ML20213G580

Safety Evaluation Re Util 861027 Request for Relief from Exam Requirements of Section XI of ASME Boiler & Pressure Vessel Code for Shell & Nozzle Welds in Regenerative Hxs. Request Granted

ML20213G580
Person / Time
Site:	Point Beach
Issue date:	05/07/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20213G556	List: ML20213G553 ML20213G580
References
NUDOCS 8705180353
Download: ML20213G580 (6)

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NUCLEAR REGULATORY COMMISSION t, j wassiNoTON, D. C. 20655

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION WISCONSIN ELECTRIC POWER COMPANY POINT BEACH NUCLEAR PLANT, UNIT NOS. 1 AND 2 DOCKET N05. 50-266 AND 50-301 REQUESTS FOR RELIEF FROM ASME CODE SECTION XI EXAMINATION REQUIREMENTS

!. BACKGROUND By letter dated October 27, 1986, Wisconsin Electric Power Company (the licensee) requested relief from the examination requirements of the 1977 Edition through Sunner 1979 Addenda of Section XI of the ASME Boiler and Pressure Vessel Code for the shell and nozzle welds in the regenerative heat exchangers at Point Beach Nuclear Plants, Unit Nos. I and 2. The licensee provided information in support of its determination that the Code requirements were impractical to perform and proposed an alternative to the Code requirements. Inaccordancewith10CFR50.55a(g)(6)(1),the staff has evaluated the licensee's deteminations and proposed an alternative examination. The staff has concluded that the necessary findings could be made to grant relief from the Code requirements. The requests, Code requirements, the licensee's deteminations, and our bases for granting the reliefs are contained herein.

II. REQUESTS AND SUPPORTING INFORMATION A. Relief Requests RR-1-12 and RR-2-12

- to examine less than the required number of welds in the regenerative heat exchangers.

B. Exam Area

'I Class 1 Tubesheet-to-Shell Welds Class 1 Nozzle-to-Shell Welds (SeeFig.A-7 attached)

C. ASME Section XI Category & Item Number 8-B, 2.60 B-D, 3.150 D. ASME Section XI Examination Requirement A volumetric examination of 100% of all tubesheet welds and nozzle welds during the second 10-year interval, g5180353870507 p ADOCK 05000266 PDR

E. Alternative Examinations Proposed By Licensee Instead of examining all three Class 1 tubesheet-to-shell welds and all six Class 1 nozzle-to-shell welds, the licensee proposed to examine tubesheet-to-shell weld RHE-2 and nozzle-to-shell welds RHE-N1 (inlet)andRHE-N4(outlet). These welds are all located on the botton, heat exchanger (see Fig. A-7 for an outline of the RHE and weld locations).  ;

F. Licensee's Reason for Limitation The regenerative heat exchanger (RHE) provides the major single source of radiation exposure accumulated during a normal refueling outage inservice inspection project. The " regenerative heat ,

exchanger" is actually three shell-and-tube heat exchangers i connected in series. The RHE is designed to recover heat from the '

reactor coolant system letdown stream by reheating the charging stream during normal operation. The letdown stream flows through the shell of the RHE and the charging stream flows through the tubes.

To ensure adequate coverage of the component welds with a minimum of exposure, the multiple stream concept should be carried out in all the welds Class 2 cap-to-shell welds. Class 2 tubesheet-to-shell welds, and two of six Class 2 norrle-to-shell welds are examined in accordance with allowances in IW8-2500 and IWC-2500 of ASME Section XI. By extending the multiple stream concept to the Class 1 '

tubesheet-to-shell and norrie-to-shell welds, a good cross-section l

of the regenerative heat exchanger would be exam < ned while a significant reduction in radiation exposure from this component would be achieved.

Following are some of the items the licensee took into consideration in the preparation of this request.

1. Radiation Levels Currently, the average dose rates at the regenerative heat i exchanger are:

1.5 rem /hr f 4.0 rem /hr feneral area (at 18")nsulationsurface(oncontaci 7.0res/hrshellsurface(oncontactundertheinsulation) i l

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2. Total Estimated Man-Rem Exposure Involved In the Examination [

Considering the tasks associated with conducting an esamination

on a particular examination area. the following time intervals have been required in the past

0.2 man-hours for insulation removal 1 0.1 man-hours for weld cleaning and preparation

! 0.7 man-hours for conducting the examination ,

i 0.2 man-hours for insulation replacement l

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! Using the preceding dose rates and times, the following whole body and extremity exposures can be calculated per examination: i

WholeBody(usinggeneralareadoserates)

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! 1.5 res/hr for insulation removal of 0.2 man-hours = 0.3 man-rem i

1.5 ren/hr for weld cleaning and preparation of 0.1  ;

man-hours = 0.15 man-rem  ;

, 1.5 rem /hr for the examination of 0.7 man-hours = 1.05 man-rem j 1.5 ren/hr for insulation replacement of 0.2 man-hours = 0.3 man-rem Total Whole Body Dose Per RHE Exam = 1.8 man-res >

Extremities (hands,usingcontactdoserates): r r

4.0 res/hr for insulation removal of 0.2 man-hours = 0.8 man-rem 7.0 rem /hr for weld cleaning and preparation of 0.1

man-hours

, 7.0 res/hr for the examination of 0.7 man-hours = 4.g man-rem 4.0 res/hr for insulation replacement of 0.2 man-hours = 0.8 man ren t .

i Total Whole Body Dose Per RHE Exam = 7.2 man-rom The exposure savings per inspection interval, by a reduction i

, of six examinations, would be 10.8 man-ren whole body and 43.2 l man-rem extremities.

3. Shielding When exposure is utilized to place lead blankets and shields

over non-examination areas of the RHE, the general area dose i

rates are reduced by approximately 501, but the dese rates are *

' still the highest encountered during an inservice inspection project. Also, the examiner who is conducting the examination i

does not have the benefit of the shielding. .

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4. Previous Inspection P n ilts Simply stated, all 9 " cations which were recorded durian inspections to this point were found to be either insign ficant or geometric in nature. An insignificant indication is either a non-relevant indication or an indication which is equal to er greater than the examination recording level but less than the evaluation level.

5. Consequences of Weld Failure The consequences of a failure of one of the RHE welds have essentially been addressed in the plant's Final Safety Analysis Report (FSAR). In the FSAR, to evaluate chemical and volume control system (CVCS) safety, failures or malfunctions were assumed concurrent with a loss-of-coolant accident (LOCA) and the consequences analyzed. A LOCA and a concurrent RHE weld failure is included in the more general category of a rupture in the CVCS line inside containment. During such an occurrence, the remote-operated valve located near the main coolant loop, upstream of the RHE, is closed on low pressurizer level to prevent supplementary loss of coolant through the letdown line rupture. The RHE would also evertually be isolated, with leakage being confined to containment, in the case of

. a weld failure without a LOCA.

!!!. STAFF EVALUATION AND CONCLU$!ONS i The staff finds that the information presented by the licensee supports its conclusion that the Code-required examinations are impractical to perform on some of the welds of the regenerative heat excnangers at Point Beach Units 1 & 2. Imposition of the requirements on the licensee is not warranted when the limited volumetric examinations that can be performed on some of the upper shell welds, the levels of radiation to which the examination personnel would be subjected in performing the limited examinations, the licensee's proposed alternative examination, and the consequences of failure of a weld in the heat exchangers are considered.

Information contained in an appendix to the letter of October 27, 1986, details the extent of examination of the welds for which the licensee requests relief. These welds were previously examined to the extent practical, the extent ranging from 255 to 1005. The examination results showed insignificant or geometric indications. In addition, the consequences of failure of a regenerative heat exchanger weld were analyzed and the conclusions drawn were that the re enerative heat exchanters would be isolated from the primary loop y the remote operated valve 'n the letdown line and leakage would be conf ned to the containment.

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The licensee proposes to examine the welds in the bottom shells of the regenerative heat exchangers in accordance with Section XI requirements.

Although similar welds in the upper shells, such as RHE-6 and RHE-10 (shell-to-tubesheet welds). can be examined to Code requirements, the gain in safety would not cospensate for the additional exposure to radiation of examination personnel. The bottom shells receive reactor coolant directly from the primary loops, thereby subjecting the welds and base material to more severe operating conditions than the upper shells and making this part of the component an area most likely to develop inservice flaws. Therefore, examination of the welds in the bottom shells will provide adequate assurance of the continued structural integrity of the regenerative heat exchangers shells.

Based on the results of previous examinations perforined on the upper shells, the licensee's proposed examination of the lower shells, and the consequences of failure of a shell weld, the staff concludes that relief from the Code required examinations of the regenerative heat exchangers upper shell welds may be granted as requested.

Principal Contributor: G. Johnson Date: NAY 0 71987 l

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