ML20044E128

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Insp Rept 50-346/93-11 on Stated Date.Violations Noted.Major Areas Inspected:Exam of Two Rc Inventory Control Events on 930403 & 13
ML20044E128
Person / Time
Site: Davis Besse 
Issue date: 05/13/1993
From: Lanksbury R
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML20044E113 List:
References
50-346-93-11, NUDOCS 9305210306
Download: ML20044E128 (13)


See also: IR 05000346/1993011

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U. S. NUCLEAR REGULATORY COMMISSION

REGION III

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Report No. 50-346/930ll(DRP)

Docket No. 50-346

Operating License No. NPF-3

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Licensee: Toledo Edison Company

Edison Plaza, 300 Madison Avenue

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Toledo, OH 43652

facility Name: Davis-Besse Nuclear Power Station

Inspection At: Oak Harbor, Ohio

Inspection Conducted: April 19, 1993, through April 22, 1993

Inspectors:

R. K. Walton

J. B. Hopkins

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E. R. Duncan

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Approved By:

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sh1lgs

R. D. Lanksbyry,~ cniN

Date

Reactor Projbcts Section 3B

Inspection Summary

Inspection on April 19. 1993, throuah April 22. 1993

(Report No. 50-346/930ll(DRP))

Areas _ Inspected: A special inspection was performed by the resident

inspector, a Region 111 inspector, and the NRR licensing project manager to

examine details and determine the root cause(s) of two reactor coolant

inventory control events. The events included an overfill of the reactor

vessel on April 3,1993, and an inadvertent transfer of reactor coolant system

(RCS) inventory to the borated water storage tank (BWST) on April 13, 1993.

Both events occurred during the licensee's eighth refueling outage.

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Results:

The April 3,1993, event, in which the reactor vessel was overfilled, was due

to the use of a surveillance test procedure that was not compatible with

refueling operations coupled with weaknesses in operator cognizance of

equipment and system status. A non-cited violation was identified due to test

procedure inadequacies. Operator knowledge of overall plant status was weak

in that operators elected to leave a makeup supply valve in its as-found

condition following restoration from the test. Operators were unaware they

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had inadvertently established a gravity-driven flow path from the BWST to the

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RCS.

Additionally, the inspectors found that operators were not closely

monitoring RCS level, since the event went undetected for almost 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.

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9305210306 930514

PDR

ADOCK 05000346

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The April 13, 1993, event, in which about 13,570 gallons of RCS inventory was

inadvertently transferred to the BWST, was due to an equipment operator

performing two attachments of a procedure out of sequence. An administrative

controls procedure addressed the proper method for documenting the performance

of steps and how to obtain deviations, but was not followed. The failure to

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properly implement the administrative controls procedure was a violation.

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Some weaknesses in operator knowledge of the decay heat removal system were

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noted since isolation valves sere not immediately closed from the control room

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once operators recognized the loss of inventory flow path.

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DETAILS

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Persons Contacted

Toledo Edison Company

D. C. Shelton, Vice President, Nuclear

  • G. A. Gibbs, Director, Quality Assurance

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  • L. F. Storz, Plant Manager

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  • S. Jain, Director, Engineering

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  • E. M. Salowitz, Director, Pla ining
  • J. K. Wood, Operations Manager

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  • D. Stephenson, Independent Safety Engineering

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  • R. W. Schrauder, Manager, Nuclear Licensing
  • G. Honma, Supervisor, Licensing

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  • M. Turkal, Engineer, Licensing
  • D. Wuokko, Supervisor, Regulatory Affairs
  • K. C. Prasad, Staff Engineer, Nuclear Engineering
  • D. W. Schreiner, Supervisor, Performance Engineering
  • L. Simon, Operations Assessor, Performance Engineer
  • D. L. Haiman, Manager, Engineering Assurance and Services
  • D. L. Eshelman, Superintendent, Shift Operations (Acting)

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(see attachment I for a list of personnel interviewed by the inspectors)

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  • Denotes those personnel attending the April 21, 1993, exit meeting.

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Overview

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When both reactor coolant system (RCS) inventory control events

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occurred, the plant was shutdown for a routine refueling outage and

decay heat was being removed using decay heat removal train #2

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both events, core cooling was not interrupted and core temperatures were

not affected.

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On April 3,1993, with the reactor vessel head installed but not

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torqued, reactor vessel water level slowly increased over a 3-hour

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period without the knowledge of control room operators. This resulted

in overfilling the vessel and water spilling out and around the vessel

stud hole area. This spilled borated water necessitated reperforming

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work in the vicinity of the reactor vessel head and caused additional

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radiation exposure to workers.

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On April 13, 1993, while performing valve operations on the decay heat

removal system, about 13,570 gallons of RCS inventory were inadvertently

transferred to the borated water storage tank (BWST) through decay heat

removal train #1 piping. While control room operators immediately

detected the loss of inventory, the loss continue for about 22 minutes

until the loss flow path was determined and isolated. During this time.

the pressurizer and about one-half of one RCS loop were drained.

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Operators recovered from the event by refilling and reventing the RCS.

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April 3.1993 Event - Reactor Vessel Overfill

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Initial Plant Conditions

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On April 3, 1993, with the plant in Mode 6 (REFUELING), the core was

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reloaded with fuel and the reactor vessel was drained to several inches

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below the reactor vessel flange (80 inches above the centerline of the

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hot leg piping). Decay heat was being removed by decay heat removal

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(DHR) train #2 and core temperature was being maintained at about 85 F.

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At 11:07 a.m., purification flow for DHR train #2 was secured since the

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lineup conflicted with a planned makeup pump quarterly surveillance

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test. At 11:30 a.m. (EDT), the vessel head was set on the vessel

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flange, but not tensioned. During the following shift, at 4:23 p.m.,

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operators completed the makeup pump #1 quarterly test and made

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preparations to place purification flow from DHR train #2 back in

service.

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Operator and Plant Response

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Operators on the afternoon shift restored from DB-PF-03372, " Quarterly

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Makeup Pump #1 and Valves Inservice Test and Inspection," by performing

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attachment 3 of DB-PF-03372. After the equipment operators completed

valve restoration in the plant, attachment 3 was turned over to the

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reactor operator (RO) to reposition control room valves. The R0, who

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wanted concurrence from the assistant shift supervisor (AST) prior to

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repositioning the remaining four valves, handed the procedure to the AST

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and indicated that the operators had completed the attachment as far as

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they could.

The AST took the precedure and put it on his pile of

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paperwork and proceeded working on other items.

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At 6:22 p.m., operators placed in service the purification subsystem

associated with the operating decay heat removal train in accordance

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with DB-0P-06012. Operators were unaware that by placing purification

makeup in service with makeup pump #1 three-way suction valve MU6405 in

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the "open from BWST" position, a 3 gallon-per-minute (gpm) gravity-

driven flow path was established between the BWST and the vessel.

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Vessel level began to slowly increase.

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Three hours later, at 9:20 p.m., operators noted that RCS narrow range

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level indication had increased from 80 to 87 inches which indicated that

vessel level was at the top of the flange, and any additional inventory

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had nowhere to go except past the o-ring seals on the untensioned vessel

head. The shift supervisor, who believed that the RCS level indicator

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could be in error, sent an operator to monitor the #2 decay heat pump

suction pressure, and directed RCS level lowered to 85 inches. After

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confirming that the indicator was accurate, operators decreased RCS

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level to 82 inches and observed that over the next hour, level increased

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about 1 inch.

Operators then closed makeup pump #1 isolation valve

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MU6407 and noted that level stabilized at 83 inches. At 11:06 p.m.,

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operators returned RCS level to 80 inches.

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The overfill of the reactor vessel resulted in water spilling out and

around the vessel stud hole area which necessitated expending about

5.2 person-rem of exposure to recover. The licensee documented this

event in Potential Condition Adverse to Quality Report (PCAQR) 93-0194.

Licensee's Corrective Actions

At the end of the inspection period, the licensee was evaluating the

addition of a procedure caution step to ensure that the makeup

purification system was not in use prior to performing DB-PF-03372.

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superintendent of operations (acting) and the operations manager

discussed this event with each shift supervisor who in turn discussed

this event with their operating crews. The discussion focused on the

use of plant drawings prior to executing system status changes, and

improving the quality of communications on shift.

The licensee was also evaluating a procedure change to ensure that

control room operators would more closely track and trend RCS level when

RCS inventory was low and level changes were not expected.

Additionally, the licensee was planning a program to address known

deficiencies in communications, command and control, and knowledge of

integrated systems operations, with the plant in Mode 6.

Insoector Evaluation

The inspectors noted that the operators who reviewed DB-PF-03372 prior

to the test found that the procedure was not compatible with existing

plant conditions.

Specifically, performing the makeup pump quarterly

test with the decay heat removal system lined up for purification

through the makeup system had a potential to lift a relief valve in the

decay heat removal system. As a result, purification was secured prior

to performing the test.

Restoration step 4.35 specified that makeup system valves be positioned

per attachment 3 or as required by the shift supervisor (SS). Both the

SS and AST failed to evaluate the effect of leaving makeup valve MU6405

in the "open from BWST" position and failed to recognize that this

produced a gravity drain path from the BWST to the vessel.

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inspectors considered this to be a weakness in the operators' cognizance

of changing equipment status and its effects on interfacing systems with

the plant in Mode 6, and a weakness of the procedure for its use with

the plant in Mode 6.

10 CFR Part 50, Appendix B, Criterion V, required that activities

affecting quality be prescribed by procedures of a type apprqpriate to

the circumstances.

Contrary to the above, DB-PF-03372 did not

adequately address necessary precautions with the plant in Mode 6 and

resulted in overfilling the vessel. This was a violation.

However, the

violation will not be subject to enforcement action because the

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licensee's efforts in identifying and correcting the violation met the

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criteria specified in Section VII.B of the " General Statement of Policy

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and Procedure for NRC Enforcement Actions."

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The inspectors found the monitoring of important plant parameters was

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deficient.

An increasing RCS level was not detected for almost 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.

The inspectors concluded that the command and control aspects of test

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performance were less than desirable.

Specifically, the AST did not

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review the restoration step of attachment 3 to DB-PF-03372 until almost

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3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> after it was completed.

In addition, the SS and AST did not

want to reposition makeup valve MU6405 per the attachment and left the

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valve in its initial position (as allowed by the procedure).

While this

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might not have changed the outcome of the event, it appeared indicative

of a less than adequate cognizance of changing equipment status and the

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effects on interfacing systems with the plant in Mode 6.

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The AST used the computerized tagging system and determined that makeup

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valve MU6405 had a "Do Not Operate" tag on it.

Both the AST and SS

annotated on the attachment next to the designated valves the numbers

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referencing tag clearances which they believed were active. However,

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the AST misinterpreted information on the computer tagging system, since

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no tags were hanging on makeup valve MU6405, and the SS did not

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independently verify the AST's conclusion. The control switch for

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makeup valve MU6405 was located in the control room and was not danger

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tagged.

Neither individual checked the local switch for tags.

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inspectors considered this to be inadequate-attention to detail on the

part of the AST and SS. Operators received training on the use of the

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computerized tagging system before the outage; however, their

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proficiency on the system appeared to be lacking due to their infrequent

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use of the system.

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Inspector Conclusions

The inspectors concluded that the this event was due to the use of a

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surveillance test procedure that was not compatible with refueling

operations coupled with weaknesses in operator cognizance of equipment

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and system status. This event resulted in additional radiological

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exposure to individuals assigned to recover from the event.

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A non-cited violation was identified because DB-0P-03372 did not include

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the special precautions necessary to perform the surveillance test

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procedure with the plant in Mode 6.

Weaknesses were found in operator

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monitoring of RCS parameters, command and control during the conduct of

testing, and attention to detail.

No violations or deviations were identified for this event; however, one

non-cited violation was identified.

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April 13. 1993 Event - Inadvertent Transfer of RCS Inventory to the BWST

Initial Plant Conditions

On April 13, 1993, the plant was in Mode 5 (COLD SHUTDOWN) with DHR

train #2 in operation. A nitrogen bubble in the pressurizer maintained

the plant at 38 psig. The RCS loops were filled and pressurizer level

was 90 inches. Operators had completed adding water to the BWST from

the clean waste receiver tank at 11:40 a.m.

The control room was busy

making preparations for an integrated safety features actuation system

test scheduled to start the following day.

After adding water to the BWST, operators prepared to place the BWST

into recirculation. The AST reviewed DB-0P-06012, section 4.3,

" Recirculation of the BWST using Decay Heat Pump #1 While the RCS is on

Decay Heat Cooling," and completed 3 of the 5 prerequisite steps.

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AST gave the procedure to an equipment operator (E0) with the

instructions to review, then perform, attachment 8 (a prerequisite step)

followed by attachment 10 (in the body of the procedure).

The E0 took the procedure to the operator study room and checked the

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lineup against plant drawings and planned the job. The E0 recognized

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there were valves in both attachments 8 and 10 in the same contaminated

area and planned to perform portions of attachment 10 outside the

contaminated area prior to performing attachments 8 and 10 inside the

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contaminated area. The E0 returned to the control room with attachment

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10 and had the R0 position a valve in attachment 10 without completing

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the prerequisite lineup in attachment 8.

This was done out of sequence

since attachment 8 was not yet completed. The R0 was unaware that the

E0 was performing an attachment out of sequence because he was busy with

other plant operations and did not thoroughly question the E0. The E0

requested that DHR pump #1 suction valve DH1517 and BWST return

isolation valve DH2733 be repositioned per attachment 10. However, the

R0 did not want them repositioned until the BWST fill lineup was

restored. The operator decided to continue with the procedure and

position DH1517 and DH2733 last.

The E0 checked valve positions per attachment 10, then dressed out in

anti-contamination clothing to perform attachments 8 and 10.

Attachment 8, step 19., required positioning DH1517 and DH2733 which

the E0 recognized could not be done yet. The E0 skipped step 19. and

continued with attachment 8.

The E0 then conservatively checked shut

other valves not required by the lineup to ensure that both trains of

decay heat removal were not cross-connected. Without completing

attachment 8, the E0 then commenced repositioning the last 3 valves in

attachment 10. The E0 recognized that the containment spray system was

lined up in a recirculation mode and that valves DH66 and DH68 shared a

common return line with the core spray pump to the BWST. The E0 called

the control room, received permission to open valves DH66 and DH68, and

opened these valves.

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Operator and Plant Response

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At 1:51 p.m., the control room R0 and SS observed a decreasing

pressurizer level and verified that RCS pressure was also decreasing.

This indicated that RCS inventory was being lost rapidly.

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operators did not know where the RCS inventory was going or its flow

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path.

At 1:53 p.m.,

the pressurizer low level alarm annunciated and

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less than a minute later, the pressurizer level indicator was offscale

low.

The control room dispatched two E0s to verify that operating decay

heat pump #2 suction pressure was sufficient to prevent pump cavitation.

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At 1:57 p.m., operators entered abnormal procedure DB-0P-02522, "Small

RCS Leaks." During the following minutes, valves were operated in an

attempt to isolate the leak, replenish lost inventory, and maintain RCS

pressure. A reactor operator made an announcement over the plant

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communications system to inform personnel that the high pressure

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injection (HPI) system was being started. Subsequent to this

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announcement, however, operators recognized that since the #2 pump power

supply breaker was racked out, and the #1 pump was lined up to

recirculate the BWST, the HPI system was not available as an injection

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source.

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At 2:10 p.m.,

the E0 who opened DH66 and DH68 (w.rcn initiated the

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event) arrived in the control room and informed operators of the valves

he had operated. With this information and the observation that BWST

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level was increasing, control room operators recognized that the flow

path was from the RCS, through suction isolation valve DH1517, through

decay heat remaval train #1, and into the BWST.

The SS dispatched the

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E0 to close valves DH66 and DH68, and directed another E0 to rack in the

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breaker to motor-operated valve DH1517.

At 2:13 p.m.,

the power supply breaker to DH1517 was racked into the

switchgear and energized. The R0 then closed DH1517 from the control

room which terminated the event.

Post-Event Review of Plant Response

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The licensee's Data Acquisition Display System (DADS) continuously

monitored various plant parameters for tracking and trending. The

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inspectors reviewed selected parameters during the inspection period and

concluded the following:

The hot leg level monitoring system (HLLMS), an alternate method

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of determining RCS inventory, indicated that RCS loop 1 remained

filled during the event.

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The HLLMS for RCS loop 2 indicated that loop 2 started draining

after the pressurizer was drained.

Its final level was about 420

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inches above the centerline of the RCS hot leg piping, or about 7

feet above where the pressurizer surge line tied into RCS loop 2.

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The physical arrangement of RCS piping prevents directly draining

the vessel to below the top of active fuel. Also, because the

pressurizer surge line tapped into loop 2, loop 1 would not begin

to drain until loop 2 was essentially empty.

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An analysis of decay heat removal loop 2 flow rate and core

temperatures during the event indicated that decay heat removal

was not affected by the event.

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The flow rate from the RCS to the BWST was initially about

1000 gpm and decreased as RCS pressure decreased. At the end of

the event, the flow rate was less than 200 gpm.

To ensure that the RCS hot legs remained filled and vented, nitrogen

pressure in the pressurizer was being maintained at 38 psig.

During the

event, the R0 opened the nitrogen supply valve to the pressurizer in an

attempt to maintain pressurizer pressure above 25 psig.

The inspectors

noted that the addition rate of 100 psig nitrogen through the installed

1-inch supply line did not keep up with the drain rate of the RCS

through the 8-inch return piping to the BWST. The net effect was that

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RCS pressure dropped during the event which resulted in a decreasing

flow rate from the RCS to the BWST. The inspectors noted that the

addition of nitrogen during the event had the potential to escalate the

consequences of the event if operators had not detected and mitigated

the event.

Licensee's Corrective Actions

On April 13, 1993, around midnight, the licensee completed equalizing

pressure between the two RCS loops and pressurizer which allowed RCS

level to equalize. Operators then refilled the RCS fram about 170

inches in the pressurizer to a level of about 300 inches and

repressurized the system per DB-0P-06000, " Filling and Venting the

Reactor Coolant System."

The operations superintendent (acting) requested that this event be

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evaluated under the Transient Assessment Program (TAP). The TAP team

consisted of members with experience in plant operations and other

specialties who review plant transients and other abnormal events to

identify root causes.

By reconstructing the events through interviews,

unit log entries, procedure reviews, and assessing data from DADS and

other sources, the team evaluated both plant and operator response to

the event.

The inspectors noted that the TAP team quickly assembled and commenced

their investigation prior to shift turnover.

The team produced a report

which was issued in its final form on April 23, 1993. The report

examined the event in detail, and explained contributing causes to the

event along with facts, conclusions, and observations.

The report

explained corrective actions to be taken, and made recommendations to

management.

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The operations superintendent and operations manager discussed this

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event and the April 3, 1993, event with each shift supervisor who in

turn discussed this event with their operating crews.

The discussion

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focused on the use of plant drawings prior to executing system status

changes and improving the quality of communications on shift.

The

licensee was also evaluating a procedure change to DB-0P-06012 to

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preclude flow initiation until well into the body of the procedure.

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Additionally, the licensee was developing a program to address known

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deficiencies in communications, command and control, and knowledge of

integrated systems operations when the plant is shutdown.

Inspector Evaluation

The inspectors noted that the E0 performed attachment 8 and attachment

i0 in parallel in lieu of completing attachment 8 prior to attachment 10

as required.

The inspectors also noted that a similar event occurred on

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December 17, 1992, when an operator lined up the clean liquid

radioactive waste system using an attachment which was not reviewed by

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the senior operator prior to placing the system in service (reference

inspection report 346/92019-01(DRP)). As corrective action to that

eve.it, the licensee revised DB-0P-00000, " Conduct of Operations," to

require that all prerequisites be signed off by a senior operator prior

to initiating the procedural steps.

The E0 performing valve lineups incorrectly believed that if the

prerequisite could not be performed and the intent of the procedure was

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not changed it would be proper to proceed without senior operator

approval. This was not in accordance with DB-0P-00000, section 6.8.5.

Failure to properly implement DB-0P-00000, Revision 2, section 6.8.5,

was a violation (346/930ll-01(DRP)) of Technical Specification 6.8.1.a.

which required that written procedures be established, implemented and

maintained covering activities referenced in Regulatory Guide 1.33,

November 1972, Appendix A, item A.4.

The inspectors determined that training was provided to the operators on

Revision 2 to DB-0P-00000, which included step 6.8.5, but noted that the

E0 was unaware of the requirements. The inspectors concluded that the

training provided to operators on Revision 2 of DB-0P-00000 may not have

been adequate.

During the event, control room operators recognized the flow path from

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the RCS to the BWST through decay heat removal train #1 piping, but at

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the time, no one recognized that closing valves DH13B and DH148 from the

control room would have immediately terminated the event.

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operators focused on closing valve DH1517 which was not immediately

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operable from the control room since the breaker for DH1517 was racked

out.

The inspectors believed + hat the event could have been terminated

earlier had the control room operators recognized that valves DH13B and

DH14B could have been closed. Additionally, although the E0 reviewed

the system drawings prior to starting the procedure, he did not

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recognize the consequences of performing the lineup out of sequence.

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The inspectors considered this to be a deficiency in operator knowledge

of the decay heat removal system.

The inspectors noted that communications between the E0, R0, and AST

were inadequate, since no one questioned the task being performed by the

E0 and no one was aware that steps were being performed out of sequence.

Additionally, the R0 was unaware that the lineup was being performed

until the E0 requested that control room operated valves be

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repositioned.

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During the event, control room operators used abnormal procedure, DB-0P-

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02522, "Small RCS Leaks," but determined that the procedure was of

little use since it did not address the current plant conditions. The

licensee recognized the restrictions of using these abnormal procedures

in Mode 5, and endorsed as good operator practice to make use of the

abnormal procedures during a plant casualty.

Licensee management

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expected the operators to utilize the procedure as a guideline when in

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Mode 5.

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The inspectors noted that the licensee failed to announce to plant

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personnel that a loss of RCS inventory had occurred. Operators were

weak in implementing management's expectations of making such an

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announcement. The inspectors believed that if the E0 who positioned

valves DH66 and DH68 had heard such an announcement, the event could

have been terminated earlier.

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Inspector Conclusions

The root cause for this event was the failure of the E0 to perform DB-

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OP-06012 in its proper sequence. Administrative controls addressed

documentation of completed steps, and if used properly, could have

prevented this event. The inspectors noted weaknesses in operator

knowledge of the decay heat removal system in that control room

operators did not terminate the event by closing valves DH13B and DH14B,

and the E0 did not know the consequence of opening valves DH66 and DH68

with the decay heat removal system lined up as it was when the event

occurred.

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The inspectors noted that information to be reviewed relevant to this

event (DB-0P-06012, attachment 8) was not available to the inspectors,

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but was reconstructed with the operators' assistance.

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The licensee's use of the TAP team to evaluate and take appropriate

action to determine the root cause of the event was considered a

strength by the inspectors.

One violation and no deviations were identified for this event.

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5.

Violations For Which A " Notice of Violation" Will Not Be Issued

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The NRC uses the Notice of Violation to fornally document the failure to

meet a legally binding requirement. However, because the NRC wants to

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encourage and support licensee initiatives for self-identification and

correction of problems, the NRC will not issue a Notice of Violation if

the requirements set forth in 10 CFR Part 2, Appendix C, Section VII.B

are met. Violations of regulatory requirements identified during the

inspection for which a Notice of Violation will not be issued are

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discussed in paragraph 3.

6.

Exit Interview

The inspectors met with licensee representatives denoted in paragraph 1

,

during the inspection period and at the conclusion of the inspection on

April 21, 1993, and summarized the scope and findings of the inspection

activities. The licensee acknowledged the findings. After discussions

with the licensee, the inspectors determined there was no proprietary

information contained in this inspection report.

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ATTACHMENT 1 TO INSPECTION REPORT 50-346/93011

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PERSON

INTERVIEWED

TITLE

D. Barnhart

Equipment Operator

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G. Chung

Assistant Shift Supervisor

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D. Eshelman

Superintendent, Operations (acting)

M. Gore

Equipment Operator

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S. Martin

Shift Supervisor

L. Myers

Shift Supervisor

C. Pocino

Equipment Operator

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D. Schreiner

Supervisor, Operations Assessment

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S. Strahl

Assistant Shift Supervisor

T. Whalen

Reactor Operator

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D. Wood

Equipment Operator

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