ML19318B343
| ML19318B343 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 06/20/1980 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19260E316 | List: |
| References | |
| NUDOCS 8006250268 | |
| Download: ML19318B343 (10) | |
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General Offices: 212 West Michigan Avenue. Jackson, Michigan 49201 e Area Code S17 788-0550 n
June 20, 1980 Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Branch No 5 U S Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPE BIG ROCK POINT PLANT - QUANTITATIVE THERMM, AND STRESS ANALYSIS OF SPENT FUEL POOL STRUCTURE AS A RESULT OF POOL BOILING This letter provides information concerning two issues relating to Consumers Power Company's request to expand spent fuel storage capacity at Big Rock Point.
The issues are 1) integrity of structural elements in the event of boiling in the spent fuel pool, and 2) provision of makeup water to the spent fuel pool in the event containment cannot be entered.
By letter dated February 1, 1980, Consumers Power Company committed to supply the NRC a quantitative analysis on the effects of pool boiling on the concrete structure, racks and liner of the Big Rock Point Plant spent fuel pool. This analysis was intended to answer concerns raised as a result of submittals by Consumers Pcwer Company on December 28, 1979, (response to Question 3 of that submittal), and January 16,1980, (response to Item h of that submittal). The results of the analysis conclude that during the worst case condition, the stress-es that develop are within design limits. Transmitted herewith is one (1) copy of the NUS Analysis entitled, " Structural Analysis of the Spent Fuel Pool Liner and Concrete Due to Coolant System Failure for the Big Rock Point Nuclear Power Plant-NUS 3567", one copy of the related themal analysis of the spent fuel pool wall, and one copy of a letter from NUS to Mr e Larsen (CPCo) dated May 20, 1980, with its attachments.
With respect to the second issue, response number h of Consumers Power Company letter dated January 16, 1980, requires minor correction. A revision to this response is attached.
Changes are indicated by a vertical line in the margin.
David P Hoffman (Signed)
David P Hoffman Nuclear Licensing Administrator CC JGKeppler, USN w NRC Resident Inspector - Big Rock Point Attachments (3) s 006250 2GJf g
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Item 4 Discuss the capability to detect loss of pool cooling and loss of water level in the event an accident occurred which would prevent entry into containment for an extended period of time.
Discuss the capability to cool the pool water and provide makeup to the pool if equipment inside the containment failed and containment could not be entered.
Re.ponse The capability to detect the loss of pool cooling is provided in the control room by status indication of spent fuel pool cooling systems (SFPCS) pump motor operation. An indication that both pumps are not operating identifies a possible loss of forced pool cooling.
There is no instrumentation presently installed in the plant specifically designed to provide direct indication of spent fuel pool water level.
Capability to detect a reduction in the water level in the pool is possible by a local constant area monitor and a criticality monitor. These monitors alarm in the control room on high radiation that could result from a reduced pool water level. We will, however, install remote indicating spent fuel pool water level instrumentation prior to the installation of the new spent fuel storage racks, to provide means to augment the existing capability.
As ' discussed in telephone conversations with USNRC staff, a lack of capability to cool the pool water is not considered significant as long as the effect of boiling conditions in the pool will not adversely affect the integrity of the racks, liner and concrete structure, that evaporative losses from the pool
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6 will not cause overpressurization problems in the containment and the level of water can be maintained to prevent uncovering of the stored spent fuel.
A qualitative evaluation has been done to address the effects of pool boiling on the rack, liner and concrete structure. The results of the evaluation con-clude that boiling conditions are not postulated to adversely affect the fuel racks, liner or concrete structure. A discussion of this finding can be found in Consumers Power Company's response to Question 3 in the December 28, 1979, submittal.
Overpressurization of containment as a result of pool boiling is considered unlikely due to the fact that the boil-off rate is so small (approximately 11 gpm in the worst case, see April 23, 1979, submittal). As a result of this very small energy re, lease, it is concluded that the containment enclosure spray will prevent containment overpressurization since it is designed to prevent over-pressurization in the event of a LOCA.
The capability to provide makeup water to the pool (actuated from outside contain-ment) will be available prior to completion of the spent fuel pool rack modifica-tion project. Three types of water are being considered for the makeup source to the fuel pool:
a) demineralizer water, b) treated waste water, c) fire water. This will ensure makeup capability.for an extended period of time in the event containment cannot be entered and that makeup capability will be more than enough to offset evaporative losses.
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NUCLEAR UCENSING 5803-002 May 20,1980 Mr. Carl Larsen Engineering Supervisor Generating Plant Modifications Dept.
Consumers Power Company 1945 Parnell Road Jacksen, Michigan 49201
Subject:
Big Rock Point Plant - Elevated Temperature Considerations
Dear Mr. Larsen:
Per our conversation during our May 7,1980 meeting please find enclosed the following two NUS internal memos.
1.
Internal Memo R. Sacramo to G. Antonucci - EMD-RFS-013
" Structural Integrity of the Spent Fuel Racks after a Fool System Failure at Big Rock Point Nuclear Power Plant".
2.
Internal Memo - R. Sacramo to G. Antonucci -
EMD.-RFS-014
" Big Rock Point - Effects of the gent Fuel Pool Concrete Strength at Coolant Boiling Temperature".
At your convenience, we can discuss these memos. If you have any questions please call me.
Very truly yours,
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j G. J. Antonucci Project Manager cc: Mr. Joe Gallo NUS of Michigan File P. D. Arrowsmith I. L. Renehan F. E. Muellner i
R. Sacramo
EM D-RFS-014' j
i CORPORATION INTERNAL CORRESPONOENCE TO:
George I. Antonucci, Jr.
CATE:
May 16,1980 FROM:
Ray Sacramo #f COPIES: J. Wawrzeniak
SUBJECT:
Big Rock Point - Effects of the Spent Fuel Pool Concrete Strength at Coolant Boiling Temperature
REFERENCES:
1.
Internal memo 5148-INT-030, "May 8,1980 Big Rock Spent Fuel Pool Modification Meeting - Responses to Intervenors," dated May 8,1980 2.
CONF-790408-3, " Strength Properties of Con: rete at Elevated j
Temperatures," April 2,1979 3.
Telecon between Dave Blanchard of CPCO and H. Eckert of NUS, March 27,1980 4.
NUS Report 3567, " Structural Analysis of the Spent Fuel Fool I.iner and Concrete Due to Coolant System Failure for the Big Rock Point Nuclear Power Plant," April 18, 1980 In the event that the Big Rock Point spent fuel pool coolant system were to fail, the temperature of the coolant could eventually reach the boiling point, 23fF. The structural integrity of the spent fuel pool concrete at this higher temperature was addressed in Reference 4. An additional concern was posed at the referenced meeting as to what concrete degradation, if any, could be expected if the boiling condition were to exist for a prolonged period of time.
The purpose of this memo is to. address this question. It should be noted, however, that although the concrete compressive strength does effect the totalload carrying capacity of the wall and floors, the major factor is the yield strength of the ieinforcement in moment carrying loading conditions.
From Reference 3 the 28-day strength of the Big Rock Point Spent Fuel Pool Concrete is fc = 2500 psi. This strength will decrease at higher temperatures.
A literature study included in Reference 2 provides upper and Jower bounds on 1
the percent of concrete strength reduction at temperatures up to 1600*F. Based on the literature study of Reference 2, a reduction to 80% of the 25-day concrete strength was used as a lower bound in the Reference 4 structural integrity analysis.
The compressive strength of concrete also increases with age. This increased strength was not taken into account in the Reference 4 structural integrity analysis. The test results of 6 to 19 month old concrete cylinders of a lime-stone aggregate mix were presented in the Reference 2 technical paper. The r
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EM D-RFS-014 May 16,1980 Page Two concrete cylinders were heated to their test temperature at a rate of 30*F/hr and maintained at the test temperature for'14 days. The compressive strength at failure for the various test temperatures was compared to the 28-day com-pressive strength at normal temperature (approximately 70 F). The results showed that for older concrete, the ccapressive strength at 237 F was ap-proximately 130% of the 28-day old st:ength at normal temperature. Since only 80% of the 28-day strength was considered in the Reference 4 structural analysis, a margin of 130/80 = 1.625 may be realized.
Other considerations which would prolong the permitted time that the spent fuel pool coolant could remain at boiling are listed below.
1.
The temperature gradient across the spent fuel pool walls will decrease as a function of time after the maximum gradient is reached. This is due to the cutside pool walls and flocr in-creasing in temperature. The results would be a decrease in concrete compressive stresses.
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2.
Although the longer the duration of heating a test specimen, the larger the loss in strength, this loss of strength does stabilize after a period of long isothermal exposure (Refer-ence 2). Isothermal conditions will be reached in the 2.0' and 3'-6" walls by 14 days (the time maintained at temper-ature before testing). The 6'-9 " wall and 6'-0" floor would also be cl,ose to approaching these conditions; therefore, the loss in concrete strength would be reaching a stabilizing point.
3.
Since the age of the spent fuel pool concrete is well in ex-cess of the 6-19 month old concrete, the compressive strength would be at least that of the test specimen.
The effects of aggregatewouldalsoinfluence the strength of heated concrete.
For example:
1.
lean mixes (low cement / aggregate ratio) lose less strength due to heating then richer mixes; 2.
concrete made with limestone aggregate degrades less due to heating than concrete mad,e with siliceous aggregate.
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2MD-RFS-014 May 16,1980 l
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l The lower bound reduction percentage,.8fe, discussed earlier would encom-pass the above effects of aggregate mixtures. The margin of 1.625, based on concrete age compressive strength, may be Icwer if the pool concrete was made with a siliceous aggregate.
- In summary based on available test data, the concrete strength used in the Reference 4 structural analysis represents a lower bound value. The effects of prolonged ecolant boiling conditions would not degrade the compressive strength beyond the value analyzed, for the following reasons..
1.
Lower bound values to encompass the effects of aggregate mixture were considered.
2.
The loss'of strength would stabilize after a period of long isothermal exposure.
3.
The actual strength of aged concrete, like that at the Big Rock Point spent fuel pool, would be much higher than the 28-day strength used in the structural analysis.
A further literature search will continue,to better understand the effects of aggregate mixture on concrete strength.
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d EM D-RFS-013 CORPORATION INTERNAL CORRESPONDENCE G. Antenucci, Jr. /
DATE:
May 12,1930 To:
FROM:
R. Sacramo //f COPIES:
H. Eckert I.
awrzeniak
SUBJECT:
Structural Integrity cf the Spent Fuel Racks After a Pool Coolant System Failure at Big Rock Point Nuclear Power Flant
REFERENCES:
- 1. USNRC Standard Review Plan 3.8.4 "Other Category I Structures,"
November 24, 1975.
- 2. ASME Boiler and Pressure Vessel Code: Section III, Division 1, Appendices Nuclear Power Plant Components,1977 Edition.
3.
Nuclear Systems Materials Handbook, TID-26666, Volume 1,
" Design Data" Book 2.
Property Codes 2101, 2102 and 2105, Revision 0, September 30, 1976.
4.
Specification #5148-P-103, " Revision 2" Design Input Require-ments for. Big Rock Point Spent Fuel Rack Modification Project, May 14,1979.
In the event that the spent fuel pool coolant system were to fail, the temper-ature of the coolant could eventually reach the boiling point. De maximum boiling temperaturs of the coolant, 23f F, would occur at the top of the active length of the spent Mel assemblies. Bis represents an 8fF increase in temperature from the design temperature of the racks,150*F, identified in Reference 4.
De change in temperature would cause the racks to experience a slight ther-mal expansion. With the racks not being restrained, and constructed of the same material, no additional stresses will develop. Only the change in rack material strength properties requires investigation to assure ::tructural integ-rity of the racks. If design conditions for the racks can be maintained after the temperature rise, rack distortion would be prevented, and the distances to assure criticality will be maintained.
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t EMD-RFS-013 May 12,1980 Page Two A comparison of the strength properties for the existing aluminum racks and new stainless steel racks at the design and boiling temperature is given Strength properties were obtained 'from References 2 and 3, respec-below.
tively, for the stainless steel and aluminum racks.
Ultimate Temperature Yield Strength Strength Su ocsi)
Rack Material
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Sv Oc si) 150 27500 73000 304 Stainless Steel 237 24125 69150 150 39755 43605 Aluminum Alloy 6061-T6 237 38316 43360
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T be yield strength of the stainless steel racks decreases by 12.3% while the yield strength of the aluminum racks decreases by only 3.6%.
De stainless steel racks were designed in accordance with the elastic design criteria of Reference 1. Bis criteria permits only the extreme fibre stresses to slightly exceed yleid. Be new racks meet this criteria for the worst design condition, which also included seismic loads. For the abnormal loading condition of pool coolant boiling, the plastic design criteria of R
Reference 1 allows the entire cross section to reach 90% of yield.
margin realized under this design criteria is well in excess of the 12.3%
reduction in material yield strength. Werefore,the new stainless steel racks would meet the plastic design criteria of Reference 1 for even'the combined loading condition of seismic loading during boiling conditions of the coolant.
In the case of the existing aluminum racks, the same analogy would hold true.
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l EMD-RFS-013 May 12,1980 Page Wree In summary, the new spent fuel s:crage racks would withstand the worst design loads, even at boiling conditiens of the coolant, while maintaining structural integrity and criticality limits. 2e reduction in the aluminum racks' yield strength would be only 3.6L This reduction in strength is ser.11 and, hLnce, the effect of boiling is insignificant..
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