ML20091Q445
| ML20091Q445 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/31/1992 |
| From: | Parker T NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-008, IEB-88-8, TAC-M69673, TAC-M69674, NUDOCS 9202040411 | |
| Download: ML20091Q445 (7) | |
Text
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Northem States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401 1927 Telephone (612) 330 5500 January 31, 1992 U S Nuclear Regulatory Conunission NRC Bulletin 88 08 Attn: Document Control Desk Washington, DC 205$5 PRAIRIE IS1AND NUCLEAR GENERATING PIANT Docket Nos. 50 282 License Nos. DPR 42 50 306 DPR 60 Response to NRC Bulletin 88 08, " Thermal Stresses in Piping
.Qnnnected to Reactor Coolant Systems" (TAC Nos D19673 andf69674)
Reference:
Le t te r,
A.
S.
Hasciantonio (NRC) to T.
M.
Parker (NSP), dated November 4, 1991, NRC Bulletin 88 08, " Thermal Stresses in Piping Connected to Reactor Coolant Systems" This letter is provided in response to Bulletin 88 08, " Thermal Stresses in Piping Connected to Reactor Coolant Systems".
We initiated an evaluation and actions upon receipt of Bulletin 88-08 and the responded to the Bulletin by letters dated associated supplements and we September 30, 1988 and June 2, 1989.
Per the referenced letter, we have been asked to further respond to Action 3 of the original Bulletin.
While our 1988 response to Bulletin 88-08 did not commit to continuous temperature monitoring, we have since then implemented temperature monitoring for both Prairie Island units. We have determined that 'is monitoring complies with the guidelines given in the referenced " Evaluation Critecia for Responses to NRC Bulletin 88 08, Action 3 and Supplement 3." swnmarizes the review of Prairie Island activities in regard to this Bulletin, following the outline of the Evaluation Criteria."
Please contact us if you have any questions related to our response.
/
lKf it/ V l homa M Parker Manager. l Nuclear Support Services 1 i 03000.1 g) < ', 9202040411 920131 l PDR ADDCK 05000286 O PDR
_._._. ____._,... _ __ m.. m...__._, Northern States Power Company USNRC Page 2 of 3 I January 31,-1992 c: Regional Administrator - Region III. NRC Senior Resident Inspector, NRC Nim Project Manager, NRC J E Silberg Attachments
- 1. Affidavit
- 2. Prairie Island Response to Bulletin No. 88 08
+ e A Y r l 4 t h h r
= UNITL 4TES NUCLEAR REGUIATORY COMMISSION NORTHERN STATES POWER COMPAtW PRAIRIE ISLAND NUCLEAR CENERATING PLANT DOCKET NO 50 282 50 306 Thermal Stresses in Piping Connected to Reactor Coolant Systems Northern States Power Company, a Minnesota corporation, with this letter is submitting information requested by NRC Bulletin 88-08. This letter contains no rastrict 4 or other defense information. NORTHERN STAT P COM ANY ~ By Thomas M Parker Manager, Nuclear Support Services Onthis8/ ay of _ /9fc2 before me a notary public in and for said County, personally [/ppeared Jhomas M Parker, Manager, Nuclear Support Services, and being first duly sworn acknowledged that he is authorized to execute this . document on behalf of Northern States Power Company, that he ' sows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are rue and that it is not interpos-i for delay. W sa .?LO g i c ::::::::::.:::::::::::::.:::.:::: O NOTARY PUBUC-M!NNESOTA MARCiA h. LaCORE H, IPIN COUNTY My Commssion Ex;mes Sept 24,1933 ar::::::::::::::,wwsw :::::::::^:a
i PPAIRIE IS1AND RESPONSE TO BULLEf1N No. 88-08 THERMAL STRESSES IN PIPING CONNECTED TO REACTOR COO 1ANI SDJf,143 1.0 OBJECTIVE To provide continuing. assurance that unisolable sections of all piping connected to - the reactor coolant system (RCS) will int be subjected to thermal stratification and thermal cycling that could causo fatigue failure during the remaining life of the Prairle Island plant. 2.0 - D POSE -To summarize actions taken and planned by the Prairie Island plant, z including procedures and criteria to prevent crack initiation in l susceptible unisolable piping. 3.0 JnENTIFICATION OF POTENTIALI_Y SUSCEPTIBLE PIPING (1j The only Prairic Island lines which meet the characteristics of the " Evaluation Criteria" (1) A, B, C, and D are the auxiliary pressurizer spray lines'between the charging line and the main pressurizer spraj line. Prairie Island has one charging line which is always in service (i.e., there is no alternate charging line where one line is out of service). (2) Prairie Island lines which meet the characteristics of " Evaluation Criteria" (2) A, B, and C are the residual heat' removal (RHR) lines. Leak-off piping from the RHR ' vrlves is routed to the Pressurizer Relief Tank-ar.d potentiel leakage can be monitored and corrective action taken if necessary. 4.0 ACTIONS 'TAKEN AND PIANNED The following actions were considered and implemented as appropriate: (1) The' auxiliary spray line is a branch line off of the charging line so 1 the option of reducing the pressure of the water upstream of the i . isolation valve below the ROS pressure during power operation is not -applicable to the Prairie Is1 nd configuration. (2) ' The option of-relocating check valves in assumed to be for the caso of potential in leakage of cold water and having the check valve beyond 25 pipe diameters would be so that the cold water would not be in close proximity to the turbulent region containing hot water from the reactor coolant loop. This has also been determined to be not applicable for the Prairie Island configuration. (3) Temperature monitoring has been installed on the auxiliary spray lines for both Unit i and Unit 2 for detection of piping thermal cycling due 2,-_._
Attachtnent 2 Page 2 of 4 to valve leakage into the RCS. i A. Type and location of sensors. a. RTDs were used for temperature sensors. b. Locating temperature monitoring instrumentation between the first elbow and tiie first check valve is for lines such as high pressure safety injection, and is t applicable for auxiliary spray lines. c. RTDs on the euxiliary spray lines were installed near the " tee" connection to the main pressurizer spray line and on the " cold" portion of the line, as well as on intermediate positions for Unit 1. The critical location was judged to be the " cold" portion of the pipe just downstream of the check valve since that area would be expected to show a relatively 1arge top to-bottom temperature difference in the event of valve leakaAe. d. RTDs were located within six inches of the welds. e. RTDs were installed at the top and at the bottom of the pipe at the monitoring locations. B. Determination of baseline tumporature histories. Baseline temperature histor.ies were obtained for the auxiliary spray lines following the September 1990 outage for Unit 2 and the June 1991 outage for Unit 1. This monitoring demonstrated that no valvo leakage was occurring and that there was not adverse temperature. stratification or cycling. Baseline temperature histories were compared against the Reference 1 " Evaluation Criteria"; a. The top-to bottom temperature differences were monitored downstream of the check valve.. Average results were: ' i 9 Unit 1 Unit 2 Top 220* F 145*F Bottom 200* F 135*F Difference 20* F 10*F These top to bottom temperature differences are woll within the 50* F guideline in the " Evaluation Criteria." The cooler temperatures on Unit 2 can be explained by the lack af thermal insulation on the valve, b. Top and bottom temperature time histories were in-phase for both Unit 1 and Unit 2 (i.e. the top-to-bottom temperature difference is relatively constant). ? ..,_,i.. ,-._r.- ,.,,s... .,m.m m-.
_. _ m _. m - - - _ _ _.. m ..._.m, q.___._m_ --.. -_ _.. ~. t t ' Atta.hnent 2 Page 3 of 4 i c. Peak to peak temperaturt: fluctuations were monitored and vere i found to be not more than 5' T in a 24 Four period 'the "Evalwation Criteria" adys they should not. t.xceed 60'F). C. Monitoring time intervals. a.- Monitoring was. performed at the followin6 titaas: 1. Monitoring was done for the auxiliary spray lines at the beginning of power operation, after startup from the refueling. ohutdovns in Occober 1990 for Unit 2 and in June 1991 for Unit 1. Tae.pral.tico of collecting monitoring data following startup from refueling outages wili continue in the fu ure. 2 Monitorine, has been done continuously f or Unit 2 since ' October 1990. On Unit 1, monitoring was _ donc during tractup following the June 1991 outage and then monthly for the next threm months. Since the:Jata has proven to be so conatant., consideration - will be g'ven to increasing thin interval to not mori thau six months, between refee ling outages. 6 b. ine monito ing period has been continuous for Unit! 2 since October-1990. Monitoring periods on Unit 1 have varied from several days to ' snapshots" to verf fy that the deta has rbraained constant. Tha practice of monitor *ng and recording temperau. ares continuous;f for a period not less than 24 brurs will coetinue fa the future. ( .-D..Exceedance Criter'a. i The conditions determincd frem temperature moni*oring have not 1 required any corrective action to date. a The maximum. temperature difference. between the top and the bottom uf the pipe at - the c,ritical location have remained bslm 50*T (r.:tual has been 10 ' 20' F). The Unik 1 auxiliary spray line has a 40 foot horizontal section Icading _ to the pressurizer spray tee connection. Temperature monitoring has shown that convective heat transfer-keeps this length of line relatively warm. The temperature drops by about 3* F for each foot going away from the hot source at the tec. The natural convective b )a c transfer
- currents in this long horizontal section cause the middle of the line to.have a top-to bottom temperature difference of about 20* F at the far end -(370-350* F), about 70* F in the middle (465-395*F), and about 15'F was measured near the tee (480 465'F).
Monitoring data has shown this is a steady t v ., - +,, --,,,,e. s -r,,-s 3 ..,g_ w-,-,,-r.c.p.n-n--7,w-, m-,,re-n .m.r-
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I l' age 4 of 4 i temperature distribution with no cycling occurring. Therefore, there is no fatigue concern for this situation and the slight global bending which might result is judged to be easily accommodated within the flexibility of the pipe hangers without increasing stress. n b. Top and bottom temperature histories have remained in phase and loth the top and the bottoic ceak to peak temperature r fluctuations have been le.is than o F over a 24 hour period ("Evalu tion Criteria" says not greater than 60'F). m c. Top and bottom tempetiture histories have remained in phase and the bottom peak tooeak temporature fluctuations have been less than 6.'F over a '?4 t our perled (" Evaluation Criteria" ) says not greater than 50* F). d. Temp 3ratureu nt each location have remained relatively ccostant and are simihr to the initially recorded baseline histories. (4) pressure monitoring cannot pre vide a measurement of thermal cycling in 4 the unisolable_ pipe sections and was determined not suitable for use 4' on the auxiliary spray lines f - C t t i ,.+~e ..E+,"#ne. -,-..<e.., wr---e.mm.---,.mmw-+-- e v e w -es -r m -,-w e-,,,-,. -.. -,,er,.-=, ,c-- ow_,,.-, m.=,..,4. --.c _}}