ML20086D104

Ro:On 950609,failure of Primary Coolant Return Line Flow Sensor to Initiate Trip Occurred.Flow Sensors Checked After Debris Removal & as of 950626 Problem Considered Resolved

ML20086D104
Person / Time
Site:	05000083
Issue date:	06/30/1995
From:	Vernetson W FLORIDA, UNIV. OF, GAINESVILLE, FL
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20086D106	List: ML20086D104 ML20086D394
References
NUDOCS 9507070459
Download: ML20086D104 (6)

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_7 UNIVERSITY OF

@ FLORIDA Nuclear Reactor Facility 202 Nuclear Sciences Center Department of Nuclear Engineering Sciences P.O. Box 118300 Gainesville, Florida 32611-8300 Tel: (904) 392-1429 Fax:(904) 392-3380 l l

June 30,1995 Regional Administrator, Region II 14 Day Report:

U.S. Nuclear Regulatory Commission Failure of Primary Coolant i 101 Marietta Street, N.W., Suite 2900 Return Line Flow Sensor - l Atlanta, GA 30323 Debris Removal 1

Dear Sir:

Re: University of Florida Training Reactor Facility License: R-56, Docket No. 50-83 Pursuant to the reporting requirements of paragraph 6.6.2 (a), (c) and (g) of the UFTR l Technical Specifications, a description of what was originally considered a potential violation of the technical specifications was reported by telephone on June 12, 1995 with a following telecopy on June 13,1995 (Attachment I) and a so-called 14 day written report is submitted with this letter including occurrence scenario, NRC notification, evaluation of consequences, corrective action and current status. The potentially promptly reportable occurrence involved the failure of the primary coolant (PC) return line flow sensor to initiate a trip on no fl6w during the Quarterly Scram Check (Q-1) Surveillance on June 9,1995. This 14 day written report is delayed one week per agreement with Mr. Ed McAlpine of Region IIin a telephone conversation discussing the delay on June 23,1995.

Scenario On June 9,1995, during the Quarterly Scram Check Surveillance (Q-1), it was found that the PC retmn line flow sensor would not cause a reactor trip. The trip check was attempted three tunes to ensure that an error in the procedure or in electrical jumper installation was not the mne P46nce rMiny on the flow sensor indicated it had failed in the closed (shorted) position. Since this discovery was made at shutdown near the end of the day, no further checks were attempted on this day.

On Monday, June 12, 1995, under Radiation Work Permit (RWP) 95-3-I, the piping union containing the flow sensor was removed and inspected. The sensor float inspected satisfactorily, as well as the seats in the bridgewall. When the float was removed and manually placed over 9507070459 95063o PDR ADOCK 05000083 S PDR r - ogg- m _ u..mue.i.,umu kp

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Eegional Administrator, NRC Region II L Page 2 l June 30,1995 i

the sensor, it operated normally. Further inspection of the piping union revealed a piece of mauled plastic or other material, which had become lodged in the float seat, preventing the float '

from dropping to the trip position. This piece of material was removed for further checks with no other problems noted. Subsequently, the sensor was reassembled and the piping union reinstalled in the system. The primary water was introduced into the system and the loss of PC i return line flow trip was tested satisfactorily three times. The weekly checkout, daily cha+ ant i and quarterly scram checks were all completed satisfactorily as well. Subsequently, a visual  !

check of the PC storage tank on June 26,1995 did not reveal the presence of any other debris i

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material at this lowest point in the system. -

NRC Notification After discovery and removal of the debris on June 12, 1995, the Reactor Safety Review Subcommittee (RSRS) was not available for a meeting. Therefore, prior to an RSRS meeting, t NRC Region II was informed of this event per a telephone conversation with Mr. Ed McAlpine l on June 12,1995 relative to the potential violation of technical specifications. The situation was l confirmed in a following fax transmittal, delayed with Mr. McAlpine's permission until June 13,  !

1995 (Attachment I). A second fax on the same day corrected the date reference for the initial notification. At this time the potential failure was described and the key technical specification i sections were reviewed. There was also agreement to treat the event as reportable, with Mr. McAlpine calling a second time on June 12,1995 to assure that the reactor would not be restarted without a review of the event by the RSRS and obtaining their permission to restart; this control was already in place.

The RSRS Executive Committee met on June 13, 1995 to discuss the failure of the primary coolant return line flow sensor. The event itself was reviewed to include the ennentially redundant natme of this U#--g safety system setting and its repair on June 12,1995. De ,

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+a on Comminee did agree that the failure was pmbably reportable as had been E----i  !

June 12,1995. A physical ernminatinn of the debris itself was undertaken in the reactor cell. 3 The Committee also dim =I the possible nature of the debris, its radiatinn level, the ,

commitmant to mLm a =~*n1 analysis on it, and its possible travels in the primary system. ]

! De t'ammittee also discussed potential for a core blockage and heat transfer and other pumdAg enneidamtinns and effects. He evaluation was that heat transfer is no real concern for such dehrin and that this is probably an isolated piece since other water samples and d=- == af the fiber and resins in the primary system had not indicated the presence of such

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debris in the past. It was also noted that the passage of such small pieces of debris as would be allowed through the core would also be eMad to have small effects on reactivity, ne Committee also discussed the one call to and the other call from Ed McAlpine at NRC Region II on June 12,1995 concerning this event. The Committee did make several changes to the memorandum on the failure event discussed at the meeting. All items on the

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Region'al Administrator, NRC Region II Page 3 June 30,1995 memorandum were die-d and the Committee recommended restart with the NRC to be contacted prior to restart. The Committee also proposed that the contents of the PC storage tank be checked sometime in the near future when convenient to see if there is debris of any kind present. It was also noted that any such debris would likely remain at the bottom of the tank or break into small pieces and be removed in the demineralizer cleanup system. It was also noted that there has been no significant change in resistivity for this occurrence indicating that t this occurrence is not related to the event on March 9,1995 when there was a large decrease in resistivity. (See "14 Day Report - Izakage of Primary Coolant Heat Exchanger" dated April 3,1995.) As requested, Mr. McAlpine at NRC was contacted later on June 13 as previously committed. He was not opposed to restart but simply wanted to make sure the event had been adequately reviewed. Subsequent restart on June 13,1995 and operations through '

June 30,1995 have been without incident.

Evaluation / Corrective Action By checking surveillance records, it was determined that the previous Quarterly Scram Check j (Q-1) was performed satisfactorily on April 11,1995, and had a drainage time of 38 seconds j to yield the required no flow trip on the return line sensor. The failed check on June 9,1995  ;

was noted to be well within the required quarterly frequency specified in Table 3.2 of the UFTR i Technical Specifications. Drainage times for Q-1 checks on 12/28/94,9/30/94,6/29/94 and l 3/28/94 were 38 seconds, 39 seconds, 38 seconds and 37 seconds, respectively. Afu t- i system was repaired on June 12, 1995, the drainage time was 36 seconds on each of three l checks indicating a possible slight improvement in the time to trip, though the general feeling l of reactor management is this may or may not be an indicator that the piece of problem m* rial i i

had been lodged in the return line for some time. There does not appear to have been any clear trend on the time for the reten line flow trip to occur, though values measured three times after  ;

debris removal are 1-2 seconds faster than any of the previous several surveillances had indicated.

The UFTR Tachnical SpWWa== address the return line flow sensor trip in two sections, as well as denoting the WW of the flow checks in a third section. In Section 2.2, " Limiting  ;

l Safety Systema Settings," Speh 7 on Page 4 requires that "the primary coolant flow rate j shall be manhnsed at the return line." In additinn, Table 3.2 entitled " Specifications for Reactor i Safety System Tripa," on Page 8 under PA-ry Cooling System, =pecinen "no outlet flow" to j result in an ==tann=eir rod < hop type safety system trip. Finally, Table 3.2 entitled, " Safety l System On hnity Tests," under component or scram function, Ests " loss of primary coolant

flow" and specifies the operability check frequency as "4/ year (4-month maximum interval)."

l All three technical =pa iWon references essentially state the flow is to be monitored at the return line for a no-flow condition.

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j. Regional Admini*ator, NRC Region II Page 4 l June 30,1995 L

i L If a condition had existed which would normally cause a trip from the return line flow sensor, l

.i i.e., a complete loss of primary coolant outlet flow, other redundant trips would have initiated ,

j a reactor trip. These trips were all functional at the time of this occurrence and are summarized '

as follows:

1. The primary coolant flow is detected and measured at the inlet of the core via a strain  ;

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i gauge and monitored at the control console. A reduction of primary flow below l 30 gpm would cause a trip.

[ 2. The core water level has a trip at 42.5", or 2" above the fuel. At no flow outlet conditions, the water would no longer reach the required height and would initiate a i

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3. If power is lost to the primary coolant pump, a trip would occur.

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! 4. If the temperature of the water at the outlet of any fuel box reaches 150* F, there is an I

' audible alarm and at 155' F there is a process (rod-drop type) trip.

t The debris itself resembles a piece of shrink-wrap or wire insulation or perhaps sealing material, j although in its present state it is unidentifiable. It is roughly 3/8" in diameter and somewhat over 1" long. It is hard and tends to crumble rather than bend. A radiation reading on the piece j of debris as of June 12,1995 gave a value of 0.45 mR/hr using a Geiger counter (E-140 #1048).

! Images of the piece of debris are shown in the attached photographs (Attachment II). It was evaluated as unreasonable to assume this material travelled through the core area for several I reasons:

1 j 1. At the bottom of the fuel boxes, a flow di==iaa plate reduces the streaming of the

primary naal==t Ahhough no exact dimannin=< of the plate exist, diagrams in the j j UFIR training ==anale would suggest not allowing passage of the material.

i j 2. Spacing of the fuel plates in the bundles and the proximity uf one fuel plate to another

h of fuel box tolermanen would not allow such a piece of debris to pass  ;

j unobstructed.

t l 3. Debris or other material this size could almost certainly not pass through the primary

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F coolant pump without damaging the pump or seals.

i i 4. Should the ==* rial reach the heat exchanger, the foreign material would become lodged i in the heat exchanger plenum since the tubes through which primary coolant passes are i very small.

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i Region'al Administrator, NRC Region II l Page 5 j June 30,1995

5. The demineralizer/ cleanup loop takes flow from the heat exchanger outlet and returns i flow to the core outlet line and then to the PC storage tank. However, the deminernlizer system has a resin bed as well as a ceramic filter as shown in Figure 5-1 from the UFTR Safety Analysis Report (Attachment III). Therefore, passage of such debris through this system is impossible. l

. Therefore, it is only plausible that the material was either in the piping or was introduced at the  ;

j top of the fuel boxes when the core was open, such as during a fuel inspection, a fuel loading j j procedure or perhaps when other core maintenance work was performed a number of years ago.

Plans are in place to get several spectra of the piece of debris and also to irradiate it for analysis l I

j of elemental composition. To date, a spectrum of the debris as is shows a number of peaks with l no clear conclusions possible. It is possible further spectral analyses will yield more information 1

. on the source of the debris and how long it has been present.

1 l During the safety review of this event on June 13,1995, it was noted that even if such debris j were to block part of the core flow, mixing in a box would prevent fuel damage. If sufficient i

debris were to block the core, then other trips would act as noted above. In addition, each of the fuel boxes is instrumented with thermocouples set to alarm at 150* F and to yield a process l  !

i trip at 155' F, well below any possible fuel damage point. However, this piece of material i appears to be an isolated and relatively small piece of debris which, even ifit reached the core area, would have little effect on heat transfer and cooling of the fuel at the low flow velocities l

j required to cool this core. Its reactivity effects would also be relatively small because it appears

! to be some sort of hydrocarbon bearing material. Its actual reactivity worth was measured on 5

June 30,1995 prior to commencing activation analysis and found to be about 4 x 10 Akfr when j inserted in the center vertical port under Run Request 95-43. Such a reactivity worth is small j and tends to indicate the debris is probably composed primarily of hydrogen, carbon and oxygen

as for shrink wrap inmistinn for wiring or similar materini In additinn, the demineralizer

system with its fiber will remove ==m11 pieces of debris as weII. It is the jad=,=* of UFIR j ==3= =2 and the RSRS Executive Committee that the effectively rerhmdant trips on flow and ,

j low cooling requiral in this core indicate such a small piece of debris would not cause a serious l problem. De length of time since the core was last opened was also judged by the RSRS to i

! indicate there is not likely to be any more debris in the system. A check on June 26,1995 by l boroscope under Maintenance I.og Page 95-22 indicated no such debris ==*rini in the PC )

j storage tank, which is the lowest point in the primary coolant system and directly downstream  ;

of the return line flow nenenr where the piece of debris was located. His check essentially j l concluded chech on the UFTR itself. Spectral analysis on a high purity germanium (HPGe) )

! gamma sgwuswyy system was initiated soon after restart operations. De results of spectral

analysis prior to decontamination and after decontamination with demineralized water have been j inconclusive to date. Future plans are to perform activation analysis on the sampic as well, j though it is unlikely any further useful information will be obtained, j Regional Administrator, NRC Region II i

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, . l l l Page 6 June 30,1995 Current Status /Consecuences Following successful checking of the flow sensor after debris removal on June 12,1995 and restart on June 13,1995, along with checks to assure there is no debris in the PC storage tank on June 26,1995, this problem is considered resolved. 'lhe system is operating normally. The

source of the debris is not known but suspected to be some sort of material inadvertently ,

2 dropped into the system during one of the times the fuel boxes were open for fuelinspection or other checks, perhaps many years ago. l 4 As indicated, the RSRS Executive Committee met on June 13, 1995 to review this everit and

. approve restart operations after checks were' completed on the return line flow sensor. 'Ihe i Committee essentially agreed with actions taken and with the initial staff evaluation that the occurrence did represent a potential violation of the UFTR Technical Specifications and should be treated as promptly reportable. Reactor Management and the RSRS Executive Committee l agree there has been no significant compromise to reactor safety in the occurrence and no impact l on the health and safety of the public. Other than considering the event in the next regular  !

RSRS meeting, based on results of continuing spectral analysis.on the debris material, this

occurrence is now considered closed.

i If further information is needed, please advise.

Sincerely, 4

h'

, William G. Vernetson Director of Nuclear Facilities WGV/dms

Attachments i Copies

U.S. NRC D -- nt Control Desk Ted S. Michaelt, NRC Project Manager

, Reactor Safety Review Subcommittee D. Simpkins, Reactor Manager i

Sworn and subscribed this. So

• day of June,-1995. .

rs. ,, s Y?wA~.

Notary Phblic DN MOREHOUSE y MY C0hMSSON f CC102416 EXPtRES I x7 August 27,1997 80eED THauinor FAm usumanctasc.

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