ML20237G728

Safety Evaluation Re Fast Neutron Fluence for Fracture Toughness Requirements for Protection Against PTS Events. Plant Satisfies Fracture Toughness Requirements for Protection Against PTS

ML20237G728
Person / Time
Site:	Millstone
Issue date:	08/24/1987
From:	Office of Nuclear Reactor Regulation
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ML20237G719	List: ML20237G717 ML20237G728
References
TAC-59964, NUDOCS 8709020386
Download: ML20237G728 (3)

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1. jog UNITED STATES

!' o NUCLEAR REGULATORY COMMISSION h E f WASHINGTON, D. C. 20555

% /

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO FAST NEUTRON FLUENCE FOR FRACTURE TOUGHNESS REQUIREMENTS FOR PROTECTION AGAINST PRESSURIZE 0 THERMAL SHOCK EVENTS 10 CFR 50.61 NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE UNIT 2 00CKET NO. 50-336

1.0 INTRODUCTION

By letter dated January 23, 1986, t.he Northeast Nuclear Energy Company (Ref. 1),

the licensee for the Millstone Unit 2 nuclear power plant, submitted information on the material properties and the fast neutron fluence of the reactor pressure j vessel, in compliance with the requirements of 10 CFR 50.61. Additional j information regarding the pressure vessel fluence was submitted at the staff's j request on July 6 and July 31, 1987 (Ref. 2 & 3). We have reviewed the ]

material properties and chemical composition and found them acceptable, j l

The following evaluation concerns the estimation of the fluence to the pressure l l vessel for 32 effective full power years (40 calendar years) of operation and  !

the corresponding value of the RT pts' l

2.0 EVALUATION I The intermediate-to-lover shell circumferential weld 9-203 of the reactor ,

i pressure vessel has been identified by the staff as the controlling material, i l therefore, the applicable value of the fluence for the estimation of the is the azimuthal peak incident on the inside surface of weld 9-203.

RT}[iouldbenotedthatthelicensee(Ref.2)identifiedtheintermediate ItP l l plate C505-1 as the controlling element. The difference is due to the i l different criterion as to what is the controlling element. The licensee l" accepted the difference of the [(Screening Criterion) - RT ] at 32 effective l fullpoweryearswhilethestaffconsideredtheelementwhNilwillreach first the screening criteria of 10 CFR 50.61. Although the above difference.

at 32 effective full power years for the plate C501-1 is smaller than the I

weld 9-203, the latter will reach the screening criterion at a lower va.lue of the fluence due to a higher chemistry factor, hence, we have selected weld 9-203 as the critical element.

The fluence estimate was performed using the 00T.3 two dimensional discrete I

ordinates code, the P expans angular quadrature. kowever,ionTorthescatteringcrosssectionandtheSthecode(withtheC set) has not been benchmarked for the purpose of estimating fast (E > 1.0 MeV) neutron fluence to the pressure vessel, but nevertheless it showed good agreement with measured quantities from the W-97 surveillance capsule. The staff requires a benchmarked code for the estimation of the fast neutron fluence to the pressure vessel. However, in this case because of the large margin of the critical element at 32 effective full power years, the licensee added 40% to the previous estimate to cover potential uncertainties due to code benchmarking. At about 1991 another surveillance capsule has been scheduled for removal. The analysis associated with the capsule 8709020386 DR 870824 p ADOCK 0500033$

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. . measurements is the same as that required for the estimation of the pressure vessel fluence. The licensee will then perform the analysis with a i benchmarked code and if the results support an adjustment of the 32 effective i full power year value of the RT pts they will apply for such change. I The equation specified in 10 CFR 50.61, as applicable for the Millstone Unit 2 l reactor is:

0 RT pg3 = I+M+(-10+470xCu+350xCuxNi)xf .27 where: I = Initial RT d = -55 F I M = UncertaintMkargin = 48* F Cu = w/o Copper in weld 9-203 = 0.30 Ni = w/o Nickel in weld 9-203 = 0.06 f = peak fluence (F'>

gg 1.0 MeV) 2 on weld 9-203 l in units of 10 n/cm = 7.0 Jj The above values are in agreement with the NRC staff's evaluation. The )

, Chemistry Factor (CR, 'F) was determined to be 137.3.

The value of f, peak fluence for 32 effective full power years of operation includes the 40% adjustment discussed above. l J

=- 0 Then RT pts = 55+48+(-10+470x0.30+350+0.30x0.60)x7.0 27 7.0+137.3x1.69=232.2-7.0=225.2 F which is lower than 300 F, the applicable 10 CFR 50.61 criteria and, hence, is I acceptable.

The RT pts margin is = [(screening criterion) - RTpts] = 300-225.2 = 74.8 F Note:

Solving the RTC505-1andwe18t$equationforthescreeningcriteriaforplate 203 one finds:

C505-1 f = 27.88 9-203 f = 19.69 which justifies the selection of weld 9-203 as the critical element.

3.0

SUMMARY

AND CONCLUSIONS We have reviewed the information submitted by the Northeast Nuclear Energy Company, the licensee for the Millstone Unit 2 plant, in compliance with the requirements of 10 CFR 50.61. We find that the estimated value of the fast neutron fluence to the pressure vessel to have conservative error margins and thus is acceptable. The value of the RT based on this fluence estimate is lessthanthe10CFR50.61screeningcri@ionandisacceptable. In addition, the controlling material has been properly identified. The justifications given for copper and nickel contents and the initial RT are acceptable. ThemarginhasbeenderivedfromconsiderationofthebasbTfor these values, following the PTS Rule, Section 50.61 of 10 CFR Part 50.

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The staff concludes, based on the considerations discussed above, that the Millstone 2 plant satisfies the fracture toughness requirements for protection I l

against pressurized thermal shock.

4.0 REFERENCES

1. Letter from J. F. Opeka, Northeast Nuclear Energy Company to NRC, dated January 23, 1986.

2. Letter from E. J. Mroczka, Northeast Nuclear Energy Company to USNRC, dated July 6, 1987.

3. Letter from E. J. Mroczka, Northeast Nuclear Energy Company to USNRC, dated July 31, 1987 l Principal Contributor:

l L. Lois Dated:'%[jG 2 4191El l

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