ML20058N422
| ML20058N422 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 12/14/1993 |
| From: | Simpkin T COMMONWEALTH EDISON CO. |
| To: | Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9312210397 | |
| Download: ML20058N422 (4) | |
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) Commonwrith Edison
( C 7 1400 Opus Place
( p/ Downers Grove. Hiinois 60515 December 14,1993 Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation l
U.S. Nuclear Regulatory Commission i
Attn:
Document Control Desk l
Subject:
Zion Nuclear Generating Station Unit 1& 2 l
Request for Exemption from 10 CFR 50.61, Fracture Toughness l
Requirments for Protection Against Pressurized Thermal Shock i
NRC Docket No. 50-295 and 50-304
References:
(a) September 1,1993 T. Simpkin letter to Dr. T. Murley (b) October 5,1993 T. Simpkin letter to Dr. T. Murley (c) December 3,1993 T. Simpkin letter to Dr. T. Murley
Dear Dr. Murley:
Pursuant to 10CFR50.12(a), Commonwealth Edison Company (CECO) requests an exemption for Zion Station from the requirements of 10CFR50.61 as it relates to the determination of certain material properties. Specifically,10CFR50.61(aX4) requires that the reference temperature for a reactor vessel material be determined in accordance with Paragraph NB-2331 of the ASME Code. An alternate methodology for determining the reference temperature has been proposed in References (a) through (c).
An exemption to the stated requirement of 10CFR50.61 is appropriate in that compliance is not necessary to achieve the underlying purpose of the rule, which is to ensure that reactor vessels in service are not susceptible to fracture as a result of pressurized thermal shock. The attachment to this letter provides a detailed justification for the exemption request in accordance with the guidelines established in CFR50.12(a).
4 details supporting the technical adequacy of the alternate methodology are provided si R-eferences (a) through (c).
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Dr. 'k'homas E. Murley December 14,1993 To the best of my knowledge and belief, the statements contained herein are true and correct. In some respects these statements are not based on my personal knowledge but upon information received from other CECO and contractor employees. Such information has been reviewed in accordance with company practice and I believe it to be reliable.
Please direct any questions you may have regarding this matter to this office.
Sincerely,
- b. ;
Y T.W. Simpkin Nuclear Licensing Administrator Attachments cc:
J.B. Martin, Regional Administrator - RIII C.Y. Shiraki, Project Manager - NRR J.D. Smith, Senior Resident Inspector - Zion Office of Nuclear Facility Safety - IDNS i
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1 ATTACHMENT JUSTIFICATION FOR EXEMPTION FROM 10CFR50.61 (a)(4)
DETERMINATION OF REFERENCE TEMPERATURE EXEMPTION:
Commonwealth Edison Company (CECO) requests an exemption from 10 CFR50.61 (a)(4) as it relates to the determination of the reference temperature for material used in reactor vessels. The stated section requires that the reference temperature be determined in accordance with Paragraph NB-2331 of the ASME code.
DISCUSSION:
10CFR 50.61(a)(4) requires that the initial reference temperature for nil ductility transition be determined in accordance with Paragraph NB-2331 of the ASME Code.
This methodology utilizes Charpy V-notch and drop-weight test data to establish the initial reference value for nil ductility transition temperature. Application of this methodology will result in the Zion vessels exceeding the PTS screening criteria prior to the expiration of the operating licensen. The limiting weld material would be the WF-70 material.
An alternative methodology to the provisions of 10CFR50.61 has been proposed with References (a) through (c). This alternative approach utilizes drop-weight test data and fracture mechanics to demonstrate that the actual reference temperature for weld material WF-70 is much lower than that predicted by the Code methodology. The alternative approach demonstrates that the Zion vessels will meet the PTS screening criteria for the duration of their operating licenses.
BASIS:
As discussed in the following sections, the requested exemption meets the three necessary criteria of 10CFR50.12(a)(1). In addition, there are special circumstances present which qualify for consideration for an exemption per the criteria established in 10 CFR 50.12(a)(2).
A.
Criteria for Granting Exemption is met per 10 CFR 50.12(a)(1):
1.
The requested exemption and the activity which would be allowed thereunder are authorized by law.
If the criteria established in 10 CFR 50.12(a) are satisfied, as they are in this case, and if no other prohibition oflaw exists to preclude the activities which would be authorized by the requested exemption, and there are no such prohibitions, the Commission is authorized by law to grant this exemption request.
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2.
The requested exemption will not present undue risk. to the public.
The proposed methodology utilizes drop-weight test data and fracture mechanics to demonstrate the non-brittle nature of the WF-70 weld material in the temperature range ofinterest. This approach is supported by actual material fracture toughness testing data. The material behavior demonstrated by the WF-70 test results is bounded by the ASME Code j
reference toughness curve.
l Additionally, flux reduction measures have been implemented to further i
limit the amount of radiation induced embrittlement experienced by the Zion vessels. The periodic removal and testing of the surveillance specimens will allow CECO to monitor the condition of the vessels, thus ensuring that brittle behavior is precluded during operation.
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3.
The requested exemption will not endanger the common defense and security The common defense and security are not in any way compromised by this exemption request. The proposed change does not alter the physical plant in any manner.
At least one of the special circumstances are present per 10 CFR 50.12(a)(2):
10CFR50.12(A)(2)(ii) indicates that an exemption would be warranted if application of tne regulation is not necessary to achieve the underlying purpose of the rule.
The PTS rule was adopted to ensure that operating reactors were adequately protected from pressurized thermal shock. This is accomplished through limitations on the amount of radiation-induced embrittlement to be tolerated. In the case of Zion Station, weld material WF-70 does not meet the PTS screening criteria using the methodology provided in the ASME Code. However, using the alternate methodology proposed by CECO which utilizes fracture mechanics, the limiting weld material will meet the pts screening criteria. Additionally, the material behavior of WF-70 more closely resembles the behavior predicted by the fracture mechanics approach. Thus, there is confidence that the Zion reactor vessels will not be susceptible to PTS for the duration of their operating license.
This achieves the underlying purpose of the rule without applying the provision of the rule which requires application of the methodology provided by the ASME Code.
Absent the requested exemption, Zion Station will either cease operation prematurely or be required to expend significant resources to demonstrate the non-brittle nature of the Zion vessels. This exem'ption request will allow the utilizution of a methodology which predW non-brittle behavior for the duration of the operating licenses.
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