ML20084L925
| ML20084L925 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 08/30/1974 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML20084L928 | List: |
| References | |
| 629-74, NUDOCS 8305240225 | |
| Download: ML20084L925 (3) | |
Text
4. : _ _..
~~ - - - - ~ -' - ~ ~ - - - - - - - ~ - - - - - ~ - - - - - - - - - ~
-~ --
'$$k C!,m w; lth Edis n g-g/ One First flational Plaza. Ch.cego, lilenois Adoress Reply to: Post Office Box 767 Chicago Illinois 60690 BBS Ltr.8629-74 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 August 30, 1974 0 !ID 50-237 W
Q'g'bu*b dd Mr. James G. Keppler, Regional Director p.
Ngo'$7k F H Directorate of Regulatory Operations-Region III 2
g gg b.f U. S. Atomic Energy Comission et [g{L 799 Roosevelt Road 2,
'fy 3
Glen Ellyn, Illinois 60137 7/
SUBJECT:
LICENSE EPR-19. DRESDEN NUCLEAR POWER STATION, UNIT 2, k
FINAL CONTROL ROD DRIVE /A'Oy.ALY REPORT ON DRIVE B-11. SN 7
-v.
References:
- 1) Letter of March 21, 1974 to Mr. O' Leary from B. B. Stephenson
- 2) Lotter received August 21, 1974 to Mr. Byron Lee, Jr. from James G. Kopplar
~
On March 14, 1974, control red B-ll, SN.761-C gava indication of an unacupled condition when it was withdrawn following a scram tcct. Pre-liminary information was submitted in reference 1.
Since then a meeting was held on July 22, 1974 at General Elcetric, San Jose, to acquaint the AEC with the results of the investigation of B-11 and the conclusions reached.
This letter suma rizes the initial events, subsequent investigations, and conclusions.
On March 14, 1974 a routinc scram test was performed on twenty-five (25) CRD's.
Following testing, CRD S/N 761C (core location B-11) was returned to position "48" at wnich time the "48" indication disappeared and the " rod overtravel" alarm annunciated. The CRD was recoupled and ar.bsequent attempts to withdraw at position "4d" verified that a positive coupling had been obtained. The CRD was then scramed three (3) times in an attempt to duplicato the uncoupling. The uncoupling check following the third scram identified that an inadvertent uncoupling had occurred. Following these tests, the CRD was recoupled, as confirmed by an uncoupling check at position "48" and subsequently inserted to "00".
The three symetrical rods were also inserted to enhance core monitoring capabilities.
. As part of tho investigation of B-11, G.E. representatives were present at the sito for the initial examination. The initial inspection consisted mainly of measuring the overall length (i.e., flange to end of fully amated uncoupled rod) and examining the inner filter assembly for damago and correct installation.
h
$ r(a 00PY SENT REGION m
0305240225 740030 n A C "'
PDR ADOCM 05000237 J'1O U
'a S
{
n a
1_.
g a
Mr. James G. Koppler August 30, 1974 j
The uncoupling rod was confirmed to be properly seated against the inner filter prior to installation of the measuring gage. The overall length (173.406 1 031) was measured several times and determined to be 173.890 inch or approximately.5 inch longer than the maximum
- allowable overall dimension.
The outer filter and the spud were then remored for decontamination. In an attempt to determine if the filter was inserted cn the stop piston connector to any degree, a hooked shaped piece of weld wire was engaged in the filter and an attempt was made to withdraw the filter. The filter moved freely with a minimum of force. Normal disassembly of the CRD continued with the resulting observations.
Inner Filter: The inner filter wiper ring did not exhibit a 360' wear pattern (i.e., approximately 1/2-3/4 inches on circumference of ring was not sealing in bore of index tube). The land of the filter (i.e., outer diameter) Just below the wiper ring and the outer filter diameter just above the ring exhibited a wear pattern which could be caused by misorienting (i.e., cocking) the filter in the bore of the index tube. One leg of the filter etaining spring was, displaced inward approximatel; 1/4 to 3/8 inches and spread out radially about 3/8 of an inch. Some raised metal was observed on both legs of the spring. No damage to the back side of the spring (i.e.,, damage which would be caused if the filter was pulled off stop piston connector) could be observed. Tne inner filter was very clean inaicating that a Jarge degree of bypass flow had occurred.
Stop Picton: The stop piston connector was observed to have two (2) areas on the flat which exhibited signs of impact with the retainer spring (i.e.,
raised metal) and two (2) scored areas leading from those impact treas across the chamfer and down the connector outer diameter. There was ne t'.gn of distortion or rais:d metal on the lip of the connector head whlen would Le indicative of the filter being removed from a properly engaged oposition en the stop piston conncetor.
Index Tube: There was a scored area in the bore of the index tubo which started approximately one foot from the spud end and ran for approxinately two feet. This discrepancy could have been caused by the misorientation of the inner filter.
In summary, CRD S/N 7610 is considered to have uncoupled as a result of detachment of the inner filter. This detachment is considered to have occurred as a result of improper assembly which damaged the filter retainer spring (i.e., spring repair techniques when used were not effective) or improper assembly which resulted from a failure.to securely lock the filter after engagement on the stop piston connector. This conclusion has been reached as a result of the following:
- 1) No evidence of damage was observed which would have resulted if a properly locked filter had been pulled off of the stop piston connector.
s l
=
1 4
I/c.Jameu0,K:ppl$r August 30, 1974
,l
./
- 2) No vehicle for rotating a properly locked filter is known to exist. Observations of index tubes following testing of San Jose and in the field has to date always identified a singular wear pattern caused by the collet fingers which verifies that no random rotation of the index tube has occurred.
CONCLUSIONS
- 1) CRD S/N 761C did inadvertently uncouple as a result of detachment of the inner filter.
- 2) Detachment of the inner filter is considered to have been caused by improper assembly of this filter during the Spring 1972 outage for filter modification.
- 3) Uncoupling of a control rod /CRD can only occur at position "48" as a result of detachment of the inner filter, therefore if a CRD is verified to be coupled at position "48", moving this rod into the core and reposi-tioning thereafter can occur without fear of an inadvertant uncoupling.
If, however, the CRD is repositioned to "48", a coupling verification must always be performed.
In reference 2 it is stated that "in the future any control rod drive which gives an uncoupled indication will be fully inserted without attempting to recouple it."
Our procedures are being changed to reflect gg this. It is our feeling, however, that this measure is unnecessary. A gj y/
drive can only uncouple from this phenomenon at position "48".
An uncoupleC%g g blade should immediately be shown to have followed the drive by inserting the drive until neutron response can bo verified. Attempts should then be made to relatch the drive. If the drive can be relatched and pass an uncoupling test at position "46", it then becomes a known quantity and should be used as a normal drive. From this point on, it should be consid-pred to be more susceptible to repeat this event, but the uncoupling can occur only at position "48".
If a drive cannot be recoupled, it must be assumed that this phenomenon may not be the cause, and the drive should be inserted to "00".
This matter will be resolved with the Directorate of Licensing, There is como concern for the_other 76 drives overhauled in the Spring of 1972. At present, there are plans to overhaul approximately 77 drives during the next refueling outage in November, 1974. Of these 77, 27 of them are included in the other 76 overhauled in 1972 by G.E.
These 27 will be checked carefully to detect damaged springs or a detached filter.
It will be detomined from the inspection of these 27 if it is necessary to look at the remainder of these drives during future outages.
Sincerely, M -....
Q) 9&h
/
B. B. Step". nson Superintendent LBS IJDido
/
-f.
/m\\ Com e:lth Edison
~f50-237 o-
[ d c;4 ) One Fint sonal Plan. Cmcago. libnois O
(v] Addrm Reply to: Post Office Box 767 O2!cago, Ilhnois 60690 BBS Ltr.#207-74 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 52 e
March 21, 1974
,e
' 1
)? S L-f* y. et D Mr. J. F. O' Leary, Director
.,/gO' q
Directorate of Licensing 4.p.g 7, s
U. S. Atomic Energy Commission Washington, D. C.
20545 D
SUBJECT:
- LICENSE DPR-19 DRESDEN NUCLEAR POWER STATION, UNIT 42, REPORT
~
OF ABNORMAL OCCURRENCE PER SECTION 6.6.B.I.a OF THE TECHNICAL SPECIFICATIONS.
UNCOUPLI!r, OF C0!TTROL ROD DRIVE B-11
References:
- 1) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura, 1410 hours0.0163 days <br />0.392 hours <br />0.00233 weeks <br />5.36505e-4 months <br /> on March 14, 1974.
Telegram: Mr. J. Keppler,1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on March 14, 1974.
- 2) Dugs: P&ID M-34
Dear Mr. O' Leary:
This letter is to report a condition relating to the operation of the unit at about 0134 hours0.00155 days <br />0.0372 hours <br />2.215608e-4 weeks <br />5.0987e-5 months <br /> on March 14, 1974 A routine 25 control rod drive (CRD) scram test was being conducted to satisfy the two(2) week test requirc: ment of Section 4.3.C.3 of the Technical Specifications.
CRD B-11 while being withdrawn to position "48",
subsequent to scramming, went into an overtravel condition.
The overtravel indication is indicative of an uncoupled CRD. This malfunction is contrary to section 3.3.B.1 of the Technical Specifications which requires that each control rod shall be coupled to its drive or completely inserted and the control rod directional or control valves disarmed electrically.
PROBLEM Unit #2 was operating at 327 MWe. Routine surveillance testing had been completed and 25 control rod drive scram testing had begun. Rod B-11 was successfully scram tested with a 90% insertion time of 3.01 seconds.
At 0134 hours0.00155 days <br />0.0372 hours <br />2.215608e-4 weeks <br />5.0987e-5 months <br /> on March 14, 1974 while in the process of withdrawing the drive to position "48", a " rod overtravel" alarm annunciated and both the four rod and full core displays for the rod went blank. At 0222 hours0.00257 days <br />0.0617 hours <br />3.670635e-4 weeks <br />8.4471e-5 months <br />, the drive was given a continuous withdraw signal which cleared the overtravel alarm and returned the position "48" indication. The drive was subsequently inserted and withdrawn in 6 notch increments. TIP traces were taken to verify that the blade followed the CRD.
In addition, the drive was giv,en a continuous withdraw signal at "48" to verify it had recoupled.g y
?
'i$ d 7 MPY SENT T?EGION a
m
r o
a o
Mr. J. F. O'Le W March 21, 1974 At 1103 hours0.0128 days <br />0.306 hours <br />0.00182 weeks <br />4.196915e-4 months <br />, the CRD was scrammed three (3) times to see if the uncoupling could be duplicated.
The drive was scrammed successfully two (2) times. However, af ter the third scram, while withdrawing, the drive went to overtravel. - This time, friction testing equipment was set-up to determine the pressure drop across the drive which would indicate if the CRD had uncoupled. At 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> friction testing was initiated. The trace clearly shows the blade was uncoupled (Fig.1). The test was conducted by slowly increasing the drive water pressure to approximately Pr+50 psig.
During the tests, the drive recoupled. At 1725 hours0.02 days <br />0.479 hours <br />0.00285 weeks <br />6.563625e-4 months <br />, the CRD was coupled and inserted to position "00".
Drive B-11 (06-43) was disarmed and taken out of service at 1905 hours0.022 days <br />0.529 hours <br />0.00315 weeks <br />7.248525e-4 months <br />.
I INVESTICATION CRD flange no. 761C was overhauled and placed in position B-11 during the spring 1972 refueling outage.
Scram times prior to the over-travel and during attempts to uncouple a second time plus a withdraw stall flow are listed below:
INSERT TIMES (Sec.)
M 3
107 20%
5,01
- 907, 1007 Buffer 0
2-10-74 0.36 0.54 0.81 1.76 3.05 3.65 0.43 3-4-74 0.34 0.50 0.79 1.75 3.03 3.64 0.43 3-14-74 0.32 0.49 0.77 1.73 3.01 3.62 0.43 3-14-74 0.33 0.49 0.76 1.69 2.95 3.55 0.43 3-14-74 0.30 0.46 0.74 1.68 2.95 3.54 0.42 3-14-74 0.34 0.50 0.77 1.72 2.98 3.58 0.42 Withdraw stall flow for B-11 on 2-10-74 was 2.2 gym.
A review of the data indicates no abnormal conditions.
CORRECTIVE ACTIONS The corrective action taken was to couple the CRD, insert it to position "00", electrically disarm it and take it out of service at 1905
-hours March 14, 1974.
The control rod drive will be removed during the next extended maintenance ' outage. At that. time, a thorough inspection will be made to determine the mode of failure and a follow-up letter submitted to your i
i office.
s g -
e e
S u :_..
~
Mr. J. F. O' March 21, 1974 EVALUATIONS This drive uncoupling did not endanger public health or safety because the blade was capable at all times of being inserted into the i
reactor core. Additionally, the drive recoupled whenever it was given an insert signal. This uncoupling phenomenon occurred once before, February 19, 1973. At that time, three(3) CRDs experienced uncoupling during reactor startup. The anomaly was explained as having occurred because of dislocated inner filters. At this time the failure mechanism is not known, therefore, a follow-up letter will be issued subsequent to B-11's overhaul.
Sinc <erelv/
' &,s
. t r,s tu y.'S'ephenson Superintendent BBS:MST:do e
9 9
+
a 9
s 4
- q:'
e-rw
,-/
..