ML20211M369
| ML20211M369 | |
| Person / Time | |
|---|---|
| Site: | Pennsylvania State University |
| Issue date: | 10/08/1997 |
| From: | Randy Erickson PENNSYLVANIA STATE UNIV., UNIVERSITY PARK, PA |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9710140171 | |
| Download: ML20211M369 (3) | |
Text
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. .% e (814) 86L9580 PENNSTATE 'Os!!!!"
Rodney A.Erkkson The Penn9hania state Unhersity Vnc President for Research 3N Old Main Dean of the oraduate sdniol Unisersity Park,PA WOWN October 8,1997 Document Control Desk United States Nuclear Regulatory Commission Washington, DC 20555 RE: Reportable Occurrence - TS 3.2.6 License R-2, Docket No.50-005
Dear Sir or Madame:
This letter is to inform you of a reportable occurrence at the Pennsylvania State University Breazcale Nuclear Reactor (PSBR) on September 29,1997. This letter is being submitted in accordance with Sections 6.5.2 and 6.6.2 of the PSBR Technical Specifications (TS). The initial i verbal report of this occurrence was made by Dr. C. Frederick Sears, Director, Radiation Science and Engineering Center via telephone to Marvin Mendonca of the Non Power Reactors and Decommissioning Project Directorate on October 3,1997. The telephone notification was confirmed in writing that same day with copies faxed to Mr. Mendonca and Thomas Dragoun, Region 1. The telephone call was initiated as an information call to Mr. Mendonca regarding the event; during that call it was decided that it should be treated as a reportable occurrence.
PSBR TS 3.2.6, SCRAM TIME states: 'The time from scram initiation to the full insertion of any control rod from a full up position shall be less than I second." On September 29,1997 the PSBR Transient Rod (TR) was found to have a scram time in excess of I second.
Description of Event:
An experiment involving a considerable amount of fuel element movement in the immediate vicinity of the Safety and Shim Rods was conducted on September 29,30, and October 1,1997. The purpose of the experiment was to determine the change in behavior of new instrument 12 wt % fuel elements before and after pulsing. As fuel movements were being conducted on September 29* at about 0930, it was noticed that the fuel movements were causing some movement of reactor tower components in the vicinity of the Transient Rod. A decision was made to do a visual freedom of scram check for the Transient Rod. Procedures already called for such checks for rods next to fuel assemblies which were being moved. When the Transient Rod was scrammed for the visual check it was cbserved that the scram insertion of the transient rod appeared smooth but sluggish.-
Operations were halted and testing and laintenance of the transient rod was undertaken.
As found measurements for the Transient Rod indicated a drop time of between one and two seconds. Inspection, cleaning and lubrication of the Transient Rod mechanism was performed.
No definitive cause for the sluggishness was found although clearly lubrication improved the freedom of motion. Four successive scram time tests were conducted with all falling under i second. There were no indications that the sluggish movement was in any way related to the ;
experiment and its fuel movements. The reactor was retumed to operation on September 29* at about 1144.
Review of Event:
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At the time the sluggish scramming of the TR was discovered and corrected it was felt there were three TSs which had applicability to the event. They are:
TS 3.1.3, SHUTDOWN M ARGIN which states: "The reactor shall not be operated unless the shutdown margin provided by control rods is greater than 1.75 x 10 (-3: dk/k (-$0.25) with:
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- a. ' All movable experiments, experiments with movable parts, and experimentid facilities in their most reactive state. i
- b. The highest reactivity worth control rod fully withdrawn.
TS 3.2.1, REACTOR CONTROL RODS which states:"There shall be a minimum of three l
operable control rods in the reactor core." ;
TS 3.2.6 SCRAM TIME states: 'The time from scram initiation to the fullinsertion of any control rod from a full up position shall be less than 1 second."
He Safety (SA), Shim (Sil), and Regulating (RR) Rods were operable. During the above mentioned experiment there were routine scram freedom checks of the SA and SH ns fuel was being moved m the vicinity of those rods. Those checks demonstrated normal motion of those two rods. Annual scram time testing of the SA, SH, RR has always found them to be well under the one second requirement. In fact their scram times are usually measured to be on the order of a half second or less. The visual observations of performance during the experiment were consistent with the annual measurements. Thus TS 3.2.1 was satisfied.
Based on satisfying TS 3.2.1 we initially felt that since TS 3.2.6 was satisfied for the required three operable control rods this was not a reportable occurrence. The discussion with our NRC Project Manager on October 3" when he was called to inform him of the event led us to classify the event as reportable since TS 3.2.6 uses the words "any control rod".
Routine scram time records were reviewed for the past several decades and discussions were hehl with knowledgeable staff members. Only the TR has ever exhibited scram times approaching the one second limit. When routine tests or observations have shown TR scram times near the one second limit maintenance beyond that scheduled on a routine basis has been performed to decrease the time. The review determined that over the last decade the scram times for the TR have gradually increased to where the annual surveillance's have shown times in the 8(X) to high 9(X) millisecond range.
After considering the history of TR scram times over the past several years it was decided to again shut down and perform a more thorough inspection, cleaning and lubrication. On the morning of October 2,1997 a more detailed inspection, cleaning and lubrication was undertaken. Following that the scram times were again checked. The scram times were then measured to be about 6(X) milliseconds and visual and audible observations indicated the freedom of motion had been greatly enhanced. (Note the 6(X) millisecond time is from scram initiation to rod bottom, the oscilloscope traces indicated that there is now some rod bounce upon bottoming and a second bottoming is observed at about 800 milliseconds from initiation. Some of the other rods also exhibit such behavior. This degree of evidence of freedom of motion for the TR had not been present in the remembered past few years.)
Based on the inspections and lubrications of the TR it appears that inadequate lubrication or deterioration of an o-ring seal at the bottom of the TR air cylinder was the cause of the sluggish behavior. Review of some correspondence earlier this year with General Atomic (GA), the reactor vendor, indicated a potential cause for the increased scram times might be deterioration of that o-ring seal in the TR mechanism. Communications are being undertaken with GA to acquire more information and to determine the availability of replacement o-rings and related components (if any). With the latest lubrication there is no evidence of any sluggishness.
Beginning October 6*, the TR scram times are being measured at the beginning of each week of operation prior to beginning morning checkouts. The results of these measurements will be monitored and trended to determine whether further corrective actions are needed as well as to determine what is an appropriate surveillance interval. A more complete record of as-found conditions and maintenance performed will be kept to assure this level of deterioration of performance does not again occur. We are phmning a Transient Rod overhaul at the next annual fuel inspection unless needed earlier or continued evaluation indicates such overhaul is not needed.
If routine inspection, cleaning, and lubrication does not assure that proper operation can be maintained the reactor will be shutdown and the overhaul performed at an earlier date.
With. regard to the shutdown margin TS, an analysis was performed to determine what the actual -
shutdown margin would have been if the TR had failed to scram and the highest worth rod withdrawn also failed to scram. This analysis covered operations from shutdown up to 750Kw (presently our highest operatingpower level due to fuel temperatures).' The results of this analysis demonstrated that the actual mimmum shutdown margin would have been about -$1.50. Using the full dermition for shutdown margin vice actual rod conditions (ie. TR at its actual position and the SA fully withdrawn) would produce a minimum shutdown margin of about $0,50. Thus TS 3.1.3 was satisfied at all times, it is noted that at no time Sd the Transient Rod fail to scram or fail to move when requested to move, Corrective and Preventative Actions:
The immediate action involved cessation of operations for inspection, cleaning, and lubrication to return the TR to operation within the TSs. Upon assurance that the TR was operating within TSs the reactor was returned to operation.
Follow up action included a briefing of alllicensed personnel, a second inspection and lubrication to funher improve the operation of the TR, and a detailed review of TR performance history A weekly testing of the TR scram time was put in place to gather information upon which future maintenance and surveillance can be planned. Presently it is planned to overhaul the TR mechanism during fuel inspection in the Spring of 1998. The reactor vendor is being contacted to gather further information regarding the o-nng seal and its lubrication.
If you have any question regarding this matter, please call Dr. Sears at 814 865-6351.
Sincerely, Rodney A.Erickson Vice President for Research Dean of the Graduate School RAE:CFS/pjs 4053.97
- pc: M. Mendonca, NRC Headquarters T. Dragoun, NRC Region i G.J McMurtry E, H. Klevans J. H. Mahaffy
- C. F, Sears Subscribed to the sworn before me on this N day of balls ,1997, Notary Public in and for Centre County, Pennsylvania. ()
L~ ( f PAMELA J U FE Notary PubEc
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