ML20009G258

Valve/Impact Assessment of Proposed Reg Guide 1.150

ML20009G258
Person / Time
Issue date:	06/30/1981
From:	NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:
Shared Package
ML20009G256	List: ML20009G255 ML20009G258
References
REGGD-01.150.00, REGGD-1.150.00, NUDOCS 8108040041
Download: ML20009G258 (7)

Text

,

[

n

,/

VALUE/lMPACT STATEMENT L,

1. PROPOSED ACTION demonstrated without doubt that the flaw will not grow and has not been growing,a ratherlarge flaw can be tolerated.

1.1 Description Crack initiation and growth is also a potential problem in cases where it is probable that no crack exists, but where The present inservice examination procedures for there is a cluster of small rounded inclusions. These clusters ultrasonic examination require improvement in order to of inclusions should be monitored by UT to ensure absence consistently and reliably characterize flaws in reactor of encks and crack growth, pressure vessel (RPV) welds and RPV nozzle welds. The apparent low level of the reproducibility of detection, Where the rate of flaw growth is expected to be large or location, and characterization of flaws leads to lengthy is uncertain, even a small flaw may be of concern. To discussions and delays in the licensing process. Much permit determination of growth rate, the UT procedures attention is paid to the integrity of RPV welds during the should be such that results of successive UT examinations licensing process because the failure probability of a reactor can be compared. With present procedures, these results pressure vessel is considered to be sufficiently low to cannot be compared because of variation in instrument exclude it from consideration as a design basis accident.

system characteristics. UT instrument system characteristics T,he assumption of a low probability relies heavily on depend on the characteristics of the system's different regularly repeated inservice examination by ultrasonic components. Variation in the characteristics of calibration testing (UT) of welds, blocks can also affect results.

1.2 Need for Proposed Action Guidelines are needed so that uncertaintiesin flaw charac-terization may be reduced or eliminated. The safety of the As more reactors start producing power, as those in components is evaluated with the help of fracture mschanics.

operation grow older, and as more inservice examinations Flaw sizes need to be known ior fracture mechanics evalua-are performed, the number of detected flaws with uncertain tions. Uncertain determination of flaw sizesleads to uncer-characteristics (size, orientation, and location) is likely to taintiesin the determination of the safety of the components.

A increase. Flaw characterization is essential for flaw evalua-Uncertainties in component safety lead to delaysin licensmg.

f j tions required by the ASME Code and by NRC to determine There is a need to specify and standardize the performance

,( / the structuralintegrity of nuclear reactor components when required of most UT system components to achiese better such flaws exist. It is essential to have valid background consistency in UT results so that delays in the licensing data for the flaw evaluations required by Section XI of the process may be reduced.

ASME Code. Based on the information gathered according to ASME Code requirements, it is often difficult to assess This guide will provide supplementary procedures with whether or not the flaw has grown between examinations.

the objective of improving conventional UT procedures, as The procedures now in use do not require the recording of defined in the ASME Code. This guide is based partly on the certain information that can be important in later analysis information available in literature concerning both U.S. and for determi5ng the location, dimensions, oricntation, and European procedures and partly on the judgment of the growth rate of flaws.

NRC staff and their consultants. On the basis of support work being performed at the Oak Ridge National Laboratory, The lack of standardizatior. in the use of UT equipment the staff plans to issue a revision to this guide that should and procedures leads to uncertiinty concerning the results further improve flaw characterization.

obtained. For example, transdecer characteristics such as beam spread, damping characteristics, and frequency The use of new techniques such as holography or synthetic for peak response are not def' ed, and there is no provision aperture imaging of flaws by UT that have not been imple-m to keep track of thae from one examination to the other.

mented into practice and could considerably increase the Similarly, characteristics of ether UT system components cost of inservice examination is not being proposed here.

nch as the pulser, receiver, amplifier, and video display screen may vary from one examination to another, and all I.3 Value/ Impact of Proposed Action these characteristics can influence the magnitude of the flaw indications. Therefore, well-defined criteria for supple-1.3.1 NRC mentary UT procedures are needed so that it will be possible to correctly characterize ~aws, estimate flaw growth, and Reporting UT examination results asindicated in this guide have reproducible results from inspections performed at would help the NRC staff and their consultants to better different times using different equipment.

assess the results of the data. At present, the NRC staff

/S must spend a great deal of time on controversy over deter-l

)

In many instances, the rate of flaw growth can be even mining the safety of components from inconsistent UT more important than the flaw size. For example,if a flaw is results. Lack of faith in flaw size determination from found in an RPV nozzle or belt-line region and it can be uncertain UT results points toward the adoption of some 8108040041 810630 PDR REGGD 01.150.00 R PDR 1.150-9 1

l

)

conservative safety measures that are undesirable, for the

i. Providmg more consie t UT procedures for Raw n

most part, to the industry managers. Licensing delays occur characterization, therei, leading to procedures that because decisions have to be made on the basis of uncertain ensure lower probability of missing large Daws and in formatio 1 Ilaw size determination from consistent UT ensuring greater safety for the pu blic, industrial results would help remove or reduce the uncertainties and workers, and government employees.

debates over the safety issues. Because of the above, NRC staff time for review of reported data and interpretation of indications is likely to be reduced.

1.3.3.2 Impact. There will be major impact in the followMg three areas:

/.3.2 Other Gorcenment hencies

a. Quality control of tN UT equipment Not applicable, unless the government agency is an At present,requirementsin the t SMii Code fer quality applicant, such as 1VA.

control of UT equipmera are marginal; for example, there are no direct requirements to control the quality of U T transducers. Criterion ill," Control of Measuring 1.3.3 Industry and Test Eca!pment " J Appendix 3,"Quslity Assur-ance Criteria for Nuclear Power Plantsand Fuel Repro-(

lhe value/ impact on industry of the regulatory guide cessing Plants," to 10 CFR Part 50 requires,in part, that positions is stated by each position in the appendix to this measures be established to ensure that instruments used value/ impact statement. Some highlights of the value and in activities affecting quality are properly coatrolled, impact of the regulatory guide positions are stated below.

calibrated, and adjusted at specified periods to maintain accuracy within necessary limits. The recommendations of this guide will help to bring about uniformity in the

1. 3. 3.1 ralue. Ihis regulatory guide specifies suvlemen-quality control procedures among different companies tary procedures that will lead to the following advantages:

and will ensure that quality control measures are taken to ensure reliability and reproduubiMy of UT results.

a. Atta%ng greater accuracy and consistency in Gaw No new UT equipment will be needed to follow the characterization.

recommendations of this guide. Ilowever, the quality control measures recommended f ar UT equipment l

b. Providing information for consistent flaw characteriza-will impose extra cost burdens that are difficult to l

tion at NRC review time and thus reducing NRC statf estimate withoat feedback from industry.

I effort in review of flaw indications.

b increase ih examination time

c. IIelping assess Daw growth.

This guide woulti recommend, for the first time, that

d. Providing a more reliable basis for flaw detection and indications with significant length ofindication travel evaluation, which should help in the uniform enforce-(larger than the standard calibration holes) or with ment of rules and the avoidance of delay in licensing significant depth dimensions be recorded. It is not decisions.

expected that the slag type of flaws, which are common among welds, or geor.ietric reflectors will give signif-

e. Reducing licensing time for reviewing examination icant traveling indications within the guidelines pro-results, w hich will aid in the reduction of reactor down-posed. Ilence, no substantial increase in recorded time during examinations and will be of great benefit indications as a result of this recommendation is I

to industry. With present construction costs of about expected; however, the exact increase is difficult to I.3 bdlion dollars for a 1000-megawatt reactor and the predict or estimate.

average size of a reactor running around 1100-megawatt capacity, the savings per day by eliminating reactor Reporting of indications associated with flaws larger downtime are likely to be 5500,000 or more, than 1 inch (indications larger than I inch plus beam spread at 20 percent DAC level)is also new. RPV welds

f. Avoiding unnecessary repairs due to flaw size uncer-are examined by radiography, and no flaws targer than tainties.

three-quarters of an inch are acceptable in these welds.

Because of this acceptance length, only new service-

g. Reducing radiation exposure to personnel by helping induu ! flaws larger than I inch,of which there should to eliminate unnecessary repairs. The radiation not be many, are expecte ! to be identified and reported exposure during repairs is usually many times the as a result of this recommendation.

exposure during examination, so a net reduction in radiation exposure is expected.

Because of the above two new reporting recommenda-tions, there may be an increase in examination time

h. Reducing margins of error in estimates of flaw growth and dollar cost that is difficult to estimate. This will and thus helping reduce overconservative estimates depend on how many significant flaws are detected and decisions on flaw acceptance.

and how large and complex they are.

1.150-10

l

c. Radiation exposure 2.3 Comparison of Technical Alternatives Recommendations of this guiJe apply to the examina-Imposing inservice examination of RPV welds by the use N./

tion of RPV welds and RPV nozzle welds. RPV welds of holography, synthetic aperture imaging technique, or are usually examined by automated equipment, and acoustic emission, all of which are stillin the stage of proto-data are collected on tape. Therefore, no increase in type development and have not been proved effective for radiation exposure is anticipated as a result of the field use, would not be justifiable on the basis of either regulatory guide positions addressing RPV weld cost or effectiveness.

examinations.

RI V nozzle welds are sometimes examined by 2.4 Comparison of Procedural Alternatives automated equipment but in most cases by manual UT. An increase in radiation exposure to examination Leaving the situation as it is would mean that continued personnel may be expected while RPV nozzles are attention and manpower would have to be devoted by the being manually examined. The probable percent NRC staff to investigate the uncertainties associated with increase in examination time or radiation exposure is flaw growth on a case-by-case basis. The low level of impossible to estimate without field data and research confidence in the present techniques means that excessive effort. Requirements for reporting traveling indica-margins would continue to be used in the flaw-acceptance tions and indications associated with flaws Lrger than cnteria. Also, unnecessary cutting and repair attempts to 1 inch may lead to an increase in occupational remove suspected flaws may result.

exposure in those cases in which the above indications are found and additional examination is required. The The procedures recommended in this guide have been magnitude of this additional exposure can only be shown to be effective in practice, although they are not in assessed on a case-by-case basis. It should be note.1 general use in the United States. Including these procedures that radiation levels at vessel nozzle regions are as regulatory guide recommendations shculd result in their reported to range from 0.5 to 2.0 rem / hour. Total wider use and consequently their improvement. After these person-rem doses can be drastically reduced by procedures have been accepted by the industry, we will shielding and local decontamination.

seek their inclusion in the ASME Code. Some of these procedures have already been sent to the ASME for considera-The guide is not expected to have any adverse impact on tion and inclusion in the present ASME Code procedures other government agencies or the public.

for ultrasonic examinations.

y 1.L4 Public 2.5 Decision on Technical and Procedural Alternatives No impact on the public can be foreseen. The only identifiable value is a slight acceleration in the review On the basis of the above, it appears desirable to issue 2 regulatory guide to provide recommendations for improving process.

ASME Code procedures. These recommendations, which 1.4 Decision on Proposed Action are based on the advanced state-of-the-art UT procedures in current use by some organizations, would improve the The Office of Nuclear Reactor Regulation (NRR) has ability to detect and characterize flaws without imposing stated the need for this guide to help them and their new, unproved techniques for flaw detection on industry.

consultants in evaluating the size and significance of the tiaws detected during inservice examination to ensure the

3. STATUTORY CONSIDERATIONS integrity of reactor pressure vessels between periods of examination. It would therefore be advisable to issue this 3.1 NRC Authority guide.

The authority for this guide is derived from the safety

2. APPROACll requirements of the Atomic Energy Act of 1954,asamended, and the Energy Reorganization Act of 1974,asimplemented 2.1 Technical Alternatives by the Commission's regulations. In particular, 50.55a,

" Codes and Standards," of 10 CFR Part 50 requires, in Alternatives would include requiring the use of holography, part, that structures. systems, and components be designed, synthetic aperture imaging, acoustic emission, neutron fabricated, erected, constructed, tested, and inspected to radiography, or a combination of the above during RPV quality standards commensurate with the importance of inservice examination.

the safety function to be performed.

2.2 Procedural Alternatives 3.2 Need for NEPA Assessment One alternative is to leave the situation as it is. A second The proposed action is not a major action, as defined by alternative is to request change of the ASME Code require-paragraph St.5(a)(10) of 10 CFR and does not require an n;ents environmentalimpact statement.

1.150-11

4. RELATIONSillP TO OTilER EXISTING OR PRO-difficult for the NRC staff or their consultants to review, POSED REGULATIONS OR POLICIES analyze. and assess the UT data to determine the flaw size and evaluate the system safety when the data are made Recommendations of this guide would be supplemental available to NRC at a later date. The present data obtained to the requirements of Section XI, " Rules for Inservice from UT equipment of uncertain and unspecified performance Inspection of Nuclear Power Plant Components," cf the lead to discussions and delays in the review process resulting ASNIE Code, which is adopted by 50.55a, " Codes and in loss of NRC staff time and loss of plant availability Standards," of 10 CFR Put 50.

and poveer generation capacity for the utilities. These situations definitely need to be avoided as much as possible.

5. SUS 151 A RY This guide is aimed at achieving this purpose by issuing recommendations that will be supplementary to the existing This guide was initiated as a result of a request from ASNIE Code UT procedures. The issue remains whether to NR R. Preliminary results of the round robin UT examination wait for the development of advanced NDE techniques and procedures following ASN1E Code procedures indicate a continue with the present ASNIE Code procedures resulting need for additional guidelines to the existing ash 1E Code in uncertainties, delays, and discussions or to encourage procedures to control equipment performance, calibration improvement in the present state of the art of conventional block specifications,and scanning procedures to improve the UT. The decision appears to be obvious that we should use reproducibility of results and detectability of througa-thick-conventional UT based on engineeringjudgment until some ness flaws.

new techniques for flaw detection and sizing can be proved effective in the field. This guide is aimed at providing the Atinimum ASNIE Code requirements do not specify the recommendations needed to improve on the ASN!E Code details of recording requirements that are essential to UT requirements until proven advanced NDE techniques evaluate flaws. Th'.s deficiency in the Code rules makes it are available.

O l

O 1.150-12

APPENDIX TO VALUE/ IMPACT STATEMENT Values that will result from this regulatory guide are now apply to the examination of the RPV, require calibra-much easier to perceive than the impact. It is very difficult tion against the calibration block only " prior to use of the to assess the real impact because the kind of statistical data system." It is considered that the present IW7 ASME Code needed is simply not available at this time.One wayin which rules are not adequrte to control potential prob! cms in the we hoe to estimate the impact is through industry feed-variation of instrument performance characteristics. There-back at'ter the guide has been issued.

fore, the recommended calibration before and after each examination is a more reliable approach to instrument We have made an attempt, in a qualitative manner, to performance checks. The above position is not more con-estimate the value/ impact of regulatory guide positions, servative than the previously accepted 1974 Code rules, but is position by position, as follows:

more conservative if 1977 rules are considered.

1. INSTRUMENT PERFORMANCE CIIECKS Considering the requirements of Article 4,Section V (1977), the sbove position will mean a calibration check Recording the characteristics of the ultrasome testing each week the system is in use or before and alter each (UT) examination system will be useful h later analysis for RPV examination, whichever is less, instead of before each 4

determining the location, dimensions, orientation, and examination. A calibration check against the calibration growth rate of flaws. System performance checks to deter-block takes 15 to 30 minutes for manual UT and for mine the characteristics of the UT system will be made automated UT equipment where provision is rnade to shortly before the UT examinations. Each UT examination calibrate the equipment without having to remove the trans-will thereforc be correlated with a particular system per-ducers from the rotating scanning arm of the mechanized formance check. This practice will help to compare results.

scanner. In some cases, transducers have to be rertoved

'Ihese determinations will help make it possible to judge from the scanning arm for calibration of the UT instrument; whether differences in observations made at different times in these cases, a calibration check may take from 30 to 60 are due to changes in instrument characteristics or are due minutes. The added cost of the above would be in terms of to real changes in the flaw size and characteristics, additional time spent by the examiner and would occur each week or once for each RPV examination, depending it is recommended that, as a minimum, instrument on whether or not the examination h completed in less checks should be verified before and after examining all the than a week. No additional radiation exposure is expected welds that need to be examined in a reactor pressure vessel because of this posPion.

during one outage.

3. NEAR SURFACE EXAMINATION AND SURFACE Performance of these instrument checks is likely to add RESOLUTION a few thousand dollars to test equipment cost and to take I to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of examination time before and after each reactor This position recommends that ar' estimation of the pressure vessel (RPV) examination. The examination equip-capability to effectively detect defects at the metal front ment is usually idle between examinations. Performance and back surfaces of the actual component should be made checks on the examination equipment could be performed and reported. This will not require any additional calibration during)hese idle periods. These performance checks are not or examination time but will simply require an estimate of likely to reduce the number of examinations that a particular this capability by the examiner, which will be reported to UT system could perform in a year. No additionalradiation NRC. No additional radiation exposure is expected because exposure is expected because of this position.

of this position.

2. CALIBR ATION

4. BEAM PROFILE According to this positior system calibration should be This position recommends that the beam profile (for checked to verify the distances.nplitude correction (DAC) each search unit used) should be determined if any signif-curve, as a minimum, before and after each RPV examina-icant flaws are detected during the RPV exarnination.

tion (or each week the system is in use, whichever is less) or each time any componer.* (e.g., transducer, cable, connector, Assuming that no more than three search units are lixely pulser, or receiver) in the examination system is changed.

to be used during an RPV examination, this step is likely to require no more than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of examination time. No Subartide 1-4230, Appendix I,Section XI, ASME B&PV additional radiation exposure is expected because of Code (1974 edition), which applied to the inspection of the this position.

O RPV, required calibration using the basic calibration block at "the start and finish of each examination, with any change

5. SCANNING WELD-METAL INTERFACE

(~

in examination personnel and at least every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> during an examination." llowever, the 1977 rules of Article 4 This position recommends that the beam angles used to (T-433),Section V, which are referenced by Section XI and scan welds should be based on weld / parent-metal interface 1.150 13

reometry and at least one of these ang!cs should be such that on the screen larger than the indication on the screen from the bcam is almost perpendicular f il 5 degrees to the perpen-the cabbration holt, (1/2 mch hole for a 12-inch we:d ihcular) to the webl/ parent-metal mterface, unless it an be t hic k ne ss, 3/8-inch hole for an h-inch thicknessh this demonst.ated : hat We (Code-unacceptable) planar flaws recommendation will ot result in any more recording of unfavorably oriented can be detected by the UT technique.

indications. If the RPV welds being examined have several indications with travel in excess of the cahbration hole On the bam ofinformation avadable,it appears that it is diameter, the examination and recording time will be diffv ult' A d to detect large planar flaw s fe.g., senice-mduce d increased for the innestigation of these flaws, %endmg fatigue or stress corrosion crac's) oriented at right angles to on the number of these indications. Slag inclusions in wc!ds the surface, using the ASMF C 3 U T procedure. Iloweser, are generally long cylindrical uefects and do not hase much the optmn is bemg provided to demonstrate that such flaws depth unless they are associated with shrinkage or service-can be lotated by conventional methods or by using new mduced cracks. ihese slag melusions are not expected to adunces in UI techniques. In tSese cases, the techmque will merease the nurnber of indications that will be recorded.

be acceptaNe as a volumetric eumination nrthou. Otherwv, increase in cumination time will depend on the number, the use of high-intensity radiography or tandem-probe Uf site, and com;lexity of geometry of through-thickness techni< pie, among other techniques, should be considered.

indications.

The above type of flaw is the most significant but the l'or RPV girth or : mule welJs where examination is most ditficult to detect. llecause of this, the present recom-performed by automated equipment and data are recorded mtndations are bemg made despite their potential impact or tape, this position will mean no increase in examination on cmt and ra.hation exposure.

time or radiation exposure; but interpretation, analysis, and reportmg time for these depth indications willincrease. The lhe pottatialimpact may be as follows:

extra burden in terms of dollar cost will depend on the number, site, and complexity of flaws, and there are no Additional NRC staff time may be needed to evaluate rational bases or data available at this time to estimate the a

the effectiveness of Ul' techniques on a generie basis to increase in the cost of examination.

detect perpendicular ri nar flaws. After techniques are a

recognized to accomplLh the above, NRC staff time that is l'or RPV welds, mostly notile welds, where examination bemg spent currently on evaluating problems en a plant-by-is performcd manually and data are not recorded on tape, plant basis is expected to be considerably reduced.

this position will mean extra examination time and increased radiation exposure to the examiners. Increase in dollar cost

b. Reactor downtime may increase, depending on the and radiatiei exposure will -*n depend on the number, examinMion time differentials between the conventional site, and complexity of indica: ons, and there are no bases l

and refined t chniques. lhis may, however, be offset by a or data available to estimate tius increase.

reduction in the downtime c. rently needed for NRC experts to evaluate data that sometimes requires further 6.2 Nontraveling Indications clarification and reeumination.2 A Ihis pWtion also recommends the recording of nontravel-

c. Additional cost might be incurred in changes needed ing indicitions above 20 percent DAC level that persist for j

to add transducers or data-gathering capability to existing a distance of more than I inch plus the beam spread.

automated equipment or to automate curren t manual According to NB-5320, Radiographie Acceptance Standards, cuminations Automation of current manual techniques is Section 8'i, Dnision I, ASME Code,1977 edition, flaws hkely to reduce radiation exposure to personnel.

lamer than 3/4 int or weld thicknesses abose 2-1/4 inches are not acceptable, liecause of this requirement, it is

6. SIZING AND RFCORDING OF INDICATIONS expected that no flaws larger than 3/4 inch in length are present in the RPV welds, and if indications are detected 6.1 Traseling Indications that suggest flaws larger than 3/4 inch, there is a strong possibility that these may be ser ice-induced flaws. Service-Ili position recommends the recording of traveling induced Haws are rare in RPV welds, yid it is therefore mdications. If RPV welds do not have any travelindications not expected that additional indications would have to be recorded because of this position. Ilowever, if such indica-i"Probab lity or Detecting Planar Derects in lleav) WallWelds by tions (over 1 inch) are detected, examination time for i

U trasonic Tethniques According to hnting Codes," Dr. Ing. ilans-automated recording and examination time plus radiation yrgen Mei er, Quahty Department..r M. A.N., Nurnberit, D Mou Nurnberg ii $.

exposure for manual UT examinations will be increased.

There are no rational bases or data available to estimate the "Intenm Technical Re l'<ive Return L ane Nonle (port on llWR leedwater and Control Rod impact of regulatory position 6.2, tac king," N U RI &O 312. J uly 197 7, r. 3 3"Analnis or the Ultrasonic I xaminations or PVRC wcIJ Sreci-7. REPORTING OF RESULTS mens i s s, 202, and 203." R. A. Iluc hanan,1% ssure Vessel Rewarch Committee (PV RC) Report, August 1976.

4" summary or the Detection and haluatio This position recommends that the areas required to be tions < 1 dwin flatch Unit i Reactor Prewure \\n or U,1,trasonic Indica-examined by the ASME Code that have not been effectively eswl, January 1972,

)

Georgia Power Company.

examined and an estimate of error band in siring the flaws l

l

1. ! !S : 4

-- ~

should be brought to the attention of the NRC when the of this guide, those inservice and presenice examinations results are reported. This effort may take about 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> in performed in the past. Such a policy would tend to be overly conservatise and would put a heavy burden on all reportwriting time.

plant owners. Although UT examinations have missed some M.1%IPLEM ENT ATION flaws in the past, there appears to be no immediate danger from the estimated flaw distribution probability to warrant it should be noted tha't the recommendationsof this guide such a strong action. Therefore, this alternatise was not are not intended to apply to those preservice examination adopted.

S tests already completed. Ilowever, the licensees may consider icpeating their preservice examination tests or

1. .2.2 Second,11ternative uung the recommendations of this guide any time at their option to avoid possible flaw interpretation problems at a in the past, several instances have been noted where the later date. Flaw interpretation problems may occur if minimal Code UT examination procedures have not been traveling indications identified as sigraficant according to adequate for detecting and sizing flaws. Discussions and the recommendations of this guide do not correlate with undesirable licensing delays were frequently the result. As preservice volumetric NDI: results and hence would be more plants begin producing power and existing plants grow assumed to have been service induced it would be difficult older, more flaws may be expected in the weld areas. These to show that these indications arose from fabrication flaws.

flaws may be generated as a result of fatigue, stress corrosion, lherefore, licensees would be well advised to consider tr or other unanticipated factors it is imperative that the abose possibilities.

guide recommendations for supplementary UT examination procedures be used in the future to maintain an acceptable RI Alternatives level of safety at these welds. The second alternative was therefore selected for applying this guide to the preservice The following ahernatives were considered in applying and inservice examination of RPV welds.

the recommendations of this guide.

It is expect'ed that inservice LTI' examinations will detect

1. To apply the recommendations of the guide to all the flaws generated during plant operation, whereas preservice presenice and inservice examinations that have examinations will provide UT examination data for sub-already been performed, sequent comparisons. First, a radiographic examination is performed of all the vessel welds under Section 111 of the

2. lo apply the recommendations of the guide to all ASME Code. After this examination, a UT preservice exam-future preservice and inservice examinations per-ination of welds is performed to serve as a supplementan formed after the issuance of the guide.

volumetric examination. Because of the above, these pre-service examinations are not as important as inservice exam-8.2 Discussion of Alternatives inations. It was tt refore decided that the guide recommenda-tions should applr sojudging the inservice examination results 3.2.1 First <ttfernative for those examinations performed immediately after the issuance of the guide; however, the guide recommendations Alternative I would infer that all RPV welds e.anined should apply to preservice examinations beginning 6 months as per the current code requirements are at a quality level after the issuance date. The NRC staff considered this that would not ensure an acceptable safety performance.

approach best because of the difficulties beirg experienced l'his approach would also mean that all the plants would in reviewing inservice UT examination data from the have to repeat, in accordance with the recommendations different plants.

1.150-15

UNIVE D SVOTES NUCLEAR REOULATORY COMutSSION f

W ASHING TON. D. C. 20555 Post AGE AND P EEs PAID OF FICI AL BUSINESS u a MuCLE AR REGuLAYomy PE N ALTY FOR PRIV ATE USE, $300 COMusssaoM L

L l

c v>

e 4

M1 E

6'.0I L

8 5

JUL 15198W (2A,,,g,,7 is o

O N

ND 6;

I O

- - -