ML20205B037

Notation Vote Approving SECY-98-289 Re Proposed Amends to 10CFR21,50 & 54 Concerning Use of Alternative Source Terms at Operating Reactors

ML20205B037
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Issue date:	02/25/1999
From:	Vietticook A NRC OFFICE OF THE SECRETARY (SECY)
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References
FRN-64FR12117, RULE-PR-21, RULE-PR-50, RULE-PR-54 AG12-1-021, AG12-1-21, SECY-98-289-C, NUDOCS 9903310133
Download: ML20205B037 (26)

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I hk Pbrt February 25,1999 COMMISSION VOTING RECORD DECISION ITEM: SECY-98-289 TITLE: PROPOSED AMENDMENTS TO 10 CFR PARTS 21,50, AND 54 REGARDING USE OF ALTERNATIVE SOURCE TERMS AT OPERATING REACTORS The Commission (with all Commissioners agreeing) approved the subject paper as recorded in the Staff Requirements Memorandum (SRM) of February 25,1999.

This Record contains a summary of voting on this matter together with the individual vote sheets, views and comments of the Commissioners, and the SRM of February 25, j 1999.

i

-M Annette Vietti-Cook Secretary of the Commission Attachments:

1. Voting Summary

2. Commissioner Vote Sheets

3. Final SRM cc: Chairman Jackson Commissioner Dicus Commissioner Diaz i Commissioner McGaffigan Commissioner Merrifield OGC EDO PDR DCS 9903310133 990325 S?l

s .

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VOTING

SUMMARY

- SECY-98-289 RECORDED VOTES NOT APRVD DISAPRVD ABSTAIN PARTICIP COMMENTS DATE CHRM. JACKSON X 1/29/99 COMR. DICUS X X 12/29/98 COMR. DIAZ X X 1/20/99 COMR. McGAFFIGAN X X 2/1/99 COMR. MERRIFIELD X X 1/7/99 COMMENT RESOLUTION in their vote sheets, all Commissioners approved the staff's recommendation and some provided additional comments. Subsequently, the comments of the Commission were incorporated into the guidance to staff as reflected in the SRM issued on February 25, 1999.

.i .L Commissioner Comments on SECY Commissioner Dicus' Comments on SECY-98-289 i approve the notice of proposed rulemaking for publication and certify that the rule should not have a negative economic impact on a substantial number of small entities.

SECY-98-289 states that "No Agreement State implementation problems are expected.,,"

because the rulemaking is specific to NRC licensed nuclear power plants. Staff should be aware, however, that should a licensee use the alternate source terms offsite emergency planning officials in both Agreement and Non-Agreement states may have questions regarding any impact of the alternative approach on their planning activities.

Commissioner Diaz' Comments on SECY-98-289 I approve the staff recommendation to publish the notice of proposed rulemaking for a 75-day public comment period.

I encourage the staff to continue working with industry and complete the pilot initiatives on an expedited basis. The experience gained from the pilots can then be used in developing the associated regulatory guide and standard review plan that should be part of the final rulemaking package to be submitted to the Commission by July 30,1999.

Commissioner McGaffiaan's Comments on SECY-98-289 I approve the notice of proposed rulemaking. I commend the staff for their work thus far on this rulemaking which has the potential to improve plant safety, reduce occupational exposure by plant workers, and reduce unnecessary burdens on licensees.

There is one issue, however, that needs to be clarified. Both Commissioner Dieus and Commissioner Merrifield have raised it. Commissioner Dicus has warned that the NRC staff should be prepared to address the concems of planning officials in both Agreement and Non-

. Agreement States with respect to potentialimpacts of this rulemaking on emergency planning,'

and Commissioner Merrifield has cited the history leading to this proposed rule, namely that it is not intended for relief from emergency planning requirements under 10 CFR 50.47, and has stated that the staff should not take any action on requests to use revised source terms to change emergency planning requirements without first seeking approval from the Commission.

I agree with both Commissioner Dicus and Commissioner Merrifield, but I would go a step further and take care of both their concerns simply by adding a sentence (attached) to the proposed 10 CFR 50.67(a) that would bar use o. revised source terms to seek relief from emergency planning requirements. The added sentence makes it possible to avoid dealing case-by-case with requests for such relief. I would also add to the statement of considerations language (attached) that would provide a basis for the bar but also leave the door open to its future removal by separate rulemaking devoted to that purpose. If the staff so chooses, it can, at a later date, make a recommendation to the Commission on whether, and how, to use revised source terms in emergency planning.

E . . .

, l I am also proposing som, . additions to the draft press release, to provide more emphasis to our expectation that revised source terms could improve overall safety.

( Insert for Pace 19 L

The paragraph also bars, for the time being, the use of revised source terms to seek relief from emergency planning requirements. Given the numerous other external factors associated with emergency planning requirements, the decision on a request for such relief would necessarily need to be made on a host of other issues besides the issue of revised source terms. The Commission may, at a later date, consider how to use revised source terms in reexamining emergency planning requirements.

Insert for Pace 35 l The revised source term shall not be used to justify any reduction in emergency planning 3 l requirements under 50.47(b).

Commissioner Merrifield's Comments on SECY-98-289 l In the regulatory analysis, the staff indicated that there is a high level of industry interest in the proposed rule. The staff also indicated that numerous related applications were anticipated for  ;

such things as changes in allowable containment and ECCS leak rates and changes in isolation  !

valve actuation timing. In light of this potentialincrease in licensing activity, in its final rulemaking package, the staff should provide the Commission with additionalinformation regarding the anticipated agency resource implications, the priority given to license amendments related to a revised source term, and the anticipated impact the additional licensing workload will have on NRR's licensing action backlog reduction efforts.

In its rulemaking plan for implementation of a revised source term at operating reactors dated June 30,1998 (SECY-98-158) and in a paper to the Commission dated September 6,1994, l the staff stated that this rulemaking would not consider applications of the revised source term that seek relief from emergency planning requirements under 10 CFR 50.47. While some may wish to conclude from this decision that in the future the Commission would support changes in emergency planning requirements based on a revised source term, I do not believe that this decision is dispositive of how the Commission would act on a request of that nature. Indeed,

given the numerous other external factors associated with emergency planning requirements, I

such a decision would necessarily need to be made on a host of other issues besides the issue of a revised source term. Therefore, to repeat the obvious, the staff should not take any action on such future requests to change emergency planning requirements without first seeking approval of the Commission.

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DRAFT Environmental Assessment PROPOSED REVISION OF 10 CFR PARTS 21,50, and 54 Use of Altemative Sources Terms at Operating Reactors

[SECY-98-289, approved February 25,1999)

S.F. LaVie, NRR/DIPM/PERB

DRAFT ENVIRONMENTAL ASSESSMENT REVISION OF 10 CFR PARTS 21,50, AND 54 The Nuclear Regulatory Commission (NRC) is proposing to amend its regulations to allow the holders of operating licenses at currently operating reactors to voluntarily amend their l design bases to replace the current accident source term with a revised source term from i NUREG 1465, Accident Source Terms for Light-Water Nuclear Power Plants. l Identification of Action The NRC is proposing to amend 10 CFR Part 50 by adding a new section,650.67, to addres.i the use_of altemative accident source terms. Section 50.67 would apply to all holders of opr, rating licenses issued before January 10,1997, that seek to amend their facility design basi', to replace the current accident source term with an alternative source term on or after the publication date of the final regulation. These licensees would be required by 650.67 to  ;

evaluate the radiological consequences of the design basis accidents previously analyzed in the -

safety analysis report, and to request a license amendment under 650.90. Acceptance criteria

. for the accident radiological consequence analyses appear in 650.67. These criteria are accident dose guidelines for evaluation of releases of radioactivity to the environment and the resulting exposures to persons offsite, and dose criteria for plant personnel occupying the  !

control room during postulated accidents.

The proposed rule amends a current regulation by establishing alternate iequirements that ,

licensees may voluntarily adopt. The NRC concluded that the existing analytical approach I based on the current source term continues to be adequate to protect public health and safety; therefore, the NRC does not intend to backfit the altemative source terms or the changes in accident dose guidelines and control room habitability criteria on operating power reactors.

Because the proposed revision to the regulation would not constitute a backfit, the bases for existing nuclear power plants must be preserved. For this reason, the current accident dose guidelines in $100.11 and the current control room habitability criteria of Appendix A to 10 CFR Part 50 would remain in effect for those licensees that do not apply for the use of an attemate source term.

The NRC is also proposing to amend 10 CFR Part 50 by revising 10 CFR Part 50, Appendix A, GDC-19 to use a dose criterion based on total effective dose equivalent. The revised criterion, which would be an alternative to the current doso criterion in GDC-19, is applicable only to applicants for construction permits under this part, or applicants for a design certification or combined license under 10 CFR Part 52, that apply on or after January 10,1997, or holders of operating licenses using an alternative source term.

Need for the Action Usg of Altamative Source Terms Current operating light-water reactors were licensed, in part, on the basis of safety analyses that used fission product release assumptions presented in the Technical Information Docu-ment (TID) 14844, Calculation of Distance Factors for Power and Test Reactor Sites (1962).

Although initially applied to the evaluation of proposed reactor sites, these fission product release assumptions, known collectively as the " source term," have been used in several regulatory applications related to light-water reactors. This source term was a key input to many of the design analyses associated with currently operating reactors and is a significant EA-1

l l component of the design basis for these facilities. During the period since the publication of l

TID-14844, significant advances have been made in understanding the timing, magnitude, physical form, and chemical form of fission product releases from severe nuclear power plant accidents, in 1995, the NRC published NUREG-1465, Accident Source Terms for L/ght-Water Nuclear Power Plants, which utilized these source term insights to produce revised estimates of the accident source term. These source terms are described in terms of radionuclide compo-sition and magnitude, physical and chemical form, and timing of release. For design basis accident assessments, the NUREG-1465 source terms are comparable to the TID-14844 source term with regard to the magnitude of the noble gas and radioiodine release fractions.

However, the revised source terms provide a more representative description of the radionuclide composition and release timing.

The objective of NUREG-1465 was to define revised accident source terms for regulatory application for future light water reactors. The NRC's intent was to capture the major relevant i insights available from severe accident research to provide, for regulatory purposes, a more realistic portrayal of the amount of the postulated accident source term. These source terms were derived from examination of a set of severe accident sequences for light water reactors of current design. Because of general similarities in plant and core design parameters, these results are considered to be applicable to evolutionary and passive LWR designs. The NRC considered the applicability of the revised source terms to operating reactors and determined that the current analytical approach based on the TID-14844 source term would continue to be adequate to protect public health and safety and that operating reactors licensed under this approach would not be required to reanalyze design basis accidents using the revised source terms. The NRC also concluded that some licensees may wish to use alternative source terms in analyses to support operational flexibility and cost-beneficiallicensing actions. These actions could reduce unnecessary regulatory burden.

In January 1997, the NRC amended its regulations in 10 CFR Parts 21,50,52,54, and 100 (61 FR 65157). That regulatory action provided siting criteria f >r future sites and relocated source term and dose requirements for future plants into Part M. Because these dose require-ments tend to affect reactor design rather than siting, they are n ore appropriately located in Part 50. Because the revised criteria would not apply to operating reactors, the non-seismic and seismic reactor site criteria for operating reactors were retainei as Subpart A and Appendix A to Part 100, respectively. The revised reactor site criteria were aided at Subpart B in Part 100, and revised source term and dose requiremedts were relocated 'o 950.34. The existing source term and dose requirements of Subpart A of Part 100 would remain in place as the licensing bases for those operating reactors that do not elect to use an altemative source term.

The NRC retained the requirements for the exclusion area and the low population zone, but revised the associated numerical dose guidelines to replace the two differeni doses for the whole body and the thyroid gland with a single, total effective dose equivalent (TEDE) value.

The dose guidelines for the whole body and thyroid, and for the immediate 2-hour exposure period, were largely predicated by the assumed source term being predominantly noble gases

- and radioiodines instantaneously released to the containment and the assumed " single critical organ" method of modeling the intemal dose used at the time that Part 100 was originally published. However, the current dose guidelines, by focusing on doses to the thyroid and wnole body, assume that the major contributor to doses would be radiolodine. Although this may be appropriate with the TID-14844 source term, it may not be true for a source term based on a more complete understanding of accident sequences and phenomenology. The l postulated chemical and physical forms of radioiodine in the revised source terms are more amenable to mitigation and, as such, radiolodine may not always be the predominant radionuclide in an accident release. The revised source terms include a larger number of EA-2

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1 radionuclides than did the TID-14844 source term as implemented in regulatory guidance. The i whole body and thyroid dose guidelines ignore these contributors to dose. The TEDE, using a ,

l risk-consistent methodology, assesses the impact of all relevant nuclides upon all body organs. I l

Although it is expected that,-in many cases, the thyroid could still be the limiting organ and radiolodine the limiting radionuclide, this conclusion cannot be assured in all potential cases.

The revised source terms postulate that the core inventory is released in a sequence of phases over several hours, with the more significant release commencing at about 30 minutes from the start of the event. The assumption that the 2-hour exposure period starts immediately at the onset of the release is inconsistent with the phased release postulated in the revised l source terms. A detailed rationale for the use of 0.25 Sv (25 rem) TEDE as an accident dose j guideline and the use of the 2-hour exposure period resulting in the maximum dose for future '

light water reactors (LWRs) is provided at 61 FR 65157. The considerations that formed the l basis for that rationale are also applicable to operating reactors that elect to use the revised source term. The NRC believes that it is technically appropriate and logical to extend the dose guidelines, established for future LWRs using the revised source term to operating reactors that elect to use the same revised source term.

The NRC determined that, for use with the revised source terms, accident dose guidelines and control room habitability should be expressed in terms of TEDE, and that the 2-hour exposure period should be based on the 2-hour period that yields the maximum dose. The proposed 850.67 incorporates these acceptance criteria.

Conforming Change to GDC-19 The proposed change to GDC-19 is not related to the use of alternative source terms at operating reactors but is included to address a deficiency identified in the regulatory framework for early site permits, standard design certifications, and combined licenses under Part 52.

Sections 52.18,52.48, and 52.81 establish that applications filed under Part 52 Subparts A, B, and C, fespectively, would be reviewed according to the standards given in 10 CFR Parts 20, 50,51,55,73, and 100 to the extent that those standards are technically relevant to the proposed design. Therefore, GDC-19 is pertinent to applications under Part 52. The recent Part 100 rulemaking (61 FR 65157) established accident TEDE guidelines (in 950.34) for applicants under Part 52, but did not establish a revised control room dose criterion. Therefore, exemptions from the dose criterion in the current GDC-19 were necessary in the design certification process for the Westinghouse AP-600 advanced light water reactor in order to use the 0.05 Sv (5 rem) TEDE criterion deemed necessary for use with the revised source terms. '

The proposed change would eliminate the need for exemptions by future applicants under Part

52. The proposed change would also be applicable to future applications under Part 50 that are filed on or after January 10,1997.

EnvironmentalImpacts of the Action The implementation of an altemative source term at an operating power reactor would replace the traditional TID-14844 source term with a source term that would be based on the insights gained from extensive accident research activities. The actual accident sequence and progression are not changed; it is the regulatory assumptions regarding the accident that would be affected by substituting an attemative source term. Use of an attemative source term alone cannot increase the core damage frequency (CDF) or the large early release frequency (LERF) or actual offsite or onsite radiation doses. (Although actualdoses would not increase, analysis results may show an increase in some postulated doses because additional radionuclides would be considered and dose modeling would be more comprehensive.) The source term is EA-3

used in analyses performed to assess the adequacy of the plant design to contend with a .

design basis accident (DBA) in order to ensure adequate defense in depth and adequate safety -l margins. The attemative source term could be used to justify changes in the plant design that j cocid have an impact on CDF or LERF or that could increase offsite or onsite doses. These

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potential changes are subject to existing requirements in the NRC's regulations. Thus, the level  !

of protection of public nealth and safety provided by the NRC's regulations would not be I decreased by this proposed rulemaking.

The Commission directed the NRC staff to assess the impacts of implementing the revised source term at operating reactors. The results of this study were presented to the Commission in SECY-96-154, Results of the Revised (NUREG-1465) Source Term Re-Baselining for Operating Asactors. The major areas examined included the effect on individual offsite and control rcam dose, the effect on doses used in equipment environmental qualification, and the effect of pctential modifications that m!ght be enabled by the revised source term. The study also assessed the margin afforded by the revised source term in comparison to assessments performed using the integrated severe accident assessment code, MELCOR. The study indicated that the impact of implementing the revised source term at operating reactors would produce lower postulated doses in the majority of cases. The NRC intends to address the exceptions in the regulatory guidance that will be developed to support the proposed rule and in the processing of the individuallicense amendments. The best estimate MELCOR analyses indicaed that the design basis dose calculailens using the revised source terms still have a substantial margin (a factor of two or greater). The study also indicated that many of the plant systems that are likely to be considered for modification are not involved in risk significant sequences and are, therefore, not likely to have a substantial offsite risk impact using a measure such as LERF.

There is an expectation that many of the attemative source term applications may provide concomitant improvements in overall safety and in reduced occupational exposure, as well as economic benefits. In light of the wide range of possible applications and the voluntary natu,e of this proposed rule, it is not reasonable to quantify possible outcomes. Occupational exposures may be reduced through reductions in maintenance efforts associated with maintaining unnecessarily limiting leakage, timing, or filtration requirements. Overall safety may be improved through (1) reduced emergency diesel generator loading, (2) improved contain-ment ventilation system performance due to removal of filter media, and (3) closer synchro 11zation of accident mitigation feature actuation with the onset of major fission product release. There may be improvements in safety margins realized due to the upgrading of analysis assumptions, methods, and acceptance criteria.

The radiological consequences of DBAs would not be increased by the use of the revised source term. The proposed dose guidelines are comparable, in level of protection, to the existing guidelines. The proposed rule would not affect non-radiological plant effluents and would have no other environmental impact. Therefore, the NRC concludes that there would be no significant non-radiological environmental impacts associated with the amendments to the regulations.

Alternatives to the Action As required by Section 102(2)(E) of National Environmental Policy Act (NEPA) (42 U.S.C.A.

4332(2)(E)), the NRC staff has considered possible altematives to the proposed action. Most of the attematives considered were related to administrative details such as location of the proposed rule and the means of providing regulatory guidance. These altematives are neutral with regard to environmental impact and wN not be considered further. With regard to EA-4

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. I environmental impacts, the alternatives can be reduced to (1) retain the existing accident source term i.e., the no-action attemative, and (2) allow the use of the revised source term.

The first altemative considered by the NRC was to retain the existing accident source term, i.e., the no-action attemative. This was not considered to be an acceptable altemative, because it would preclude the use of an altemative source term by operating reactors and the .

potential reductions in regulatory burden. This rulemaking alternative would also preclude potential concomitant improvements in overall safety and in reduced occupational exposure. ]

The environmentalimpact of a postulated DBA would be unchanged. The foreclosure of potential concomitant improvements could prevent some actions that could reduce the risk t and/or consequences of accidents. Because it is not possible to predict the source term applications that may voluntarily be proposed by license with any degree of certainty, this aspect is not evaluated further.

The second attemative considered by the NRC was to allow the voluntary use of the revised source term at operating plants, including the use of dose guidelines and dose criteria consistent with the characteristics of the raised source term. This attemative would establish the requirements for use of an attematives source term in a new section to Part 50 while retaining the existing tegulations in 10 CFR Part 100 Subpart A and GDC-19. The proposed approach was chosen as the best rulemaking attemative. It is believed that the proposed rule would result in an improvement in the allocation of resources both for the NRC and for industry.

The iridustry would be allowed to propose applications of an altemative source term that could reduce unnecessary or ineffective requirements in the facility design basis. The NRC and the industry stand to gain from having appropriate regulatory requirements and guidance needed to facilitate preparation and NRC staff review of licensee submittals. Limited resources could be diverted to safety issues of greater significance. The environmentalimpacts of the proposed use of the revised source term were addressed earlier in this assessment and it was concluded that there would be no significant environmental impact. Given the conclusion of no significant impact and the economic benefits that could be achieved, this attemative is clearly superior to the no-action altemative.

Alternative Use of Resources No altemative use of resources was considered. The proposed rule would apply only to existing operating reactors and the use of an altemative source term for analysis purposes has no impact on the use of resources. Although this rule also makes conforming changes related to future plant licensing, the environmental impact of the future plant licensing would, by regulation, be assessed as part of the plant licensing.

Agencies and Persons Consulted The NRC staff developed the proposed rule and this environmental assessment. No outside agencies or consultants were used in developing this assessment. The NRC staff i obtained advice from the NRC Advisory Committee on Reactor Safeguards.

Conclusion I Tna proposed amendments to 10 CFR Parts 21,50, and 54 to allow the holders of ope.ating licenses at currently operating reactors to voluntarily amend their design bases to replace the current accident source term with an attemative source term, would not have a significant effect on the quality of the human environment.

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This conclusion is based on the following:

1. Tne foregoing environmental assessment.

2. The proposed accident revised source term and the proposed accident dose guidelines were incorporated into the NRC's regulations in Parts 50 and 100 for future plant licensing by a final rulemaking on January 10,1997. . The environmental assessment for that final rule made a finding of no significan' impact. Because the proposed rule would be a logical extension of these provisions tc ;perating reactors, a similar finding is appropriate.

3. The revised source term reflects the 6gnificant advances that have been made in -

understanding the timing, magnitude, and chemical form of fission product releases from severe nuclear power plant accidents. This attemative source term provides more physically based estimates of the accident source term. The NRC sponsored significant review efforts by' peer reviewers, foreign research partners, industry groups, and the general public (57 FR 33374).

' References

1. Accident Source Terms for Light-Water Nuclear Power Plants, NUREG-1465, February 1995 i l

2. Calculation of Distance Factors for Power and Test Reactor Sites, Technical Information j Document (TID) 14844, March 1962

3. Results of the Revised (NUREG-1465) Source Term Re-Baselining for Operating Reactors, SECY-98-154, June 1998

4. Amendments to 10 CFR Parts 50, 52, and 100, and issuance of New Appendix S to Part 50, SECY-96-118, May 1996 EA-6

AG12-1 PDR 1

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REGULATORY ANALYSIS PROPOSED REVISION OF 10 CFR PARTS 21,50, and 54 Use of Alternative Sources Terms at Operating Reactors l

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[SECY-98-289, approved February 25,1999] l l

S.F. LaVie, NRR/DIPM/PERB

REGULATORY ANALYSIS REVISION OF 10 CFR PARTS 21,50, AND 54 Use of Alternative Source Terms at Operating Reactors I. STATEMENT OF PROBLEM This regulatory analysis addresses a proposed rule that will revise 10 CFR Parts 21,50, and 54. This rulemaking was initiated to enable holders of power reactor operating licenses issued before January 10,1997, to voluntarily amend their facility design basis to replace the

. current accident source term in design basis radiological consequence analyses with an attemative source term. Although this proposed rule is based on the accident source terms presented in NUREG-1465, Accident Source Terms for Light-Water Nuclear Power Plants, l which will be endorsed by the NRC staff in a proposed regulatory guide, the rule will refer to altemative source term to enable the use of a future attemative to NUREG -1465. (in this analysis, revised source terms refers to NUREG-1465.) This rule also incorporates proposed conforming revisions to 10 CFR Part 50 to eliminate the need for certain exemptions from Part 50 requirements for future applicants under Part 52. In addition to future applicants under Part 52, the proposed conforming change to @50.34(f) affects the small class of applicants that had a construction permit or manufacturing license pending on February 16,1982. This proposed change would allow this small class of applicants to use an attemative to the TID-14844 source term in showing compliance with $50.34(f).

This regulatory analysis is presented in two parts, corresponding to the two considerations stated above.

A. Use of Alternative Source Terms at Operating Reactors

1. Background

a. Accident Source Term A holder of an operating license (licensee) for a light-water power reactor was required by regulations issued by the NRC (or its predeessor, the U.S. Atomic Energy Commission) to submit a safety analysis report in support of its license apN.::ation that assessed the radiological consequences of potential accidents and evaluated the proposed facility site. The NRC staff used this information in its evaluation of the suitability of the reactor design and the proposed site as required by 10 CFR Parts 50 and 100. Section 100.11 requires an applicant to assume (1) a fission product release from the core, (2) the expected containment leak rate, and (3) the site meteorological conditions to establish an exclusion area and a low population zone. A footnote to $100.11 provides guidance that the fission product release be based on a major accident that would result in substantial release of appreciable quantities of fission products from the core to the containment atmosphere. A note to @100.11 references Technical Information Document (TID) 14844, Calculation of Distance Factors for Power and Test Reactors, published in 1962 by the U.S. Atomic Energy Commission, as a source of guidance and as a point of departure for addressing site-specific considerations. This fission product release, known as the TID-14844 accident source term, was ur9d to evaluate the radiological consequences of design basis accidents (DBAs) to determine compliance with various requirements in 10 CFR Parts 50 and 100 in all of the operating reactors licensed to date. Although originally used for site suitability analyses, the accident source term is a design RA-1

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parameter for accident mitigation features, equipment qualification, control room operator radiation doses, and post-accident vital area access doses. The TID-14844 source term was

, explicitly stated as a required design parameter for everal Three Mile Island (TMI)-re'ated '

l requirements. The NRC considers the accident sout e term an integral part of the design basis because it was a significant input to a large portion o' the plant design.

The NRC staff's methods for calculating acciden doses, as described in Regulatory Guide 1.3, Assumptions Used for Evaluating the Potential 4 sdiological Consequences of a Loss of Coolant Accident for Boiling Water Reactors, and f%ulatory Guide 1.4, Assumptions Used for Evaluating the Potential Radiologicel Consequenc 3 of a Loss of Coolant Accident for Pressurized Water Reactors, and in the Standard Review Plan, were developed to be consistent with the TID-14844 source term and the whole body and thyroid dose guidelines stated in $100.11. In that regulatory framework, the source term is assumed to be released immediately to the containment at the start of the postulated accident. The chemical form of I the radioiodine released to the containment atmosphere is assumed to be predominantly elemental with small fractions of particulate and organic iodine forms.

I Radiation doses are calculated at the exclusion area Doundary (EAB) for the first 2-hours and at the low population zone (LPZ) for the assumed 30-day duration of the accident. The whole body dose comes primarily from the noble gases in the source term. The thyroid dose is based on inhalation of radioiodines. In analyses performed to date, the thyroid dose has generally been limiting. The design of some engineered safety features, such as containment spray systems and containment, ventilation exhaust, and control room charcoal filters, are predicated on these postulated thyroid doses. This regulatory framework has provided a consistent analytical approach for evaluating the spectrum of potential consequences from DBAs.

Since the publication of TID-14844, significant advances have been made in understanding i the timing, magnitude, and chemical form of fission product releases from severe nuclear power I plant accidents. Many of these insights developed out of the major research effort started by the NRC and the industry after the accident at TMI. In 1995, the NRC published NUREG-1465, '

which utilized this research to provide more physically based estimates of accident source l terms that could be applied to the design of future light-water power reactors. In NUREG-1465, I the NRC staff provides a representative accident source term for a boiling-water reactor (BWR) and for a pressurized-water reactor (PWR). These source terms are described in terms of I

radionuclide composition and magnitude, physical and chemical form, and timing of release.

L Where TID-14844 addressed three categories of radionuclides, the revised source terms categorize the accident release into eight groups based on similarity of chemical behavior.

Where TlD-14844 assumed an immediate release of the activity, the revised source terms have five release phases that are postulated to occur over several hours, with the onset of major core damage occurring after 30 minutes.

Where TID-14844 assumed radioiodine to be predominantly elemental, the revised source terms assume radioiodine to be predominantly cesium lodide (Csi), an aerosol that is more amenable to mitigation mechanisms. For DBAs, the NUREG-1465 source terms are comparable to the TID-14844 source term with regard to the magnitude of the noble gas and radioiodine release fractions. However, the revised source terms present a more representative description of the radionuclide composition and release timing. In SECY-94-302, Source Term-Related Technical and Licensing Issues Pertaining to Evolutionary and Passive Light-Water-Reactor Designs, the NRC staff determined that the first three phases (coolant, gap, and early in-vessel) are appropriate for design basis evaluations.

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l The NRC staff initiated several actions to provide a regulatory basis for operating reactors to voluntarily amend their facility design bases to enable use of attemative source terms in design basis analyses. First, the NRC staff solicited information on how such source terms might be implemented. In November 1995, the Nuclear Energy Institute (NEI) submitted its generic framework (Electric Power Research Institute Technical Report TR-105909, Generic Framework for Application of Revised Accident Source Term to Operating Plants). This report and the NRC response were discussed in SECY-96-242 (November 1996). Second, the NRC staff initided a comprehensive assessment of the overallimpact of substituting the NUREG-1465 source terms for the TID-14844 source term at two typical facilities. This was done to evaluate the issues involved with applying this revised source terms at operating plants. SECY-

^ 98-154 (June 1998), described the conclusions of this assessment. Third, the NRC staff accepted license amendment requests related to implementation of these revised source terms at a small number of pilot plants. The staff is currently reviewing these pilot projects. Insights from these pilot plant reviews will be incorporated into the regulatory guidance that will be developed in conjunction with this rule. Fourth, the NRC staff initiated an assessment on whether rulemaking would be necessary to allow operating reactors to use alternative source terms. The proposed rule described herein and the supporting regulatory guidance that will be developed as part of this rulemaking have resulted from this assessment. The NRC staff plans to issue the supporting regulatory guidance for public comment on the same date as it publishes the final rule.

b. Accident Dose Criteria and Control Room Dose Criteria in Part 50, Appendix A, GDC-19, the NRC staff presents radiation dose criteria that are used to assess the suitability of the plant design with regard to maintaining control room habitability during DBAs. In $100.11, the NRC staff presents radiation dose guidelines that are used to assess the suitability of the plant design with regard to offsite exposures during design basis events. The dose guidelines for the whole body and the thyroid and the immediate 2-hour exposure period were largely predicated by the assumed source term being predominantly noble gases and radioiodines instantaneously released to the containment and the assumed j

" single critical organ" method of modeling the internal dose used when Part 100 was originally  !

published. However, the current dose guidelines, b;focusing on doses to the thyroid and the j whole body, assume that radioiodine will be the major contributor to doses. Although this may I be appropriate with the TID-14844 source term, it may not be true for source terms based on a  !

more complete understanding of accident sequences and phenomenology. The postulated l chemical and physical form of radioiodine in the revised source terms is more amenable to '

mitigation and, as such, radioiodine may not always be the predominant radionuclide in an accident release. The revised source terms assume a larger number of radionudides than did I the TID-14844 source term as implemented in regulatory guidance. The whole bMy and thyroid dose guidelines ignored these contributors to dose, j in the period since these regulations were issued, there have been significant developments in the principles and scientific knowledge underlying standards for radiation dose limitation and assessment. These developments include not only updated scientific information on radionuclide uptake and metabolism, but also reflect changes in the basic philosophy of radiation protection. In 1991, the NRC staff revised 10 CFR Part 20, Standards for Protection Against Radiation, to reflect these developments. The accident dose guidelines in 9100.11 and GDC-19, were not changed when Part 20 was revised because the requisite revision to the l licensing basis of each operating power reactor was not warranted. The standards in Part 20 include the dose quantity, total effective dose equivalent (TEDE), which is defined as the deep dose equivalent (for extemal exposure) plus the committed effective dose equivalent (for i RA-3 4

Intemal exposure). The deep dose equivalent (DDE) is comparable to the present whole body dose. The committed effective dose equivalent (CEDE)is the sum of the products of doses (integrated over a 50-year period) to selected body organs resulting from the intake of radioactive material multiplied by weighting factors for each organ that are representative of the radiation risk associated with the particular organ. The TEDE, using a risk-consistent methodology, assesses the impact of all relevant nuclides upon all body organs. It is expected that the thyroid could still be the limiting organ and that radioiodine could still be the limiting I radionuclide, and that the current whole body and thyroid guidelines could provide adequate protection; however, this conclusion cannot be assured in all potential cases. The NRC staff recommended in SECY-96-242 that dose guidelines expressed in terms of TEDE be required if a licensee elects to use a revised source term. In a staff requirements memorandum dated February 12,1997, the Commission directed the NRC staff to incorporate TEDE in this proposed rulemaking.

The dose guideline for the EAB in @100.11 is specified with a 2-hour exposure period commencing immediately following the onset of the fission product release. This exposure period was predicated, in part, on the traditional source term assumption that the activity would be immediately available for release at the onset of the accident. The combination of these two assumptions resulted in the maximum postulated dose. The revised source terms postulate a

. release that occurs in phases, with the significant release starting after about 30 minutes and i continuing for about 90 minutes (through the early in-vessel phase only). Because of this, an exposure period starting at the onset of the fission product release may not represent the limiting case. The NRC staff recommended in SECY-96 242 that dose guidelines expressed in j terms of the worst 2-hour dose be considered if a licensee elects to use the revised source  ;

terms. In a staff requirements memorandum dated February 12,1997, the Commission  !

directed the NRC staff to incorporate the worst 2-hour dose in this proposed rulemaking. l

2. Existing Regulatorv Framework

a. Accident Source Term The proposed rule for impiementation of attemative source terms is applicable only to facilities that obtained an operating license, under 10 CFR Part 50, before January 10,1997.

The regulations in this part are supplemented by those in other parts of Chapter 1 of Title 10, including Part 100. Part 10dcontains language that qualitatively defines a required accident source term and contains a note to Section 100.11 that discusses the availability of TID-14844.

However, this note did not mandate the use of TID-14844. With the exception of 650.34(f), that addresses additional TMI-related requirements, there are no explicit provisions in Title 10 requiring the use of the TID-14844 accident source term. Section 50.34(f) is only applicable to a limited number of construction permit and manufacturing license applications pending on February 16,1982, and to applications under Part 52.

Regulatory Guides 1.3 and 1.4 specify the methods and assumptions acceptable to the NRC staff for assessing the consequences of design basis loss of coolant accidents (LOCAs) as required by $100.11. These regulatory guides provide guidance involving accident source terms, much of which is derived from TID-14844. Other guides specify accident source terms either directly or by reference to Regulatory Guides 1.3 and 1.4. None of these guides, however, explicitly refers to TID-14844. The NF C publishes regulatory guides to describe methods acceptable to the NRC staff for implementing specific parts of the NRC's regulations.

Because compliance with these guides is not required, applicants are permitted to propose attematives for NRC staff consideration. Although NRC staff licensing reviews have been RA-4 l

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• i based on Regulatory Guides 1.3 and 1.4, the option for a licensee to propose attematives has l been and remains a possible regulatory mechanism to implement a source term other than the one in TID-14844.

An applicant for an operating license is required by 650.34 to submit a final safety analysis report (FSAR) that describes the facility and its design bases and limits, including a safety l analysis of the site and facility. Guidance in performing these analyses is given in regulatory guides. In its review of the more recent applications for operating licenses, the NRC staff has used the review procedures in NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Powerplants (SRP). These review procedures reference or i

provide acceptable assumptions and analysis methods. Although compliance with the SRP is not required, in practice, many applicants adhere to the guidance in the interest of facilitating NRC staff review. Operating license applications docketed after May 17,1982, are required in 950.34(g) to contain an evaluation of the facility for conformance with the SRP. The facility .

FSAR documents the assumptions and methods actually used by the applicant in the required I l

safety analyses. The NRC staff's finding that a license may be issued is based on the review of the FSAR, as documented in the safety evaluation report (SER). Through inclusion in the i FSAR, these assumptions (including source term) and the licensee's methods of evaluation become part of the design basis of the facility.

Thus, from a regulatory standpoint, the requirement to use the TlD-14844 source term is a licensee commitment (typically expressed as a commitment to Regulatory Guide 1.3 or 1.4) documented in the facility FSAR. The licensee may effect a change in its licensing basis, including the FSAR, by applying for an amendment to its license under fl50.90-50.92, or on its own volition within the provisions of $50.59. Because of the extensive use of the accident ,

source term in the design and operation of a power reactor, and because of the potentialimpact l on postulated accident consequences and margins of safety of a change in such a fundamental design assumption, the NRC has concluded that an attemative source term should be implemented by a license amendment under $g50.90-50.92.

b. Accident Dose Criteria and Control Room Dose Criteria The accident dose guidelines for operating reactors licensed before January 10,1997, are presented in 6100.11. These guidelines are expressed in terms of whole body and thyroid dose. Two guidelines are provided. The first is for the EAB for the 2-hour period immediately following the onset of radioactivity release. The second is for the LPZ for the duration of the event. General Design Criterion 19 (GDC-19), ControIRoom, of Appendix A to 10 CFR Part 50, establishes minimum requirements for the design of the control room, including a requirement for radiation protection features adequate to permit access to and occupancy of the control room under accident conditions. The GDC-19 criteria are expressed in terms of 0.05 Sv (5 rem) whole body dose, or its equivalent to any organ. SRP Section 6.4, Control Room Habitability Systems, contains guiaance that defines equivalent as 0.3 Sv (30 rem) to the thyroid and 0.3 Sv (30 rem) to the skin.

in January 1997, the NRC amended its regulations in 10 CFR Parts 21,50,52,54, and 100 to (1) provide site criteria for future sites and (2) relocate source term and dose requirements for future plants into $50.34. The guidelines of $100.11 remain in p! ace as the licensing basis for operating reactors licensed before January 10,1997. In relocating the source term and dose requirements for future reactors to 650.34, the NRC retained the requirements for the EAB and the LPZ, but revised the associated numerical dose guidelines to replace the two different doses for the whole body and the thyroid gland with a single, total effective dose RA-5

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equivalent (TEDE) value. The dose guideline for the EAB was expressed in terms of the 2-hour period that yielded the maximum dose. The NRC did not, at that time, amend the control room dose criterion in GDC-19.

In a staff requirements memorandum dated February 12,1997, the Commission directed that the amended dose guidelines be made applicable to operating plants choosing to use a (

revised source term. Therefore, an attemative source term cannot be implemented without a '

modification of the accident dose critoria and the GDC-19 criteria. It is this needed modification that makes the proposed rule necessary. l B. Conforming Changes for Part 52 l 1

Part 52 govems the issuance of early site permits, standard design certifications, and combined licenses for nuclear power facilities. Part 52 is used in conjunction with applicable requirements of Part 50. The TMI-related requirements in 950.34(f) were specifically incorporated by reference in $52.47(a)(ii). This incorporation by reference is necessary because {50.34(f) limits applicability to specifically identified facilities for which an application for a construction permit was pending on February 16,1982. The NRC staff expects that future plants will use the revised source terms, or an approved altemative, in supporting safety analyses. Because 9950.34(f)(2)(vii), -(viii), -(xxvi), and -(xxviii) contain specific references to the TID-14844 source term, these sections need to be revised. The control room habitability criteria in GDC-19 were incorporated by reference in $52.47(a)(i). This criterion is expressed in terms of whole body dose or its equivelent to any part of the body rather than in terms of TEDE.

Exemptions from these requirements were necessary for the Westinghouse AP-600 final design approval and design certification. The proposed rule would address changes to these anted sections in order to avoid the need for exemptions for subsequent applicants under Par' M ]

The conforming changes to $50.34(f) would also be applicable to the small subset of specifically listed applicants that had a construction permit application pending on February 16, 1982. The NRC does not expect these applications to be pursued further. However, should one of these applications be reactivated, the applicant would, in effect, be given the option of using an approved alternative to the TID-14844 source term. *

11. OBJECTIVE OF PROPOSED RULE )

A. Use of Alternative Source Terms at Operating Reactors The objective of this proposed regulatory action is to set up a regulatory framework for the voluntary implementation of attemative source terms as a change to the design basis at currently licensed power reactors, thereby enabling potential cost-beneficial licensing actions while continuing to maintain existing safety margins and defense in depth.

This would be accomplished by l l

e Providing revised accident dose criteria and control room habitability dose criteria that l are consistent with the characteristics of the revised source terms and that reflect updated scientific information on radionuclide uptake and metabolism, and also reflect j current radiation protection standards; and RA-6

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e Requiring submittal of a license amendment that contains an evaluation of the consequences of applicable design basis accidents previously analyzed in the safety

! analysis report.

1 Because conformance to the proposed rule is voluntary and would not constitute a backfit, l the licensing bases for operating reactors that do not adopt an altemative source term must remain in the regulation. Therefore, the proposed rule is designated as a new section, 50.67, applicable to operating reactors licensed before January 10,1997, that are proposing to use an altamative source term. The existing requirements in Part 100 and GDC-19 are maintained for operating reactors that continue to use the TID-14844 source term.

The NRC staff will prepare a regulatory guide and an SRP section in support of this rule.

The drafts of these guidance documents will be issued for public comment at the time the final rule is published (September 1999).

B. Conforming Changes for Part 52 The objective of this proposed regulatory action is to eliminate the need for applicants under Part 52 to request exemptions from certain of the NRC's regulations. The need for these exemptions was identified during the Westinghouse AP-600 advanced reactor design certification proceeding.

This would be accomplished by e Explicit references to the TID-14844 source term in 650.34(f) would be revised to read  !

accident source term. A footnote would be added to define an accident source term in generic terminology (similar language to the corresponding footnote in Part 100).

• GDC-19 will be revised to incorporate a revised dose criterion that is applicable only to applicants for construction permits under this part, or a design certification or combined license under 10 CFR Part 52 who apply on or after January 10,1997. The current dose criterion would remain in effect for those operating reactors that continue to use the TID-14844 source term.

111. ALTERNATIVE APPROACHES A. Use of Alternative Source Terms at Operating Reactors The no-action altemative of retaining the existing accident source term was not considered in the development of the proposed rulemaking. In SECY-96-242', the NRC staff made recommendations to the Commission on how the revised source terms could be implemented at operating reactors. The staff requirements memorandum on SECY-96-242 directed the NRC staff to (1) complete the re-baselining study, (2) complete pilot plant evaluations, (3) commence rulemaking, and (4) include the TEDE terminology and the worst 2-hour methodology.

The first attemative considered by the NRC was to continue using current regulations for accident dose criteria and control room dose criteria. This is not considered to be an j acceptable attemative. The NRC had previously determined in the January 1997 Part 50 and l Part 100 final rule that dose guidelines expressed in terms of whole body and thyroid doses I

were inconsistent with the use of the revised source terrr . With regard to the EAB dose l

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I guideline, the NRC also determined that the dose guideline applies to that 2-hour period  !

resulting in the maximum dose.

l The second attemative considered by the NRC was to replace the existing guidelines in 9100.11 and the existing criteria GDC-19 with revised dose criteria. This is not considered to be an acceptable attemative because the provisions of the existing regulations form part of the licensing bases for many of the operating reactors. Therefore, these provisions must remain in effect for operating reactors that do net implement an attemative source term. In addition, this rulemaking attemative would also be inconsistent with the NRC's philosophy of separating plant siting criteria and dose requirements. The approach of establishing the requirements for use of attemative source terms in a new section to Part 50 while retaining the existing regulations in Part 100 Subpart A and GDC-19 was chosen as the best rulemaking attemative.

The NRC considered alternatives with regard to providing regulatory guidance to support l the new section to Part 50. The first attemative was to issue no additional regulatory guidance. ;

This was not considered to be acceptable altemative because, in the absence of clear l regulatory guidance, licensee efforts in preparing applications, and the NRC staff review of I submitted applications, could be hindered by differences in interpretations and technical l positions. This could result in the inefficient use of licensee and NRC s'aff resources, could l cause licensing delays, and could lead to less uniform and less consisteat regulatory implementation. The second attemative was to replace the existing regu~atory guides that address accident radiological consequences with new revisions. This was not considered to be an acceptable attemative because the provisions of the existing regulatory guides form part of the licensing bases for many of the operating reactors. Therefore, these provisions must  ;

remain in effect for operating reactors that do not imp'ement an alternative source term. The l third attemative was to issue a new regulatory guide on the implementation of the revised source terms that would include revised assumptions and acceptable analysis methods for each design basis accident in a series of appendices. The approach of issuing a new regulatory guide was chosen as the best attemative. To provide review guidance for the NRC staff, a new section on design basis radiological analyses using alternative source terms would be added to the Standard Review Plan.

B. Conforming Changes for Part 52 Because these revisions are conforming changes for a rule issued earlier, the no-action attemative was not considered to be acceptable. No reasonable attemative was identified for the necessary $50.34(f) revisions. The reference to TID-14844 needs to be removed.

With regard to a revised control room dose criterion, the revised criterion could have been implemented by changing Part 52 (that cross-references Part 50), by a changing @50.34(a), or by changing GDC-19. A change to GDC-19 was found to be the simplest and clearest approach and, therefore, was considered to be the acceptable altemative.

IV. EVALUATION OF VALUES AND IMPACTS The NRC has determined that the public health and safety and the common defense and security would continue to be adequately protected if the oroposed rule is implemented. The NRC has qualitatively determined that the potential values asaciated with the revised source terms are substantial enough to justify the rule. This proposed rule is voluntary for operating l RA-8 1

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reactors. (The conforming changes for Part 52 will be mandatory for future applicants.) The basis for these conclusions is discussed in the sections to follow.

A. Use of Alternative Source Terms at Operating Reactors

1. Values This proposed rule would allow operating reactors to voluntarily replace the traditional TID-14844 source term with a source term that is based on the insights gained from extensive accident research activities. The accident source term is a design parameter for accident mitigation features, equipment qualification, control room operator radiation doses, and post-accident vital area access doses. The design of some engineered safety features, such as containment spray systems and containment, ventilation exhaust, and control room charcoal filters, is largely predicated on the radiation doses postulated using these source terms. It is expected that an altemative source term, with its improvements in the understanding of chemical / physical form and release timing, could be used to effect reductions in operational and maintenance requirements associated with some of these systems. These reductions would have economic benefit.

The implementation of an altemative source term does not, in itself, have economic value.

It is the modifications to the facility structures, systems, components, and procedures, enabled by an alternative source term that give rise to the associated values and impacts. Because this is a voluntarily action on the part of the licensee, it is expected that licensees will not pursue applications of an attemative source term unless it is perceived to be in their benefit to do so.

Because of this conclusion and the large number of possible applications varying in scope and extent, the NRC has not performed quantitative value-impact analyses. In 1996, NEl informally polled the industry to determine how cften and for what uses licensees might apply the NUREG-1465 source terms. 'Although the poll was informal and does not constitute any commitment to act, the results of the poll indicate the level of interest in the proposed rule. The esponses received represented 43 operating power reactors. Of these,41 reactors plan to use the revised source terms to pursue plant modifications. Anticipated applications includes the following:

e change in allowable containment and ECCS leak rates (24 plants) e change in isolation valve actuation timing (31 plants) e simplification of filtration units (27 plants) e change in mitigation system actuation timing (22 plants) e change in equipment qualification (2 plants)

There is an expectation that many of the attemative source term applications may provide concomitant improvements in overall safety and in reduced occupational exposure, as well as economic benefits. Because of the wide range of possible applications and the voluntary nature of this rule, it is not reasonable to quantify possible outcomes. Reductions in occupational exposures may be realized through reductions in maintenance efforts associated with maintaining unnecessarily limiting leakage, timing, or filtration requirements. Improvements in overall safety may be realized through reduced emergency diesel generator loading, improved containment ventilation system performance due to removal of filter media, and closer RA-9 L_

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synchronization of mitigation feature actuation with the onset of major fission product release, to l provide just three examples. There may be improvements in safety margins realized due to the )

upgrading of analysis assumptions, methods, and acceptance criteria.

It is believed that the proposed rule would result in an improvement in the allocation of resources both for the NRC and for industry. The industry would be allowed to propose applications of alternative source terms that could reduce unnecessary or ineffective requirements in the facility design basis. Limited resources could be diverted to safety issues of greater significance.

2. Costs Since the implementation of an alternative source term is a voluntarily action on the part of the licensee, licensees are not expected to pursue applications of an attemative source term l unless it is perceived to be in their benefit to do so. Because of this conclusion and the large number of possible applications varying in scope and extent, the NRC has not performed quantitative value-impact analyses.

3. Imoacts it is difficult to determine with exactitude the actual impacts of the proposed rule since it does not mandate or approve any specific source term as a substitute to TID-14844. However, to provide some idea of the potentialimpact, the NRC assumed for purposes of this regulatory analysis that a licensee would seek to replace the traditional TID-14844 source term with a source term that is based on the NUREG-1465 source terms. Using NUREG-1465, the actual accident sequence and progression are not changed; it is the regulatory assumptions regarding the accident that will be affected by substituting the alternative source term. Use of an attemative source term alone cannot increase the core damage frequency (CDF) or the large early release frequency (LERF) or actual offsite or onsite radiation doses. (Although actual doses would not increase, analysis results may show an increase in some postulated doses because additional radionuclides will be considered and dose modeling will be more comprehensive.) The accident source terms are used in analyses performed to assess the adequacy of the plant design to contend with a DBA in order to ensure adequate defense in depth and adequate safety margins.

An alternative source term could be used to justify changes in the plant design that could have an impact on CDF or LERF or that could increase offsite or onsite doses. These potential changes are subject to existing requirements in the NRC's regulations. The supporting regulatory guide for this rule will discuss the need for an evaluation of the impacts of an alternative source term implementaticn, including consideration of reductions in defense in depth, safety margins, or both. Consistent with Regulatory Guide 1.174, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the l Current Licensing Basis, the draft guide will indicate that PRA insights may have to be considered if the proposed changes to the design basis are not addressed in currently approved NRC staff positions.

l The Commission directed the NRC staff to assess the impacts of implementing the NUREG-1465 source terms at operating reactors. The results of this study were presented to the Commission in SECY-98-154, Results of the Revised (NUREG-1465) Source Term Re-Baselining for Operating Reactors. The major areas examined were the effect on individual offsite and control room dose, the effect on doses used in equipment environmental RA - 10

qualification, and the effect of potential mcdifications that might be enabled by the revised source terms. The study also assessed the margin afforded by the revised source terms in comparison to assessments performed using the integrated severe accident assessment code, MELCOR. The study indicated that the impact of implementing the revised source terms at operating reactors will produce lower postulated doses in the majority of cases. The NRC intends to address the exceptions in the regulatory guidance that will be developed to support the proposed rule and in the processing of the individuallicense amendments. The MELCOR best estimate analyses indicated that the design basis dose calculations using the revised source term continue to have a substantial margin (a factor of two or greater). The study also indicated that many of the plant systems that are likely to be considered for modification are not involved in risk significant sequences and are, therefore, not likely to have a substantial offsite risk impact using a measure such as LERF. At the present time, the only approved alternative to the TID-14844 source term is that in NUREG-1465. The NRC expects that any future proposed alternative source term will be subjected to the same level of scrutiny as was used in approving NUREG-1465.

On the basis of these considerations, the NRC concludes that approval of an alternative source term based upon NUREG-1465 would not involve a significant increase in the probability or consequences of accidents previously analyzed, nor would it create a new or different type of accident or result in a significant reduction in safety margin.

The NRC does not intend to approva any source term that is not of the (,ame level of quality as NUREG-1465, or that has not had the extensive peer review as did NUREG-1465. Any alternative source term is expected to provide the same level of protection as does NUREG-1465. Thus, the NRC concludes that this rule itself is unlikely to have any significant impact on public health and safety and will continue to provide reasonable assurance of adequate protection.  ;

1

4. Backfit Considerations The NRC has determined that the backfit rule,10 CFR 50.109, does not apply to this proposed regulation, and, therefore, a backfit analysis is not required because these amendments do not involve any provisions that would impose backfits as defined in 10 CFR 50.109(a)(1). The proposed @50.67 amends the NRC's regulations by establishing alternate requirements that may be voluntanly adopted by operating reactors licensed before January 1997 that have adopted, or are proposing to adopt, an alternative source term.

5. Imoacts on Other Programs. Other Agencies The proposed rule would not affect Federal, State, or local Govemment agencies, or Agreement State licensees because the rule would affect only the licensing and operation of .

nuclear power plants that are regulated by the NRC under Part 50. Within the NRC, the l cognizant office is the Office of Nuclear Reactor Regulation, which is sponsoring this proposed rule. No other NRC office is affected by this proposed rule.

B. Conforming Changes for Part 52

1. Values The proposed conforming changes would eliminate the need for future applicants under Part 52 to apply for exemptions from certain paragraphs in @50.34(f) and GDC-19. This would RA - 11

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eliminate the costs associated with preparing and processing an exemption request. By eliminating the need for exemptions, the integrity of the regulations would be maintained.

2. Costs Because the conforming changc: would eliminate the need for future applicants under Part 52 to apply for exemptions from certain paragraphs in 950.34(f) and GDC-19, it is expected that costs would be reduced, not increased.

3.Imn=de Because these are conforming changes for regulations already promulgated, there could be no significant increase in the probability or consequences of accidents previously analyzed, nor would a new or different type of accident be created, nor would there be a significant reduction in safety margins.

l The proposed conforming changes to $50.34(f) would also be applicable to the small subset of specifically listed applicants that had a construction permit application pending on Febr;ary 16,1982. The NRC does not expect these applications to be pursued further. However, if one of these applications would be re-activated, the applicant would be given the option of using an approved altemative to the TID-14844 source term. If an affected applicant chose to use an alternative source term, the impact discussion and conclusions above for the proposed $50.67 would apply. .

4. Backfit Considerations i

The NRC has determined that the backfit rule,10 CFR 50.109, does not apply to this ,

proposed regulation and, therefore, a backfit analysis is not required for this proposed '

regulation because these amendments would not involve any provisions that would impose backfits as defined in 10 CFR 50.109(a)(1).

e The proposed changes to 650.34(f), by removing the explicit reference to TID-14844, would allow future applicants under Part 52 to use an alternative source term without the

need for seeking exemptions, and would allow the small class of applicants for which a construction permit or manufacturing license was pending on February 16,1982, to use an approved altemative to the TID-14844 source term in showing compliance with

$50.34(f). With the exception of the Westinghouse AP-600 final design approval process, there are no pending Part 52 applications. (Westinghouse requested an exemption from the affected paragraphs in $50.34(f) to use the revised source term.)

e The proposed change to GDC-19, would require future applicants under Part 50 or Part 52 after January 10,1997, to show compliance with the 0.05 Sv (5 rerM TEDE dose 4 criterion. There are no applicants in this status at the present time.

5. imnada on NRC Staff Other Proorams. and Other Ananda=

The proposed rule would not affect Federal, State, or local Govemment agencies, or Agreement State licensees, because the rule would only affect the licensing and operation of nuclear power plants that are regulated by the NRC under Part 50. Within the NRC, the cognizant office is Nuclear Reactor Regulation, which is sponsoring this proposed rule. No other NRC office is affected by this proposed rule.

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i V. DECISION RATIONALE A. Use of Alterns'.!v: Scurce Terms at Operating Ree'. ors The decision to create : .~.e." =ention in Part 50, i.e., 650.67, and to include the following

. provisions: the need for a license amendment, the accident dose criteria in g50.34(a)(1)(ii), and the 0.05 Sv (5 rem) TEDE dose criterion for the control room was based on the following rationale:

a. The objective of providing a regulatory framework for the voluntary implementation of attemative source terms as a change to the design basis at currently licensed power l reactors would enable potential cost-beneficial licensing actions and continue to maintain existing safety margins and defense in depth.

i j b. The need for accident dose criteria and control room habitability dose criteria that are

! consistent with the characteristics of the revised source tum and that reflect updated

, scientific information on radionuclide uptake and metabolism, and current radiation i

! protection standards.

c. The provision that an attemative source term be implemented in a facility's design basis by a license amendment, which addresses the NRC staff concem that the current language of $50.59 could be interpreted as allowing this change without prior approval.

(The NRC is currently considering changes to $50.59. The approach taken in 650.67 is not inconsistent with the proposed language in $50.59.)

d. The results of the NRC staff re-baselining study that did not identify any significant concems related to implementation of the revised source term.

e. The NRC philosophy of separating plant siting from plant design, as evidenced by the January 1997 Part 50 and Part 100 final rule.

f. The need to maintain the existing licensing basis for the operating reactors that continue to use the TID-14844 source term.

~ B. Conforming Changes for Part 52 The decision to address needed conforming changes to Part 50 and to include the 0.05 Sv (5 rem) TEDE dose criterion for the control room was based on the following rationale:

a. The desire to eliminate the need for exemptions from comp!' 'nce with the affected

! sections.

l b. The need for control room habitability dose criteria that are consistent with the

!' characteristics of the revised source term and that reflect updated scientific information on radionuclide uptake and metabolism, and current radiation protection standards.

VI. IMPLEMENTATION in the interest of facilitating stakeholder participation in this rule and allowing interested licensees to proceed with the development of applications, the Commission decided to separate RA-13

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development of the proposed rule from the proposed draft guide and SRP section. This l regulatory analysis addresses only the proposed rule. The following are the major milestones:

Proposed rule to the Commission 12/15/98 Final rule, draft guide, draft SRP section to 7/30/99 the Commission Final guide, SRP section to the Commission 1/24/00 ,

i Because this is a voluntary rule for operating reactors, there would be no effective date or required schedule for implementation on the part of licensees. No backfit would be involved.

The proposed rule language is provided in the Federal Register notice for which this l regulatory analysis applies. The accident dose criteria and the control room dose criteria in the proposed rule are readily quantifiable and enforceable. These guidelines and criteria are ,

performance based, i.e., the proposed rule does not prescribe how to meet the requirement. l Vll. REFERENCES l

1. Accident Source Terms for Light-Water Nuclear Power Plants, NUREG-1465, February 1995

2. Calculation of Distance Factors for Power and test Reactor Sites, Technical Iniormation Document (TID) 14844, March 1962

3. Results of the Revised (NUREG-1465) Source Term Re-Baselining for Operating Reactors, SECY-98-154, June 1998

4. Amendments to 10 CFR Parts 50, 52, and 100, and Issuance of New Appendix S to Part 50, SECY-96-118, May 1996

5. Use of the NUREG-1465 Source Term at Operating Reactors, SECY-%-242, November  :

I 1996 I

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