely cold temperatures were not suf5cient for closure of the issues. The qualification program for safety-related support equipment did not adequately address operability of equipment covered by the Technical Specifications. The monitoring program for the diesel fuel quality during cold weather and the corrective actions to address surveillance of the service water system were still in progress. No new violations were identified, i
9302100286 930127 PDR ADOCK 05000271 G
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1.0 SCOPE OF INSPECTION The purpose of the inspection was to review the status of several issues identified previously, during NRC inspection of the licensed program, and to determine the adequacy of the licensee's corrective actions in resolving each issue. Four of the issues reviewed were long term corrective actions proposed by the licensee to address problems experienced during the April 23,1991, loss of offsite power. These issues were discussed in the Augmented Team Inspection Report No. 50-271/91-13 and in the followup Inspection Report No.
50-271/91-21. Three other issues were identified during the electrical distribution system 50-271/92-functional inspection (EDSFI). in July and August 1992 (Inspection Report No.
81). One additional issue, pertaining to the adequacy of the licensee's environmental qualification program for safety related support equipment, was identified by the resident inspectors and described in Inspection Report No. 50-271/92-21.
2.0 STATUS OF PREVIOUSLY IDENTIFIED ITEMS 7.1 (Closed) Unresolved item No. 50-271/91-21-01 pertaining to the revision of the service water hydraulle flow model.
On April 23,1991, Vermont Yankee Nuclear Power Station (VYNPS) experienced a complete loss of offsite power (LOOP) which was documented in the Augmented Inspection Team Report No. 50-271/91-13. During the recovery from the LOOP event, the licensee observed a significant reduction of the service water flow through the emergency diesel generators. An analysis performed by the licensee indicated that the problem was caused by an increased overall system pressure and flow partly due to corrosion and tuberculation of the service water discharge piping. Following the LOOP, the licensee committed to perform several short and long term corrective actions. The status of these was reviewed during the followup inspection of August 1991. At that time, five activities remained unresolved. One of these activities was the revision of the service water hydraulic flow model.
During the current inspection, a review of the status of the hydraulic flow model determined that the revision had been completed. The model predicted the revised system losses in the suction and discharge piping of the diesel generators and in the discharge line to the deep basin. For this effort, the licensee utilized data recorded during the post-LOOP tests as well as data obtained during the emergency core cooling system integrated test during the most recent refueling outage. The results of the revised model, summarized in a Yankee Atomic Electric Company (YAEC) memorandum dated June 30,1992, were reasonable in consideration of the flow measurements observed during the LOOP. This item is closed.
Regarding the hydraulic flow model, the inspector also inquired how the revised losses impacted the service water flow to the emergency diesel generators. This issue is discussed in Section 2.2.
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2.2 (Open) Unresolved item No. 50-271/91-21-02 regarding revision of the service water surveillance procedure.
As a result of the service water problem experienced during the LOOP event, the licensee committed to revise the service water surveillance procedure. The revisions were to include the monitoring and equipment configuration required to confirm operability of vital equipment during abnormal and accident conditions.
The inspector noted that the procedure had not been revised. However, based upon the results of the revised hydraulic now model, YAEC had made recommendations regarding monitoring points, instrument accuracy requirements, and acceptance criteria. The recommendations were included in two YAEC memoranda dated August 19 and September 28,1992. Recognizing that the service water flow to essential components had limited margin, under certain conditions, the August 19 memorandum also recommended frequent surveillance of the system to ensure that further fouling of the lines would not result in inadequate cooling to the components. The YAEC concerns regarding service water now to essential component were further addressed in another YAEC memorandum dated October 5,1992. This memorandum also included a safety assessment which concluded that the degraded condition of the diesel generator supply and discharge piping did not present an operability concern at the time. The conclusions were based on conservatism contained in the service water performance study, VYC-855, " Fluid Flow Analysis of the Service Water System at Vermont Yankee"; in the operator awareness of the service water degradation; and in the procedural steps currently in place to address mitigation of a postulated accident in conjunction with a LOOP and the failure of one diesel. To address long term operability concerns, the recommendations provided in the memorandum included continued monitoring and cleaning or replacement of degraded piping. Calculation VYC-855 had not been issued at the time of the inspection.
Based on the above, the service water surveillance requirements remained unresolved.
2.3 (Closed) Unresolved Item No. 50-271/91-21-03 regarding the capability of the de buses to tolerate voltage transients.
An evaluation of the causes leading to the April 1991 LOOP event concluded that it was initiated by a voltage transient affecting one of the de buses used to power the switchyard protective relays. The transient was partly the result of inadequate maintenance performed on the switchyard battery chargers. To address this issue, the long term corrective actions proposed by the licensee included an evaluation of potential transients affecting the de buses and of the changes that would be necessary to tolerate such transients.
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During the current inspection a review of the licensee's actions in this area determined that an evaluation was performed and battery maintenance procedures were revised to preclude operation of the de bus without the damping effects of the battery. In addition, the battery charger maintenance procedure, OP 5247, Revision 1, specifically requires measurement of s
de voltage ripple using an oscilloscope or chart recorder to ensure the adequacy of filters.
The maximum acceptable ac component specified by the procedure is 5% of the de bus voltage. Furthermore, all major battery system maintenance is scheduled during plant shu:down periods. These actions were considered adequate to minimize the exposure of solid state relays to voltage transients. Therefore, this item is closed.
2.4 (Closed) Unresolved item No. 50-271/91-21-04 relative to the vulnerability of the switchyard equipment to common moda/ common cause failures.
The transients experienced by one of the switchyard de buses resulted in the improper actuation of breaker failure relays and in the loss of the offsite power. To address this finding, the licensee committed to evaluate the vulwability of the switchyard protection relay design to common mode and common caus M. tres and methods to improve the design.
During the current inspection, the status of the licensee's efforts in this area was reviewed.
The licensee provided an evaluation contained in a memorandum, dated December 30,1991.
The analysis concluded that the current design for the switchyard protection scheme met the original design practice recommendations of the Northeast Power Coordinating Council and the requirements of 10 CFR 50, Appendix A, General Design Criterion 17. Based upon the inspector's review of this analysis, this item is closed.
2.5 (Closed) Unresolved Item No. 50-271/91-21-05 pertaining to potential vuhierabilities of static protective relays.
The licensee's review of the April 1991 LOOP causes determined that the transients experienced by the switchyard de bus, while maintenance was being performed, had resulted in the failure of two zener diodes associated with two switchyard breaker failure relays. The licensee had previously experienced similar problems with other solid state relays associated with the emergency diesel generators. In view of the above, the licensee committed to evaluate potential vulnerabilities of the safety-related static protective relays.
To address this issue, the licensee prepared a list of all the protective relays used at VY and submitted it to the respective manufacturers, Westinghouse and General Electric. In the accompanying letter, they asked whether enhancement to the relay surge protection designs had been performed. Two Westinghouse relays, including the failed breaker relays used at VY, had undergone modifications. These relays were replaced with newer style ones. For the relays manufactured by General Electric, they received applicable service advice letters (SALs). None of the issues addressed by the SALs involved surge protection. This item is close _.
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2.6 (Open) Unresolved Item No. 50-271/92-21-03 ngarding the adequacy of the
qualification program for equipment not included in the Technical Specification.
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In August 1992, VYNPS identified performance concerns regarding the cooling capability of the reactor recirculation units (RRUs) located in the corner rooms of the reactor building.
The RRUs, degraded as a result of silting or micro-biologically induced corrosion, were safety-related and their function was to maintain the environment of the corner rooms below the design limits of the core cooling equipment located therein. A subsequent evaluation performed by the licensee concluded that the RRUs had not degraded sufficiently to cause the rooms temperature to exceed the temperature to which the core cooling equipment was qualified. Howner, a basis for maintaining operability (BMO) analysis concluded that the replacement of the cooling coils in the near term was necessary. The RRUs performance was being monitored on a regular basis. At the time of the current inspection, the cooling coils in three of the four RRUs already had been replaced. The coil of the fourth RRU was being replaced.
As indicated in Inspection Report 50-271/92-21, the disposition of the RRUs issue had been considered acceptable. However, the inspectors had expressed several programmatic concerns regarding: (1) acceptability of the current VYNPS pos'. tion pertaining to system and component operability when safety-related support equipment is involved; (2) acceptability of the time frames included in the current 11vironmental Qualification Plan (EQP) for resolution of environmental qualification issues; and (3) impact of these issues in the maintenance activities during power operation. The current inspection evaluated the licensee's conclusions pertaining to the environmental qualification of the core cooling equipment and the status of the concerns previously raised by the NRC.
Based upon a list prepared by the licensee, the equipment located within the corner rooms was qualified for temperatures ranging from ll5'F to 194*F. These data were derived from the applicabie qualification documentation review (QDR) reports. In contrast, the maximum calculated temperature for these areas was 150'F. To address the qualification status of components qualified for less than 150'F, the licensee had reviewed the applicable QDRs and determined that, in each case, adequate margins existed in the analyses performed in accordance with DOR guidelines to justify qualification of the components. However, the QDRs had not been revised and apparently no plans had been made to update them. A review of several QDRs confirmed the conclusions of the licensee. However, the following _
observations were made:
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The 150*F maximum temperature was based on the last RRU differential pressure (dP) measured. Since the measurements changed randomly from one period to the-next, it would have been more conservative for the analysis to use the maximum dP measured during the period of observation.
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No acceptance criteria had been established for future RRU performance. Absent such criteria, it was not clear how the licensee would ensure that the qualification temperature for the affected components woPld not be exceeded.
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There were no provisions to revise the QDRs when the qualification parameters changed as required by Section IV.2.1 of the VYNPS Environmental Qualification Plan.
Shortly after the completion of this inspection, the replacement of the last RRU coil was
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completed. Therefore, qualification with degraded RRUs was no longer an issue.
To address the operability concern, the statements contained in the Technical Specifications (TS) and in the Operability Determinations / Basis for Maintaining Operhtion (BMO) Guideline
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were reviewed. The TS, in defining " Operable," appropriately stated " Implicit within the defm' ition [of operable] shall be the assumption that all necessary attendant instrumentation,...
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or other auxiliary equipment that are required for the system, subsystem, train, component, or device to perform its function are also capable of performing their related support function." In addition, the BMO guideline properly addressed operability of TS components, including significance, timeliness, and relationship with environmental qualification (EQ).
However, the time frames for preparing BMOs for safety-related non-TS components found to be inoperable or degraded (15 and 30 days, respectively) appeared to have been selected without operability considerations of the supported component or system.
Section V of the EQP also recognized the need for maintaining the equipment within the EQ program operable and environmentally qualified. The EQP also recognized the importance of addressing found discrepancies "in a timely and responsive manner " However, the time frames or addressing qualification and operability appeared to have been selected
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independently from the safety function of the component and the limiting conditions for operations contained in the TS.
Generic Letter (GL) 88-07 states that, "When a potential deficiency has been identified... in the environmental qualification of equipment..., the licensee is expected to make a prompt
determination of operability (i.e., the system or component is capable of performing its intended design function), take immediate steps to establish a plan with a reasonable schedule to correct the deficiency, and have a written justification for continued operation." This operability determination requirement is applicable to all safety-related equipment whether i
covered or not by the plant TS and is the basis for establishing subsequent actions in the resolution of identified deficiencies. The same criteria apply to equipment which is rendered inoperable for maintenance activities. Therefore, restoration to service of inoperable equipment not contained in the TS within thirty days, as required by the EQP, may be appropriate only if the operability of the equipment it supports is also demonstrated and if the requirements of the GL for accident conditions are also satisfie _ -
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i Discussions with the licensee indicated that review and revision of the EQP and of the BMO Guideline to reflect the guidance of Generic Letters 88-07 and 91-18 were underway.
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Therefore, the acceptability of these documents and of the LCO-Maintenance guideline j
continues to be unresolved pending their finalization and issuance.
2.7 (Closed) Unresolved Item No. 50-271/92-81-09 relative to the potential 5,ubmersion l
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of the diese! generator fuel oil transfer pumps.
A walkdown of the diesel generator fuel oil transfer system performed during the Jnly and August 1992 EDSFI determined that a postulated failure of the fuel oil storage tank could result in the flooding of the transfer pump pit. The team's conclusion was the result of their observing that a conduit penetration orifice between the tank and pump pits, below the
i flooding level, had been left unsealed. The transfer pumps were not qualified for submersion.
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During the current inspection, the inspector verified that the orifice had been satisfactorily
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sealed. This item is closed,
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2.8 LQnen) Unresolved Item No. 50-271/92-81-10 pertaining to the diesel generator fuel oil temperatum control.
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- During the 1992 EDSFI, the team observed that the diesel generator fuel oil storage tank was located above ground and, hence, exposed to the external temperatures._ The team also determined that occasional minimum temperatures recorded at the site were well below the
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l pour point specified for the oil. Therefore, they expressed a concern that the fuel might gel during severe winter temperatures at the site, and clog the stainers of both transfer pumps.
The storage tank was not heat traced and the monitoring procedure was not considered adequate to ensure fluidity of the fuel at all times and, hence, to prevent a common mode failure of the diesels.
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In their letter No. BVY 92-136, dated December 7,1992, the licensee stated that during sub zero weather, the fuel was transferred once every two hours from the storage tank to the house heating boiler day tank to meet the house heating needs. Therefore, the monitoring of the day tank level via low level alarm switch LSL-108-6B effectively and automatically monitored the fuel oil transfer. The licensee also stated that they had revised operating
procedure 3140 to monitor the fuel oil temperature during transfer, and to compare the pump suction line temperature to the fuel oil pour point if gelling was suspected. In addition, the
letter committed to collecting oil temperature data under various meteorological conditions to
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evaluate the potential for oil gelling,
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During the current inspection, a review of alarm response sheet 6-G-9 indicated that it had been revised to monitor oil temperature at the pump suction, in the event of a low level alarm, and to contact Chemistry if the temperature at the pump suction was below 5'F. The inspection also determined that a collection data sheet had been prepared for the purpose described above. The inspector noted that: (1) during the twenty years of plant operation, the licensee never experienced oil gelling; (2) the oil mass in the storage tank (75,000 gallons) was large enough to retard gelling; (3) recent oil analyses showed pour points well below the specified O'F and, hence, well below normal minimum temperatures for the site; and (4) the licensee's awareness regarding gelling concerns was heightened. Based on the above, the inspector judged the oil gelling issue not to be an immediate safety concern and the administrative controls currently in place adequate to assure operability of the diesels until the licensee's evaluation could be completed. This item continues to be open pending review of the licensee's completed analysis.
2.9 (Closed) Unresolved Item No. 50-271/92-81-11 regarding potential fuel oil transfer piping damage.
During the 1992 EDSFI, the team observed that approximately 15 feet of fuel oil transfer piping downstream of each pump had been installed within inches from each other, outside the pump house. No protection had been provided against external damage from hazards in the area or from a tornado missile. Therefore, the redundant transfer systems were subject to a common cause failure.
During the current inspection a walkdown of the installation was performed and it was determined that vehicle barriers had been installed. However, no protection had been provided for tornado generated missiles. Pertaining to this issue, in their letter to the NRC, dated December 7,1992, the licensee stated that they had reviewed it relative to their Station Blackout (SBO) response. They had determined that the probability of experiencing a tornado at Vermont Yankee was about 2 E-05 occurrence per year or 9.8 E-05 occurrence
per year per square mile. On the basis of this and previous similar studies, the expected probability of damage to the transfer piping would be less than 1 E-06. Therefore, they
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concluded that the probability was sufficiently small not to warrant further immediate action.
The licensee also stated that this issue would be formally addressed in their IPEEE program.
A review of the licensee's response to the NRC regarding the SBO rule, letter No.
BVY 91-88, dated September 30,1991, confirmed the probability data pertaining to tornado occurrence. On the basis of the installed vehicle barriers and the licensee's commitment to formally review the tornado issue under the IPEEE program, this item is closed.
3.0 UNRESOLVED TrEMS l
Unresolved Items are matter about which more information is required to ascertain whether i
they are acceptable items or violations. One unresolved item identified during this inspection
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is discussed in Section 3.0 of this report.
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4.0 EXIT MEETING
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The inspector met with the licensee personnel, denoted ir. Attachment 1, at the conclusion of the inspection, on December 18,1992 and summarized the scope of the inspection and the
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inspection results. In particular, the inspector informed the licensee the bases for rat closing :
the environmental qualification and the lube oil monitoring issues.-
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ATTACHMENT 1
I PERSONS CONTACTED
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Vermont Yankee Nuclear Power Corooration
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- B. R.- Buteau.
Engineering Director T. M. Drouin Mechanical Engineer.
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- R. P. Grippardi Quality Assurance Supervisor
- S. J. Jefferson Assistant to Plant Manager
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H. M. Metell Principal Engineer i
J. Osmond.
Electrical Engineer R. D. Pagodin Technical Services Superintendent
j-D. _L. Phillips Elec. Engrg. & Construction Supervisor
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- - D. A. Reid -
Plant Manager
R. J. Wanczyk Operations Superintendent
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Yankee Atomic Electric Comoany -
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A. Doyle Systems Engineer
- W. K, Peterson - Manager Quality ' Assurance s
U. S. Nuclear Regulatory Commission
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H. Eichenholz Senior Resident Inspector
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P. Harris Resident Inspector
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- Indicates personnel present at the exit meeting of December 18, 1992.
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