ML19254F502
| ML19254F502 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 11/06/1979 |
| From: | Groce R Maine Yankee |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7911090543 | |
| Download: ML19254F502 (9) | |
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0 November,6, 1979 United State's Nuclear Regulatory Commission Washington, D.C.
20555 Attentian:
Office of Nuclear Reactor Regulation Mr. Robert W. Reid, Chief Re ferences:
(a) License No. DPR-36 (Docket No. 50-309)
(b) USNRC Letter to MYAPC dated September 24, 1979 (c) USNRC Letter to YAEC dated January 17, 1979
Dear Sir:
Subject:
Questions Pertaining to Cycle 5 Reload Fuel In reference (b) you requested info, nation pertaining to the Cycle 5 i
Reload Fuel which will be supplied by Exxon Nuclear Comp.iny.
Attachment A contains responses to your specific request for information.
Attachment B is a drawing of the waar sleeve which will be installed in the Exxon supplied fuel.
Cycle 5 operation is scheduled to commence on or about March 1,1980.
Although ENC will supply Cycle 5 reload fuel, Yankee Atomic Electric Company (YAEC) is performing the fuel management and safety analysis to support Cycle 5 licensing requirements. These analyses are being performed with methods previously reviewed and approved by the NRC and applied in the Maine Yankee Cycle 5 and Cycle 4 Reloads.
YAEC also intends to submit ECCS analysis using the model previously applied to Yankee Rowe and generically approved for Yankee PWR's in Reference (c).
It is our intent to submit these analyses on or about December 1, 1979.
We trust this information is acceptable to you, however, should you have any questions, please feel free to contact us.
Very truly yours, nf~
- c.r---
Robert H.' Groce Senior Engineer - Licensing JWH/kaf f32 7911090 b3
ATTACHMENT A NRC COMMENT INFORMATION REQUEST NRC Comment The items detailed in this attachment are addressed primarily at the capability of the reload fuel design to mitigate the guide tube wear that was observed in the CE NSSS facilities.
The overall capability of the reload fuel to perform its intended structural, thermal-hydraulic, physics, and power generation functions is beyond the intended scope of this attachment.
However, since sotm of the reload fuel desiga features to mitigate guide tube wear may effect other aspects of the fuel design capabilities, some overlap into reload areas is unavoidable.
It is our understanding that the reload fuel design will use sleeves in the upper section of the guide tubes to function as more resistant wear surfaces.
This design feature is similar to that used by Combustion Engineering as an interim modification.
Please note that CE attributes guide tube wear to flow-induced vibration of the Control Element Assemblies (CEAs).
Sleeving the Control Rod Guide Tubes (CRGTs) is not expected to eliminate vibration of the CEAs.
In regard to vibration of the CEAs, CE has performed loop-flow tests and installed a number of flow-codifying test assemblies in specific CE designed plants.
The results of these tests are not yet complete.
However the flow-modifying test assemblies are designed to eliminate or to reduce the flow-induced vibration of the CEAs.
Since current sleeving designs have not eliminated or reduced vibration of the CEAs, the long term vibration effects of the CEAs should be considered.
Address the following items before or in your planned reload submittal.
An eariv submittal of-this information will expedite the couplet ion o f_our review.
Response
o Fuel with flow-modifying features are presently being irradiated at Maine Yankee.
The flow-modifying features are expected to reduce, but not eliminate vibration of the CEAs. There is no known method of eliminating vibration of the CEAs without completely immobilizing them which would obviously interfere with normal CEA motion and the SCRAM function.
In order to make the fuel and CEAs compatible, the available options are:
1.
Reduce the level of vibration of the CEA's so that wear is maintained at an acceptable level 2.
Provide a surface in the guide tube which is resistant to wear by the CEA or 3.
A combination of the above.
Maine Yankee has chosen the third and most conservative option.
NRC Request
'^
A. De s i gn - In fo rma t ion Provide detailed drawing of the proposed reload fuel design. In particular describe and discuss those components and principles used in the reload fuel design to mitigate guide tube wear and vibration of the Control Element Assembly (CEA).
Response
Attachment B is a drawing of the guide tube wear sleeve which will be inserted in each of the guide tubes of the fuel assembly. The guide tube wear sleeve is made of stainless steel and has a hard chrome plated surface on the inside diameter. Dimples have been formed on the exterior of the tube to provide a light interference fit with the guide tube I.D. The purpose of the dimples is to center the sleeve in the guide tube and to prevent relative motion between the sleeve and the guide tube. The wear sleeves are installed in the guide tubes prior to installation of the upper end fitting. A flange at the top of the sleeve is trapped between the guide tube and the upper end fitting, thus preventing ejection of the sleeve from the guide tube during reactor operation. NRC Request B. Test Data 1. Provide information on any out-reactor, loop-flow prototype testing of the reload fuel design. This information may include results of flow visualization tests, thermal-hydraulic flow tests, and flow-induced vibration of the CEAs. Discuss the results, conclusions, and correlations obtained from these tests.
Response
A control element assembly (CEA) flow-induced vibration test was performed to verify that flow-induced CEA vibration could be induced in a single fuel assembly /CEA test setup, and to determine the vibrational and wear characteristics of the CEA interfacing nith a test fuel assembly having both unsleeved and sleeved guide tube assemblies. This flow-induced vibration testing was conducted in Exxon Nuclear's (ENC's) Portable Hydraulic Test Facility (PHTF). A Maine Yankee CEA and the ENC proof-of-fabrication fuel assembly both with and without guide tube wear sleeves where utilized. The interfacing hardware installed in the facility was designed to simulate in-reactor assembly inlet and exit flow conditions, as well as the in-reactor fuel assembly and CEA support arrangement. The PHTF vibration test program verified that CEA flow-induced vibration which could incur guide tube wear, as observed in the reactor, was also observed in the single fuel assembly /CEA test setup. Flow-induced vibration was detected with both the unsleeved and sleeved guide tube configurations. The vibration was monitored using eddy current sensors and a data acquisition system which calculated the power spectral density and Lutocorrelation function. The vibration frequency was 4 Hz with an amplitude of 0.002 to 0.005 inch without sleeves and 0.000 to 0.002 inch with sleeves. '"7 334 _7_
Th i s test program showed that vibration amplitude, and resultant ' wear, was rcJuced by the incorporation of sleeves. The sleeves improve the hydraulic draping and reduce the guide tube flow by reducing the annular gap, and also He a mechanical barrier against guide tube damage. A second portion of the test program was conducted in ENC's high pressure flow loop. The test conditions were: temperature 6000F, pressure 2000 psia, andflow 1950 gpm, with buffered borated water. The purpose of this test was to show that the wear sleeve design would successfully resist the control rod vibration at reactor temperature and flow conditions without significant wear. Af ter 250 hours of operation one sleeve was removed for examination and replaced with a new sleeve. Shiny areas were observed on both the CEA and on the wear sleeve but no measurable wear was observed. At 1000 hours of operation all the sleeves were removed and examined. Plating thickness from approximately 0.00025 to 0.00150 inch were tested. Burnished areas and discoloration were observec. Meta 11ographic and SEM analyses, however, showed no measurable change in plating thickness ( 0.00005 in) and no change in the composition of the plated surface. Both the CEA and the wear sleeves were in excellent condition at the conclusion of the test. The design plating thickness is 0.001 to 0.0015 inch. Assuming a maximum wear rate of 0.00005 inch per 1000 hours, the life of the specification plating thickness will be 20,000 hours which is more than adgequate to cover the expected life of a fuel assembly wh'ch includes up to two cycles in a CEA location and one or two cycles in a non CEA location NRC-Request 2. Provide information on any in-reactor demonstration essemblies that verifies the wear performance characteristics of the reload fuel design. Discuss, and compare, the performance of the in-reactor test assemblies with the prototype test assemblies and the current CE-designed fuel assemblies.
Response
There is no in reactor demonstration of Exxon supplied fuel whica incorporates a guide tube wear sleeve. However, all CE NSSS facilities have been operating since 1978 with chrome plated stainless steel wear sleeves to prevent degradation of guide tubes due to CEA vibration. The experience to date has been excellent. Consequently, chrome plated stainless steel has been demonstrated to be an acceptable surface to provide compatability with the CEAs. The performance of the ENC supplied wear sleeves is expected to be as good as or better than those supplied by Combustion. NRC Comment 3. Items 1 and 2 should include details of any examinations performed such as: (a) Methods of examinations i.e. : destructive, eddy current, periscope, borescope, mechanical gage, metallographic, flow visualization, T.V. ' ^ 7
(b) Areas of fuel assembly and guide tubes examined. (c) Results of examinations. (d) Numbers of samples in each data base including operations parameters such at-core location, Effective Full Power I:ours, time in service unoer CEAs, neutron fluence, coolant flow, thermal cycles, and any other related core parameter. (e) Qualification of test procedures.
Response
See 1 and 2 NRC-Request 4. Provide all correlations supported by your tests relative to guide tube wear during reactor operations over the reactor life of the reload f ael.
Response
To date no measurable wear has been observed on ENC supplied chrome plated wear sleeves, the re fo re, there is no correlation relative to guide tube wear with chrome plated stainless steel wear sleeves.. NRC Request 5. Provide information on c,ntrol rod scram tests that demonstra' a CEA scrambility for the reload fuel design. Address degraded scramability over the reactor life of the reload fuel. Include any strain, deflection, or time limits on control rod functions.
Response
Maine Yankee has been operating since 1978 with wear sleeves installed in the upper section of the CEA guide tubes. Normal SCRAM testing has demonstrated that the SCRAM time is not significantly affected by the wear sleeve. The wear sleeve provided by Exxon Nuclear results in the same geometry (relative to the SCRAM function) as that which is in the fuel presently in operation. Therefore, no change is expected in SCRAM time as a result of the ENC supplied wear sleeve. This will be verified by normal SCRAM testing prior to Cycle 5 startup. There is no expected degradation of scramability over the reactor life of the reload fuel since no significant wear of the CEA wear sleeve is anticipated. No strain deflection or time limits on control rod funtions arc anticipated. NRC Request C. Analysis b 1. Provide information and your evaluation of the chemical compatability between the sleeving and the CRGT. This evaluation shculd include consideration of corrosion p- .uct buildup, and coolant boiling in the annulus between the sleeving and the guide tubes. Res7onse Close coupled zircaloy and stainless steel is presently in service in almost every light water reactor in the United States. There is r.o known problems resulting from stainless steel zirconium couplings. Combustion Engineering has installed chrome plated stainless steel wear sleeves in fuel which it has fabricated and no problems have been observed. Since the annulus between the wear sleeve and guide tube in the Exxon supplied fuel is open at the top and bottom, it is anticipated that normal flow will prevent any corrosion product buildup and coolant boiling between the sleeve and guide tube. Flow in the annulus was demonstrated by the high temperature flow test discussed above. A well-defined pattern of discoloration was noted on the outside surface of the wear sleeves indicating flow was present. NRC Request 2. Provide the results of your stuctural analyses summarizing the CRGT loads and the primary and secondary stress intensitites for normal operation fuel handling, and accident loading conditions. The analyses should clearly demonstrate that a coolable geometry is maintained for all loading conditions, and that scram capability o'f the control rods is not impaired beyond " acceptable limits." Provide and discuss the determination of these " acceptable limits."
Response
The guide tube wear sleeve is not a structural component of the fuel assembly. The sleeve which Combustion Engineering supplied was installed on irradiated fuel to restore structural integrity of the fuel assembly. The Exxon sleeve is provided solely as a wear surface and is not considered a part of the structure. Scram capability of fuel assemblies with badly worn guide tubes was questioned because of the possibility of a CEA finger jamming in a hole worn in the guide tube. Since no wear is expected in the guide tubes, this problem will not exist for the ENC fuel assemblies. NRC-Request 3. Discuss your structural design bases and the allowable stresses used in the structural analysis. Indicate what provisions have been made to account for wear in the design, and what amount of wear would be unacceptable. Discuss the propensity for hydrogen uptake in the guide tubes as a function of wear. Discuss the effects of notch se ns itivity, irradiation hardening, hydrogen content of the Zircaloy, and thermal cycling, on the analysis. Discuss any differential thermal expansion or stress relaxation between the sleeving and the guide tubes. How does this relaxation effect the design and operational performance? Rrrnonse There is no structural design basis with respect to the guide tube wear sleeve since it is not considered a structural component of the fuel assembly. There provisions to account for wear in the design of the guide tube since no 2r ao is anticipated. However should such wear occur in the wear sleeve, <._ c c penetration of the chrome plating would be considered unacceptable for continued use with a CEA; however this would not result in degradation of the fuel assembly structure. There is no anticipated effect on hydrogen uptake in the guide tubes as a function ot' wear since no wear of the guide tubes is expected during the life of the fuel. There is no additional degradation of the guide tubes as a function of irradiation hardening or hydrogen pickup or thermal cycling over or above that normally anticipated in the basic fuel assembly design analysis. The guide tube wear sleeve is expected to prevent any degradation of the guide tube by CEA contact. The CEA wear sleeve is free to expand in the downward direction and therefore any d* fferential thermal expansion or radiation induced growth will be accommodated througout the life of the fuel. As the reactor is brought to operating temperature, differential thermal expansion will tend to tighten the wear sleeve in the guide tube at operating conditions. It is not expected that this will have any adverse effect on the operational performance of the sleeve. NRC Request 4. Discuss any administrative, or operational procedures indicated p rude nt, or necessary, by your analyses. Resp _onse No administrative or operational procedures relative to guide tube wear will be necessary with the present fuel design since no degradation of the fuel assembly structural members is anticipated. The life of the wear sleeve is expected to be longer than the residence time in a CEA location. e NRC-Request D. Fuel-Surveillance Provide details of a planned surveillance program (see item B.3) for the next and future end-of-cycle outage and your commitment to carry out this program. We request that this program be submitted far NRC review before Laplementation. The fuel surveillance program should assure that the existing and reload fuel performs in accordance with design.
Response
Maine Yankee is presently developing a sur veillance program for the future end-of-cycle outages. It is anticipated that surveillance of the kind and quantity as nec' sary to demonstrate continued safe operation of the fuel will be conducted. You will be notified of any such surveillance programs which might be developed prior to implementation. b.
Mh' Request ~~ CEA Sur_veillance You are requested to propose a CEA surveillance program which should include examinations and evaluations of the CEAs because of their continued vibration. The CEA surveillance program may include examinations addressed at identification of fatique cracking, stress corrosion cracking, abrasion, denting, toison material degradation (c ompac tion, and leakage), and other phenomena w'aich could impede their movement, degrade their design function, or reduce their design life. Responte Maine Yankee is currently working with Combustion Engineering to develop a CEA surveillance program. Our CEA vendor has assured us that the original design lifetime is not affected by the vibration which has been observed to result in CEA guide tube wear. One CEA from Maine Yankee was evaluated by pool side and hot cell examination and observed wear as a result of interaction with fuel assemblies was found to be insignificant. NRC will be advised of any significant progress in this area and will be informed of this program prior to implementation. NRC Request F. _ Limits; of Degradation Epecify the acceptance criteria, to be used in your surveillance programs, for continued use of the existing fuel, reload fuel and the CEAs. Justify the basis upon which these criteria have been determined. Specify the acceptance for repaired fuel and discuss the repair procedures. Specify the rejection criteria to discontinue the use of the fuel and the CEAs. _ Response Our vendor has assured us that there are no problems to be anticipated as a result of CEA vibration in the guide tubes. Appropriate accaptance criterion will be included in the surveillance program which is currently being developed. NRC will be informed of this program prior to implementation. '^7 339 Attacht:ent B END FITTING n a (STAINLESS STEEL) \\ s REMOVAL TOOL ENGAGEMENT HOLES l BRAZE JOINT K:R:111A () iid F- ~ h TUBE (STAINLESS STEEL) ) [ I.D. HARD CHROME PLATED i / .399 NOMINAL l.D., i, . I,.:. .014 NOMINAL WALL l!- l l.b.,,, i ~ jlli f EXTERNAL DIMPLES I PROVIDE LIGHT INTERFERENCE i x g,, y, i GUIDE WBE 1.D. .i APPROX. c. .gy ph, 3.} 'j{.'w't [4 $bY.:J: ,,,re. y .: g-p, M,:l[' ,, l t Fr f.4 a ;ii' i n s {f)J ih> 'l![ GUIDE TUBE WEAR SLEEVE ,i L l fhll::..:I!!bl ill MAINE YANKEE NUCLEAR STATION f t o. 4 M, 7 340 -}}