ML20037B183
| ML20037B183 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/06/1972 |
| From: | James Shea, Silver R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20037B177 | List: |
| References | |
| NUDOCS 8009080563 | |
| Download: ML20037B183 (7) | |
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UNITED STATES
-f N ATOMIC ENERGY COMMISSION
- ( M ','
wAssisoros, o.c.
os4s JUN 6 W2 Files (Docket No. 50-10)
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Ziemann, Chief, ORB #2, DL Q.
,w DRESDEJ 1 FR0 SED EMERGENCY CORE COOLING SYSTCI-(ECCS)
In a previous memo on this subject dated November 10, 1970, J. Shea i
concluded:
'Ihe proposed modification, which includes the emergency condenser, the post-incident containment cooling system and the firemain system as engineered safety features in addition to a new core spray system, results $n a significant improvement in core protection over the com-plete spectrum of pipe breaks up to and including double-ended rupture of the largest pipe, the 22-inch recirculation pipe. Tne DNPS-1 containment was designed-to contain' the total enel-gy released by a IDCA but not the molten core.
In this respect, therefore, the proposed modification will provide a new capability that does not now exist. It has not been detennined, however, that a single core spray system is sufficiencly reliable or that peak clad temperatures between 2000 F and 3000 F are tolerable. 'Ibese areas are to be investigated more thoroughly by CEC. Following an acceptable resolution of the concerns we have identified, it is expected that changes to the Technical Specifications will be made to assure that the emergency condenser, post containment cooling system, the firemain system or supply of emergency core cycling water i
and the new core spray system are properly tested at a frequency sufficient to assess the overall ECCS reliability.
l Tne infomation required to resolve the remaining questions was requested in our letters to CE dated December 28, 1970, and July 22, 1971.
In letters dated Farch 26, 1971, October 7, 1971, Nove=ber 8, 1971, November 22, 1971, and Februan 8, 1972, Cormonwealth Edison provided additional infomaticn related to reliability, acceptability of peak clad temperatures and proposed technical specifications. Several answers re-lated to-reliability are not acceptable and CE will be asked to provide additional infomation on this subject. Additional infomation on the acceptability of peak clad temperatures has been provided. Because of the issuance of the Interim Acceptance Criteria for Emergency Core Cooling Systems dated June 19, 1971, DFL requested by letter dated July 22, 1971, a
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Files JUN 81972 that CE resnalyze thei" prcpesed ECCS. ?,:o a"eas, reliability and acceptability of peak clad temeratures, remain unresolved. Em ever, as concluded in J. Shea's memo tc file dated Nove2er 10, 1970, the prcposed modification does result in a significant igroverent in co"e safety.
Tnerefore, we have concluded that CE shculd be authorized to install and operate the ECCS, as proposed, and resolve the reraining questions en reliability on about the same schedule as requested for resolving confor-mance with the Interim Criteria. We have further concluded that cperation of Dresden Unit No. 1 with the proposed ECCS does not present significant hazards consideratiens not described cr irplicit in the Dresden 1 Safety Analysis Report (Hazards Su=ary Report) and that there is reasonable assurance that the health and safety of the public will not be endangered. CE has proposed technical specifications which we have mcdified.
A detailed evaluation of the additional in# oration provided by CE in response to our lotters dated December 20, 1970, and July 22, 1971, is presented in Attachment A.
'Ihe remaining questions which we propose to ask CE concerning system reliability are listed in Attachrent E.
ic[w / h h__c Richard D. Silver Operating Reactors Eranch #2 Directorate of Licensing 1
3 S
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ames J. Shea Operating Reactors E"anch #2 Directorate of Licensirs Enc 1ccu"es:
Attac'cr.en A - Evaluation of CEC Information Attac'rr.ent E - Additional Inferaticn Requ' zed cc.
DJSkovholt, DL TJCarter, DL DLZiemann, DL RDSilver, DL JJShea, DL RMDiggs, DL MJinks, DR (2)
Compliance (3)
A?IACBETT A EVALUATIO" OF CEC INF0F'.ATION 1
i'axir m Ener:e Burst In a letter dated November 22, 1971, CEC reported that the energi required to lifc the 470-ten Dresden Unit 1 pressure vessel 8 inches is 200,000 calories. Eased on the assumption that 425 cals/p is a conservative threshold fer rapid fuel dispersal and pra pt depcsition of energy into the coolant and assuming a 10% therral to mechanical energ/ conversion, CEC has calculated that dropping a control rod with a raxirm reactivity worth of 2.6% delta k/k is required to cause damage to the new energency core spray water delivery system.
Ncral control rod reactivity worth, according to CEC, is in the range of C.2 to 0.4% delta k/k with a raxim s of 1.25.
For si~.ilar evaluaticns, we conservatively used an enthalpy of 250 cals/g as the prcmpt energy threshold with a more realistic ther al-mechanical energy conversion efficiency. h'e are unable to complete our evaluation in the custaca j ranner because CEC has not reported the total enes contained in fuel rods with enthalpies in excess of 280 cals/gm that could be promptly deposited in the coolant.
(k'e note that Figure 1 of the CEC October 7,1971 submittal shows that a raxir m rod reactivity wcrth in excess of 1.53: delta k/k is required to exceed enthalples of 2E0 cals/ p.)
2.
Ccnsideration of FIECHT Test Results Applying the FLECHT core spray data to Dresden 1 would reduce the raxic a peak clad terperatu=e that occurs followirq srall prira~y system breaks, assu.ing 100% emergency condenser effectiveness frcm 2375 F to 21000F, according to GE estirates reported by CEC letter dated Farch 26, 1971. 'Ihis will be confirmed, in accordance with require ents to satisfy the interim design criteria, and wil_
be further evaluated when the new results are presented.
3 Redundant Erercency Condenser and Core scrav Isolation valves Ey letter f ated Octcber 7,1971, CEC announced that redundant emergency ccndenser valves have been purchased for insta11sticr cn the Dresden 1 emergency ecndenser condensate return lines. Tne acceptability cf all de-cperated motors on the emergency ccndenser cutlet and all ac-Operated mcte"s on the core spray isolaticn valves is dependent on provisions for redundant ensite de and ac power according to a Dece: er 9,1971 mero from the Division of Reacter Standards, DRS.
. L.
Fi"e F2in as the Source of E~errency Core Coolinc Eater 1 PSH requirerents for the new core spray pumps are appan.ntly 10 psig, not 100 psig as originally repc-ted. A minis:n fire 9.in pressure of 50 psig is adequate therefor.
Reliability cf the firerain system, according to the Farch 26, 1971, CEC letter, is based on the ability to deliver water from the system to the suction of the ccre spray pumps via either of two independent lines. Ability cf the supply lines to withstand earthquakes has not Deen established, a detail necessary to satisfy the requirerents for a reliable source of emergency core cooling water.
5.
Frercency Diesel Generater The 500 kW emergency diesel generator of Dresden 1 is capable of satisfying the energency core cooling electrical requirements according to Table II of the Parch 26, 1971 CEC letter. We agree with DES that it is reasonable to defer an evaluation of tha ndequacy of a single emergency diesel generator pending completien of CE's study of the system required by the Interim Criterion on ECCS.
6.
Isolation of Containment Scray from the Firemin System Ey letter dated Farch 26, 1971, CEC explained that the raximum corr-tainment pressure is the same with and without contairrent spray as previously reported. With centaircent spray, however, the containment pressure decreases more rapidly. It will be necessa~/ to isolate the containment spray system only if the firemain pressure decreased below 50 psig, and when the core spray system is in the post-incident mode. Considering the isprobable combination of events that could result in slower containment vessel depressurisation, the interdependence of core spray - contairrent spray is acceptable.
7.
ECCS Activation Simals Let water level in the prira j steam dru. cr high centsdrcent pressu"e will actuate the ccre spray system. The 1cw core spra: injection pressure rakes the precise response characteristics of the liquid level signal less important, tecause of the pressu"e decay time, than high pressure irdection systers. Tnese signals and set pcints are similar to other Eh?s and are acceptable on this basis.
8.
Preoperational Tests fcr ECCS Tne intent tc complete full performance checkout of the system (without actual injection of fire + n water) is clearly eviden in the F2"On 26, 1971 suttittal by CEC. Tne prcposed checkou is acceptable.
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Cc-rinei E=iarle and Elevdc m Assu ctions
" Class I" design standards were used for the new additicns to the old facility, according to inforration submitted by CEC letter datea Fa ch 26, 1971. 'Ihe c1d facility has not been reevaluated and likely does nc: meet the cu rent " Class I" desip standards. Tne ECCS pipire has be'n installed in the c'entainment with wide separation from e
other pipir6 that coula cause pipe whip or create missiles followirs rdg ure. We tre satisfied with the provirions that have been rade to 'assu e ECCE integrity and reliability.
iv.
Technical Specification Chances E*/ letter dated February 8,1972, CE prcposed technical specificaticn chrges. Tnese changes, which we have rodified,are suitable fcr inclusicn in the Technical Specifications. The modified specifications include operability snd curvcillance recuirerents for all emergency core coolir6 systems and ccrnpenents except the thit 2 and Ur.it 3 service kater p'rps (and diesel genemtors' which because they are ranually started can only be considered long tenn backups to the diesel fire g==se s.
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i ATTACHMENT B ADDITIONAL. INFORMATION REQUIRED l.
Discuss the maximum reactivity worth of a control rod ever the full cperating range, including cold, cold to hot, hot standby and lew through full power under the three categories, (1) In-sequence rods, (2) Worst non-sequenced rod in an otherwise sequenced' pattern, (3) Worst possible configuration, as is done,
'for*cxample, in the Dresden 2 and 3 SARs. An acceptable criterion for Dresden 1 is that a,280 cal /gm fuel enthalpy shall not result from the drop of a non-sequenced rod in an otherwise sequenced p a t t e'r n.
~ Indicate over the full operating range where 280 cal /gm peak enthalpy~1s exceeded for the rod drop accident.
For category 1 and 2 ranges where 280 cal /gm might be exceeded, indicate the fraction of operating time normally associated with such ranges and any mitigating changes which might be made in the calculations such as more realistic initial source levels in the "zero power" range and details of procedures needed to prevent non-sequenced rods.
2.
Prompt energy' deposition into the reactor coolant may occur at fuel
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enthalpics as low as 280 cals/gm in contrast to the 425 cals/gm assumed in your October 7,1971 presentation to DRL.
Show the relationship between reactivity insertion, prompt energy deposition and mass of promptly dispersed fuel for a range of assumed fuel enthalpy thresho'As between 280 and 425 cals/gm.
Identify the con-ditions necessa'ry to ' cause (1) excessive vessel lif t and (') excessive loss of reactor vessel integrity or reduction in ECCS effectiveness, e.g., ove rp re s sure, considering the various modes of permissible operation from cold-solid startup to hot operating conditions.
3.
The design of the. valves in the emergency condenser return lines and of the core opray isolation valves are required to meet the single failure criterion. The acceptability of all de-operated motors on the -isolatica' condenser condensate return line valves and all ac-operated motors on the core spray isolation valves is dependent on previsions for' redundant onsite de and ac power.
If redundant and independent onsite ac and de power supplies are to be provided and ecch of a pair of valves with the sc=c type of operators is to be powered from different sources, the design would be acceptabic.
In the absence of redundant ac and redundant de power, one valve of ecch pair must be ac powered and the other de powered to satisfy the single failure criterion. Which of these alternatives will you take to meet the single failure criterion?
i 2-4.
Rexarding the cdcquacy of information' available to the opcrator under accident conditions, you have indicated'those lastruments which monitor the operability of the proposed core spray system but you have not indicated those instruments which mor.itor vital
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information on the condition of the primary coolant system and primary containment. You are requested to augment your response in this regard.
5.
Provide an evaluation of the adequacy of the seismic design of the fire protection system.
If the system does not mect the criteria for seismic design of the core spray system piping and equipment-described in your letter of March 26, 1971, discuss your plans for upgrading this system sufficiently to assure availability of water under design basis earthquake conditions.
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