ML20058A174
| ML20058A174 | |
| Person / Time | |
|---|---|
| Site: | Millstone, Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 11/03/1978 |
| From: | Counsil W NORTHEAST UTILITIES |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19289A035 | List: |
| References | |
| NUDOCS 7811130193 | |
| Download: ML20058A174 (14) | |
Text
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L IJ November 3, 1978 Docket Nos. 50-213 50-245 Director of Nuclear Reactor Regulation Attn:
Mr. D. L. Ziemann, Chief Operating Reactors Branch #2 U. S. Nw lear Regulatory Commission Washington, D. C.
20555
References:
(1)
D. L. Ziemann letters to W. G. Counsil dated June 13, 1978.
(2)
W. G. Counsil letter to D. L. Ziemann dated August 1,1978.
(3)
W. G. Counsil letter to D. L. Ziemann dated October 13, 1978.
Gentlemen:
Haddam Neck Plant Millstone Nuclear Power Station, Unit No.1 Spent Fuel Scorage Racks In Reference (1), Connecticut Yankee Atomic Power Company (CYAPCO) and Northeast Nuclear Energy Company (NNECO) were informed that as a result of the swelling phenomenon of the high density spent fuel storage racks at the Haddam Neck Plant, the NRC Staff requested additional information in order to complete their evalua-tion of this event. In Reference (2), CYAPCO and NNECO submitted information in respanse to the NRC Staff request. In those instances where the information was l
not yet available, a schedule was provided.
In the attachment to Reference (2), it was stated that the schedule for submitting information was based on an evaluation program that was developed to address both (a) the structural adequacy of the B4C material when exposed to a spent fuel pool environment, and (b) whether a correlation exists between the rate of gas generation, l
total accumulated dose and fuel can deflection. To address Item (a), a requalifica-l tion program was developed and described to the NRC Staff at a meeting on June 21, 1978. The first three major tests of that program have been completed, and the results of these tests were presented to the NRC Staff on Thursday, October 26, 1978. Accordingly, this letter forwards the Carborundum Company Tect Program Report No. CBO-N-78-299 which describes the requalification program tests and results. Due to the proprietary nature of the material contained in this report, CYAPCO and NNECO request that this information be withheld from public disclosure in accordance with the provisions of 10CFR2.790 (an affidavit is provided with the report). A non-proprietary version of this report is included as Attachment (3) to this letter.
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-- 2 The Test Program Report plus the results of additional analyses have provided the hformation necessary to address the NRC Staf f concerns in the attachment to heference (1). Therefore, CYAPCO and NNECO hereby submit the attached information (Attacluent (1)), in response to the NRC Staff questions in Reference (1). Also, the analyses addressing Item (b) above have been completed and are summarized in Attachment (2).
It is the conclusion of CYAPCO and NNECO that the results of the first three tests as contained in the Test Program Report, demonstrate and verify the original deter-mination that the B C material will maintain its structural adequacy when exposed 4
to a spent fuel pool environment. In the long term, this conclusion will be supplemented by the results of the fourth test of the requalification program and a surveillance program nionitoring samples in the spent fuel pool (s). Therefore, it is the intent of CYAPCO and NNECO to pursue internal " plant design change pro-cedures" for the purpose of ventinr, the spent fuel racks to preclude gas pressure buildup. This internal procedure would be based on the Test Program Report and, of course, would be reviewed in accordance with 10CFR50.59.
Should this design change be approved and found not to constitute an unreviewed safety question, it is anticipated that the vented racks will be used to store spent fuel no earlier than December 1,1978 at the lladdam Neck Plant and Millstone Unit No. 1.
Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY NORTilEAST NUCLEAR ENERGY COMPANY 17f01161 W. G. Counsil Vice President Attachments 4
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DOCKET NO. 50-213 50-245 ATTACHMENT NO. 1 IIADDAM NECK PLANT MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 ADDITIONAL INFORMATION i
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l OCTOBER 1978 l
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ATTACHMENT NO. 1 DOCKET HOS. 50-213 AND 50-245 HADDAM NECK PLANT MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 ADDITIONAL INFORMATION Provided below are the answers to the NRC Staff questions enclosed with Reference (1).
In those instances where so stated, the NRC Staff concern will be addressed in the presentation of the requalification program results to be given to the Staff on Thursday, October 26, 1978.
1.
Provide a description and schedule of your program to investigate and resolve the effects of gas generation within the annular space containing the boron carbide (B C) neutron absorbing material utilized in your spent 4
fuel storage rack design.
Provide the results of any work completed to date including those efforts which took place prior to the observation of fuel rack swelling at the Haddam Neck Plant.
Response
This information was provided in Reference (2).
2.
a.
The mechanism and rate of gas generation including quantity and composition of the gases.
Response
This information will be provided in the test report and will be discussed with the NRC Staff on October 26, 1978.
b.
The magnitude of the stresses in the neutron absorber plates considering the limiting loading conditions for the unvented geometry for the rack with the maximum anticipated swelling and demonstrate that such stresses are acceptable. This analysis should consider mechanical properties of the material including the effects of irradiation, temperature, and strain rate.
Response
The B C neutron absorber plates have a minimum compressive strength 4
greater than 12,000 psi,and this strength would be virtually unaffected by the effects of the irradiation exposure and temperature experienced to date in the Haddam Neck pool environment.
It is projected that the racks which experienced the highest swelling (i.e., those cells which had the inner cell walls contact the stored fuel assembly) could have experienced an internal pressure of approxi-1
2 mately 60 psig.
If it is conservatively assumed that this pressure is resisted solely by compressive loading on the edges of the boron carbide plates, the maximum compressive stresses on the plates are calculated to be less than 2,600 psi which is acceptable when compared to actual strength of 12,000 psi.
c.
Qualification testing which will demonstrate satisfactory material performance of the B C plates in the spent fuel pool environment 4
- for the design life of the racks including the ef fects of irradia-tion and temperature.
Response
This information will be provided in the test report and will be discussed with the NRC Staff on October 26, 1978.
d.
Should you propose a design change which would expose B C plates 4
to the pool water, 1)
State the maximum percentage of boron oxide, B 02 3, in the B C.
Since B 023 is soluble in water, it will either be 4
necessary to assune that this amount of boron is leached from the boron plates or to experimentally demonstrate that this will not happen during the life of the racks.
Response
This information will be provided in the test report and will be discussed with the NRC Staff on October 26, 1978.
11)
Address any possible corrosion effects in the annulus between the absorber plate and its protective canning and its safety consequences conside' ring the environnent.
Response
f l
The boron carbide plates contain boric oxide which when exposed to the spent fuel pool water might form a boric acid solution in the annulus between the absorber plate and its protective canning. General corrosion of the type 304 stainless steel cans is negligible in this environment.
There are also small quantities of leachable chlorides and fluorides (less than 100 ppm total) in the finished plates; but as none of the seal welds on the cans are load bearing 0
welds and the nornal service temperatures of less than 120 are less than the threshold for significant halide induced stress corrosion, the potential for and effects of this type of corrosion are not significant. Because venting of the cans obviates the need for a leak-tight seal, the effect of such corrosion, should it be postulated to occur, would be to provide greater water flow through the annulus and thereby reduce the halide concentration in the water.
l
3 iii)
Identify the structural effect of long-term exposure of the B C plate to boric acid, if applicable.
4
Response
This information will be provided in the test report and will be discussed with the NRC Staff on October 26, 1978.
iv)
If there has been swelling of the pool racks, determine the magnitude of the stresses in the neutron absorber plates considering the limiting loading condition for the vented geometry for the rack with the highest swelling and denonstrate that such stresses are acceptable. This analysis should consider mechanical properties of the material including the effects of irradiation, temperature, and strain rate.
Response
In the design of the lladdam Neck Plant and Millstone Unit No. 1 spent fuel storage racks, the minimum strength require-ments for the boron carbide neutron absorber plates were based on the following criteria:
a)
The neutron absorber plates are required to have sufficient flexibility to conform to the most adverse curvature of the fuel can during SSE or OBE conditions.
b)
The minimum modulus of rupture, which occurs with wetted plates, is assumed to coexist under conditions where the modulus of elasticity is a maximum (i.e., under dry conditions). This results in a conservative overestimate of the required bending strength for either wet or dry conditions.
The stresses in the neutron absorber plates within vented fuel storage cans will be equal to or less than those considered in the design of the racks.
v)
Provide the results of qualification testing which will demonstrate satisfactory material performance of the B C 4
l plates in the spent fuel pool environment for the design i
life of the racks including the effects of irradiation, temperature, water, and boric acid.
Response
This information will be provided in the test report and will be discussed with the NRC Staff cn October 26, 1978 y
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Docket Nos. 50-213 50-245 ATTACHMENT NO. 2 IIADDAM NECK PLANT MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 GAS GENERATION CORRELATION l
OCTOBER 1978
ATTACHMENT NO. 2 DOCKET NOS. 50-213 AND 50-245 HADDAM NECK PLANT MILLS'IONE NUCLEAR POWER STATION, UNIT NO. 1 GAS GENERATION CORRELATION The free paths of the spent fuel storage cells in the Haddam Neck spent fuel racks, which had been used to store spent fuel, have been measured; and the calculated gas generation in these cells was correlated with the radiation dose received by neutron absorber plates.
A model was developed to determine the increase in internal cell volume and pressure within a particular cell based on measurements made with a specially designed free path measurement gauge (FPMG) which employed a linear variable differential transformer (LVDT).
The cumulative dose was calculated for each cell based on the known burnup and decay time for the fuel assembly stored in each cell. The method for calculating cumulative dose was developed from the NRC Branch Technical Position APCSB 9-2:
" Residual Decay Energy for Light Water Reactors for Long-Term Cooling."
A linear regression was performed to determine the correlation between gas generation and cumulative dose.
Figure 1 shows the correlation between the gas generation and cumulative dose. The line which has been drawn was predicted by the linear regression.
As can be seen from this figure, the data points tend to group in clusters about particular ranges of cumulative dose.
These clusters represent the groups of assemblies from the same core with the more recent cores showing higher doses and correspondingly higher cumulative gas generation.
The rate of gas generation shows a side variation above and below the regression line.
The reason for this variation was reviewed in detail and found to be primarily due to the exposure a particular cell received from the assemblies stored in the cells adjacent to it.
A survey of the data points above and below the predicted line indicated that in the case of cells with high gas generation, they were generally surrounded by cells storing assemblies from the same or more recent cores, while for cells with low gas generation, those cells were generally surrounded by empty cells or cells storing assemblies from the sane or older cores.
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8 10 12 le 16 10 2o 22 24 26 29 30 32 CUMULATIVE DOSE (RADS X 105 Figure 1 CONNECTICUT YANKEE FUEL STORAGE CELL GAS GENERATION Versus CUMULATIVE DOSE
Docket No. 50-213 50-245 ATTACHMENT NO. 3 HADDAM NECK PLANT MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 CARBORUNDUM TEST PROGRAM REPORT NONPROPRIETARY VERSION OCTOBER 1978
C AR EBO R U N D U M The Carborundum Company Electro Minerals Division Post Office Box 423 Niagara Falls, New York 14302 TESTING PROGRAM
SUMMARY
Overview Technological trends relative to on-site spent fuel storage facilities have led to the use of boron carbide containing materials as neutron absorbers in compact spent fuel rack designs. However, in the last few months, un-certainties have arisen regarding the use of these materials in spent fuel pool environments.
Since Carborundum has engineered boron carbide materials for use in compact spent fuel racks, a testing program was implemented which would address material concerns expressed by the Nuclear Regulatory Commission staff, engineering designers and utilities.
A four-part testing program was designed and presented to the Nuclear Regulatory Commission staff in order to evaluate the effects of spent fuel pool environmental conditions on Carborundum's boron carbide materials and to provide information for license submittals involving Carborundum boron carbide materials. The testing program was designed to subject materials to an environment prototypical of a commercialspentfuelgools. Test parameters included the use of a full-spectrum gamma source in the 10 -108 RAD per hour range and water chemistry representative of BWR and PWR spent fuel pools. Tests were conducted in accordance with established, l
accepted analytical procedures and in compliance with quality assurance programs.
All test specimens were statistically randomly selected from a grand population that was produced from materials manufactured under standard production procedures.
l THE TESTING PROGRAM HAS SHOWN THAT BOTH PLATE AND COMPOSITE BORON CARBIDE MATERIALS EXCEED ALL ENGINEERING DESIGN CRITERIA EVALUATIONS AND THAT THERE ARE NO INDICATIONS l
THAT THE MATERIALS WILL PRESENT PROBLEMS WITH THE USE IN EITHER BWR OR PWR SPENT FUEL ENVIRONMENTS WHEN MATERIAL BEHAVIOR CHARACTERISTICS ARE INCORPORATED INTO RACK DESIGN.
I-l
CARBDRUNDUM The Carborundum Company Electro Minerals Division
- Post Office Box 423 Niagara Falls, New York 14302 TESTING PROGRAM SCOPE To determine the effects of radiation on Carborundum boron carbide materials OBJECTIVE Generic approval for the use of Carborundum boron carbide materials in spent fuel rack design TESTING PROGRAM PARAMETERS
- y radiation prototypical of spent fuel pool
- Dose rates in the 10 -108 RAD / hour rate 6
- Water chemistry prototypical of spent fuel pool TEST PROGRAM Mechanical Properties Test
- To determine the mechanical properties of B C 4
plate and composite materials when simultaneously exposed to y radiation (109 & 1010 RAD) and water Gas Generation Test
- To determine the quantity and composition of gases l
generated l
Leachability Test
- To determine if boron will leach from B C materials 4
when simultaneously exposed to y and DI water l
l Long Term Mechanical Properties Test l
1
- To determine the long term (1011 RAD) mechanical properties of B C materials 4
1 MECHANICAL PROPERTIES TEST Objective - To verify the adequacy of the mechanical properties of B C plate and composite materials when 4
simultaneously exposed to radiation and water 8
l Radiation - Dose Rate 10 107 RAD / hour Dose 109, 1010 RAD Samples - plate in D1 water plate in borated water composite in DI water composite in borated water l
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CAABOAUNDUM The Carborundum Company Electro Minerals Division Post Office Box 423 Niagara Falls New York 14302 MECHANICAL PROPERTIES TEST cont'd.
Results - MOR, M0E, UTS Test - Samples: All samples were selected using accepted random sampling techniques from archive standard production material Summary - B C plate and composite materials maintain 4
accepted mecgnical properties after ex-posure to 10 RAD gamma and prototypical BWR and PWR spent fuel pool environments Plate MOR 5000 psi M0E 13.0 x 105 Composite UTS 6500 psi M0E 1.7 x 105 psi
- B C plate and composite materials exhibited 4
dimensional stability after exposure to 1010 RAD gamma and prototypical BWR and PWR spent fuel pool environments
- B C plate and composite materials exhibited 4no significant weigh loss after exposure to 1010 RAD gamma and prototypical BWR and PWR spent fuel environment PLATE MECHANICAL
_ DI WATER __
_B0 RATED WATER Baseline 10W RAD 10iu RAD 103 RAD 10iu RAD MOR(psi) 7375 5586 4902 5226 5066 5
M0E (psi x 10 )
17.4 17.5 12.7 17.7 14.1 COMPOSITE MECHANICAL
_ DI WATER _
_B0 RATED WATER Baseline 1DV RAD 10iu RAD 10V RAD 10iv RAD UTS (psi) 8838 8457 6591 8160 7695 5
M0E (psi x 10 )
2.24 1.64 1.73 1.67 1.75 NOTE:
Each datum value represents the mean of measurements taken on separate sets of samples
CARBORUNDUM The Carborundum Company Electro Minerals Division Post Office Box 423 Niagara Falls, New York 14302 GdSGENERATIONTEST Objective - To determine the quantity and composition of gases generated that can provide a basis for the evaluation of the gas generation mechanism 8
Radiation - Dose Rate 10 +107 BAD / hour 9
l 10,10 u RAD Dose Samples - plate composite Results - Quantity and composition of gases generated Test - Samples: All samples were selected using accepted random sampling techniques for archive standard production material Sumary - Polyethylene reference material generated hydrogen gas at a rate consistent with literature
- B C plate material generates gas with major 4
fraction H2 and minor fraction CO2
- B C composite material generates gas with 4
H2 as predominant species LEACHABILITY TEST Objective - To determine rate of boron leachability from B C plate under influence of a simultaneous 4
exposure of y and DI water 8
9 Radiation - Dose 10, 10, 1010 RAD Results - Determine B in sample water Tests - Samples: All samples were randomly selected using accepted sampling techniques from archive production lot material Summary - B C plate exhibited no signLficant loss of 4
0 RAD y and 4
boron during exposure to 10 DI water
- Extended exposure of 8 C plate to DI water 4
alone predicts less boron leachability than can be attributed to B 023 impurity
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CAABDRUNDUM The Carborundum Company Electro Minerals Division Post Office Box 423 Niagara Falls, New York 14302 LO'NG TERM MECHANICAL PROPERTIES TEST Objective - To determine the long term mechanical properties of 8 C materials when simultaneously 4
exposed to radiation and water 8
Radiation - Dose Rate 10 +l107 RAD / hour Dose 10l RAD l
Samples - plate in DI water composite in DI water Schedule - Start Date: October 1978 Completion:
Early February 1979 CORRELATION WITH ACTUAL OPERATING EXPERIENCE Test results provide strong parallels with data from actual operating experience Test data shows the experimental environment to be prototypical of LWR spent fuel pools ABBREVIATIONS MOR - Modulus of rupture as determined by appropriate ASTM test methods i
M0E - Modulus of elasticity as determined by appropriate ASTM test methods UTS - Ultimate tensile strength as determined by appropriate ASTM test methods l
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