ML19296D327

Submits Info in Response to NRC Request Re Occurrences of Control Rod Failure to Fully Insert.Failures Occurred Dec 1975 & Corrected May 1976.Provides Summary of Past Control Rod Drive Malfunctions.No Incidences Since May 1979

ML19296D327
Person / Time
Site:	Cooper
Issue date:	02/22/1980
From:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
To:	Ippolito T Office of Nuclear Reactor Regulation
References
LQA8000077, NUDOCS 8003030500
Download: ML19296D327 (4)

Text

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LQA8000077 COOPER NUCLtAR STAYloN

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61.I Nebraska Public Power District " " "'A"e"ro"~D!i n"".^ii N' g _ _. _ _. _ _ _ _ __ _ ___ _ _ __ _ _ m ._ ..m- . . _ _

7ebruary 22, 1980 Mr. Thomas A. Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Ippolito:

The following information is provided in response to your request on occurrences of failure of control rods to fully insert and a summary of other control rod drive malfunctions (unlatching):

1. Failure of Control Rods to Fully Insert There have been no occurrences of control rods fail'.ng to fully insert during 1978 and 1979. The only incidents of control rods failing to fully insert occurred during a scram on December 13, 1975. Two rods in location 34-39 atd 14-27 inserted to notch position 02, nJ nther rods fully inserted. The two rods vere manually insected to .c ch position 00. The rods were test scram-med manual *y on December 23, 1975 and inserted again to notch position 0; . On a scram, the Technical Specifications require individual rods to insert 90% in seven seconds. This requirement was achiev ed by the rods so no LER was submitted to the NRC for this event. The control rod drives were replaced in May 1976 and an examination of the control rod drives during overhaul revealed general we st but no specific cause for the failure of the rods to fully instrt.

2. Control Reid Unlatchings There have been two incidents cf control rod unlatchings; one during the 1977 Refueling and Maintenance Outage and one during normal pcver operation on November 11, 1978. A summary of each incident is provided below:

During t e 1977 Refueling and Maintenance Outage while performing the core suberitical check, control rod 18-19 unlatched from its control *od drive. The control rod was fully withdrawn (position

48) at the time of the event. The rod was relatched to its control rod drive per Procedure 2.2.9. This control rod drive had been replaced earlier during the outage anc'. was replaced again 3O/

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4 Mr. Thomas A. Ippolito .

February 22, 1980 Page 2.

cfter the unlatching incident. The normal method of unlatching the control rod drive for control rod drive removal would not work, so an alternate method requiring removal of the fuel surrounding the control rod was used to unlatch the control rod drive. Examination of the control rod drive upon removal from the vessel revealed that the uncoupling rod was slightly bent and the spud fingers were slighcly deformed. Additionally, the uncoupling rod had been installed improperly in the control rod drive during control rod drive installation in the vessel in May 1976 and was the cause of the damage to the uncoupling rod and spud. LER 50-298-77-52 was submitted to the NRC documenting this event. A rebuilt control rod drive was installed in location 18-19 later in the outage and was latched satisfactorily.

During normal power operation on November 11, 1978, while per-forming Procedure 6.4.1.2-Withdrawn Control Rod Operability, control rod 30-31 unlatched from its control rod drive. The con-trol rod was fully withdrawn (position 48) at the time of the event. The control rod and control rod drive were relatched per Procedure 2.2.8. The control rod drive was subsequently replaced with a rebuilt control rod drive during the Spring 1979 Refueling and Maintenance Outage. As in the 1977 incident, the normal method of unlatching the control rod drive would not work, so the al-ternate above core method requiring removal of fuel surrounding the control rod was used to unlatch the control rod drive. Examination of the control rod drive upon removal from the vessel revealed that the uncoupling rod was improperly installed in the control rod drive during its installation in the vessel in April 1977. LER 50-298-78-34 was submitted to the NRC documenting this incident. A rebuilt control rod drive was installed in location 30-21 later during the outage and was latched satisfactorily.

3. Other Malfunctions During the 1977 Refueling and Maintenance Outage, control rod drive 22-23 would not unlatch in the normal manner used for control rod drive removal. The alternite method requiring removal of the fuel surrounding the control rod and unlatching from above was used to unlatch the control rod drive. Examination of the control rod drive upon removal from the vessel revealed that the uncoupling rod had been improperly installed in the control rod drive during its installation in the vessel in October 1976. A rebuilt control rod drive was installed in the vessel in location 22-23 during the outage and was latched satisfactorily.

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Mr. Thomas A. Ippolito February 22, 1980 Page 3.

During the 1978 Refueling and Maintenance Outage, control rod drive 14-27 would not unlatch in the normal manner used for control rod drive removal. A repeat of the alternate above core method of unlatching the control rod drive used in 1977 was used to unlatch the control rod drive. Upon removal from the vessel, examination of the control rod drive revealed that the uncoupling rod was improperly installed in the control rod drive. This control rod drive was installed in the vessel in May 1976. A rebuilt control rod drive was installed in location 14-27 later during the 1978 outage and was latched satisfactorily. An additional problem occurred during the 1978 outage during the installation of control rod drive 34-31. A control rod drive was removed from location 34-31 and replaced with a rebuilt control rod drive. The control rod drive was inserted into the core to latch it to its control rod but the control rod drive would not latch. Several attempts at latching were all negative. The control rod drive was subsequently removed from the vessel and an examination of the control rod drive re-vealed that the uncoupling rod was bent and a spud finger was broken off of the control rod drive and remained in the vessel.

The fuel, fuel support piece, and control rod dere removed from the location and the spud finger retrieved from the vessel. A rebuilt control rod drive was reinstalled in the vessel and was latched satisfactorily, stroked and timed, and latar test scrammed. The control rod was also inspected but no damage found. The specific cause for the incident was not determined, however, it is suspected that the spud and uncoupling rod were damaged during installation of the control rod drive into the vessel.

During the 1979 Refueling and Maintenance Outage, three control rod drives in locations 26-11, 22-35, and 26-31 would not unlatch in the normal manner used for control rod drive removal. This in-cident indicated that these three control rod drives had uncoup' ling rods improperly installed in the control rod drive during instal-lation in the vessel. These control rod drives were installed in the vessel in October 1976. An investigation was made on all control rod drives installed in the vessel during 1976 and 1977.

Thirteen control rod drives installed during this period were checked to determine if they would uncouple in the normal method used for control rod drive removal. (Five of the thirteen control rod drives would not uncouple in the normal method and indicated improperly installed uncoupling rods. All the control rod drives that would not uncouple in the normal method used for control rod drive removal (the five control rod drives found during the in-vestigation and the hree control rod drives found previously for a total of eight) were uncoupled using the alternate above core method requiring removal of the fuel surrounding the con *rcl rod.

Mr. Thomas A. Ippolito -

February 22, 1980

" age 4.

Examination of the eight control rod drives revealed that all had improperly installed uncoupling rods. All eight control rod drives were replaced with rebuilt or new control rod drives and latched satisfactorily during the 1979 Refueling and Maintenance Outage.

All the control rod unlatching and other malfunctions (described in 2 and 3 above) were caused by improper assembly of the uncoupling rod in the control rod drive during control rod drive installation into the vessel. To eliminate these problems, a protective cover was designed that fits on each spare control rod drive. The cover fits over the spud and uncoupling rod, verifies proper alignment and placement of the uncoupling rod in the control rod drive and protects the spud and uncoupling rod from possible damage during transportation of the control rod drive from the control rod drive repair area to the vessel. The cover is removed just prior to installation of the control rod drive into the vessel.

There have been no incidents of other control rod drive malfunction in 1979 since the Cycle V startup in May 1979.

Sincerely,

\__M4 m_,

J. M. Pilant Director of Licensing and Quality Assurance JMP:PLB:cg