ML19256G473
| ML19256G473 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 12/28/1979 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| TASK-09-01, TASK-9-1, TASK-RR NUDOCS 7912310355 | |
| Download: ML19256G473 (5) | |
Text
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CORSumBIS s
M l Power i
Company m
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rj cene, i omc.: 2i2 west u.c Ngan Avenue. Jackson, Mict 'Jan 40201
- Area Code 517 788-0550 J
December 28, 1979 Director, Nuclear Reactor Regulation Att Mr Dennis L Ziemann, Chief Operating Reactors Branch No 2 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - PROPOSED EXPANSION OF SPENT FUEL STORAGE: RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION NRC letter dated November 28, 1979 requested additional information concerning the proposed expansion of spent fuel storage at Big Rock Point.
The questions asked and the related responses are as follows:
Question 1 With regard to installation considerations, your October 1,1979 and October 19, 1979 responses indicate that no rack will be handled in the vicinity of stored spent fuel. Verify and provide a basis for your conclusion that the possibility of a dropped or tipped rack on an empty rack will not impact and damage an adjacent rack with stored spent fuel.
Response 1 Installation of the new spent fuel racks will be in accordance with detailed procedures.
The procedures, which will be prepared by the installation contractor, will address specific transit paths and installation sequences to assure no damage to stored spent fuel from a postulated dropped rack.
A copy of the detailed installation procedures will be submitted for NRC review prior to commencement of any movement of racks in the spent fuel pool.
Question 2 Specify all arear or parts of the new racks which are not Type 304 stainless steel, and verify that the significance of corrosion, if any, related to these parts has been considered.
1656 028 7912310
2 Response 2 All parts of the new racks are fabricated from Type 304 stainless steel except for the leveling legs which are made from ASTM 276-UNSS21-800 hars. This material is an austenitic stainless steel of the 16-8 type with additives such as msnganese and silicon to improve the yield strength to almost twice that of Type 304 SS.
Corrosion tests performed and reported by manufacturers on the UNSS21-800 material indicate even better corrosion recistance properties than Type 304 SS when subjected to similar tests.
(
Reference:
ARMCO Product Bulletin S-56A.)
Question 3 Sections 3.2.1 and 4.16 of our Fire Protection SER dated April 4, 1979 acted that, due to lack of separation criterion for electrical cabling of redundant fuel pool cooling systems, postulated fires in various areas may result in loss of cooling systems for the spent fuel pool. We noted that the structural effects on the spent fuel pool due to boiling resulting from loss of the redundant systems had not been addressed and that you were evaluating the effect of boiling on pool integrity. Amendment 25 dated spril 4, 1979 required that you submit the results of this evaluation and any required protective actions by June 30, 1979. By telephone conversation with our staff you stated that your reply to our concerns was addressed in your April 23, 1979 submittal related to spent fuel pool capacity expansion. We have reviewed the April 23, 1979 submittal and f;nd your reply does not fully address our concerns. Therefore, we request that you verify with a detailed discussion that the increased thermal loads resulting from a double pump failure will not adversely affect the spent fuel pool racks, liner (including welds), and concrete structure.
In our fire protection reviews we have allowed credit to be assumed for fire damaged equipment 72 houra after a fire, provided licensees can provide information to assure that repairs can be made within a 72-hour period.
We, therefore, request that your discussion include the effects on the racks, liner, and structure of the coolin'g systems being unavailable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if repairs can be made within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
If repairs cannot be made within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, discuss the effects of the longer period of coot;ng system unavailability associated within the longer repair time. Discuss the measu.es that will be used to minimize the time period in which the cooling systems woulu not be available.
The discussion of the effects of loss of cooling systems should address the currently licensed storage rack design and capacity and your proposed rack design and capacity.
Response 3 We have evaluated the effect of boiling conditions on the spent fuel pool's integrity and have determined that should such an unlikely event occur, no corrective actions will be required to ensure integrity of the stored fuel kE
3 racks, liner or concrete structure other than providing makeup water to the pool to account for evaporative losses.
The onset of boiling conditions has been conservatively estimated to commence 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br /> after failure of the pool cooling system for the normal refueling case and 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> for the full-core off load case.
The fuel racks (both existing and new) will not suffer degradation in structural integrity that could result in any adverse changes in the geometry of the racks or their integrity in maintaining the stored fuel assemblies at the design spacings. The gradual heating of the pool and the minor temperature gradient that would exist along the racks and liner will not cause failure of the welds.
Short-Term Effects In the short term, following the onset of boiling conditions and prior to concrete equilibrium temperature conditions, a thermal gradient will be created in the first few feet of the concrete. This thermal gradient will result in greater stress due to its steeper slope than during equilibrium conditions.
A review of published literature (references attached) on the effects of midrange temperature on concrete indicates that a reduction in the residual compressive strength of the concrete in the first few feet of the wall and floor could be expected, but that overall structural integrity will be unaffected. No leakage in excess of present makeup capability can result even if the liner is ruptured, due to the integrity of the concrete pool structure.
Long-Term Effects Long-term effects following the establishment of a uniform temperature gradient through the pool walls and floor will be less severe than in the short-term case in terms of imposed stresses, since the slope of the gradient is less steep and it ext, ends across the entire thickness.
An overall reduction in the residual compressive strength of the pool structure of 10%, averaged over the entire thickness, has been conservatively assumed for this case.
It is expected that with the design margins available in the structure, the structure will not fail or deform to such an extent as to cause a loss of structural integrity.
No significant change would result in present as-licensed plant conditions regarding the potential for or severity of pool boiling as a result of the proposed fuel rack expansiSn. An increase in the number of fuel assemblies stored in the pool will only decrease the time required to reach boiling conditions. All other factors are present plant-licensed conditions.
In t: 3 unlikely event of a double pump failure in the spent fuel pool cooling system, appropriate actions will be taken by the plant staff to attempt i656 030
4 restoration of forced fuel pool cooling before pool boiling should occur.
However, as discussed above, should boiling conditions occur, there will be no adverse effects on the integrity of the spent fuel pool racks, liner or concrete structure.
David P Hoffman (Signed)
David P Hoffman Nuclear Licensing Administrator CC JGKeppler, USh3C Attachment 1656 031
REFERENCES FOR RESPONSE 3 1.
Freskakis, G N, et al, " Strength Properties of Concrete at Elevated Temperatures," Conf 790408-3, 1979.
2.
Abrams, M S, " Compressive Strength of Concrete at Temperatures to 1600 F,"
3.
Effect of Long Exposure of Concrete to High Temperatures, Concrete Information, Portland Cement Assoc, ST32-3-53.
4.
Hannant, D J, "The Effects of Heat on Concrete Strength," Engineering (London) Vol 197, No 5105, February 1963.
5.
Nasser, K W, et al, " Mass Concrete Properties at High Temperatures," ACI Journal Proceedings, April 1958.
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