ML19294B252
| ML19294B252 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 02/04/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19294B245 | List: |
| References | |
| NUDOCS 8002280050 | |
| Download: ML19294B252 (6) | |
Text
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UNITED STATES y
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WASHINGTON. D. C. 20555 5
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49.....,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 19 TO PROVISIONAL OPERATING LICENSE NO. DPR-45 DAIRYLAND POWER COOPERATIVE LA CROSSE BOILING WATER REACTOR (LACBWR)
DOCVET NO. 50-409
1.0 INTRODUCTION
By letter dated January 17,1980 (Reference 1), Dairyland Power Cooperative (DPC) requested an amendment to Provisional Operating License No. DPR-45.
The amendment would modify the Technical Specifications for the La Crosse Boiling Water Reactor (LACBWR) to extend the current cycle 6 operation.
2.0 DISCUSSION The requested change in the Technical Specifications applies only to fuel cycle 6.
The change involves the current 15,000 MWD /MTU exposure limit on the lead fuel assembly within the core.
It is presently estimated that the highest exposed fuel assembly in the LACBWR will reach this limiting exposure on February 4,1980.
DPC requests that an incremental increase of 350 MWD /MTU be granted initially and that one or more additional incremental increases of approximately 300 MWD /MTU be considered as each interim limit is approached.
DPC proposed to furnish additional reactor coolant and gaseous effluent radioactivity data for our consideration prior to each proposed incremental increase in the fuel exoosure limit.
Upon review of the information provided by DPC, the staff requested that specific limits be imposed on the monitored reactor conditions during any extended cycle 6 operations.
The limits, agreed to by DPC (Reference 2),
on the monitored reactor conditions provide assurance that any fuel degradation will be held to a minimum during the extended cycle 6 operations.
These limits, and the basis of these limits are discussed below.
80022800 @.
. 3.0 EVALUATION 3.1 Exposure Limit The exposure limit of 15,000 MND/MTU for the lead burnup fuel assenbly was first incorporated in the Technical Specifications associated with cycle 5 operation.
The primary purpose of the exposure limit was to reduce the potential for extensive fuel failure.
A more complete discussion of the basis of this limit is provided in our Safety Evaluation Report (SER) (Reference 4) supporting cycle 5 operation.
The SER for cycle 5 acknowledged that the staff would consider any new evidence in support of operation beyond the 15,000 MWD /MTU limit.
Near the end of cycle 5 (E0C), DPC requested authcrization to operate beyond the 15,000 MWD /MTU limit on the lead asscmbly.
The staff denied the request because no new evidence was provided to justify that operation beyond that limit would not result in gross fuel failure. However, DPC considers the cycle 6 core con-figuration unique in that it contains only 12 irradiated Allis-Chalmers Type II fuel assemblies and they are all located in the outer row of the core.
This is contrasted with 64, 48, 47, 48 and 40 irradiated Allis-Chalmers fuel assemblies at the beginning of cycles l A, P. 3, 4 and 5 respectively which were scattered throughout the core.
Operating experience at LACBWR has shown that the outer row of 28 fuel assenblies have a much loi e rate of failure than the 44 interior fuel assemblies.
This < and has been attributed to the lower power density at these lor.oions, and the minimal effects of control rod movements which cause local power peaking in the fuel rods near the tips of the control rods.
The outer control rods are fully withdrawn at the beginning of cycle (B0C) and generally remain withdrawn during normal cycle operations.
Since all the high exposure fuel in the LACBWR is in low power density peripheral core positions, minor clad defects that may be present or may develop during continued operation would be expected to develop very slowly, and the consequences of such failures would be minimal.
The probability of a failed fuel rod propagating a failure in an adjacent rod is remote because of the low power densities present in the peripheral core positions.
Alpha activity monitoring of the reactor coolant will provide indications of any gross fuel rod failures during the cycle 6 extension period.
Additional on-line measurenents to monitor the fuel performance and to minimize fuel degradation during the extended cycle 6 operations are discussed below.
. Based on the above considerations, and review of the LACBWR operating experience, the staff is in agreement with DPC concerning the uniqueness of the cycle 6 core configuration.
Because the cycle 6 lead burnup fuel assembly is located at the periphery of the core, the staff has concluded that the operating experience does support reconsideration of the existing 15,000 MWD /MTU exposure limit.
3.2 Limits on Monitored Reactor Conditions At the request of the staff, DPC has proposed that the allowable limits (Reference 2) on monitored reactor conditions for the extended cycle 6 operation shall not exceed those values measured during E0C-5 operations.
These limits should assure that fuel degradation during the extended cycle 6 period will be no more than that observed at the E0C-5, which are briefly described as fol:0ws:
At the E0C-5, all defective assemblies were Type II Allis-Chalmers assemblies. A total of 17 probably defective assenblies, including 5 assemblies with possible indications of fuel clad defects, were identified by the licensee.
These 5 assemblies did not exhibit any visible defects. Therefore a reasonable assecsment wculd in-dicate that at least 12 defective and possibly as many as 17 defective assemblies were observed during E0C-5 inspections.
The number and extent of failed (defective) fuel assemblies at EOC-5 was in good agreement with the 16 + 3 fuel clad failures predicted and determired acceptable by tee NRC staff in our SER supporting cycle 5 operation.
The proposed limits which are based on E0C-5 measurenents are more restrictive than the current Technical Specification requirements which have been previously approved (Reference 3) by the staff.
Since the current limits h6ve proved to be an effective control to limit the severity and extent of fuel failures at LACBWR, we have concluded that the more restrictive limits should provide assurance that the 12 high exposure Type II fuel assemblies will not exhibit unacceptable degradation during the extended cycle 6 operations. A comparison of the recent January 10, 1980 LACBWR measurenents with the current Technical Specification limits, and with the more restrictive limits proposed for the cycle 6 extension period are provided below.
. Monitored Limits For Measured Values on Reactor Current Technical Cycle 6 January 10, 1980 Condition +
Specifications Limits +
Extended +
(85% power)
Gross Alpha
-6
-6
-6 Activ i ty**
5.0x10 u Ci/gm 0.9x10 Ci/gm 0.4x10 Ci/gm 131 1
Dose Equivalent **
0.2 u Ci/gm 0.082 u Ci/gm
.017 u Ci/gm Off-gas Activity at 150 cu. f t.
Hold up Tank Effluent Monitor 750 Ci/ day 571 Ci/ day 246 Ci/ day 3.3 Operating Limits on MCPR and Exposure The staff approved (Reference 3) the operating limits, Minimum Critical Power Ratio (MCPR), for the LACBWR cycle 6 operation up to a core average exposure of 8134 MWD /MTU.
This core average exposure is coincident with the 15,000 MWD /MTU exposure on the lead burnup fuel assembly.
In Reference 3 the staff noted that turbine trip and generator load rejection pressurization transients with postulated failures of the bypass valves were not performed.
Instead, the licensee addressed these events as being similar to the MSIV closure overpressure analysis which was provided.
Even though we agreed that phenomenalogically these events are similar, the effects on the calculated ACPR may differ significantly.
- However, since these pressurization transients are only limiting at, or near, the End of Cycle-All Rods Out (E0C-ARO) conditions, the 15,000 MWD /MTV exposure limit precluded the two pressurization transients as limiting events because the rods would not be fully withdrawn at the equivalent 8134 MWD /MTU core average exposure.
This condition based on the 15,000 MWD /MTV exposure limit on the lead fuel assembly would leave approximately 2500 MWD /MTU of remaining full power capability.
The requested change which would allow additional accumulative exposure on the lead burnup fue' ssembly would also result in additional control rod withdrawals to mani; _in the desired power levels.
Likewise the postulated pressurization transients could then become limiting events with respect to the allowable ope ating limit MCPRs.
At less fhan full power operation these values are adjusted downward
+
in accordance with Technical Specification requirements.
- Activity in primary coolant
. Therefore, until the licensee provides supporting analyses that the pressurization transients cannot cause penetration of the cycle 6 approved operating MCPRs, the exposure limit on the lead burnup fuel assembly shall be limited to 15,600 MWD /MTU.
This limit leaves approximately 1500 MWD /M11J core average exposure before reaching the E0C-AR0 condition where the margin to the setpoints for opening safety valves is reduced because the rods are fully withdrawn and the resultant reactivity collapse when the rods are scrammed following a pressurization transient is slowest.
At 1500 MWD /MTU before the end of cycle the margin between the highest pressure achieved and the safety valve opening pressure is acceptable because sufficient control rods remain partially inserted in the core during normal operation (control rod bite) to reduce reactor power when all rods are scrammed before the pressure increases to the safety valve setpoint.
Our design criteria of no pressure relief during transients is therefore satisfied.
The basis for the new exposure limit on the lead fuel assembly /MTV on has been discussed with the licensee. Operation beyond the 15,600 MWD the lead burnup fuel assembly, even if the monitored reactor conditions are below the limting values discussed in Section 3.2, will require NRC approval of the licensee's analyses of the above described transients.
The staff 'inds the proposed changes to the Technical Specifications which would allow operation of LACBWR beyond the originally approved (Reference 3) cyc!e 6 exposure limit acceptable.
Our acceptance is based on new operating limits described in Sections 3.1, 3.2, and 3.3.
It is also noted that our evaluation and approval is applicable only to the cycle 6 core configuration.
4.0 ENVIRONMENTAL CONSIDERATION
S We have detemined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made this detenninat on, we have further concluded that the amendment involves an ac' ion which is insignificant frog the standpoint of environmental inipact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
5.0 CONCLUSION
We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the healch and safety of the public will not be endangered by operation in the proposed manner, and (3) 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 or to the health and safety of the public.
6.0 REFERENCES
1.
F. Linder (DPC) letter to D. Ziemann (NRC), LAC-6739, requests Technical Specification Change on F posure Limit at E0C-6, January 17, 1980.
2.
F. Linder (DPC) letter to D. Ziemann (NRC), LAC-6767, supplements LAC-6739, January 28, 1980.
3.
D. Ziemann (NRC) letter to F. Linder (DPC), transmitting Amendment 16 approving cycle 6 operation at LACBWR, May 25, 1979.
4.
R. Reid (NRC) letter to J. Madgett (DPC), transmitting Amendment 11 approving cycle 5 operation at LACBWR, March 3,1978.
Date:
February 4, 1980