ML17342A742
| ML17342A742 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 06/25/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17342A740 | List: |
| References | |
| NUDOCS 8707130326 | |
| Download: ML17342A742 (8) | |
Text
ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PEOUEST FOR RELIEF FROM VISUAL EXAMINATION R
U FLORIDA POWER AND LIGHT COMPANY UKY Ih I.
BACKGROUND INFORMATION By letter dated June 2, 1987, Florida Power and Light Company (FPL, the licensee) requested relief (Relief Request No. 16) from the visual examination requirement of the 1980 Edition through Winter 1981 Addenda of Section XI of the ASME Code during hydrostatic testing of repaired control rod drive housings at Turkey Point Unit 3.
Two dummy control rod drive housings had to be repaired after cracks were discovered in the pressure retaining boundary.
The Code requires a hydrostatic test to be performed after repairs by welding on the pressure retaining boundary during which a VT-2 (visual) examination of the repaired areas is conducted to detect eviderce of leakage.
The licensee has determined that the visua-l examination requirement is impractical tc perform and provided information in support of the determination.
This report provides an evaluation of the informztion submitted and the staff's bases for granting the request pursuant to 10 CFP, 50.55a(g)(6)(i}.
II.
INFORMATION RELATED TO PELIEF RE VEST NO. 16 A.
Component Identification Class 1
Reactor Pressure Vessel Control Rod Drive Dummies G7 and G9 Examination Category:
B-O and B-P Examination Item Number:
B14.10 and B15.11 Exam)nation
Description:
Pressure Retaining Welds in Control Rod Drive Housings B.
Examination Reouirements IWB-2500-1, Perform volumetric or surface examinations of 10% of the peripheral control rod drive housings during the inspection interval.
IWA-7530 and IWA-4500, prior to return of the plant to
- service, and following a repair or replacement, a
preservice inspection shall be performed.
8707l3032b 870625 i
P R
ADOCK 05OOD p
IWA-5000, after repairs by welding on the pressure retaining
- boundary, a system hydrostatic test shall be performed.
IWA-5246, the visual (YT-2) examination following a repair or replacement of a component may be limited to the repaired or replaced component, but shall include any connection made to the existing system.
C.
Relief Requested FPL requests relief from the visual (YT-2) examination requirements of the repaired control rod drive housings number Gi and G9.
D.
LICENSEE 'S BASIS FOR RELIEF Florida Power and Light Company provided the following reasons for requesting relief from the Code requirement:
1, Location The (2) two repaired control rod drive housings (both dummies) are located in the center of the reactor pressure vessel head.
2.
Initial Preparation for Examinations In order to perform the initial visual and liquid penetrant examinations, the following preparations had to be performed:
a.
The RPI cables had to be removed from the surrounding CRD housings.
b.
The surrounding CROM coil stacks had to be removed.
c.
Radiation surveys were taken on the head.
The outside diameter of the closure head area ranged from 2R to 3R depending on where you were located.
d.
Access requirements were looked at.
The clearance between the CRDN housings were recorded as Sk" between each housings.
3.
Initial Examinations a.
Visual examination was performed in order to identify and locate the leaking CRDMS.
t b.
The liquid penetrant examination method.was used to confirm the suspect areas.
In order to perform the liquid penetrant examination, an examiner had to be lowered dovrn onto the head from above.
c.
Following the above examinations, a remote visual examination was conducted and recorded on video tape.
These examinations included the two leaking
- dummies, the four adjacent CRDMS which had evidence of receiving the most spray, the surrounding CRDMS in which to bound in the leakers, the additional three
- dummies, and the two additional CRDMS received a
visual and liquid penetrant examination in order to satisfy the ten-year inspection requirements.
d.
The total radiation exposure for conduct of these examinations was in excess of 5.5 REM.
4.
Repair The repair of the leaking CROM dummies consisted of removing the existino weld and replacing it with'a stainless steel cap welded by a full penetration butt weld.
Examinations performed during the repair activity consisted of the visual, liquid penetrant and radiographic examination methods.
Following the repair, a final visual, liquid penetrant, and radiographic examinations were performed that included both the construction and Section XI examination requirements.
5.
Design and Configuration Rest~ictions The current design configuration of the repair dummies requires the CRDM to be insulated with a sock.
The insulation sock restricts both the direct or remote visual examination by completely covering the entire CROM housing, therefore obstructing the direct or remote visual examination of the new weld.
6.
Accessibility During System Pressure Tests Following the repair and after the closure head is back on the vessel, the following restrictions prohibit the VT-2 examination during the RCS overpressure test:
a.
The RPV head shroud obstructs the entire length of the CRDM housings.
b.
c ~
The CRDM coil stacks and RPI cables are installed on the instrument ports.
I The insulation sock is installed on the repaired dummies.
rL ~
d.
A blank coil stack is installed over the insulated
- sock, and is attached by a clamp to the adjacent CRB'ousing.
e.
The test temperature and pressure of 2350 psi and 547 degrees F, prohibit access to the examination areas.
f.
The installation of the missile shields.
7.
In aodition to the above obstructions, the amount of associated effort and supporting work to comply with the Code requirements is not justified for the following reasons:
a.
FPL feels that because of the design change from a full penetration seal weld to a full penetration butt weld coupled with the visual, liquid penetrant and radiographic examinations performed on the repair weld, assurance of an acceptable level of quality and safety will be provided.
b.
FPL feels that with the addition of the three inspection ports, early identification of leaks from the CRDM ports will assure a continued acceptable level of quality and reduce the radiation exposure to the examiners.
c.
FPL feels that the removal of the above identified obstructions solely for the purpose of viewing the replacement welds by the visual examination method coupled with the large expenditures of manhours and man-rem that will be required will not provide a
compensating increase in plant safety.
ALTERNATIVE EXAMINATIONS PROPOSED BY THE LICENSEE Florida Power and Light Company proposed the following alternatives:
1.
Perform the visual (YT-2) examination during the reactor coolant system overpressure test to the extent practical without the removal of the insulation by examining the accessible portions and exposed surfaces and the surrounding areas located around the closure head flange surface for evidence of leakage.
2.
FPL has installed within the shroud, three (3) removable inspection/examinati'on ports and with the position of the ports and the use of a high intensity light these viewing ports will provide the examiner with a means of locating and identifying leaks that may be present during the overpressure test.
III. STAFF EVALUATION A review of the information and drawings provided by the licensee leads to the conclusion that the Code reauired visual (VT-2) examination of the repaired CRDMS is impractical to perform at Turkey Point Unit 3.
The repaired CRDMS are located near the center positions of the control rod drives on the vessel head.
The close proximity of the drive mechanisms, the insulating socks that completely cover the repaired CRDMS, the Rod Position Indication System cables interference, the head shroud, radiation levels, and high temperature prevent either direct or. remote visual examination of the repair welds during the Code required hydrostatic test.
This inaccessibility to the control rod drive housing welds is not a result of the repair weld design
- change, but existed in the original reactor vessel closure head and control rod drive mechanisms design.
The repair of the CRDMS entailed a weld design change from a seal weld to a full penetration butt weld, 304 stainless to 304 stainless material.
The welds were subjected to radiographic and liquid penetrant examinations in accordance with the requirements of Section XI.
As an alternative to the direct visual examination of the repair welds, the licensee has proposed performing a visual examination of accessible areas and surfaces surrounding the repaired CRDMS for evidence of leakage.
This examination would be accomplished by utilizing inspection ports in the head shroud and a high intensity light.
Considering the obstructions, radiation levels, and temperature in the areas of the repair welds, imposition of the visual examination requirement would place an undue burden on the licensee without providing a compensating increase in assurance of the structural integrity of the welds versus that gained by the weld design
- change, the licensee's proposed alternative, and the volumetric and surface examinations performed on the welds.
IV.
CONCLUSION Therefore, relief from the visual examination required by Section XI of the ASME Code may be granted pursuant to paraaraph 10 CFR 50.55a(g)(61(i).
This relief is based on our finding that certain specific requirements of the Code are impractical, and the alternative examination imposed will provide an acceptable level of quality and safety in assuring the structu-ral integrity of the welds.
The granting of this relief is authorized by law and will not endanger life or property or the common defense and
=-='::. ity, and is otherwise in the public interest giving due consideration to the burden that could result if the reauirements were imposed on the facility.
Dated; June 25I 1987 Principal Contributor:
G. Johnson