ML20204B375
| ML20204B375 | |
| Person / Time | |
|---|---|
| Issue date: | 02/26/1987 |
| From: | Chilk S NRC OFFICE OF THE SECRETARY (SECY) |
| To: | |
| References | |
| FRN-52FR6334, RULE-PR-50 PR-870226, NUDOCS 8703250041 | |
| Download: ML20204B375 (27) | |
Text
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'87 WR -2 P 2 34 NUCLEAR REGULATORY COMMISSIOP Y
10 CFR Part 50 Emergency Core Cooling Systems; Revisions to Acceptance Criteria AGENCY: Nuclear Regulatory Comission.
ACTION: Propcsed rule.
SUMMARY
- The Nuclear Regulatory Comission (NRC) is proposing an amend-ment that would allow the use of alternative methods to demonstrate that the emergency core cooling system (ECCS) would protect the nuclear reac-tor core during a postulated design basis loss-of-coolant accident (LOCA). The amendment is proposed because research, performed since the current rule was written, has shown that calculations perfonned using current methods and in accordance with the current recuirements result in estimates of cooling system performance that are significantly more con-servative than estimates based on the improved knowledge gained frcm this research.
In addition, the operation of sorre nuclear reactors is being unnecessarily restricted by the rule, resulting in increased costs of electricity generation. The proposed rule, while continuing to allow the use of current methods and requirements, would also allow the use of more recent infomation and knowledge to demonstrate that the ECCS would pro-tect the reactor during a LOCA. The proposed amendment, which would ap-ply to all applicants for and holders of construction pennits or operating licenses for light water reactors, would also relax reoufre-kl ments for certain reanalyses which do not contribute to safety, f
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8703250041 870226 UDR PR 50 52FR6334 PDR
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DATES: Comment period expires July 1, 1987.
Coments received after that date will be considered if it is practical to do so, but assurance of consideration cannot be given except as to coments received on or before that date.
ADDRESSES:
Submit written coments to the Secretary of the Comission.
U.S. Nuclear Regulatory Comission, Washington, DC 20555, Attention Dock-eting and Service Branch. Hand deliver coments to Room 1121, 1717 H Street NW, Washington, DC between 8:15 a.m. and 5:00 p.m. Examine com-ments received, the environmental assessment and finding of no signifi-cant impact, and the regulatory analysis at the Comission's Public Document Rocm at 1717 H Street NW, Washington, DC. Obtain single copies of the environmental assessment and finding of no significant impact and the regulatory analysis from L. M. Shotkin, Office of Nuclear Reculatory Research, Washington, DC 20555, telephone (301)443-7825.
FOR FURTHER INFORMATION CONTACT:
L. M. Shotkin, Office of Nuclear Regu-latory Research, U.S. Nuclear Regulatory Comission, Washington, DC 20555, telephone (301)443-7825.
SUPPLEMENTARY INFORMATION:
BACKGROUND Section 50.46 of 10 CFR Part 50 provides " Acceptance Criteria for Emergency Core Cooling Systems (ECCS) in Light Water Nuclear Power Reac-tors." This section requires that calculations of loss-of-coolant acci-dents (LOCA)beperformedtoshowthattheECCSwillmaintaincladding temperatures, cladding oxidation and hydrogen generation to within 2
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certain specified limits.
It also requires that a coolable core geometry be maintained and that long term decay heat rer. oval be provided. Appen-dix K to 10 CFR Part 50 sets forth certain required and acceptable fea-tures of the models used to perfom these calculations. The criteria of 10 CFR 50.46 and the calculational methods specified in Appendix K were formally issued in January 1974 after extensive rulemaking hearings and are based on the understanding of ECCS performance available at that time.
In the thirteen years following the rulemaking, the NRC, the Department of Energy (including the Atomic Energy Comission and the Energy Research and Development Agency). U.S. nuclear industry and for-eign researchers have obtained considerable information on ECCS perfor-narce. The majority of this LOCA research is complete and has greatly improved the understanding of ECCS performance during a LOCA. The methods specified in Appendix K, combined with other analysis methods currently in use, are now known to be highly conservative; that is, the actual temperatures during a LOCA would be much less than the tempera-tures calculated using Appendix K rethods. The ECCS research has gone beyond confirming that Appendix K is conservative; it has allowed quanti-fication of that conservatism. The results of experiments, computer code development, and code assessment now allow more realistic calculations of ECCS performance during a LOCA, along with reasonable estimates of uncer-tainty, than is possible using current evaluation models.
It is also known that some plants are now restricted in operating flexibility by limits resulting from conservative calculations using cur-rent models and Appendix K requirements. These restrictions may be pre-venting optimal operation of these plants. Based on research performed, 3
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it is now known that the:c restrictions can be relaxed because of improved knowledge of safety margins.
On December 6, 1978, the NRC published an advance notice of proposed rulemaking (43 FR 57157) calling for a two-phase approach to the revision of 10 CFR Part 50 and Appendix K.
The first step would have been to make procedural changes and to permit minor technical changes which would not have reduced the conservatism contained in Appendix K.
The second phase would have made further technical changes based on research results and operating experience.
NRC activity on the ECCS rulemaking was severely curtailed as a re-sult of the high priority efforts required by the TMI-2 accident. This rulemaking was domant until July 1981 when it was revived in the context of simplifying and streamlining the regulatory process.
The NRC has reviewed the coments made by outside organizations on the advance notice of proposed rulemaking as well as a number of other comments received since that time.
In general, the comenters support a rule change that would permit greater flexibility in meeting the regula-tions and would incorporate the use of presently available research in-formation. Many felt that the Phase 1 scope should be expanded to allow the use of additional information available from completed ECCS research.
Because of the delay in changing the ECCS rule, the NRC has used an interim approach, described in SECY-83172.1 to accomodate reouests for improved evaluation models, submitted by reactor vendors, for the purpose of reducing reactor operating restrictions. This interim ap-proach reouires a realistic calculation, with an evaluation of the ISECY-83-472, " Emergency Core Cooling System Analysis Methods," Noverber 13, 1983, is available for inspection and copying for a fee at the Comission's Public Document Room at 1717 H Street NW, Washington, DC.
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uncertainty in the calculation, to demonstrate that the improved evalua-tion model maintains an adequate conservatism or safety factor.
The NRC has decided to proceed with the rulemaking, but in the form of a more comprehensive amendment based on (1) the coments received since the publication of the 1978 notice of proposed rulemaking, (2) the additional research conducted and experience gained since the 1978 no-tice, and (3) recent experience applying the methods of SECY-83-472.
A report, " Compendium of ECCS Research for Realistic LOCA Analysis,"
NUREG 1230 is being prepared.
It summarizes the extensive ECCS research that has been conducted. A draft version of this report will be available at the NRC Public Document Room,1717 H Street NW, Washington, DC 20555, 30 days following publication of this proposed rule in the Federal Register.
SUMMARY
OF FROPOSED RULE CHANGES 9 50.46 Acceptance Criteria for Emergency Core Cooling Systems for Light Water Reactors:
Section 50.46(a)(1) would be amended and redesignated 0 50.46(a)(1)(1) to delete the requirement that the features of Section I of Appendix K to 10 CFR Part 50 be used to develop the evaluation model.
This section would require that an acceptable evaluation model have suf-ficient supporting justification to show that the aralytical technique realistically describes the behavior of the reactor system during a LOCA.
The staff expects that the analytical technique will, to the extent prac-ticable, utilize realistic methods and be based upon applicable experi-mental data.
The amended rule would also require that the uncertainty of the calculation be estimated and accounted for when comparing the results of the calculation to the temperature limits and other criteria of 5
[7590-01,1 I 50.46(b) so that there is a high probability that the criteria would not be exceeded. The staff expects the realistic evaluation model to retain a degree of conservatism consistent with the uncertainty of the calculation. The proposed rule would not specifically prescribe the ana-lytical methods or uncertainty evaluation technioues to be used. Howev-er, guidance would be provided in the form of a Regulatory Guide.2 It should be noted, as discussed in SECV-83-472, that the NRC has, in the pas' found acceptable a method for estimating the uncertainty that was judged to be at least at the 95% probability level. This probability level of 95% is considered by the staff to meet the high level of proba-bility required by the rule.
It is also recognized that the probability cannot be determined using totally rigorous mathematical methods due to the complexity of the calculations. Pcwever, the staff expects that any simplifying assumptions will be stated so that the staff may evaluate them to ensure that they are reasonable. Appendix K,Section II, "Re-quired Documentation," would remain generally applicable, with only minor revisions made to be consistent with the amended rule.
A new i 50.46(a)(1)(ii) would be added to allow the features of Section I of Appendix K to be used in evaluation mcdels as an alternative to performing the uncertainty evaluation specified in the amended 650.46(a)(1)(1). This method would remain acceptable because Appendix K is conservative with respect to the realistic method proposed in the amendedi50.46(a)(1)(1). This would allow both current and future 2Draft Regulatory Guide "Best Estimate Calculations of Emergency Core Cooling Systems Performance," will be issued to all licensees and will be available for inspection at the Consnissioni Public Document Room,1717 H Street, NW., Washington DC, 30 days following publication of this proposed rule in the Federal Register. Requests for single copies of the draft guide, which may be reproduced, should be made in writing to the U.S.
Nuclear Regulatory Commission, Washington, DC 20555, Attention: Director.
Division of Technical Information and Document Control.
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applicants and licensees to use existing evaluation models if they did not need or desire relief from current operating restrictions.
In ! 50.46 paragraphs (a)(2) and (3) would be totally revised to eliminate portions of those paragraphs concerned with historical imple-mentation of the current rule. These provisions would be replaced as described in the following paragraphs.
Section 50.46(a)(2) would be revised to indicate that restrictions on reactor operation may be imposed by the Director of Nuclear Reactor Regulation if the ECCS cooling performance evaluations are not consistent withtherequirementsofIl50.46(a)(1)(1)and(ii). Because of this revision, the last sentence of the existing i 50.46(a)(1) has been delet-edintheredesignated650.46(a)(1)(1).
The current rule contains no explicit requirements concerning re-porting and reanalysis when errors in evaluation models are discovered or changes are made to evalaution models. However, current practice has required reporting of errors and changes. The proposed rule would ex-plicitly set forth requirements to be followed in the event of errors or changes. The definition of a significant change is currently taken from Appendix K Section II.1.b which defines a significant change as one which changes calculated cladding temperature by more than 20*F.
The revised i 50.46(a)(3) would state specific requirements for reporting and reanalyses when errors in evaluation models are discovered or changes are made to evaluation models.
It would require that all changes or errors in approved evaluation models be reported at least annually and would not require any further action by the licensee until the error is reported.
Thereafter, although reanalysis is not required solely because of such minor error, any subsequent calculated evaluation of ECCS perfonnance 7
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requires use of a redel with such error, and any prior errors, corrected.
The staff needs to be apprised of even minor errors or changes in order to ensure that they agree with the applicant's or licensee's assessment of the significance of the error or change and to maintain a general knowledge of modifications made since staff review of the evaluation mod-el. However, past experience has shown that many errors or changes to evaluation redels are very minor and the burden of innediate reporting cannot be justified for such minor errors because they do nnt affect the immediate safety or operation of the plant. The staff has therefore pro-posed periodic reporting to satisfy the need to be apprised of changes or errors without previding undue burden on the applicant or licensee. Such report is to be filed within one year of discovery of the error and shall be reported each year thereafter until a revised evaluation rodel or a revised evaluation correcting such errors is approved by the NRC staff.
Significant errors may require more timely attention since they may be important to the safe operation of the plant. The proposed rule revi-sion would define a significant error or change as one which results in a calculated peak fuel cladding temperature different by more than 50*F, or an accumulation of errors and changes such that the sum of the absolute magnitude of the temperature changes is greater than 50'F. More timely reporting (30 days) would be required for such errors or changes. This definition of a significant change is based on staff judgement concerning the importance of errors and changes typically reported to the staff in the past. The proposed rule revision would also allow the staff to de-termine the schedule for reanalysis based on the importance to safety relative to other applicant or licensee requirements. Errors or changes that would result in the calculated plant performance exceeding any of 8
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the criteria of I 50.46(b) would mean that the plant is not operating within the requirements of the regulations and would require imediate reporting as required by 6 50.55(e) 6 50.72 and i 50.73 and insediate steps to bring the plant into compliance with 6 50.46.
Appendix K ECCS Evaluation Models:
Amendments would be made to Appendix K,Section I.C.5.b. to modify post-CPF heat transfer correlations listed as acceptable. The 1
"McDonough" reference would be replaced with a later paper which is more generally available and which includes additional data.
The heat transfer correlation of Dougall and Rohsenow, listed as an acceptable heat transfer correlation in Appendix K. paragraph I.C.S.b.
would be removed under the proposed rule revision. Research performed since Appendix K was written has shown that this correlation overpredicts heat transfer coefficients under certain conditions and therefore can produce nonconservative results. Since the Dougall-Rohsenow correlation is now known to be nonconservative under certain conditions, it is appro-priate to no longer reference it as a generally acceptable correlation.
i A number of applicants and licensees currently use the Dougall-Pohsenow correlation in approved evaluation models. Because of this, the staff has considered how this change should be implemented. There is no justi-l l
fication on grounds of safety for reoutring that applicants and licensees making use of Dougall-Rohsenow revise their evaluation models at this time. This is appropriate (even though part of the approved evaluation model,Douga11-Robsenow,isnowknowntobenonconservative)becausethe existing evaluation redels are known to contain a large degree of overall l
conservatism even while using the Dougall Rohsenow correlation. This i
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large overall conservatism has been demonstrated through comparisons be-tween evaluation model calculations and calculations using NRC's best estimate computer codes. The cost of revising the evaluation models would be high with no real benefit to safety. Thus requiring that the applicants and licensees remove the Dougall-Rohsenow correlation from their evaluation models could not be justified on a cost-benefit basis.
A new Section 1.0.5.c would be added to Appendix K to state the Com-mission's requirements regarding cortinued use of the Dougall-Rohsenow correlation in existing evaulation models. Evaluation models which make use of the Dougall-Rohsenow correlation and have been approved prior to the effective date of this proposed rule revision may continue to use this correlation as long as no changes are made to the evaluation model which significantly reduce the current overall conservatism of the evalu-ation model.
If the applicant or licensee submits proposed changes to an approved evaluation model, or submits corrections to errors in the evalu-ation model which significantly reduce the existing overall conservatism of the model, continued use of the Dougall-Rohsenow correlation under conditions where nonconservative heat transfer coefficients result would no longer be acceptable.
For this purpose, a significant reduction in overall conservatism has been defined as a " net" reduction in calculated peak clad temperature of at least 50'F from that which would have been calculated using existing evaluation redels. A reduction in calculated peak clad temperature could potentially result in an increase in the ac-tual allowed peak power in the plant. An increase in allowed plant peak power with a known nonconservatism in the analysis would be unacceptable.
This definition of a significant reduction in overall conservatism is based on staff judgement regarding the size of the existing overall 10
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conservatism in evaluation model calculations relative to the conserva-tism required to account for overall uncertainties in the calculations.
Appendix K.Section II.1.b. would be removed since this requirement wouldbeclarifiedundertheamendedi50.46(a)(3). Likewise. Appendix
- r. Section !!.5 would be amended to account for the fact that not all evaluation models will be required to use the features of Appendix K, Section 1.
These minor changes to Appendix K will not affect any exist-ing approved evaluation medels since the changes are either "housekeep-ing" in nature or are changes to " acceptable features." not " required features."
With respect to the proposed rule changes identified in this suma-ry, the Advisory Comittee on Reactor Safeguards reouests the public's coments on whether the existing rule should be " grandfathered" indefintely. That is:
1.
Should the conservative ECCS evaluation method of Appendix K be pennitted irdefinitely or should this aspect of the ECCS rule be phased out after some period of time?
Further Consnissioner Asselstine requests the public's consents on the following:
2.
Should this rule change include an explicit degree of conserva-tism that must be applied to the evaluation models?
3.
This rule change would allow a 5 to 10 percent increase in the fission product inventory that could be released from any core meltdown scenario. Should this rule change explicitly prohibit any increase in appruved power levels until all severe accident issues and unresolved safety issues are resolved?
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Should the technical basis for this proposed rule change be reviewed by an independent group such as the American Physical Society?
l FINDING OF NO SIGN!FICANT ENVIPONMENTAL
!MPACT: AVAILABILITY l
The omission has determined under the National Environmental Poli-cy Act of 1969, as amended, and the Comission's regulations in Subpart A of 10 CFR part 51, that this rule, if adepted, would not be a major Fed-eral action significantly affecting the quality of the human environment l
and therefore an environmental impact statement is not required. The primary effect of the rule wculd be to allow an increase in the peak lo-cal power in the reactor. This could be used to either tailor the power shape within the reactor or increase the total power. Changing the power shape without changing the total power would have a negligible effect on the environmental impact. The total power could also be increased, but would be expected to be increased by no more than about 5% to 10% due to hardware limitations in eFisting plahts. This 5% to 10% power increase is not expected to cause difficulty in meeting the existing envirormental limits. The only change in non-radiological waste would be an increase in waste heat rejection cemensurate with any increase in power.
For stations operating with an open (once through) cooling system, this addi-tional heat would be directed to a surface water body. Discharge of this heat is regulated under the Clean Water Act administered by the U.S. En-vironmentalProtectionAgency(EPA)ordesignatedstateagercies.
It is not iitended that NRC approval of increased power level affect in any way l
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the responsibility of the licensee to corply with the requirements of the Clean Water Act. The environmental assessment and finding of no signifi-cant impact on which this determination is based are available for in-spection at the NRC Public Document Room, 1717 N Street NW, Washington, DC. Single copies of the environmental assessment and the finding of no significant impact are available from L. M. Shotkin Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Connission, Washington DC.
20555, telephone (301)443-7825.
PAPEPWORK REDUCTION ACT STATEMENT This proposed rule acends information collection requirements that are subject to the Paperwork Reduction Act of 1980(44U.S.C.3501et seq.). This rule has been submitted to the Office of Management and Budget for review and approval of the paperwork requirements.
REGULATORv ANALYSIS The Consission has prepared a draft regulatory analysis for this proposed regulation. The analysis examines the costs and benefits of the alternatives considered by the Connission. The draft regulatory analysis is available for inspection and copying for a fee at the NRC Public Docu-ment Room,1717 H Street NW, Washington, OC. Single copies of the analy-j sis may be obtained frcm L. M. $hotkin. Office of Nuclear Pegulatory Research, Washington,DC.20555, telephone (301)4437825.
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The Commission requests public coment on the draft analysis. Com-ments on the draft analysis may be submitted to the NRC as indicated under the ADDRESSES heading.
REGULATORY FLEXIBILITY CERTIFICATION As required by the Pegulatory Flexibility Act of 1980, 5 U.S.C.
605(b), the Commission certifies that this rule, if adopted, will not have a significant economic impact upon a substantial number of small entities. This proposed rule affects only the licensing and operation of nuclear power plants. The companies that own these plants do not fall within the scope of the definition of "small entities" set forth in the Regulatory Flexibility Act or the Small Pusiness Size Standards set out in regulations issued by the Small Business Administration in 13 CFR Part 121. Since these companies are dominant in their service areas, this proposed rule does not fall within the purview of the Act.
BACKFIT ANALYSIS Although a backfit analysis is not required by 10 CFP 50.109 because the proposed rule does not require applicants or licensees to make a change but only offers additional eptions, the factors in 10 CFR 50.109(c)havebeenanalyzedasindicatedbelow. More detailed infoma-tion relevant to this backfit analysis may be found in the regulatory analysis referenced above.
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Statement of the specific objectives that the proposed backfit is designed to achieve.
The objective of the preposed rule is to modify 10 CFR 50.46 and Appendix K to pemit the use of realistic ECC5 evaluation mod-els. More realistic estimates of ECC5 performance, based on the improved kr.owledge gained from recent research on ECCS performance, would remove unnecessary operating restrictions.
2.
General description of the activity that would be required by the Itcensee or anolicant in order to complete the backfit.
The proposed amendment would allow alternative methods to be used to demonstrate that the ECCS would protect the nuclear reactor core during a postulated design basis loss of-coolant accident (LCCA). While centinuing to allow the use of current Appendix K methods and requirements, the proposed rule wculd also allow the use of more recent information and knowledge currently available to dem-onstrate that the ECCS would perfom its safety function during a LOCA.
If an applicant or licensee elected to use a new realistic model they would have to provide sufficient supporting justification to validate the model and include comparisons to experimental data and estimat.:t of uncertainty.
In accounting for the uncertainty, the analysie.ould have to show, with a high level of probability, that the ECCS perfomance criteria are not exceeded.
3.
Potential change in risk to the public from the accidental offsite release of radioactive materials.
The proposed rule could result in increased local power within 15
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the reactor core and possibly increases in total power. Power in-creases on the order of 5-10% will have an insignificant effect on risk. One effect of increased power would be to increase the fis-sion product inventory. A five percent power increase would result in a five percent increase in fission products. Thus, five percent more fission products could be released during core melt scenarios and potentially released to the environment during severe accidents.
The proposed rule wculd still require that fuel rod peak clad-ding temperature (PCT) remain below 2200*F. Because research indi-cates that significant fuel damage will not occur until 2600'F, a 400*F safety margin will remain. However, reactors choosing to in-crease power by five to ten percent would be operating with less margin between the PCT and the 2700'F Ifmit than previously. The increased risk represented by this decrease in margin and increase in fission product inventory is negligible and falls within the un-certainties of PRA risk estimates.
In addition, other safety lim-its, such as departure frem nucleate boiling (DNB), and operational limits, such as turbine design, would limit the amount of margin reduction permitted under the revised rule. The proposed rule could also potentially reduce the risk from pressurized thermal shock by allowing the reactor to be operated in a manner which reduces the neutron fluence to the the vessel.
4 Potential impact on radiological exposure to facility employces_.
Since the primary effect of the proposed rule involves the calculational rethods to te used in determining the ECC cooling per-formance, it is expected that there will be de insignificant impact 16
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[7590-01) on the radiological exposure to facility employees. Because of the reduced LOCA restrictions resulting from the new calculations it is I
possible for the plant to achieve more efficient operation and im-proved fuel utilization with improved maneuvering capabilities. As a result, it is conceivable that there could be a reduction in radi-ological exposure if the fuel reloads can be reduced. This effect is not expected to be very sigetificant.
5.
_ Installation and continuino costs associated with the backfit, including the cost of facility down times or the cest of construc-tion delay.
LOCA considerations resulting from the present rule are re-stricting the optimum production of nuclear electric power in scae plants. These restrictions can be placed into the followirg three categories:
(1) Maximum plant operating power, (2) Operational flexibility and operatienal efficiency of the plant, and (3) Availability of manpower to work on other activities.
The effect of the proposed rule will vary from plant to plant.
Some plants may realize savings of several million dollars per year in fuel and operating costs.
Significantly greater ecorcmic benefit would be realized by plants able to increase total power as a result of the proposed rule. The regulatory analysis cited above indicates that the total present value of the energy replacement cost savings for a five percent power upgrade would vary between 10 and 150 mf1-lion dollars depending on the plant. Additional inforvation con-17
[759001) corning these potential cost savings are included in the regulatory analysis.
6.
The potential safety impact of chances in plant or operational complexity including the effect on other proposed and existing regulatory requirements.
There are safety cenefits derivable from alternative fuel man-i agement schemes that could be utilized if the proposed changes were 4
1 implemented. The higher power peaking factors that would be allowed j
with the revised rule could provide greater flexibility for fuel i
designers when attempting to reduce neutron flux at the vessel.
This can result in a corresponding reduction in risk from pressur-ired themal shock, The reduced cladding temperatures that would be calculated un-i der the proposed rule offers the possibility of other design and j
operational changes that could result frem the lower calculated tem-peratures. ECCS equipment numbers, stres or surveillance require-ments might be reduced and still meet the ECCS design criteria (if I
not required to meet other licensing recuirements). Another option may be to increase the diesel / generator start time duration.
In sumery, the effect of the proposed rule on safety would have both potential positive and negative aspects. The potential i
for reduction of ECC systems in esisting or new plants is present.
However, several positive aspects may also be realized under the proposed rule. While the not effect on safety would be plant spe-cific, the effect is believed to be small.
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The estimated resource burden on the NRC associated with the proposed backfit; and the availability of such resources.
The major staff resources required under the proposed rule change would be to review the realistic models and uncertainty anal-ysis required by the revised ECCS Rule. Based on previous experi-ence with the General Electric Co. SAFER model and the learning that has resulted from these eftorts, it is estimated that approximately one staff year would be required to review each generic model sub-mitted. Ther9 are four major reactor vendors (GE already has a re-vised evaluation model approved under the existing Appendix X for jet pump plants but is currently working on a new evaluation model for non-jet pump plants and may update their methodology under a new rule) and several fuel suppliers and utilities which perfom their own analyses and potentially might subnit generic models for review.
However, it is expected that only 3 or 4 generic models would be submitted since not all plarts would benefit from the rule change.
Thus, about 3 4 staff years would be required to review the er.pected generic models. Once a generic model is approved, the plant specif-ic review is very short.
In addition, several vendors are currently planning to submit realistic models in conjunction with the use of SECY-P3 472. Therefore, staff resources would be expended to review these models in any event. Since these models would not change as a result of the revised ECCS rule, there should be no net increase in resources required over that already planned to be expended.
In sumary, while it is difficult to accurately estimate, it is expect-ed that the proposed rule change will have a small overall impact on NRC resources.
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The potential impact of differences in facility type, design or age on the relevancy and practicality of the proposed backfit.
The degree to which the proposed rule would affect a particular plant depends on how limited the plant is by the LOCA restrictions.
The Babcock and Wilcox (B&W) and Combustion Engineering (CE) compa-nies have informally indicated that they do not feel that the plants which they design are limited by LOCA and, therefore, B&W and CE plants would not be affected. GeneralflectricCo.(GE)plantsdo tend to be limited in oper6 tion by LOCA restrictions and would bene-fit from reitef from LOCA restrictions. However, this relief is i
already available for most GE plants through the recently approved SAFER evaluation mcdel. Any additional relief due to a rule change l
l would be of little further benefit. Westinghouse (W)plantswould l
l appear to directly benefit frem relaxation of LOCA limits. W plants represent the largest number of plants, however, with 47 plants op-erating and 10 additional plants being constructed. W indicates that most of these plants are limited by LOCA considerations.
9.
Whether the proposed backfit is interim or final and if interim, the justification for imposing the proposed backfit on an interim basis.
The proposed rule, when rade effective, would be done so in final form and not on an interim basis.
It would continue to permit i
the performance of ECCS cooling calculations using either realistic models or redels in accord with Appendix K.
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LIST OF SCEJECTS IN 10 CFR PART 50 Antitrust, Classified information, Fire prevention, Incorporation by reference, Intergovernmental relations, Nuclear power plants and reac-tors, Penalty, Radiation protection, Reactor siting criteria, Reporting and Recordkeeping requiremer.ts.
For the reasons set out in the preamble and urder the authority of the Atomic Energy Act of 1954, as amended, the Energy Reorganization Act of 1974, as amended, and 5 U.S.C 553, the NRC is preposing to adopt the following amendments to 10 CFR Part 50.
PART 50-DCPESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES 1.
The authority citation for Part 50 is revised to read as follows:
AUTHORITY: Secs. 102, 103, 104, 105, 161, 182, 183, 186, 189, 68 Stat. 936, 937, 938, 948, 953, 954, 955, 956, as amended, sec. 234, 83 Stat.1244,asamended(42U.S.C.2132,2133,2134,2135,2201,2232, 2233,2236,2239,2282); secs.201,asamended. 202, 206, 88 Stat. 1242, as amended, 1244,1246,(42U.S.C.5841,5842,5846).
Section 50.7 also issued under Pub. L.95-601, sec.10, 92 Stat.
2951(42U.S.C.5851). Section 50.10 also issued under secs. 101, 185, 68 Stat. 936, 955, asamended(42U.S.C.2131,2235);sec.102, Pub.L.91-190,83 Stat.853(42U.S.C.4332).
Sections 50.23, 50.35, 50.55, 50.56alsoissuedundersec.185,68 Stat.955(45U.S.C.2235). Sec-tions 50.33a, 50.55a, and Appendix Q also issued under sec. 102, Pub. L.91-190,83 Stat.853(42U.S.C.4332). Sections 50.34 and 50.54 also 21
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issuedundersec.204,88 Stat 1245(42U.S.C.5844). Sections 50.58, 50.91, and 50.92 also issued under Pub. L.97-415, 96 Stat. 2073, (42 U.S.C.2239).
Section 50.78 also issued under sec. 122, 68 Stat. 939 (42 U.S.C. 2152).
Sections 50.80-50.81 also issued under sec.184, 68 Stat.
954, as amended (42 U.S.C. 2234).
Section 50.103 also issued under sec. 108, 68 Stat. 939, as amended (42 U.S.C. 2138). Appendix F also issued under sec.187, 68 Stat. 955 (42 U.S.C. 2237).
i For the purposes of sec. 223, 68 Stat. 958, as araended (42 U.S.C.
2273),il50.10(a),(b),and(c), 50.44, 50.46, 50.48, 50.54, and 50.80(a) are issued under sec.161b, 68 Stat. 948, as amended (42 U.S.C.
2201(b));il50.10(b)and(c)and50.54areissuedundersec. 1611, 68 Stat. 949, as amended (42 U.S.C. 2201(1)); and il 50.55(e), 50.59(b),
50.70, 50.71, 50.72, 50.73, and 50.78 are issued under sec. 1610, 68 Stat.950,asamended(42U.S.C.2201(o)).
Il 50.2, 50.10, 50.21, 50.22, 50.23,50.30, 50.33, 50.33a, 50.34, 50.35, 50.37, 50.38, 50.41, 50.42, 50.43, 50.44, 50.47, 50.53, 50.54, 50.55, 50.55a. 50.56, 50.70, 50.80, 50.103, and Appendices A, E F, L, and 0
[ Amended].
2.
The authority citations following il 50.2, 50.10, 50.21, 50.22, 50.23, 50.30, 50.33, 50.33a, 50.34, 50.35, 50.37, 50.38, 50.41, 50.42, 50.43, 50.44, 50.47, 50.53, 50.54, 50.55, 50.55a, 50.56, 50.70, 50.80, 50.103, and Appendices A, E, F. L, and Q are removed.
3.
Ini50.46, paragraph (a)isrevisedtoreadasfollows:
9 50.46 Acceptance criteria for emergency core cooling systems for light water nuclear power reactors.
(a)(1)(1) Each boiling and pressurized light-water nuclear power 22
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reactor fueled with uranium oxide pellets within cylindrical Zircaloy cladding shall be provided with an emergency core cooling system (ECCS) which shall be designed such that its calculated cooling performance fol-lowing postulated loss-of-coolant accidents confoms to the criteria set forth in paragraph (b) of this section. ECCS cooling performance shall be calculated in accordance with an acceptable evaluation model and shall be calculated for a number of postulated loss-of-coolant accidents of different sizes, locations, and other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are calculated.Exceptasprovidedinparagraph(a)(1)(ii)ofthissection, the evaluation model shall include sufficient supporting justification to show that the analytical technique realistically describes the beha-vior of the reactor system during a loss-of-coolant accident. Compari-sons to applicable experimental data shall be made and uncertainties in the analysis method and inputs shall be identified and assessed so that the uncertainty in the calculated results can be estimated. This uncer-tainty shall be accounted for so that, when the calculated ECCS cooling performance is compared to the criteria set forth in paragraph (b) of this section, there is a high level of probability that the criteria would not be exceeded. Appendix K, Part II, Required Cocumentation, sets forth the documentation requirements for each evaluation model.
(ii) Alternatively,anECCSevaluationmodelmaybedevelopedin conformance with the required and acceptable features of Appendix K.
ECCS Evaluation Models.
(2) Restrictions on reactor operation may be imposed by the Director of Nuclear Reactor Regulation if it is found that the evalua-tions of ECCS cooling performance submitted are not consistent with 23 e
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paragraphs (a)(1)(1) and (ii) of this section.
(3)(1) Each applicant for or holder of an operating license or construction permit shall estimate the effect of any change to or error in an acceptable evaluation model or in the application of such a model to determine if the change or error is significant. For this purpose, a significant change or error is one which results in a calculated peak fuel cladding temperature different by more than 50'F from the temper-ature calculated for the limiting transient using the last acceptable model, or is a cumulation of changes and errors such that the sum of the absolute magnitudes of the respective temperature changes is greater than 50*F.
(ii) For each change to or error discovered in an acceptable evaluation model or in the application of such a model which affects the temperature calculation, the applicant or licensee shall report the na-ture of the change or error and its estimated effect on the limiting ECCS analysis to the Comission at least annually as specified in 5 50.4.
If the change or error is significant, the applicant or lican-see shall provide this report within 30 days and include with the report a proposed schedule for providing a reanalysis or taking such other action as may be needed to show compliance with 5 50.46 require-ments. This schedule may be developed using an integrated scheduling system previously approved for the facility by the NRC.
For those facilities not using an NRC approved integrated scheduling system, a schedule will be established by the NRC staff within 60 days of receipt of the proposed schedule. Any. change or error correction that results in a calculated ECCS performance that does not conform to the criteria set forth in paragraph (b) of this se'ction is a reportable event as des-24 l
w
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cribed in 5 50.55(e), 5 50.72 and i 50.73. The affected applicant or li-censee shall propose finnediate steps to demonstrate compliance or bring plant design or operation into compliance with 5 50.46 requirements.
4.
In 10 CFR Part 50 Appendix K, paragraph II.1.b is deleted, paragraph II.1.c is redesignated II.1.b, the text of paragraph I.C.S.b and paragraphs II.1.b and II.5 are revised, and a new section I.C.S.c added to read as follows:
APPENDIX K - ECCS EVALUATION MODELS I.
REQUIRED AND ACCEPTABLE FEATURES OF THE EVALUATION MODELS*+*
C.
Blowdown Phenomena ***
5.
Post-CHF Heat Transfer Correlations.***
b.
The Groeneveld flow film boiling correlation (equation 5.7 of D.
C. Groeneveld, "An Investigation of Heat Transfer in the Liquid Deficient Regire's," AECL-3281, revised December 1969) and the Westinghouse corre-lation of steady-state transition boiling (" Proprietary Redirect / Rebuttal Testimony of Westinghouse Electrical Corporation," USNRC Docket RM-50-1, page 25-1, October 26,1972) are acceptable for use in the post-CHF boil-ing regimes.
In addition the transiticn boiling correlation of McDonough, Milich, and King (J. B. McDonough, W. Milich, E. C. King, "An i
Experimental Study of Partial Film Boiling Region with Water at Elevated Pressures in a Round Vertical Tube," Chemical Engineering Progress Symposium Series, Vol. 57, No. 32, pages 197-208, (1961) is suitable for use between nucleate and film boiling. Use of all these correlations shall be restricted as follows:
l 25
~
, + -,,,, - - - - - - - -, - - -, - - -. -
,,---,,-,--..n
~-----.n.-n
-,-,,.-----,,---,,-,..n---
~.----.-a
4
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c.
Evaluation models approved after (effective date of rule) which make use of the Dougall-Rohsenow flow film boiling correlation (R. S.
Cougall and W. M. Rohsenow, " Film Boiling on the Inside of Vertical Tubes with Upward Flow of Fluid at Low Qualities, MIT Report Number 9079 26, Cambridge, Massachusetts, September 1963) shall not use this correlation under conditions where nonconservative predictions of heat transfer result. Evaluation models which make use of the Dougall-Rohsenow correlation and were approved prior to (effective date of rule) continue to be acceptable until such time that a change is made to, or an error is corrected in, the evaluation model that results in a signi-ficant reduction in the overall conservatism fr. the evaluation model. At that time continued use of the Dougall-Rohsenow correlation under condi-tions where nonconservative predictions of heat transfer result would no longer be acceptable. For this purpose, a significant reduction in the overall conservatism in the evaluation model would be a reduction in the calculated peak fuel cladding temperature of at least 50*F from that which would have been calculated on (effective date of rule) due either to individual changes or error corrections or the net effect of an ac-cumulation of changes or error corrections.
II. REQUIRED DOCUMENTATION 1.a.
b.
A complete listing of each computer program, in the same form as used in the evaluation model,shall be furnished to the Nuclear Regula-tory Cannission upon request.
26
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5.
General Standards for Acceptability - Elements of evaluation models reviewed will include the technical adequacy of the calculational methods, including : for models covered by 5 50.46(a)(1)(ii), compliance with required features of Section I of this Appendix X ; and, for models covered by 6 50.46(a)(1)(1), assurance of a high level of probability that the performance criteria of 9 50.46(b) would not be exceeded.
Dated at Washington, DC this N day of 4, 1987.
F the Nuc; ear Regul ry Comission.
[
b) V
(
Gamuel J. Ch ik, Secretary of he Commission.-
27
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.