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Proposed Rule

Nuclear Energy Institute; Receipt of Petition for Rulemaking

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Nuclear Regulatory Commission.


Petition for rulemaking; Notice of receipt.


The Nuclear Regulatory Commission (NRC) has received and requests public comment on a petition for rulemaking filed by the Nuclear Energy Institute. The petition was docketed on April 12, 2000, and has been assigned Docket No. PRM-50-71. The petitioner requests that the NRC amend its regulations to allow nuclear power plant licensees to use zirconium-based cladding materials other than zircaloy or ZIRLO, provided the cladding materials meet the requirements for fuel cladding performance and have received approval by the NRC staff. The petitioner believes the proposed amendment would improve the efficiency of the regulatory process by eliminating the need for individual licensees to obtain exemptions to use advanced cladding materials which have already been approved by the NRC.


Submit comments by August 14, 2000. Comments received after this date will be considered if it is practical to do so, but the Commission is able to assure consideration only for comments received on or before this date.


Mail comments to: Secretary, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, Attention: Rulemakings and Adjudications Staff. Start Printed Page 34600

Deliver comments to: 11555 Rockville Pike, Rockville, Maryland, between 7:30 a.m. and 4:15 p.m. on Federal workdays.

For a copy of the petition, write to David L. Meyer, Chief, Rules and Directives Branch, Division of Administrative Services, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.

The petition, this notice of receipt, and any comments received on the petition are available on the NRC's rulemaking website at This site also provides the capability to upload comments as files (any format), if your web browser supports that function. For information about the interactive rulemaking website, contact Ms. Carol Gallagher, (301) 415-5905 (

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David L. Meyer, Chief, Rules and Directives Branch, Division of Administrative Services, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, Telephone: 301-415-7162 or Toll Free: 1-800-368-5642 or email:

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The Petitioner

The petitioner is the Nuclear Energy Institute (NEI). NEI claims representational responsibility for establishing unified nuclear industry policy on matters affecting the nuclear energy industry, including regulatory aspects of generic operational and technical issues. NEI's members include all utilities licensed to operate commercial nuclear power plants in the United States, nuclear plant designers, major architect/engineering firms, fuel fabrication facilities, materials licensees, and other organizations and individuals involved in the nuclear energy industry.

The Petitioner's Request

The petitioner states that the NRC's current regulations require uranium oxide fuel pellets, used in commercial reactors, be contained in cladding material made of zircaloy or ZIRLO. The petitioner indicates that the requirement to use either of these materials is stated in 10 CFR 50.44 and 10 CFR 50.46.

The petitioner notes that subsequent to promulgation of these regulations, commercial fuel vendors have developed and continue to develop materials other than zircaloy or ZIRLO that NRC reviews and approves for use in commercial power reactors. Each of these approvals requires the NRC to grant an exemption to the license of the utility that requests use of fuel in these cladding materials. The petitioner requests that NRC amend its regulations to allow licensees discretion to use zirconium-based cladding materials other than zircaloy or ZIRLO, provided that the cladding materials meet the fuel cladding performance requirements and have been reviewed and approved by NRC staff.

Petitioner's Interest

The petitioner states that safe and reliable operation of nuclear power plants, including fuel performance is very important to its members, the country, and the international community. The petitioner states that the NRC regulates the use of radioactive materials and allows nuclear power plant licensees to use a variety of cladding materials once the material has been determined to have the required characteristics. The petitioner states that for the past nine years, NRC has permitted the use of cladding materials other than zircaloy or ZIRLO after approving a formal exemption request. The petitioner further notes there have been at least eight requests for exemptions during that time frame and each exemption costs in excess of $50,000. The petitioner states that the requests for exemption have become increasingly more frequent, causing significant administrative confusion and a potentially adverse affect on efficient and effective use of NRC, licensee, and vendor resources.

Justification for Petition

Sections A through D below contain the detailed discussion provided by the petitioner to support his request. The text contained in each of these sections reflects the petitioner's point of view word for word.

A. The Current Regulation Given the Diversity of Commercially Available Fuel Cladding Materials is too Narrow and Restrictive

The beneficial use of zirconium (Zr) has been recognized for many years. It has a very low neutron cross-section when separated from hafnium with which it is typically found in nature. It also has excellent corrosion resistance to oxidizing environments, such as steam and water. Certain impurities were found to decrease this corrosion resistance and early programs were established to develop alloys that produced more consistent corrosion resistance.

Primary additives were tin, as used initially in a variety of zirconium-based alloys commonly referred to as zircaloy, and niobium (Nb) favored in Canada and Russia.

Beginning in approximately the mid-1980's, nuclear fuel vendors began developing new alloy variations to improve cladding corrosion resistance in support of higher burnup fuel management strategies. The new alloy variants were initially within the ASTM [American Society for Testing and Materials] specifications for existing zirconium-based cladding. As fuel cycle burnups were projected to increase further, additional alloys were developed, some of which involved formulations outside the ASTM specifications for existing cladding material.

The tin (Sn) additive-based alloys were generally favored in the U.S. and were successfully developed in both BWR [boiling water reactor] and PWR [pressurized water reactor] reactors. Early Zr-Sn alloys tended to use relatively high tin concentrations until long term corrosion tests showed that there was an increase in the corrosion rate as a function of time. Subsequent developments of the alloy, currently defined as Zircaloy-2 and Zircaloy-4, limited tin concentration to between 1.2 percent and 1.7 percent. Most of the early zircaloy compositions were at a nominal 1.5 percent Sn. Subsequent testing of the alloy in high rated PWR plants has shown that the lower tin concentrations provide even better performance. Current zircaloy compositions tend to focus on a mean Sn composition of about 1.3 percent. That value has been established by producers to minimize the risk of manufacturing a product below the ASTM specified range. However, there is significant data to show that lower Sn compositions would provide even better corrosion resistance.

Excellent corrosion performance has also been achieved with the niobium additive-based alloys; however, these appear to be more sensitive to the coolant composition. For example, the corrosion resistance is superior to the tin additive-based alloy under PWR environments but tends to suffer from nodular-type oxidation under BWR conditions. The alloy is much less temperature sensitive and the oxide thickness is generally less than that of the corresponding corrosion layer on zircaloy irradiated under identical conditions. The optimum niobium content is probably about one percent, or such as is found in M5 or ZIRLO cladding alloys.

The major variant on the Zr-Sn and Zr-Nb systems is the Zr-Sn-Nb system developed in the US as ZIRLO and in Russia as E635. Start Printed Page 34601

As a result of these development programs, cladding materials now available include zircaloy, ZIRLO, Alloy A, M5, and Duplex. All of these alloys are zirconium-based. Since zircaloy and ZIRLO are currently the only cladding materials provided for in the regulations, utilities must obtain an exemption from the applicable regulatory requirements to use these other cladding materials. Exemption requests will become more frequent as use of new cladding materials becomes more prevalent. Once a specific cladding material is approved for use by NRC, the subsequent exemption requests do not increase safety or confidence in the performance of the cladding. They are strictly an administrative process necessitated by the restrictive language of the current regulations.

The rule should be modified to address the currently available alloys as well as those that may be developed in the future.

B. A More General Description of Cladding Material Facilitates Technical Improvements

Currently, a licensee desiring to use fuel with cladding materials other than zircaloy or ZIRLO must obtain NRC approval through an exemption request. The time delay in obtaining approval as well as expenses incurred in preparing exemption requests might cause some licensees to defer adopting new cladding materials despite performance advantages to be gained. The proposed amendments would permit use of improved cladding materials without expending NRC, licensee, and vendor resources to develop, review, and approve exemption requests for cladding materials that fully meet NRC performance requirements.

Since the current industry interest focuses on cladding materials for which the performance criteria in § 50.46(b) remain applicable, a new § 50.46(e) is proposed that provides a clear tie between the approved cladding material alloy mentioned in §§ 50.44 and 50.46 with the criteria noted in § 50.46(b).

Similarly, to facilitate technical innovation, the NRC staff often encourages licensees and vendors to conduct Lead Test Assembly (LTA) Programs to demonstrate the performance of the new fuel assembly materials. It has been the past practice of the NRC not to require licensees to obtain approval of the LTA Program before placing the LTAs in the reactor. It is not the intent of industry to change that practice by making reference to approved cylindrical zirconium-based alloys in §§ 50.44 and 50.46.

C. The Regulation as Applied to Nuclear Power Plant Fuel Loading Incurs Unwarranted Implementation Costs

The implication of the current rule language that only the use of zircaloy or ZIRLO clad fuel is appropriate requires utilities to request, and NRC to approve, exemptions to use other cladding materials. Each exemption request is estimated to cost approximately $50,000, exclusive of NRC's cost. It is also estimated that the proposed change to the regulations could avoid at least thirty exemption requests over the next 8 to 9 years.

D. The Proposed Amendment Allows the Use of Alternative Materials That Meet the Cladding Performance Requirements

The existing regulations address only zircaloy and ZIRLO cladding materials. The regulation needs to be generalized to avoid unnecessary burdens on the developers of new cladding alloys and utilities who will use those alloys. The language of this proposed amendment will encompass all zirconium-based cladding material for which the ECCS performance criteria of § 50.46(b) are applicable.

The proposed wording does not eliminate current NRC practices regarding review and approval of new cladding materials brought forward by fuel vendors. It does permit the NRC regulation to be more efficiently applied to those cladding materials demonstrated to meet the acceptance criteria of §§ 50.46(b)(1) and (b)(2).

Experience has shown that qualification of an acceptable material can only be achieved by testing. An applicant must perform high-temperature oxidation and quenching tests of the cladding material to demonstrate that the 2200-degrees F peak cladding temperature and 17 percent oxidation limits protect the cladding against embrittlement and prevent the oxidation from becoming autocatalytic. This is demonstrated by heating the cladding to various high temperatures for a variety of time periods and quickly quenching the cladding in a cold water bath.

These tests must demonstrate that failure did not occur until beyond the temperature limits and that no autocatalytic oxidation was observed. As long as the tests confirm that the 2200-degrees F and 17 percent oxidation are conservative for the cladding material, then the material design is acceptable for LOCA [loss-of-coolant accident] licensing analyses up to currently approved burn up limits.

Providing a new more general description of the fuel cladding is consistent with the NRC movement toward a performance-based, rather than prescriptive, regulatory philosophy.


The petitioner believes the foregoing reasons support why NRC should amend §§ 50.44 and 50.46, as stated above, to allow the use of other zirconium-based alloys in addition to those specified in the current regulation.

The petitioner recognizes that the stated goal of the existing regulations is to ensure adequate coolability for reactor fuel in case of a design-basis accident. However, the petitioner asserts that the proposed amendment does not degrade the ability to meet that goal. Rather, it removes an unwarranted licensing burden without increasing risk to public health and safety.

Proposed Amendments

According to the petitioner, the proposed amendments would continue to allow nuclear power plant licensees the discretion to use zircaloy or ZIRLO cladding to encase the uranium dioxide fuel pellets. The proposed amendments also would allow nuclear power plant licensees to use other cladding materials with material properties that meet accepted requirements for fuel cladding performance. The petitioner identifies the proposed amendments as follows:

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1. Section 50.44, paragraphs (a), (b), and (c)(1) are revised to read as follows:

Standards for combustible gas control system in light-water-cooled nuclear power reactors.

(a) Each boiling or pressurized light-water nuclear power reactor fueled with oxide pellets within approved cylindrical zirconium-based alloy cladding, must . . .

(b) Each boiling or pressurized light-water nuclear power reactor fueled with oxide pellets within approved cylindrical zirconium-based alloy cladding must . . .

(c)(1) For each boiling or pressurized light-water nuclear power reactor fueled with oxide pellets within approved cylindrical zirconium-based alloy cladding, it must be shown that . . .

2. Section 50.46(a)(1)(i) is revised to read as follows:

Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors.

(a)(1)(i) Each boiling or pressurized light-water nuclear power reactor fueled with uranium oxide pellets within approved cylindrical zirconium-based alloy cladding must be provided with an Start Printed Page 34602emergency core cooling system (ECCS) that must be designed so that its calculated cooling performance following postulated loss-of-coolant accidents conforms to the criteria set forth in paragraph (b) of this section. . . .

3. In Section 50.46, a new paragraph (e) is added to read as follows:

(e) Approved cylindrical zirconium-based alloys are those whose performance has been evaluated and determined by the NRC to conform to the acceptance criteria of paragraphs § 50.46(b)(1) and (b)(2).

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Dated at Rockville, Maryland this 24th day of May, 2000.

For the Nuclear Regulatory Commission.

Annette L. Vietti-Cook,

Secretary of the Commission.

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[FR Doc. 00-13515 Filed 5-30-00; 8:45 am]