Regulatory Guide 1.99

Effects of Residual Elements on Predicted Radiation Damage to Reactor Vessel Materials

ML12298A136
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Issue date:	04/30/1977
From:	Office of Nuclear Regulatory Research
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RG-1.099, Rev. 1
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REU.S. NUCLEAR REGULATORY COMMISSION A)REGULATORY GUIDEOFFICE OF STANDARDS DEV9LOPMENTREGULATORY GUIDE 1.99EFFECTS OF RESIDUAL ELEMENTS ON PREDICTED RADIATION DAMAGETO REACTOR VESSEL MATERIALS,vision 1priI 1977

A. INTRODUCTION

General Design Criterion 31, "Fracture Preventionof Reactor Coolant Pressure Boundary," of Appen-dix A, "General Design Criteria for Nuclear PowerPlants," to 10 CFR Part 50, "Licensing of Produc-tion and Utilization Facilities," requires, in part, thatthe reactor coolant pressure boundary be designedwith sufficient margin to ensure that, when stressedunder operating maintenance, testing, andpostulated accident conditions, (1) the boundarybehaves in a nonbrittle manner and (2) theprobability of rapidly propagating fracture isminimized. Appendix G, "Fracture Toughness Re-quirements," and Appendix H, "Reactor. VesselMaterial Surveillance Program Requirements,"which were added to 10 CFR Part 50 effective August16, 1973, to implement, in part, Criterion 31, neces-sitate the prediction of the amount of radiationdamage to the reactor vessel of water-cooled power* reactors throughout its service life.This guide describes general procedures acceptableto the NRC staff as an interim basis* for predictingthe effects of the residual elements copper andphosphorus on neutron radiation damage to the low-alloy steels currently used for light-Water-cooled reac-** tor vessels. The Advisory Committee on ReactorSafeguards has been consulted concerning this guideand has concurred in the regulatory position.

B. DISCUSSION

The principal examples of NRC requirements thatnecessitate prediction of radiation damage are:* Research and construction experience with low-residual-elementcompositions of these steels is accumulating rapidly and is ex-pected to provide a firm basis for acceptable procedures in the nearfuture."*Lines indicate substantive changes from previous issue.1. Paragraph II.H of Appendix G defines thebeltline in terms of a predicted adjustment ofreference temperature at end of service life in excessof 500F; paragraphs III.C and IV.B specify the ad-ditional test requirements for beltline materials thatsupplement the requirements for reactor vesselmaterials generally.2. Paragraph II.C.3 of Appendix H establishes therequired number of surveillance capsules on the basisof the predicted adjusted reference temperature at theend of service life. In addition, withdrawal of the firstcapsule (when four or more are required) is to occurwhen the predicted adjustment of referencetemperature is approximately 50°F or at one-fourthof the service life, whichever is earlier.3. Paragraph IV.C of Appendix G requires thatvessels be designed to permit a thermal annealingtreatment if the predicted value of adjusted referencetemperature exceeds 200°F during their service life.4. Paragraph II.B of Appendix H incorporatesASTM E185-73 by reference. Paragraph 4.1 ofASTM E185-73 requires that the materials, to beplaced in surveillance be those that may limit opera-tion of the reactor during its lifetime, i.e., those ex-pected to have the highest adjusted referencetemperature or the lowest Charpy upper-shelf energyat end of life. Both measures of radiation damagemust be considered.5. Paragraph V.B of Appendix G describes thebasis for setting the upper limit for pressure as a func-tion of temperature during heatup and cooldown fora given service period in terms of thepredicted valueof the adjusted reference temperature at the end ofthe service period.The two measures of radiation damage used in thisguide are obtained from the results of the Charpy V-USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, US. Nuclear Regu-latory Commission, Washington, D.C. 20555, Attention: Docketing and ServiceRegulatory Guides are issued to describe and make available to the public methods Branch.acceptable to the NRC staff of implementing specific parts of the Commission'sregulations, to delineate techniques used by the staff in evaluating specific problems The guides are issued in the following ten broad divisions:or postulated accidents, or to provide guidance to applicants. Regulatory Guidesare not substitutes for regulations, and compliance with them is not required. 1. Power Reactors 6. ProductsMethods and solutions different from those set out in the guides will be accept- 2. Research and Test Reactors 7. Transportationable if they provide a basis for the findings requisite to the issuance or continuance 3. Fuelsand Materials Facilities 8. Occupational Health4. Environmental and Siting 9. Antitrust Reviewof a permit or license by the Commission. 5. Materials and Plant Protection 10. GeneralComments and suggestions for improvements in these guides are encouraged at all Requests for single copies of issued guides (which may be reproduced) or for place-times, and guides will be revised, as appropriate, to accommodate comments and ment on an automatic distribution list for single copies of future guides in specificto reflect new information or experience. This guide was revised as a result of divisions should be made in writing to the US. Nuclear Regulatory Commission,substantive comments received from the public and additional staff review. Washington, D.C. 20555, Attention: Director. Division of Document Control.

notch impact test. Appendix G to 10 CFR 'Part 50 re-quires that a full curve of absorbed energy versustemperature be obtained through the ductile-to-brittle transition temperature region. The latter islocated by the reference temperature, RTNDT, whichis defined in paragraph II.F of Appendix G. The"shift" of the adjusted reference temperature isdefined in Appendix G as the temperature shift in theCharpy V-notch curve for the irradiated materialrelative to that for the unirradiated material,measured at the 50-foot-pound energy level ormeasured at the 35-mil lateral expansion level,whichever temperature shift is greater. In usingpublished data that report only the temperature shiftmeasured at the 30-foot-pound energy level, it hasbeen assumed herein that the adjustment of thereference temperature is equal to the 30-foot-poundshift.The second measure of radiation damage is thedecrease in the Charpy upper-shelf energy level. Inthe absence of a standard definition, the upper-shelfenergy is defined herein as the average energy valuefor all specimens whose test temperature is above theupper end of the transition temperature region. Nor-mally, at least three specimens should be included;more specimens should be included when the shelf,level appears to be marginal. However, if specimensare tested in sets of three at each test temperature, theset having the highest average may be regarded asdefining the upper-shelf energy.The measure of fluence used herein is the numberof neutrons per square centimeter (E>I MeV). An as-sumed fission-spectrum energy distribution was usedin calculating the fluence for most of the data base.*However, for application to a reactor vessel, thecalculated spectrum is used to predict fluence at agiven location in the wall. This procedure is not in-tended to preclude future use of data that are given interms of neutron damage fluence.As used herein, references to "% Cu" and "% P"mean the weight percent of copper and phosphorusas measured in the surveillance program per ASTME185-73. However, if such results are not available,the results of a product analysis may be used.Use of the procedures for prediction of radiationdamage given in the regulatory position should belimited to irradiation at 550 +/-251F, becausetemperature is important to damage recovery proces-ses. As a guideline, irradiation at 4501F has beenshown to cause twice the adjustment of referencetemperature and irradiation at 650°F, about half theladjustment produced by irradiation at 550OF for thefluence levels and the steels cited in the regulatory*The data base for this guide is that given by Spencer H. Bush,"Structural Materials for Nuclear Power Plants." 1974 ASTM Gil-lett Memorial Lecture, published in ASTM Journal of Testing andEvaluation, Nov. 1974, and its addendum, "Radiation Damage inPressure Vessel Steels for Commercial Light-Water Reactors."position when the copper content is about 0.15%. Theeffects of irradiation temperature on decrease in shelfenergy should be considered qualitatively similar tothose cited for the adjustment of referencejtemperature.Sensitivity to neutron embrittlement may be af-fected by other residual elements such as vanadiumand by deoxidation practice, as indicated by thefindings of current research. In predicting radiationdamage for materials that differ in chemical contentor deoxidation practice from those that make up thedata base, such findings should be considered. Otherresidual elements, notably sulfur, impair the initialCharpy shelf energy of these materials, and their con-tent should be kept low. Clearly, it is the remainingtoughness at end of life or at some other criticalperiod that is important. Such toughness may begiven in terms of the margin between the operatingtemperature (nominally 550°F) and the limitingtemperature based on toughness. A margin of 200degrees is desirable to permit safe management ofsystem transients. At full power, the limitingtemperature based on toughness is generally 150-200degrees above RTNDT; hence, the latter should notexceed 150-2001F at end of life. This limit also avoidsthe problems of providing for annealing, perparagraph IV.C of Appendix G. The levels ofresidual elements such as copper, phosphorus, sulfur,and vanadium that are required to achieve the limitof 200'F adjusted reference temperature at end of lifein a given reactor vessel will depend on the initialvalues of RTNDT of the beltline materials and on tle"predicted fluence at the particular locations in thevessel where the materials are used.When surveillance data from the reactor in ques-tion become available, the weight given to it relativeto the information in this guide should depend on thecredibility of the surveillance data as judged by thefollowing criteria:1. Materials in the capsule should be those judgedmost likely to be controlling with regard to radiationdamage according to the provisions of this guide.2. Scatter in the Charpy data should be smallenough to avoid large uncertainty in curve fitting.3. The change in yield strength should be consis-tent with the shift in the Charpy curve.4. The relationship to previous isurveillance datafrom the same reactor should be consistent with thenormal trends of such data. I5. The surveillance data for the correlationmonitor material in the capsule should fall within thescatter band of the data base for that material.1.99-2

C. REGULATORY POSITION

1. When credible surveillance data from the reac-tor in question are not available, prediction ofneutron radiation damage to the beltline of reactorvessels of light water reactors should be based on thefollowing procedures.a. Reference temperature should be adjusted asa function of fluence and residual element content inaccordance with the following expression, within thelimits below and in paragraph l.c.A = [40 + 1000(% Cu -0.08)+ 5000 (% P -0.008) ] [f/ 1019]whereA = predicted adjustment of referencetemperature, OF.f = fluence, n/cm2 (E>l MeV).% Cu = weight percent of copper.If % CuK 0.08, use 0.08.% P = weight percent of phosphorus.If % P5K0.008, use 0.008.If the value of A obtained by the above expressionexceeds that given by the curve labeled "UpperLimit" in Figure 1, the "Upper Limit" curve shouldbe used. If % Cu is unknown, the "Upper Limit"curve should be used.As illustrated in Figure 1 for selected copper andphosphorus contents, the above expression should beconsidered valid only for A >50°F and for f( 6 x 10'9n/cm2 (E > 1 MeV).b. Charpy upper-shelf energy should be as-sumed to decrease as a function of fluence and coppercontent as indicated in Figure 2, within the limitslisted in paragraph l.c. Interpolation is permitted.c. Application of the foregoing proceduresshould be subject to the following limitations:.(1) The procedures apply to those grades ofSA-302,. 336, 533, and 508 steels having minimumspecified yield strengths of 50,000 psi and under andto their welds and heat-affected zones.(2) The procedures are valid for a nominal ir-radiation temperature of 550°F. Irradiation below5251F should be considered to produce greaterdamage, and irradiation above 5751F may be con-sidered to produce less damage. The correction factorused should be justified.(3) The expression for A is given in terms offluence as measured by units of n/cm2 (E > 1 MeV);however, the expression may be used in terms offluence as measured by units of neutron damagefluence, provided the constant 1019 n/cm2 (E> 1MeV) is changed to the corresponding value ofneutron damage fluence.(4) Application of these procedures tomaterials having chemical content beyond thatrepresented by the current data base should bejustified by submittal of data.2. When credible surveillance data from the reac-tor in question become available, they may be used torepresent the adjusted reference temperature and theCharpy upper-shelf energy of the beltline materials atthe fluence received by the surveillance specimens.a. The adjusted reference temperature of thebeltline materials at other fluences may be predictedby:(1) extrapolation to higher or lower fluencesfrom credible surveillance data following the slope ofthe family of lines in Figure 1 or(2) a straight-line interpolation between credi-ble data on a logarithmic plot.b. To predict the decrease in upper-shelf energyof the beltline materials at fluences other than thosereceived by the surveillance specimens, proceduressimilar to those given in paragraph 2.a may~be fol-lowed using Figure 2.3. For new plants, the reactor vessel beltlinematerials should have the content of residual ele-ments such as copper, phosphorus, sulfur, andvanadium controlled to low levels. The levels shouldbe such that the predicted adjusted referencetemperature at the 1/4T position in the vessel wall atend of life is less than 2000F.

D. IMPLEMENTATION

The purpose of this section is to provide informa-tion to applicants and licensees regarding the NRCstaff's plans for utilizing this regulatory guide.This guide reflects current regulatory practice.Therefore, except in those cases in which the appli-cant proposes an acceptable alternative method forcomplying with specified portions of the Commis-sion's regulations, the positions described in thisguide will be used by the NRC staff as follows:1. The method described in regulatory positionsC. 1 and C.2 of this guide will be used in evaluating allpredictions of radiation damage called for in Appen-dices G and H to 10 CFR Part 50 submitted on or1.99-3 after June 1, 1977; however, if an applicant wishes touse the recommendations of regulatory positions C. 1and C.2 in developing submittals before June 1, 1977,the pertinent portions of the submittal will beevaluated on the basis of this guide.2. The recommendations of regulatory positionC.3 will be used in evaluating construction permit ap-plications docketed on or after June 1, 1977;however, if an applicant whose application for con-struction permit is docketed before June 1, 1977, jwishes to use the recommendations of regulatory'position C.3 of this regulatory guide in developingsubmittals for the application, the pertinent portionsof the application will be evaluated on the basis ofthis guide.41.99-4

7wA = [40 + 1000 (% Cu -0.08) + 5000 (% P -0.008)][f/10191 1)400)-ýPl,, 3000C.E0 2004-0 100E5-50C.,a,IL%I-.I I I I I III~..~~IIIIIIIIIIIIiIIIjTIIII[IIIi i i L l i i i ~ m- i i 1 11 11am 1 1 1 i i i ii i i i i i i i H HHHHH i i i i i i ! i H HHHHHHi ....II!I I i I I I i I IBI,JI0.25;M020 /,rz z0.15% Cu-0.1(IaI/ fI =I1.LOWER LIMIT% Cu = 0.08% P = 0.0082X10174 6 8. 1018246 8 101924 6FLUENCE, n/cm2 (E > 1MeV)Figure 1 Predicted Adjustment of Reference Temperature, "A", as a Function ofFluence and Copper Content.For Copper and Phosphorus Contents Other Than Those Plotted, Use theExpression for "A" Given on the Figure.

~~~U.,3UU .-20 0.25-- -------- 0.20 -0.15-0.15 0.10-- WwLITC,"___ O. 10---.05 ---I Z2 11 4 6 8 08 6 8 1092 4 6FLUENCE, n/cm2 (E > 1MeV)Figure 2 Predicted Decrease in Shelf Energy as a Function of Copper Content andFluence.Aftk --

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