ML20005E380
| ML20005E380 | |
| Person / Time | |
|---|---|
| Issue date: | 12/12/1989 |
| From: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| References | |
| FRN-54FR52946, RULE-PR-50 PR-891212, NUDOCS 9001050154 | |
| Download: ML20005E380 (18) | |
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'89 DEC 20 P3 :32 NUCLEAR REGULATORY COOHISSION 10CFRPart55 RIN:- 3150 - AD01 Fracture Toughness Requirements For Protection Against Pressurized Thermal Shock Events AGEt!OY:
Nuclear Regulatory Commission.
ACTION:
Proposed rule.
SUtHARY:
The Nuclear Regulatory Commission (NRC) is proposing to amend its regulations for light-water nuclear power plants to change the procedure for calculating the amount of radiation embrittlement that a reactor vessel receives. The pressurized thermal shock rule (PTS rule) establishes a screening criterion. -This criterion limits the amount of embrittlement of a reactor vessel beltline mate ial beyond which the plant cannot continue to operate without justification based on a plant-specific analysis. The proposed amendment does not change the screening criterion. The PTS rule also prescribes the procedure that must be used for calculating the amount of embrittlement for comparison to the screening criterion. The proposed amendment would update the procedure and make it consistent with the one given in Regulatory Guide 1.99, Revision 2, published in 14ay 1988.
DATE: Comment period expires (75. days after publication in the Federal Register). Comments received after this date will be considered if it is
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practical to do so, but assurance of consideration cannot be given except for comments received on or befcre this date.
ADDRESSES: Mail written comments to:
Secretary, U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention:
Docketing and Service Branch.
Deliver comments to:
11555 Rockville Pike, Rockville, Maryland between 7:30 an and 4:15 pm Federal workdays.
Copies of comments received may be examined at the NRC Public Document Room, 2120 L Street NW. (Lower Level), Washington,.DC.
FOR FURTHER INFORMATION CONTACT:
Pryor N. Randall, Division of Engineer-ing, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555, Telephone: (301)492-3842.
SUPPLEMENTARY.INFORMATION:
Background
Pressurized thermal shock events are system transients in a pressurized water reactor (PWR) that can cause severe overcooling followed by immediate repressurization to a high level. ' The thenmal stresses caused by rapid cooling of the reactor vessel inside surface combine with the pressure stresses to increase the potential for fracture if an ihitiating flaw is present in low toughness material. This material may exist in the reac-tor vessel beltline, adjacent to the core, where neutron radiation gradually embrittles the material during plant lifetime. The degree of embrittlement depends on the chemical composition of the steel, especially the copper and nickel contents.
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- The toughness of reactor vessel materials is characterized by a
" reference temperature for nil ductility transition" (RTNDT),whichcan be defined as follows.
For many reactors now in operation, toughness of the beltline materials at room temperature is too low to permit full pressurization of the vessel with adequate safety margins. As temperature is raised, toughness increases slowly at first; but at the temperature defined as RTNDT, toughness begins to increase much more rapidly.
The transition in toughness from low values to high that takes place above RT occurs over a temperature interval of about 150*F.
Thus at normal NDT operating temperatures, vessel materials are quite tough.
RT I ' d't'"'
(
mined by destructive tests of material specimens.
Radiation embrittlement moves RT to higher temperatures. Correlations based on test results NDT for unirradiated and irradiated specimens have been developed to calcu-late the shift in RT as a function of neutron fluence for various NDT material compositions. The value of RTNDT ** 8 given time in a vessel's life is used in fracture mechanics calculations to determine whether assumed pre-existing flaws would propagate as cracks when the vessel is stressed.
The Pressurized Thermal Shock (PTS) rule,10 CFR 50.61, adopted on July 23, 1985 (50 CFR 29937), establishes a screening criterion This screening criterion establishes a limiting level of embrittlement beyond which operation cannot continue without further plant-specific evaluation. The screening criterion is given in terms of RTNDT' calculated as a function of the copper and nickel contents of the material and the neutron fluence according to the procedure given in the to distinguish it from other procedures for PTS rule, and called RTPTS calculating RTNDT' 3
. ~ _ -
l The PTS rule requires each PWR licensee to report the results of g
the calculations of predicted RTPTS values for ecch beltline material, (including the copper, nickel and fluence values that provided the basis-l for the calculations) from the time he submits his report to the expira-l tion date of the operating license (EOL). The PTS rule further provides that if RT for the controlling material is predicted to exceed the screen-PTS ing criterion before E0L, the licensee should submit plans and a schedule for flux reduction programs that are reasonably practicable to avoid reaching the screening criterion. Finally, the PTS rule requires licensees of plants that would reach the screening criterion before EOL despite the flux reduction program to submit a plant-specific safety analysis justify-ing operation beyond de screening criterion. The licensee must submit the analysis at least 3 years before the plant is predicted to reach that limit.
Regulatory Guide 1.154, " Format and content of Plant-Specific Pressurized Thermal Shock Safety Analysis Reports for Pressurized Water Reactors" provides guidance for the preparation of the report and describes acceptance criteria that the NRC staff would use.
In response to the PTS rule, the licensees of operating reactors have submitted the fluence predictions and material composition data and (with 2 or 3 exceptions) these have now been accepted. Of greater importance are the flux reduction programs that have been undertaken by l
licensees for those plants having high values of RT PTS.
Need for the Proposed Amendment l
i The primary purpose of the proposed amendment is to change the procedure for calculating RT to reflect recent findings that embrittle-PTS l
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4 ment is occurring faster than predicted by the PTS rule for some reactor vessel materials.
Although the PTS rule was adopted on July 23, 1985, the procedure for calculating RTPTS was developed in 1981-1982 and not l
updated because a number of licensees were using the 1982 formulations as the basis for flux redu: tion programs.
Meanwhile, plant surveillance data were being added to the data base and there were extensive new and more accurate correlations made. These culminated in Revision 2 to Regulatory Guide 1.99, " Radiation Embrittlement of Reactor Vessel Mate-rials," published in May 1988.
Revision 2 provides the basis for pressure-temperature limit calculations.
Peer review of the new correlations was provided by the public comments on Revision 2.
In the regulatory analysis prepared for Revision 2, and repeated in the regulatory analysis for this proposed amendment, the NRC evaluated 1
the impact of amending the PTS rule to be consistent with the Guide.
l Copper and nickel contents and fluence values for each PWR reactor vessel were taken from the PTS submittals from licensees. When the values of RT were recalculated using these quantities and the procedure i
PTS developed for Revision 2, the results were higher for approximately half
- the vessels, including three vessels where the value may be over '60'F higher than previously thought. This would increase the probability of PTS-induced vessel failure by a factor of at least 30 for those plants.
The NRC believes these changes in the nonconservative direction are greater than can be absorbed by the uncertainties believed to exist and taken into account by the NRC when the RT
-based screening limit PTS was set.
(A margin of 48'F is added in the calculation of RT t' "V'"
PTS not only the uncertainty in the formula for embrittlement but also the uncertainties in the copper, nickel, and fluence values entered in the 5
l
formula.) Based on this new infomation, the probability of reactor vessel failure by fracture during a PTS event is presently higher in some vessels than the probability based on the procedure for calculating RT which is given in the present PTS rule.
Moreover, a few of those PTS reactor vessels will reach the screening criterion in the 1990's. Thus, the current PTS rule needs to be amended.
Explanation of the Proposed New Requirements The proposed amendment changes the procedure for calculating RTPTS i
l and requires all licensees of operating PWR's to resubmit projected values of RT using the new procedure.
If the copper and nickel PTS contents and fluence projections are the same as in the previous sub-mittal, they need only be listed.
If there are changes in these projections,justificationforthechangesmust,beprovided.
If a licensee has already submitted the information required by paragraph (b)(1) of this proposed amendment, the licensee may simply reference the earlier submittal.
The proposed amendment modifies the requirement for fluence projec-tions in the calculation of RT to take into consideration the poten-PTS tial for a request for change in the expiration date for operation of the facility. This applies to requests to change the end of licensed life from 40 calendar years after the date of the construction permit to 40 years after the date of the operating license.
It also applies to requests for license renewal and the need to consider projected values of RT at the end of a renewal ters.
PTS An additional change is proposed to be made in paragraph (b)(4) with regard to the schedule for submittal of a safety analysis justifying 6
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operation beyond the screening criterion.
In the present PTS rule, this analysis must be submitted at least 3 years before reaching the screening criterion or by one year after issuance of Comission guidance and acceptance criteria, whichever is later.
Regulatory Guide 1.154, which contains the necessary guidance and criteria was issued in January,1987.
Therefore, this alternative schedule was omitted in the proposed amendment.
However, because one or two plants might reach the screening criterion in less than 3 years after publication, when RT is recalculated using the PTS amended rule, the submittal will be required at least three years before l
reaching the screening criterion or by one year after the effective date of the amended rule, whichever is later.
The safety implications of this.
change in the schedule requirement are considered to be acceptably small, because RT increases very slowly near the screening criterion.
PTS l
Environmental Impact:
Categorical Exclusion The NRC has determined that this proposed rule is the type of action l
described in categorical exclusion 10 CFR 51.22(c)(3)(ii) and (iii).
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_ Therefore, neither an environmental impact statement nor an environmental assessment has been prepared for this proposed rule.
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Paperwork Reduction Act Statement l
t.
This proposed rule amends information collection requirements that are subject to the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.).
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This rule has been submitted to the Office of Management and Budget for i
review and approval of the paperwork requirements.
4 Public reporting burden for this collection of information is estimated to average 254 hours0.00294 days <br />0.0706 hours <br />4.199735e-4 weeks <br />9.6647e-5 months <br /> per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to the Records and Reports Management Branch L
(P-530), U.S. Nuclear Regulatory Commission, Washington, DC 20555; and tothePaperworkReductionProject(3150-0011), Office of Management and Budget, Washington, DC 20503.
Regulatory Analysis The NRC staff has prepared a regulatory analysis for this proposed amendment, which describes the factors and alternatives considered by the Commission in deciding to propose this rule.
The regulatory analysis for the proposed amendment also discusses why the screening criterion is not being changed when the procedures are changed. An anticipated public comment is for calculating RTPTS that because the probabilistic fracture mechanics. calculations used in establishing the screening criterion made use of the formula for RTPTS given in the PTS rule, the proposed change in the formula must change 8
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the calculated probabilities a.nd, in turn, change the screening crite-=
rion. As shown in the regulatory analysis, failure probabilities at the
]
same RT screening criterion for the most critical accioent scenarios PTS
. in three plants, when recalculated using the new embrittlement estimates, were somewhat lower, but the differences were quite dependent on the plant configuration and the scenario chosen.
Because of the apparent plant-to plant differences, it is better to trigger plant-specific analyses with a " trip wire" that is believed to generically bound all plants.
Furthermore, as described in the regulatory analysis, the screening criterion was based on a variety of considerations besides the probabilistic analysis.
A copy of the regulatory analysis is available for inspection and copying for a fee at the NRC Public Document Room, 2120 L Street NW.
(Lower Level), Washington, DC 20555.
Single copies of the analysis may be obtained from Pryor N. Randall, Office of Nucle 4r Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555 Telephone, (301)492-3842.
Regulatory Flexibility Act Certification 1
l l
l As required by the Regulatory Flexibility Act, 5 U.S.C. 605(b), the Commission certifies that this proposed rule does not have a significant economic impact on a substantial number of small entities. This rule specifies minimum fracture toughness properties of irradiated pressure vessel materials to ameliorate the effects of PTS events on nuclear facilities licensed under the provision of 10 CFR 50.21(b) and 10 CFR 50.22. The companies that own these facilities do not fall within the 9
q scope of the definitiun of "small entities" as set forth in the Regula-L tory Flexibility Act or the small Business Size Standards in regulations issued by the small Business Administration at 10 CFR Part 121.
l L
Backfit Analysis The NRC has concluded, on the basis of the documented evaluation i
required by 10 CFR 50.109(a)(4), that the backfit requirements contained in this proposed amendment are necessary to ensure that the facility pro-l vides adequate protection to the public health and safety, and, therefore.
l that a backfit analysis is not required and the cost-benefit standards of l
10 CFR 50.109(a)(3) do not apply. The documented evaluation given in the l
regulatory analysis includes a statement of the objectives of and reasons for the backfits that would be required by the proposed rule and sets l
forth the basis for the NRC's conclusion that th,ese backfits are not sub-ject to the cost-benefit standards of 10 CFR 50.109(a)(3).
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List of Subjects in 10 CFR Part 50 Antitrust, Classified information, Fire prevention, Incorporation by reference, Intergovernmental relations, Nuclear power plants and reactors, Penalty, Radiation protection, Reactor siting criteria, Reporting and recordkeeping requirements.
For the reasons set out in the preamble and under the authority of the Atomic Energy Act of 1954, as amended, the Energy Reorganization Act 10
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of 1974, and 5 U.S.C. 553, the NRC is proposing to adopt the following amendments to 10 CFR Part 50.
PART 50 -- 00MESTIC LICENSIts 0F PRODUCTION AND UT]LIZATION FACILITIES 1.
The authority citation of 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.
l 1244, as amended (42 U.S.C. 2132, 2133, 2134, 2135, 2201, 2232, 2233, 2236, 2239, 2282); secs. 201, as amended, 202, 206, 88 Stat. 1242, as amended 1244, 1246, (42 U.S.C. 5841, 5842, 5846).
Section 50.7 also issued under Pub. L.95-601, sec. 10, 92 Stat.
2951 (42 U.S.C. 5851).
Section 50.10 also issued under secs. 101, 185, 68 Stat. 936, 955 as amended (42 U.S.C. 2131, 2235), sec. 102, Pub. L.91-190, 83 Stat. 853 (42 U.S.C. 4332).
Sections 50.13,50.54(dd),and t
50.103 also l'ssued under sec. 108, 68 Stat. 939, as amended (42 U.S.C.
2139).
Sections 50.23, 50.35, 50.55, and 50.56 also issued under' sec. 185, 68 Stat. 955 (42 U.S.C. 2235).
Sections 50.33a, 50.55a and Appendix Q also issued under sec. 102, Pub. L.91-190, 83 Stat. 853 (42 U.S.C.
4332).
Sections 50.34 and 50.54 also issued under sec. 204, 88 Stat.
1245 (42 U.S.C. 5844).
Sections 50.58, 50.91, and 50.92 also issued L
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 L
also issued under sec.184, 68 Stat. 954, as amended (42 U.S.C. 2234).
Appendix F also issued under sec. 187, 68 Stat 955 (42 U.S.C. 2237).
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4 For the purposes of sec. 223, 68 Stat. 958, as amended (42 U.S.C.
2273), $$ 50.46(a) and (b), and 50.54(c)'are issued under sec. 161b, 68 Stat. 948, as amended (42 U.S.C. 2201(b)); il 50.7(a), 50.10(a)-(c),
50.34(a)and(e),50.44(a)-(c),50.46(a)and(b),50.47(b),50.48(a),
(c),(d),and(e),50.49(a),50.54(a),(i),(i)(1),(1)-(n),(p),(q),
(t),(v),and(y),50.55(f),50.55a(a),(c)-(e),(g),and(h),50.59(c),
50.60(a),50.62(c),50.64(b),and50.80(a)and(b)areissuedundersec. 1611, 68 Stat. 949, as amended (42 U.S.C. 2201 (i)); and $$ 50.49(d),
(h),and(j),50.54(w),(2),(bb),(cc),and(dd),50.55(e),50.59(b),
50.61(b),50.62(d),50.70(a),50.71(a)-(c)and(e),50.72(a),50.73(a) and (b), 50.74, 50.78, and 50.90 are issued under sec. 161(c), 68 Stat.
950, as' amended (42 U.S.C. 2201(o)).
2.
In 5 50.61, paragraph (b) is revised to read as follows:
5 50.61 Fracture toughness requirements for protection against pressurized thermal shock events.
a a
a a
a (b) Requirements.
(1) For each pressurized water nuclear power reactor for which an operating license has been issued, the licensee shall submit projected values of RT forreactorvesseibeltlinematerialsbygivingvalues PTS for the time of submittal, the expiration date of the operating license, the projected expiration date if a change in the operating license has been requested, and the projected expiration date of a renewal term if a request for license renewal has been subeitted.
The assessment must use the calculative procedures given in paragraph (b)(2) of this section.
The assessment must specify the bases for the projection, including the assumptions regarding core loading patterns. The submittal must list the 12
_-________-___-_-____-_-__a___-____--_-
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copper and nickel contents, and the fluence values used in the calcula-tion for each beltline material.
If these quantities differ from those-submitted in response to the original PTS rule and accepted by the NRC, justificationsustbeprovided. This assessment must be submitted by (6 months after the effective date of this section), and must be updated wheneverthereisasignificantchangeinprojectedvaluesofRTPTS, or upon a request for a change in the expiration date for operation of the facility.
(2) The pressurized thermal shock (PTS) screening criterion is 270'F for plates, forgings, and axial weld materials, or 300'F for circumferential weld materials. For the purpose of comparison with this for the reactor vessel must be calculated criterion, the value of RTPTS as follows. The calculation must be made for each weld and plate, or forging, in the reactor vessel beltline.
l Equation 1:
RTPTS = I + M + ARTPTS I
)
-(i)
"I" means the initial reference temperature (RTNDT)ofthe unirradiated material measured as defined in the ASME Code, Paragraph NB-2331.
Measured values must be used if available; if not, the follow-ing generic mean values cust be used: 0'F for welds made with Linde 80 flux, and -56'F for welds made with Linde 0091, 1092 and 124 and ARCOS B-5 weld fluxes.
(ii)
"M" means the margin to be added to cover uncertainties in the values of initial RTNDT, copper and nickel contents, fluence and the calculational procedures.
In Equation 1, M is 66*F for~ welds and 48'F 13 i
l
e t
for base metal if generic values of I are used, and M is $6'F for welds and 34'F for base metal if measured values of I are used.
(iii) ART is the mean value of the adjustment in reference tempera-PTS ture caused by irradiation and should be calculated as follows:
Equation 2: ART (iv) CF ('F) is the chemistry factor, a function of copper and nickel content.
CF is given in Table 1 for welds and in Table 2 for base metal (plates and forgings).
Linear interpolation is permitted.
In Tables 1 and 2 "Wt-X copper" and "Wt-% nickel" are the best-estimate values for the material, which will normally be the mean of the measured values for a plate or forging or for weld samples made with the weld wire heat number that matches the critical vessel weld.
If these values are not available, the upper limiting values given in the material specificationstowhichthevesselwasbuiltmahbeused.
If not avail-I able, conservative estimates (mean plus one standard deviation) based on generic data may be used if justification is provided.
If there is no information available, 0.35% copper and 1.0% nickel must be assumed.
19 (v)
"f" means the best estimate neutron fluence, in units of 10 n/ca' (E greater than 1 MeV), at the clad-base-metal interface on the l
inside surface of the vessel at the location where the material in ques-tion receives the highest fluence for the period of service in question.
l-(3) For ecch pressurized water nuclear power reactor for which the value of RT for any material in the beltline is projected to exceed PTS the PTS screening criterion before the expiration date of the operating renewal has been submitted, the licensee shall submit by (9 months after 14
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TABLE 1 CHEMISTRY FACTOR FOR WELDS, 'F
Wt-%
0 0.20 0.40 0.60 0.80 1.00 1.20 4
0 20 20 20 20 20 20 20
' O.01 to 20 20 20 20 20 20 0.02 21 26 27 27 27 27 27 0.03 22 35 41 41 41 41 41 0.04 24 43 54 54 54 54 54 0.05 26 49 67 68 68 68 68 0.06 29 52 77 82 82 82 sz 0.07 32 55 85 95 95 95 95 0.08 36 58 90 106 108 108 108 0.09 40 61 94 115 122 122 122 0.10 44 65 97 122 133 135 135 0.11 49 68 101 130 144 148 148 0.12 52 72 103 135 153 161 161 0.13 58 76 106 139 162 172 176 0.14 61 79 109 142 168 182 188 0.15 66 84 112 146 175 191 200 0.16 70 88 115 149 178 199 211 0.17 75 92 119 151 184 207 221 0.18 79 95 122 154 187 214 230 0.19 83 100 126 157 191 220 238 l
0.20 88 1 04 129 160 194' 223 245 0.21 92 108 133 164 197 229 252 l
0.22 97 112 137 167 200 232 257 l
0.23 101 117 140 169 203 236 263 O.24 105 121 144 173 206 239 268 0.25 110 126 148 176 209 243 272 0.26 113 130 151 180 212 246 276 0.27 119 134 155 184 216 249 280 0.28 122 138 160 187 218 251 284 0.29 128 142 164 191 222 254 287 0.30 131 146 167 194 225 257 290 0.31 136 151 172 198 228 260 293 l
0.32 140 155 175 202 231 263 296 O.33 144 160 180 205 234 266 299 0.34 149 164 184 209 238 269 302 0.35 153 168 187 212 241 272 305 0.36 158 172 191 216 245 275 308 l
0.37 162 177 196 220 248 278 311 l
- 0. 38 166 182 200 223 250 281 314 l
0.39 171 185 203 227 254 285 317 0.40
,175 189 207 231 257 288 320 l
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TABLE 2 CHEMISTRY FACTOR FOR BASE METAL, *F Copper.
Nickel, Wt-%
Wt-X 0
0.20 0.40 0.60 0.80 1.00
-1.20 0
EO E0 20 20 20 20 20 0.01 20 20 20 20 20 20 20 0.02 20 20 20 20 20 20 20 t
0.03 20 20
- 20 20 20 20-20 0.04
?2 26 26 26 26 26 26 0.05 25 31 31 31 31 31 31 0.06 28 37 37 37 37 37 37 r
0.07 31 43 44 44 44 44 44 0.08 34 48 51 51 51 51 51 0.09 37 53 58 58 58 58 58 0.10 41 58 65 65 67 67 67 0.11 45 62 72 74 77 77 77 1
0.12 49 67 79 83 86 86 86 l
0.13 53 71 85 91 96 96 96 0.14 57 75 91 100 105 106 106 L
0.15 61 80 99 110 115 117 117 l
0.16 65 84 104 118 123 125 125
- 0. 11 69 88 110 127 132 135 135 l'
O.18 73 92 115 134 141 144 144 l
0.19 78 97 120 142 150 154 154 0.20 82 102 125 149 159 164 165 0.21 86 107 129 155 167' 172 174 0.22 91 112 134 161 176 181 184 0.23 95 117 138 167 184 190 194 0.24 100 121 143 172 191 199 204 0.25 104 126 148 176 199 208 214 0.26 109 130 151 180 205 216 221 0.27 114 134 155 184 211 225 230 0.28 119 138 160 187 216 233 239 s
0.29.
124 142 164 191 221 241 248 0.30 129 146 167-194 225 249' 257 0.31 134 151 172 198 228 255 266 0.32 139 155 175 202 231 260 274 0.33 144 160 180 205 234 264 282 0.34-149 164 184 209 238 268 290 0.35 153 168 187 212 241 272 298 0.36 158 173 191 216 245 275 303 0.37 162 177 196 220 248 278 308 0.38 166 182 200 223 250 281 313 0.39 171 185 203 227 254 285 317 0.40 175 189 207 231 257 288 320 16
4 i
renewal has been submitted, the licensee shall submit by (9 months after the effective date of this section) an analysis and schedule for imple-mentation of such flux reduction programs as are reasonably practicable to avoid exceeding the PTS screening criterion set forth in para-graph (b)(2) of this section. The schedule for implementation of flux reduction measures may take into account the schedule for submittal and anticipated Commission approval of detailed plant-specific analyses, sub-mitted to demonstrate acceptable risk at values of RT above the PTS screening limit due to plant modificattns, new information or new anal-ysis techniques.
(4) For each pressurized water nuclear power reactor for which the analysis required by paragraph (b)(3) of this section indicates that no i
reasonably practicable flux reduction program will prevent the value of L
RT from exceeding the, PTS screening criterion befo m the expiration PTS l
date of the operating license, or the projected, expiration date if a change in the operating license has been requested, or the end of a renewal term if a request for license renewal has been submitted, the licensee shall submit a safety analysis to determine what, if any, modifications to equipment, systems, and operation are necessary 'to I
prevent potential failure of the reactor vessel as a result of postu-lated PTS events if continued operation beyond the screening criterion is allowed.
In the analysis, the licensee may determine reactor vessel materials properties based on available information, research results, and plant surveillance data, and may use probabilistic fracture mechanics techniques.
This analysis must be submitted at least 3 years before the value.of RT as defined in paragraph (b)(2) of this section is pro-PTS jected to exceed the PTS screening criterion or by one year after the effective date of this amendment, whichever is later.
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(5) After consideration of the licensee's analyses (including effects of proposed corrective actions, if any) submitted in accordance with paragraphs (b)(3) and (b)(4) of this section, the Commission may, on a case-by-case basis, approve operation of the facility at values of RT in excess of the PTS screening criterion.
The Commission will PTS consider factors significantly affecting the potential for failure of f
the reactor vessel in reaching a decision.
(6) If the Cosatssion concludes, pursuant to paragraph (b)(5) of I" **C
this section, that operation of the facility at values of RTPTS l
of the PTS screening criterion cannot be approved on the basis of the t
licensee's analyses submitted in accordance with paragraphs (b)(3) and l-(b)(4) of this section, the licensee shall request and receive Commission approval prior to any operation beyond the criterion. The request must be based upon modifications to equipment, systems, and operation of the facility in addition to those previously proposed in the submitted anal-yses that would reduce the potential for failure of the mactor vessel due to PTS events, or upon further analyses based upon new information or improved methodology.
Dated at Rockville, MD this */d day of $/O,1989.
For the Nuclear Regulatory Commission.
A 4
J es M. Tay f ecutive D Wector for Operations 18
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