ML14188B255
| ML14188B255 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 11/04/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14188B254 | List: |
| References | |
| NUDOCS 8611070211 | |
| Download: ML14188B255 (7) | |
Text
ENCLOSURE SAFETY EVALUATION ON REQUESTS FOR RELIEF FROM EXAMINATION REQUIREMENTS OF SECTION XI OF THE ASME CODE CAROLINA POWER AND LIGHT COMPANY H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 I. BACKGROUND By letters dated May 1, 1985 and April 22, 1986, Carolina Power and Light Company (the licensee) requested relief from certain inservice examination requirements of the 1977 Edition through Summer 1978 Addenda of Section XI of the ASME Boiler and Pressure Vessel Code for H. B.
Robinson Steam Electric Plant, Unit No. 2. The licensee's requests, supporting information, and alternative examinations, as well as the staff's bases for granting or denying the requests are provided herein in accordance with 10 CFR 50.55a(g)(6)(i).
II. RELIEF REQUESTS SUPPORTING INFORMATION, AND EVALUATIONS A.
RELIEF REQUEST #12 - CIRCUMFERENTIAL SHELL WELDS IN SEAL WATER HEAT EXCHANGER (CATEGORY C-A, ITEM C1.10)
Code Requirement Volumetric examination of circumferential shell welds at gross structural discontinuities during each inspection interval on 100%
of the length of each weld.
8611070211 861104 PDR ADOCK 05000261 E
-2 Code Relief Request Relief is requested from volumetric examinations of the Seal Water Heat Exchanger head-to-shell and shell-to-flange welds.
Licensee's Basis for Requesting Relief The thickness of the material utilized for the construction of this component (0.187 inch) is such that meaningful results could not be expected with ultrasonic examination as required by IWC-2500-1. The proposed alternative examination is as capable of detecting significant defects in 0.187 inch material as the Code-required volumetric examination.
Licensee's Proposed Alternative Examination Liquid penetrant examination will be performed on the welds and on one-half inch of base metal on each side of the welds for 100%
of the weld lengths in lieu of the volumetric requirements.
STAFF EVALUATION AND CONCLUSIONS The Code requirement to volumetrically examine the Seal Water Heat Exchanger head-to-shell and shell-to-flange welds is an impractical requirement because of the component's design. The volumetric examination requirement cannot be performed successfully by radiography because of the geometry involved or by ultrasonics because of the material thickness. Significant flaws that develop in material of the thickness of the Seal Water Heat Exchanger shell will either initiate at the OD surface or penetrate to the 00 surface and therefore be detected by the licensee's proposed surface examination. Based on this, the staff concludes that the relief may be granted as requested.
-3 P.
RELIEF REQUEST #13 - FULL PENETRATION WELDS OF NOZZLES IN VESSELS (CATEGORY B-D, ITEM B3.120), PRESSURIZER NOZZLE INSIDE RADIUS SECTION Code Requirement Volumetric examination of all nozzle to vessel welds and adjacent areas of nozzle and vessel.
Code Relief Request Relief is requested from volumetric examinations of the Pressurizer Nozzle Inner Radius sections.
Licensee's Basis for Requesting Relief The nozzles are integrally cast with the heads of the H.P. Robinson, Unit No. 2 pressurizer; thus, there are no welds and the configura tion of the nozzle at the inner radius section prevents meaningful volumetric examination.
Practical alternative techniques to volumetrically examine the inner radius section which would produce meaningful results are not currently available. The surge nozzle inner radius is not accessible due to the heaters connected inside the bottom head, and the retaining basket as shown on the attached sketch to the licensee's letter dated May 1, 1985.
Licensee's Proposed Alternative Examination Visual examination of the nozzle inner radii will be performed to the extent practical once during the interval only if the pressurizer is opened for other types of examinations or for maintenance purposes.
-4 STAFF EVALUATION The design of the nozzles and their inaccessibility make the required examination of the inner radiused sections impractical to perform.
The surge nozzle is surrounded by heater penetrations and the inner radius area is covered by a retaining basket; the spray nozzle inner radius area is partially obstructed by a welded coupling; the safety and relief nozzles' inner radius areas are designed such that the radius of curvature would not likely permit a meaningful ultrasonic examination, and radiography is not applicable for examination of any of the inner radius areas due to accessibility and geometry.
The licensee proposes to perform a visual examination of the inner radius areas of the nozzles to the extent practical when the pressurizer is opened for maintenance or other types of examinations once during the inspection interval. In light of the facts that (1) the nozzles are integrally cast with the vessel heads, (2) the inaccessibility for performing the required examination, (3) the limited (if not meaningless) examinations that could be performed if the requirement were imposed, and (4) the inservice history of no reported failures in the areas required to be examined, the staff finds the proposed alternative acceptable. We concluded that the relief requested may be granted.
C. RELIEF REQUEST #14 - PRESSURE RETAINING WELDS IN REACTOR VESSEL (CATEGORY B-A, ITEM NO. B1.30), SHELL-TO-FLANGE WELD Code Requirement Volumetric examination of 100% of the weld length during the inspection interval.
-5 Code Relief Request Relief is requested for deferral of the second period volumetric examination of an additional 33-1/3% of the weld length from the flange face until at or near the end of the inspection interval.
Licensee's Basis for Requesting Relief Table IWB-2500-1 Note: (6) in the 1983 Edition of Section XI allows these examinations to be performed at the end of the third period of the interval provided that 50% of the shell to-flange weld is examined by the end of the first period.
For the first ten-year interval, the flange-to-vessel weld was volumetrically examined 100% from the vessel wall in 1982.
During the first period of the second ten-year interval (1984) 33-1/3% of the length of the weld was examined from the flange face.
The examination program plan for H.B. Robinson is based on the 1977 Edition of Section XI ASME Boiler and Pressure Vessel Code with Addenda through Summer 1978. This requires examination of 100% of the weld length during the inspection interval.
The 1978 Summer Addenda allows partial deferral of examinations provided examinations are performed from the flange face during each period.
On this basis, the flanqe-to-shell weld was divided into three equal sections to correspond with the three periods of the interval.
Relief is requested only for the examination from the flange face for that one-third section scheduled presently for the second period of the inspection interval.
Relief thus granted would coincide with the 1983 Edition of Section XI with the exception that 33-1/3% of the weld would be inspected during the first period instead of 50%. The examination
-6 of an additional 16-2/3% of the weld in order to provide full compliance with the 1983 Edition is considered an unnecessary expense of resources and radiation exposure. The proposed alter native examination of 100% of the weld from both the flange face and the vessel wall at the end of the interval will provide better in-service monitoring of the area of interest since the 33-1/3% portion inspected during the first period will be reexamined at the end of the interval.
Licensee's Proposed Alternative Examination Volumetric examination from the flange face will be expanded to include 100% of the weld length in conjunction with the examination required to be performed from the vessel wall.
These examinations will be performed at or near the end of the inspection interval when the internals are removed.
STAFF EVALUATION The sampling plan required by the 1977 Edition of Section XI establishes the frequency and extent of examination of the vessel flange-to-head weld. Although the later editions of Section XI relax the frequency of examination, the extent of examination has been increased to provide greater assurance that flaws, which would experience a longer period of exposure to service conditions due to the relaxed frequency of examination, are not present. Based on the information presented in support of the request, the licensee's proposal to change the extent and frequency of examination is without technical merit or in keeping with good surveillance practices.
Performing the required examination at the required frequency does
-7 not entail undue hardship without a compensating increase in plant safety. The staff, therefore, recommends that the examination and frequency required by the 1977 Edition of the Code be maintained and the request be denied.