ML17278A869
| ML17278A869 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/23/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17278A868 | List: |
| References | |
| TAC-60739, NUDOCS 8605300668 | |
| Download: ML17278A869 (7) | |
Text
y~p,S REg~
~o ly 0O
~O
+a*++
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 ENCLOSURE 1
8S05S00gZ8 aq05aa PDR ADOCK 05000397 P
PDR SAFETY EVALUATION BY THF. OFFICE OF NUCLEAP. REACTOR REGULATION RELATING TO SATISFACTION OF LICENSE CONDITION 2.C. (8)
WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PLANT NO.
2 DOCKET NO. 50-397
1.0 INTRODUCTION
In letters dated February 4,
- 1986, and May 9, 1986, from G.
C. Sorensen of the Washington Public Power Supply System to E.
G. Adensam of the
- NRC, the licensee submitted information in response to License Condition 2.C.
(8).
The license condition requires the licensee to provide analyses showing the effects of hiqh-burnup fission gas release on loss-of-coolant accident analyses prior to startup following the first refueling outaqe.
In order to provide available peak cladding temperature (PCT) margin to offset the effect of high-burnup fission gas release, the licensee took credit for calculated PCT margin which had previously been applied to offset the effects of cladding ballooning and rupture.
In its submittals, the licensee provided revised justification for the resolution of the issue of cladding ballooning and rupture.
- 2. 0 EVALIJATION In our Safety Evaluation Report '(Reference 1),
we indicated that in 1976 we questioned the validity of fission gas release calculations in most fuel performance codes including GEGAP-III for burnups greater than 20,000 megawatt days per ton of uranium.
In References 5 and 6, GE requested that credit for calculated peak cladding temperature margin as well as credit for approved but unapplied ECCS evaluation model changes
'be used to offset any operating penalties due to high burnup fission gas release.
While the staff found this proposal acceptable in other cases
'(Reference 4), the licensee (Reference ll) had claimed credit for calculated peak cladding temperature margin to satisfy staff concerns on cladding ballooning and rupture.
As a result, the license was conditioned to require the licensee to provide for NRC staff review and approval of revised analyses showing the effects of high-burnup fission gas release on loss-of-coolant accident analyses prior to startup following the first refuelinq outage.
As discussed below, the issue of cladding ballooning and rupture has
0
~
~
~
~
subsequently been resolved for WNP-2 without taking credit for PCT margin.
Using the available PCT marqin to offset the effects of high burnup fission gas release, the licensee demonstrated in Reference 3 a minimum PCT margin of 229'F for all GE fuel types with the fission gas correction.
The analysis used the NRC method (NUREG-0418) of correcting gas release calculations for burnups greater than 20,000 MWD per ton of uranium and provided data for maximum burnups of 44,000 MWD/MT average planar exposure for high enrichment and medium enrichment GE fuel and of 38,600 MWD/MT average planar exposure for natural uranium GE fuel.
The staff has reviewed the licensee's submittal and concludes that the issue of enhanced fission gas release at high burnup (License Condition 2.C. (8)) is satisfactorily resolved for WNP-2 for the burnup limits described above.
The staff conclusion is based on (1) the demonstration of available PCT margin to accommodate the fission gas correction within the 2200'F PCT limit required by 10 CFR 50.46 and (2) the existence of additional PCT margin of approximately l50'F to 200'F for approved but unapplied ECCS models.
In addition, the staff has reviewed and approved (Reference
- 4) similar requests (References 5 and 6) that credit for calculated peak cladding temperature margin as well as credit for:
approved ECCS evaluation model changes be used to offset the effects of high burnup fission gas release on operating margin to the PCT limit.
With regard to cladding ballooning and rupture, the staff indicated in the Safety Evaluation Report (Reference I) that three fuel material models used in ECCS analyses were being generically evaluated.
These models predict cladding rupture temperature, cladding burst strain, and fuel assembly flow blockage.
We have (I) met and discussed our review with General Electric and other industry representatives, (2) published NUREG-0630, "Cladding Swelling and Rupture Models for LOCA Analysis," and (3) required fuel vendors and licensees of light water reactors with Zircaloy cladding to confirm that their operating reactors would continue to be in conformance with emergency core cooling system criteria of 10 CFR Part 50.46 if the material model of NUREG-0630 were substituted for those models in their emergency core cooling system evaluation
- models, as indicated by our letters dated November 9, 1979 from D.
G. Eisenhut to all Operating Light Water'eactors and November 26, 1979 from H.
R.
Denton to the Commissioners.
This latter requirement was made a condition of approval of the GE ECCS evaluation model '(Reference 7).
'A generic sensitivity study of fuel rod cladding ballooning and rupture phenomena during a
LOCA was submitted '(Reference
- 8) in response to this condition of approval.
As reported in the generic study, GE assessed the BWR 'ECCS sensitivity to rupture temperature by using three rupture temperature models:
(I) the GE CHASTE model, (2) the NUREG-0630 mode],
and.(3) a proposed GE model termed the adiusted model.
For the WNP-2 type of 8X8 two-water-rod fuel design, GE found that the use of the adjusted model, which is a combination of the CHASTE and NUREG models, gave a maximum impact on PCT of al0'F.
~
l E
i
~ The staff has completed its generic review of the generic sensitivity study (Reference 9). The staff review concluded the following:
'(a)
The proposed "adjusted" claddinq rupture temperature model is acceptable because it does not underestimate the incidence of rupture based on applicable data including those reported in NUREG-0630 and more recent data.
(b)
The existing cladding models for prerupture strain, postrupture
- strain, and strain used for oxidation calculations are acceptable because GE has shown that the calculated values of peak cladding temperature and percent oxidation are sufficiently insensitive to variations in claddinq strain.
These conclusions generically resolve the issues related to NUREG-0630 and the GE ECCS evaluation model.
Because the approved cladding models were used in the plant specific WNP-2 ECCS analysis (References 3 and 10), the issue of cladding ballooning and rupture is resolved for WNP-2 without taking credit for PCT margin to offs'et the cladding rupture and claddinq ballooninq uncertainties.
3.0 CONCLUSION
The staff has concluded, based on the considerations discussed above that:
(1) License Condition 2.C.
(8) has been satisfactorily resolved for maximum burnups of 44,000 MWD/MT average planar exposure for high enrichment and medium enrichment GE fuel and of 38,600 MWD/MT average planar exposure for natural uranium GE fuel, and (2) the issue of cladding ballooning and rupture is resolved for WNP-2 without taking credit for PCT margin.
The staff has concluded, based on the considerations discussed
- above, that:
( 1) there is reasonable assurance that the health and safety of
~ the public will not be endangered by operation in the proposed
- manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security nor to the health and safety of the public.
Principal Contributor:
G. Y. Suh Dated:
~
~
1 e
'T e
l
Y
~
~ I
~
7
~
REFERENCES 1.
Safety Evaluation Report related to the operation of WPPSS Nuclear Project No. 2, Docket No. 50-397, NL~REG-089?, March 1982.
2.
Letter from G.
C. Sorensen of the Washinqton Public Power Supply System to E.
G. Adensam of the NRC, dated February 4, 1'986.
3.
Letter from G.
C. Sorensen of the Washington Public Power Supply System to E.
G. Adensam of the NRC, dated May 9, 1986.
4.
Memorandum from L. S. Rubenstein of the NRC to T.
M. Novak of the
- NRC, dated June 25, 1981.
5.
6.
Letter from R.
E.
Enqel of the General Electric Company to T. A. Ippolito of the NRC, dated May 6, 1981.
I Letter from R.
E. Engel of the General Electric Company to T. A. Ippolito of the NRC, dated May 28, 1981.
7.
Letter from R. L. Tedesco of the NRC to G.
G. Sherwood of the General Electric Companv, dated February 4, 1981.
8.
Letter from R.
H. Buchholz of the General Electric Company to L. S. Rubenstein of the NRC, dated May 15, 1981.
9.
Letter from H. Bernard of the NRC to G.
G. Sherwood of the General Electric Company, dated May 11, 1982.
10.
Letter from G.
D. Bouchey of the Washington Public Power Supplv System to A. Schwencer of the 'NRC, dated September 30, 1982.
11.
Letter from G.
D. Bouchey of the Washington Public Power Supply System to A. Schwencer of the NRC, dated January 19, 1982.
i, '0 I,ta a
~
o f
l