ML20059C986

Summary of ACRS Subcommittee on Matls & Metallurgy 930816 Meeting in Bethesda,Md Re Proposed Rulemaking on Fracture Toughness Requirements for Reactor Pressure Vessels & Revs to 10CFR50.61

ML20059C986
Person / Time
Issue date:	10/04/1993
From:	Seale R Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-2895, NUDOCS 9311020089
Download: ML20059C986 (8)

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f CERTIFIED BY:

DATE ISSUED: 9/22/93 Robert Feale--10/4/93 Q&c?295 b: -

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SUMMARY

/ MINUTES OF THE ACRS SUBCOMMITTEE ON MATERIALS AND METALLURGY AUGUST 16, 1993 BETHESDA, MARYLAND INTRODUCTION The ACRS Subcommittee on Materials and Metallurgy held a meeting on August 16, 1993, in Room P-110, 7920 Norfolk Avenue, Bethesda, Maryland.

The purpose of the meeting was to review proposed rulemaking on fracture toughness requirements for reactor pressure vessels, revisions to 10 CFR 50.61, " Fracture Toughness Require-ments for Protection Against Pressurized Thermal Shock Events, "

Appendix G, " Fracture Toughness Requirements," Appendix H, " Reactor Vessel Materials Surveillance Program Requirements," and a new rule, and an implementing draft regulatory guide on reactor vessel thermal annealing, 10 CFR 50.66 and DG-1027, respectively.

A copy of the meeting agenda and handouts of the presentation are attached to the office copy of the minutes.

We have received no written comments or requests for time to make oral statements from members of the public.

The meeting began at 12 noon and adjourned at 2:30 p.m. and was held entirely in open session.

The Designated Federal official for this meeting was Elpidio Igne.

ATTENDEES:

Principal meeting attendees included:

ACRS OTHERS Dr.

R.

Seale, Chairman J.

Hawthorne, MEA T.

Kress, ACRS Member K.

Cozens, NUMARC W.

Shack, ACRS Member W.

Corwin, ORNL P.

Shewmon, ACRS Consultant R.

Hardies, BG&E E.

Igne, Staff J.

Riccio ILRC M. Mayfield A.

Hiser A. Taboada E. Hackett J.

Strosnider L.

Shao i

DISCUSSION Dr.

Scale in his opening comments, mentioned the unusual hour (12:00 noon) the meeting is convening.

This was necessary to accommodate Dr. Shewmon's schedule as he will be leaving for Europe at the end of the meeting.

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. MINUTES August 16, 1993 Materials & Metallurgy NRC Staff Presentation Introduction, Mr. L. Shao, RES Mr. Shao stated that the staff was presenting for ACRS consider-ation five documents, three documents dealing with the proposed i

revisions to the rules on fracture toughness requirements on reactor pressure vessel (RPVs) and two documents on a new rule and implementing regulatory guide on RPV thermal annealing.

Revisions to " Fracture Touchness Reauirements." Mr..A. Hiser, RES Mr.

Hiser, discussed the proposed rule package on fracture requirements for light water reactor vessels. Mr. Hiser noted that two changes in the proposed rule package have been made since the package was submitted to the ACRS.

The first change clarifies the pressurized thermal shock rule relating to " Commission Approval" to

" Director of NRR Approval."

The second change deletes in Appendix G the requirement to permit annealing.

The Appendix G change will i

be in a new proposed rule 10 CFR 50.66, " Requirements for Thermal Annealing of the Reactor Pressure Vessel," which will be one of the topics discussed at today's Subcommittee meeting.

Mr. Hiser discussed the reasons for the proposed changes, which was mainly prompted during the review of the RPV integrity at the

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Yankee Rowe nuclear power plant.

I The PTS rule does not (1) specify appropriate margin value if surveillance materials data are used, (2) define initial value of RT and (3) provide acceptable reference to requirements in NDT Regulatory Guide 1.99a, Rev. 2.

Further, the PTS rule is silent on acceptability of thermal annealing as an option for reducing RTpts

• Mr. Hiser, then mentioned the following proposed revisions to 10 l

CFR 50.61:

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Make RT analysis identical to Regulatory Guide 1.99, pts Revision 2--embrittlement estimates are then consistent.

j Incorporate thermal annealing as an acceptable option to e

reduce RTpts Restructure and clarify the PTS rule.

e In reply to a question by Dr. Shewmon, Mr. Hiser stated that acceptable data variation, number of data points, etc. of the surveillance data are defined in the rule.

Mr. Hiser, discussed the problems encountered with 10 CFR Part 50 Appendix G,

" Fracture Toughness Requirements."

He mentioned that the process for demonstrating equivalent margins for cases in which

. MINUTES August 16, 1993 Materials-& Metallurgy a Charpy upper-s1. elf energy is less than 50 f t-lb is not clear.

In reply to a question by Dr. Shewmon, Mr. Hiser stated that rith respect to anisotropic effects of material properties, the lowest Charpy energy value is used in the PTS analyses--on. older plants where Charpy data is available for only the longitudinal or high toughness orientation, the estimated Charpy energy in the low toughness direction is reduced by a factor of 0.65.

Mr. Mayfield i

stated that the reduction factor is a staff position obtained by correlating embrittlement material data base.in both orientations.

Other problems noted by Mr.

Hiser with Appendix G are core criticality during ASME pressure and leak tests and an approval process for thermal annealing.

On criticality, Mr. Hiser stated that the staff would specifically require that pressure and leak tests required by the ASME code be completed prior to core criticality.

The principal reason cited was safety concerns--

hindrance in finding leaks at high temperature.

The section on

" design to permit annealing" requirements would be deleted in Appendix G of Section III of the ASME code and referenced in Appendix G of Section XI of the ASME code.

Section III is a construction code while Section XI is becoming more of an operating plant criteria code, which is a more appropriate reference for RPV thermal annealing.

Mr. Hiser stated that Appendix H is a material surveillance prograni required to monitor radiation embrittlement of the RPV beltline materials.

This appendix 12ferences ASTM E 185 regarding the detail of the surveillance programs such as, surveillance specimen withdrawal schedules, materials required, number of specimens, etc.

In addition, Appendix H contains provisions for an integrated surveillance program. The problems with Appendix H are essentially of clarification and interpretation.

The pr Wsed revisions to 10 CFR Part 50 Appendix H will clarify versions of ASTM E 185 for various portions of the surveillance program and to eliminate the provision for reducing the amount of testing in integrated surveillance program, "where initial results agree with predic-tions."

i Dr. Seale asked before Mr. Shao lef t the meeting, questions related

• 0am generator degradation.

Mr. Shao called on to the status a

Mr.

J.

Strosnilr MRR, to respond to Dr. Seale's concerns.

Mr.

Strosnidar statt.

Utat they were working on the steam generator degradation etw orr s and will complete the staff's plan on

• ue generically in the fall of 1993.

He will addressing this contact the ACRS

,gnizant engineer about setting up a Subcommittee meeting to discuss both the operating experiences of degraded steam generators and the regulatory direction that the staff plans to pursue.

In reply to a question by Dr. Shewmon, Mr. Strosnider stated that the tube plugging criteria, defect specific management, etc., will be some topics covered at the planned meeting.

MINGTES August 16, 1993 Materials &. Metallurgy Pror>osed Rule and Regulatory Guide on Thermal Annealina, Mr.

M.

Mayfield, RES Mr.

Mayfield stated the staff has two documents on thermal annealing ready for public comments, pending the concurrence of the ACRS, the proposed rule 10 CFR 50.66,

" Requirement for Thermal Annealing of the Reactor Pressure Vessel," and the associated draft Regulatory Guide DG-1027, " Format and Content of Application for Approval for Thermal Annealing of RPV."

He noted that there have been some changes to the proposed rule and draft guide since we have received the package.

Most of the changes to the rule were editorial changes, except that the staff has deleted the recovery equations in order to make the rule more performance oriented and less prescriptive.

The equations will be in the draft regulatory guide.

Mr.

Mayfield described thermal annealing of the RPV, thermal annealing is achieved by heating the RPV to a temperature higher than the RPV operating temperature.

For commercial LWR the annealing temperature range is 650-8E'"F for 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />.

Thermal annealing recovers RPV embrittlement caused by neutron irradiation.

He mentioned that higher annealing temperature produces greater material recovery.

Further, annealing can restore upper shelf energy, reduce RT and RT and widen the pressure-temperature ng pts (P-T) curve operating v'ndow.

In reply to a question by' Dr.

Shewmon regarding the performance of hardness tests of the RPV materials to determire irradiation damage and subsequent recovery from thermal annealing, Mr. Mayfield stated that, at this point in time, no hardness tests are planned.

The staff plans to use Charpy specimens in determining material recovery.

Mr. Mayfield noted that the higher the annealing temperature the more complete the material will recover from irradiation damage.

Mr.

Mayfield mentioned that t' - upper limit of the annealing temperature may be determined by ble adjacent and connecting systems damage

' ling temperature being greater than the caused by the operating temperath u.

Mr. Mayfield stated that the need for a thermal annealing rule and regulatory guide was, in part, highlighted when Yankee Rowe proposed thermal annealing of its RPV.

Appendix G requirements on thermal annealing was inadequate.

Mr. Mayfield stated that the application for thermal annealing is subject to the approval by the Director, NRR, and must be submitted three years prior to RPV anneal. The annealing ef fectiveness must be certified before plant operation.

The contents of the thermal annealing application consist of three

parts,

1) thermal annealing operating plan,

2) requalification inspection and test program, and 3) fractare toughness recovery and re-embrittlement rate assurance program.

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. MINUTES August 16, 1993 j

Materials & Metallurgy Mr. Mayfield described draft Regulatory Guide (DG)-1027, " Format and Content of Application for Approval for Thermal Annealing of Reactor Pressure Vessels,"

The guide (1) provides guidance on 6

format and content of application for thermal. annealing-(2) describes the criteria that the NRC staff will use in evaluat-ing annealing applications, and (3) elaborates the provisions of the thermal annealing rule.

In response to a question by Dr. Shewmon on materials for the surveillance program, Mr. Muyfield mentioned that samples can be taken from the inside surface of the RPV at the beltline region.

These samples can then be fabricated into subsize or reconstituted Charpy specimen.

Welding performed on the reconstituted Charpy specimen has been shown not to change the embrittlement state.

In a reply to a question by Dr. Seale regarding the owners of Yankee Rowe nuclear power plant having a different approach or a different decision if the proposed rule had been available to them, Mr.

Mayfield stated that its dif ficult to guess the outcome--but Yankee Rowe had some other specific plant considerations, not relating to RPV thermal annealing, that may have driven their decision.

In response to a question by Dr. Shewmon on the allowable piping strain in the connected piping system, Mr. Mayfield stated that the rule or guide does not provide an allowable value of strain--but did say that the piping system will be within the applicable ASME code limits.

It was mentioned by Mr. Mayfield that the piping connected to the RPV may have to be cut or disconnected in order to stay within the code limits.

Mr. Shao mentioned that in the Russian RPV design, the piping system is connected to the RPV a large distance away from the heated beltline, so that during the RPV annealing operation performed on the Russian RPV, the strain in the connected piping system is not significantly affected.

t Dr. Shewmon, mentioned that the Russians uses hardness tests to monitor the amount of recovery the RPV experience after annealing and that the staff uses Charpy specimens exclusively.

In response to Dr. Shewmon's comments on hardness test used by the Russians, Mr. Mayfield stated that their correlations indicate that the Charpy tests with all its drawbacks results in a better measurement for irradiation embrittleness recovery--while the hardness test methodology introduces more variability in the fracture toughness results.

Dr. Shewmon noted that Westinghouse, about 10 years ago, did perform n annealing study that used hardness measurements to determine irradiation embrittlement recovery, and asked what was the correlation between hardness, and Charpy energy?

Mr.

W.

Corwin, ORNL, replied that there is a fair degree of correnpon-dence, in general, between shifts in hardness and shifts in Charpy.

The concern according to Mr. Corwin, is to quantify the relation-ship with the relatively small number of data sets available on annealed material.

Further, Dr. Shewmon was concerned about the j

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correspondence between the results obtained from subsize Charpy specimens to results obtained from full size ASTM standard Charpy specimen and then relating the result to fracture toughness.

Mr.

Corwin mentioned that a standard for testing subsize Charpy specimen needs to be developed by ASTM.

Mr. Mayfield stated that he understands Dr. Shewmon's interest in hardness versus Charpy tests, but noted that the staff is focussed on measures of RTNTD that stems from Charpy specimen testing, and that rather than introducing a new parameter, hardness, in the regulation, the staff feels that it is better to stay with the Charpy test specimen methodology with all of its uncertainties.

In reply to a question by Dr. Shewmon, Mr. Mayfield stated that when specimens are taken from inside the RPV, the RPV will not be recladded--although analysis must be performed to satisfy Section III of the ASME Code.

In reply to a question by Dr.

Shack on the contents of the annealing data base, the staff stated that they will provide a reply later.

Dr. Seale asked if the staff plans to obtain Yankee Rowe nuclear power plant RPV material and perform thermal annealing studies to decernine the adequacy of the proposed rule and draft guide.

Mr. Mayfield stated that officially the proposal is being considered, but believes that there is no intent to use Yankee Rowe RPV for any tests.

In reply to a question by Dr. Seale on industry interest about annealing.

Mr.

Mayfield stated that a recent meeting at Westinghouse discussed a RPV thermal annealing demon-stration program that may be funded by ASME.

In response to a question by Dr. Shack, Mr. Strosnider stated that 3 or 4 plants may have RT problems which may give rise to PTS screening limit NDT problems.

A list of these plants will be sent to Dr. Shack.

Closina Comments The staf f has requested that the ACRS endorse the propose revisions to the rule on fracture toughness requirements and the new rule and associated implementing regulatory guide on thermal annealing for public comments.

Public comments are due by the middle or late fall.

The public comment will be reconciled by the staff and the ACRS will have an opportunity to review the final package before it is published in final form.

t Mr. Seale thanked the staff for a well prepared presentation.

SUDC_QMMITTEE ACTION The subcommittee agreed to bring this matter for Committee consideration during the September 1993 full ACRS meeting.

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MINUTES August 16, 1993 Materials & Metallurgy FOLLOW-UP ITEMS The subsequent follow-up items were identified at-the meeting.

The staff will present to the Subcommittee updated copies of the draft Federal Register Notice for the proposed rules package, the draft thermal annealing regulatory guide, and i

regulatory analysis for each, before the September 1993 full ACRS Dr.

Shack requested information on the contents of the annealing data base used. to develop equation 1 of the draft regulatory guide.

Dr. Shack requested a list of nuclear power plants thLt may e

reach the pressurize thermal shock screening criteria before the plants end-of-life.

e Mr.

Strosnider will contact the ACRS cognizant engineer concerning the steam generator tube degradation and the alternate tube plugging criteria subcommittee meeting planned for late fall 1993.

REVIEW DOCUMENTS The following documents were the official review document that was discussed at the meeting.

Memorandum dated July 22, 1993, to J. Larkins, ACRS, from L.

Shao, RES,

Subject:

Request for ACRS Review of Proposed Rule and Draft Regulatory Guide, including the following enclosures:

1.

Amendments to 10 CFR 50.61, " Fracture Toughness Require-l ments for Protection Against Pressurized Thermal Shock Events,"

2.

Amendments to 10 CFR Part 50 Appendix G,

" Fracture r

Toughness Requirements,"

3.

Amendments to 10 CFR Part 50 Appendix H,

" Reactor Vessel Material Surveillance Program Requirements,"

4.

A proposed rule (10 CFR 50.66) a thermal annealing of the reactor pressure vessel (RPV), " Requirements for Thermal Annealing of the Reactor Pressure Vessel," and 4

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,s-MINUTES August 16, 1993 Materials & Metallurgy 5.

A draft regulatory guide (DG-1027), " Format and Content of Application for Approval for Thermal Annealing of Reactor Pressure Vessels."

ACTIONS. AGREEMENTS. AND COMMITMENTS The following actions, agreements, and commitments resulted from the meeting:

The Subcommittee decided that a briefing on this matter be heard by the full ACRS Committee during the September 1993 meeting The Subcommittee will have the opportunity to review this e

matter after the public comments have been reconciled by the staff and before it is published in final form.

NOTE:

Additional meeting details can be obtained from a transcript of this meeting available in the NRC Public Document Room, 2120 L Street, NW, Washington, DC 20006, (202) 634-3273, or can be purchased from Ann Riley and Associates, Ltd., 1612 K Street, NW, Suite 300, Washington, DC 20006, (202) 293-3950.

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