ML20246G002

From kanterella
Jump to navigation Jump to search
Summary/Minutes of Joint ACRS Matls & Metallurgy/Structural Engineering Subcommittee 890323 Meeting in Bethesda,Md Re NRC Proposed Amend to PTS Rule, Fracture Toughness Requirements for Protection Against PTS Events
ML20246G002
Person / Time
Issue date: 04/10/1989
From:
Advisory Committee on Reactor Safeguards
To:
Advisory Committee on Reactor Safeguards
References
RTR-NUREG-CR-5320, RTR-REGGD-01.099, RTR-REGGD-1.099 ACRS-2631, NUDOCS 8905150163
Download: ML20246G002 (8)


Text

_ _ _ _ _ _ _ -

DMS-oS s t a

o gjgge

-q. -- -~-': m

[

~h CERTIFIED COPY 4-M / L-L DATE ISSUED:

April 10,1989

~,

SUMMARY

/ MINUTES OF THE JOINT ACRS MATERIALS AND METALLURGY /

STRUCTURAL ENGINEERING SUBCOMMITTEE MEETING March 23, 1989 Bethesda, MD The Joint ACRS Materials and Metallurgy / Structural Engineering n

Subcommittee met on March 23, 1989 at Bethesda, MD to review 1) the NRC staff's proposed amendment to the pressurized thermal shock (PTS) rule, " Fracture Toughness Requirements for Protection Against Pres-surized Thermal Shock Events," 10 CFR 50.61 and supporting documents, and 2) the ORNL report on " Impact of Radiation Embrittlement on Integrity'of Pressure Vessel Supports for two PWR Plants "

NUREG/CR-5320.

Item one review was initiated.by the subcommittee and

- Arlotto/Serpan of RES, while item 2 review was initiated by G. Bagchi,

[

NRR.and M. Mayfield, RES.

l Notice of the meeting was published in the Federal Register on l

March 7, 1989. The schedule of items covered in the meeting and a l

L list of handouts are kept with the office copy of the minutes. There l

were no written or oral statements received or presented from members of the public at the meeting.

E. G. Igne was Cognizant ACRS Staff member for the meeting.

$50I i

ppm,q l.

4 J

DESIGNATED ORIGIEAL N W e d '-

Certified By 8905150163 890410 h

PDR ACRS 2631 PDC

Minutes / Materials & Metallurgy /

2 y

a Structural Engineeing March 23, 1989 l

Principal Attendees ACRS P.- Shewmon, Chairman of the Materials and Metallurgy Subcommittee E. Siess, Chairman of the Structural Engineering Subcommittee R. Odette, ACRS cortultant.

.NRC R. Johnson J. Ma J. Richardson F. Cheny M. Mayfield E. Serpan G. Bagchi N. Randall A. Murphy D. Guzy S. Lee R. Bosnak J. O'Brien B. Elliot H. Graves R. Woods Others

.W. Corwin, ORNL W. Pennell, ORNL R. Gambel, NOVETECH W. Shack Argonne C. Pezze, Westinghouse T. Griesbach, EPRI G. Kammerdeiner, Westinghouse Owners Group G. Holman, LLNL J. Braverman, BNL K. Balkey, Westinghouse Highlights Pressurized Thermal Shock i

1.

N. Randall, RES, discussed the proposed amendment to the PTS rule 10 CFR 50.61. He stated that the objective of this action is to update +he formula given in the PTS rule for calculating the j

level.7 radiation embrittlement in reactor vessel belt lines.

The amendment is needed to reflect today's technology, to resolve a safety. issue for certain PWRs, and to make the PTS rule consistent with Regulatory guide 1.99, Revision 2, " Radiation Embrittlement of Reactor Vessel Materials," published in May

._____._._._m_______________.___m________

Minutes / Materials & Metallurgy /

3 Structural Engineeing March 23, 1989 1988.

Based on surveillance specimen test results, it shows that the present formula significantly underestimates the

. embrittlement for certain ranges of copper and nickel contents of theie materials.

The principal amendment to the PTS rule that is being proposed is the deletion of Equations 1 and 2 in paragraph (b)(2) of 50.61 and the substitution of new cumulative procedures for the quantity RT PTS (reference temperature, pressurized thermal shock). This quantity is compared to the screening criteria U

given in the rule, 300 F for circumferential welds and 270 F for all other belt line materials.

It was noted that the screening criteria is not being changed. The proposed amendment affects all licensees of operating PWRs and all applicants for a PWR operating license just as the PTS rule did.

In general, they will be required to repeat the submittals required by the original PTS rule after recalculating, using the new formula for RT PTS, the condition of their reactor vessel relative to the screening criterion. The change should not be a surprise to the industry because Generic Letter 88-11, which implemented Reg.

Guide 1.99, Rev. 2, called the licensees attention to the fact that the staff was considering this amendment to the PTS rule.

However, it was stated that the staff expects challenges to the decision not to revise the screening criterion.

Plants for which the PTS rule amendment will reduce the E0L RTPTS I

l Y

1 Minutes / Materials & Metallurgy /

4 c

Structural Engineeing March 23, 1989 are Palisades, Fort Calhoun, Calvert Cliff Unit #1, Kewanee, and Point Beach Unit 2.

Other plants were stated to reach their EOL RTPTS at a later date or will not reach the screening criteria dur~ing their design lifetime.

PGS noted that he was surprised the a plant End-0f-life fluence 2

of about 10E20 n/cm is licensable in the U.S.

2.

T. Griesbach, EPRI, discussed the industry perspective on changes to the PTS rule.

He stated that no new information exists to suggest.that the current PTS rule is inadequate, although, he admits that updating the fluence-embrittlement curve is a good idea. He also remarked that utilities are making long-range plans i.e., flux reductions, to comply with the current PTS rule and that if the NRC changes its rules frequently, it may be a disincentive for the industry to formulate long range plans.

This reasoning was suggested by the subcommittee to be flawed because the net effect of the proposed rule change is only the reordering of the plants with PTS concern i.e., the top 10 plants affected by the current PTS rule still remains the top 10 plants j

except that the order is changed.

Embrittlement of Reactor Pressure Vessel Supports 3.

J. Richardson, NRR, briefly discussed the generic issue of radiation embrittlement of pressure vessel supports. Recent data l

from the HFIR vessel surveillance program indicate a substantial

Minutes / Materials & Metallurgy /

5

=~

Structural Engin:eing L

March 23, 1989 radiation embrittlement rate effect at low irradiation temperatures, about 1200F, for A 212, 350, 105, 36 pressure vessel support materials and its corresponding welds. The

~

neutron fluxes and temperatures at PWR vessel supports are similar as those in the HFIR vessel and thus the embrittlement rate of these structures may be greater than anticipated.

An on-going ORNL study of two plants selected for the specific plant evaluation were Trojan and Turkey Point 3, both of which are PWR plants with vessel support located in a cavity between the reactor vessel and biological shield and situated about mid-height of the core. Many of current nuclear power plant vessel supports are not situated at mid-height of the core, have low stress fields and thus should either experience smaller transition temperature shifts or is not an obvious structural concern.

For instance, most BWR vessels are supported by a compressive skirt structure at the bottom of the vessel where the fluxes are low.

The concern over radiation embrittlement is that it increases the potential for propagation of existing flaws that might exist in i

the support structures i.e., in the embedded-in-concrete-beam structure a 4 inch diameter flame cut grout hole at the point of about the maximum bending stress. Calculations performed by ORNL and presented at the meeting by W. Pennell indicate that best-estimate critical flaw sizes, corresponding to 32 EFPY, is

Minutes / Materials & Metallurgy /

6 Structural Engineeing March'23, 1989 about 0.4 inches for one plant and about 0.2 inches for the other. These flaw sizes are small enough to be of concern.

Preliminary staff conclusion froi. the Trojan analysis indicate that large uncertainties in the analyses exists, especially in flaw size and fracture tour,hness design data.

Further work is therefore needed in order to conclusively evaluate the integrity of supports. There is no immediate concern because the faulted conditions evaluated are low probability events, there is no known mechanism for flaw growth during service (low operational stresses) and that previous staff analyses indicate that reactor vessel can be supported by the inlet and outlet piping without benefit of the support structure.

4.

J. O'Brien, RES, G. Holman, LLNL, and J. Ma, NRC, discussed the structural capacity and load evaluation for the Trojan RPV supports. All indicated that the supports could resist the maximum applied loads even when uncertainties are considered.

One of the major areas of uncertainties is the matter of concrete confinement.

If adequate confinement could be demonstrated, a i

significant increase in maximum end load would result. All agreed that the cavity liner makes a negligible contribution to the capacity of the support and all agreed that residual support capacity requires further study to arrive at a definitive conclusion.

?

Minutes / Materials & Metallurgy /

7 Structural Enginreing March 23, 1989 i

Generic Issue - 15 " Radiation Effects on Reactor Vessel Supports," has been up-graded to high priority ranking from low-priority ranking. This conclusion wn reached after

- reviewing the ORNL report NUREG/CR-5320.

R. Johnson, RES, is the

~

Task Project Manager. A task action plan is being formulated.

From the information received during the meeting, it was stated by the subcommittee that the safety significance and consequences was not addressed by the NRC staff. More embrittlement and structural analyses were suggested by the subcommittee, but these must be balanced by a safety need. The subcommittee would like to be kept informed of this matter.

5.

W. Shack, ANL, briefly presented results of the evaluatier. of neutron shield tank samples from the PWR Shippingport nuclear power plant.

Shippingport neutron shield tank is quite similar l

to HFIR in terms of material (A212 B), operating temperature (130F), although the flux rate is somewhat higher 3E19 n/cm2 as compared to HFIR, about 2E18.

Preliminary results indicate a 15 ft-lb shift in transition temperature. The data is consistent I

with high flux test reactor irradiation data, but lower than HFIR data.

Shifts for samples transverse to the rolling direction are similar to those observed in the rolling direction. The base metal properties are very poor, i.e., upper shelf energy of 30-39 ft-lb, although the welds are tough, i.e., greater than 70 ft-lb at room temperature.

L.

Minutes / Materials &' Metallurgy /

8 Structural Engineeing March 23, 1989 Subcommittee Action

'A subcommittee report on the above matters will be presented to the full committee at the April 1989 meeting. A committee report is l

planned for the proposed amendment to the PTS rule and radiation embrittlement of RPV support integrity.

' NOTE:

A transcript of the meeting is available at the NRC Public Document Room, Gelman Bldg. 2120 "L" Street, NW.,

-Washington, D.C.-Telephone (202) 634-3383 or can be purchased from Heritage Reporting Corporation, 1220 L i

Street, NW., Washington, D.C. 20005, Telephone (202) 628-4888.

I l

~_

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ - _ _ _ _ _ _ _ = - ~ - _ _ _ = _ _ - _ - _ - - -

_ _ _ _