ML17194A452
| ML17194A452 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 02/05/1982 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Delgeorge L COMMONWEALTH EDISON CO. |
| References | |
| TASK-15-18, TASK-RR LSO5-82-02-038, LSO5-82-2-38, NUDOCS 8202100297 | |
| Download: ML17194A452 (13) | |
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q Docket No. 50-237 LSOS-82-02-038 Mr. L. De 1 George Director of Nuclear Licensfng Commonwealth Edison Company Post Office Box 767 Chicago, Illinofs 60690
Dear Mr. DelGeorge:
February u5*, 1982 e
SUBJECT:
DRESDEN-2, SEP TOPIC XV-18, RADIOLOGICAL CONSEQUENCES OF A MAIN STEAM LINE FAILURE OµTSIDE CONTAINMENT Commonwealth Edison Company (T. Rausch) letter dated October 15, 1981, transmitted fQr our review your safety analysis report (SAR) of SEP Topic XV-18.
EnclQsed you will f1nd our evaluation of th1s topic *.
The staff's conservative eyaluat1on revealed that present reactor coolant*
gross iodine concentration limits (20 uCi/gm) specified by the Dresden-2 technical specification would pennf t iodine concentrations in the reactor coolant that would not prevent unacceptabl~;thyroid doses at the exclusion area boundary if the plant experienced an fodfne spike prior to the accident.
Consequently, Dresden-2 is at vari~nce with current licensing guidelines unless the following practice is taken.
Because of the iodine spiKe potential (resulting from power change or de-pressurization); the staff suggests new sampling frequency and iodine limits be adopted to monitor the reactor coolant iodine activity. Acceptable iodine limits and operational procedures can be found in the General Electric Stand-ard Technical Spec1f1catfon for BWRs.
In summary, reactor coolant limits for steady state operations are set for iodine expressed as dose equivalent I-131. This equilibrium value is purposely set low (0.2 uCi/gm dose equiva-lent I-131) to compensate for the additional iodine inventory that follow changes in reactor power (iodine spikes). Operation above the equilibfium value is allowed with additional sampling and restrictions imposed on duration
- above th~ equil ibrfum value.
I 5G-o In 1 ight of the above variance and present accepted practice for cont~~l ing s //
iodine, it is recorran~nded that the licensee adopt the standard for reactor
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coolant iodine control outlined in the General Electric Standard Techrii~al
~ ( tLJ Specification for BWRs.
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NRC FORM 318 (10*80) NRCM 0240 OFFICIAL RECORD COPY*
USGPO: 1981-335-960
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_J Please 1nform us within 30 days of the action you 1ntend to take regarding this matter.
This evaluation wfl 1 be a basic input to the integrated safety assessment for your facility unless you identify changes needed to reflect the as-built conditions at your facility. This assessment may be revised in the future ff your facility design is changed or if NRC criteria relating to this subject is modified before the integrated assessment is comple~e.
cc: See next page
Enclosure:
As stated Sincerely, Dennis M. Crutchfield, Chief Operating Reactor5 Branch No. 5 Division of Licensing
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USGPO: 1981-335-960
Mr. l. DelGeorge cc Isham, Lincoln & Beale Counselors at Law
. _.One First National Plaza, 42nd Floor.
Chicago, Illinois 60603 Mr.. B. B. St_ephenson Plant Superintendent Dresden Nuclear Power Station Rural Route #1 Morris, Illinois 60450 Natural Resources Defense Council 917 15th Str~et, N. w.
Washington, D. c.
20005 U ** S. Nuc 1 ear Regulatory Commission Resident Insp~ctors Office Dresden Station RR #1 Morris, Illinois 60450
- Mary Jo Murray Assistant Attorney General Environmental Control *oi vision 188 w. Randolph Street Suite 2315
- Board of Supervisors of Grundy County Grundy County Courthouse Morris, Illinois 60450 John F. Wolf, Esquire 3409 Shepherd Street Chevy Chase, Maryland 20015 Dr. Linda W. Little 500 Hermitage Drive Raleigh, North Carolina 27612
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Illin9is Department of Nuclear Safety 1035 Outer Park*Drive, 5th Floor Springfield, Illinois 62704 U. s.. Environmental Protection Agency Federal Activities Branch Region V Office ATTN:
Regional Radiation Representative 230 South Dearborn Street Chicago, Illinois 60604 Dr. Forrest J. Remick -
305 East Hamilton Avenue State College, ~ennsylvania.16801 The Honorable Tom Corcoran *
- United States House of Representatives
- Was hi n g to n, D
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- 2 0 51 5 Robert H. Erigelken, Regional.Admin.
Nuclear Regulatory Commission Region V Office of Inspection & Enforcement 1450 Mari a Lane Walnut Creek, California -94596
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~. I DRESDEN UNIT 2
- XV-18 RADIOLOGICAL CONSEQUENCES OF A MAIN STEAM LINE FAILURE OUTSIDE CONTAINMENT I
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- INTRODUCTION i !
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Rupture of a steam line outside containment will allow radioactivity contained in the coolant to escape to the environment.
SEP Topic* XV-18 is intended to review the radiologi~al consequence~ of such failures.
This review has encompassed those design features and technical specifications which limit the amount of radioactivity that can be released.
II.
REVIEW CRITERIA Section 50.34 of 10 CFR Part 50 requires that each applicant for a construction permit or operating license provide an analysis and evaluation of the design and performance of structures, systems, and components of the facility with the objective of assessing the risk to public health and safety resulting from operation of the facility~
The steam line break accident is one of the postulated**accidents used to evaluate the adequacy of these structures, systems, and:
components with respect to public health ~nd safety.
In addition, 10 CFR Part 100.11 provides dose guidelines for a Design Basis Accident.
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III. ~ELATED SAFETY TOPICS Topic II-2.C, "Atmospheric Transport and Diffusion Characteristics for Accident Analysis" provides the meteorological data used to evaluate the offsite doses.
Topic III-5.B, "Pipe Break Outside Containment" covers the dynamic effects of the postulated pipe fai Lure *.
IV.
REVIEW GUIDELINES G~idelines for this review are contained in Regulatory Guide 1.5, "Assumptions Used for Evaluating the Potential Radiological Consequences of a Steamline Break Accident for Boiling Water Reactors" and in Standard Review Plan CSRP) Section 15.6.4, Revision 2.
V.
EVALUATION On October 15, 1981, the Licensee provided NRC with their evalua~ion of the radiological consequences following the postulated main steam line failure.
In their submittal the licensee did not provide a new evaluation of the consequences using the guidance of Standard Review Plan Section 15.6.4, Revision 2, but rather pro~ided the section
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of the FSAR (revised March 22, 1968) which described the radioliogical consequences for this accident.
The license~
listed in a table the doses at various distances from the plant with the reactor coolant activity in the "normal maximum range of approximately" 2.4 fCi/ml, and assuming a main steam line isolation valve closure time of 10.5 seconds.
The thyroid doses listed were on the order of io-3 rem at 1/2 mile and less at greater distances from the plant.
Further, the licensee stated "At the technical specifica.tion limit of 10 JJCi/ml Csic) the calculated doses would increase by approximately a factor of 10, still well below the limits of 10 CFR 100."
The staff performed a review of the lice~see's submittal as well as other information on the docket.
The submittal does not provide important parameters such as the amount of coolant released, dose conversioh factors and the as~umed atmospheric dispersion factors. In addition, the licensee's statement of the existing primary coolant technical specification limit of 10 ~Ci/ml is at variance with the current D~e~den-2 technical specification limit of 20 pCi/ml.
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The staff's review of the licensee's technical specification on primary coolant indicates that it does not contain the two-tier level (equilibrium and spike limits) currently found in lhe standard technical specification CSTS) for BWR's and, therefore, it is very difficult to evaluate with respect to current NRC practice (Standard Review Plan 15.6.4) which is based on the presumption of STS.
The Dresden-2 CD-2) primary coolant techni~al specification limit for iodine activity is a single shutdown limit of 20 pCi/ml of gross iodine activity in the coolant.
In order to permit the evaluation of the D-2 technical specification <rs> shutdown limit with current crite~ia, it is necessary to discuss the SRP acceptance criteria as based on the STS.
First, the STS permit continued uninterrupted operation as long as the coolant activity remains below the equilibrium value.
When the equilibrium value is exceeded, increased surveillance (coolant sampling) is required and a definite time period has been set to allow the facility to reduce the coolant conc~ritations below the equilibrium value.
Failure to reduce the coolant concentration below the equilibrium value in the set ti~e results in facility shutdown.
A cumulative time feature is also imposed which restricts the total time a plant can operate above the equilibrium value.
This cumulative time
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restriction provides consideration of the effects of many spikes.
The cumulative time limit restricts the total time the plant can operate_ above the equilibrium value to less than 10X of a year.
A spike limit is set and a plant reaching or exceeding this limit is required to shutdown immediately.
The SRP is structured so that the consequences of the accident occurring during unrestricted operition Cup to the equilibrium value) can not exceed a small fraction of the 10 CFR Part 100 exposure guidelines.
Because unrestricted operation is permitted up to the equilibrium value, this value is used in the analysis examining conformance to the "small fraction."
Operation is permitted above the equilibrium value by the STS, but the STS are structured to reduce the likelihood of the accident occurring during this time by at least 10% (the cumulative time limit) ~nd, hence, the SRP takes recognition of this and permits an appropriate factor of 10 increase in allowed consequences (doses up to 10 CFR Part 100>.
In no case, however; are the doses permitted to exceed 10 CFR Part 100 and, therefore, the spike limit is established.
The SRP uses this spike limit in testing the consequences again~t Part 100.
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Two other features of the STS are noteworthy.
First, STS set limits based on 1-131 dose equivalent activity and this permits direct comparision with licensing basis of the pl~nt (the 10 CFR Part 100 exposure guidelines>.
A second feature is that the STS invoke coolant sampling when plant operation Ce.g., decreasing power, etc.) is most likely to result in iodine spiking.
In order to ~valuate the D-2 TS against current criteria, the
- staff considered the D-2 shutdown limit as though it were the the STS spike limit* and then.considered the shutdown limit as though it were the STS equilibrium limit.
Because the licensee submi~tal failed to provide the coolant released during the accident, the staff's analysis utilized the D-2 FSAR value of 66,000 potinds released prior to main steam isolation valve closure.
The staff's analysis used X/Q values of 2.6 x 10-4 sec/m-3 and 2.5 x 10-S sec/m-3.for the 0-2 hour exclusion area boundary CEAB) and 0-8 hour low population zone boundary CLPZ), respectively.*
- It should be noted that these X/Q values represent a<ground level release.
Regulat-0ry Guide 1.5 p~rmits the use of an elevated C30 meter) release and would certainly produce values less than those assumed here.
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Finally, the ~-2 TS provides no limitation with regard to the iodine spectrum.
The D-2 shutdown limit is expressed in gross iodine activity as compared to the STS limits as expressed in dose equivalent I-131.
The staff in its analysis conservatively assumed that the shutdown limit of 20 µCi/ml was composed entirely of I-131.
Using these highly conservative assumptions, the dose computed is ao* rem and* 8 rem to the thyr6id at the EAB and LPZ, respectively.
These doses are less than the exposure guideline values of 10 CFR Part 100 but exceed a small fraction C10%) of the guidelines at the EAB.
The D-2 TS, therefore, provides an acceptable upper limit
-0n coolant iodine concentrations~
The existing TS requires sampling of coolant activity every 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />, and isotopic analysis of samples once every month.
This combination
- of shutdown limit and sampling/analysis provides adequate protection against coolant activity changes which occur gradually, and approach the shutdown limit over periods of a month or more.
Past experience with
~oolant iodine concentrations at D-2, however, shows that rapid changes_,
in coolant iodine concentrations (usually c~lled iodine spikes) are typical.
Increases in iodine concentrations by
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a factor of ten in one hour have been observed at D-2.
Once an iodine spike has been initiated, the rise in coolant activity level cannot be prevented.
The present technical specification, therefore, provide little assurance that coolant concentrations, once permitted to rise to levels
~pproachig 20 JCi/ml, would remain within the shutdown limits between sampling and analysis periods.
The staff has developed the STS for coolant activity which account for this spiking phenomenon by limiting equilibrium concentrations to low levels, while permitting temporary increases (spikes) to an upper shutdown level.
Appropriate sampling/analysis requirements during spikes and periods when spiking behavior is expected Ci.e., power or.pressure/
temperature changes) are included to assure detection and
~roper tracking of spikes.
A D-2 technical specification which reflects these provisions ~ould correct this deficiency.
The staff also evaluated the main steam line break accident using a typical spectrum of iodine isotopes (determined for BWR's from operating data>.
The use of,* this spectrum in the analysis produces doses that meet the small fractiorl:
criterion.
However, the D-2 TS provides n~ consideration of the spectrum in the shutdown limit and it is unlikely that any assumed spectrum can be maintained during all phases
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of operation.
Further the staff analyzed D-2 on the basis of the limits imposed by STS and the assumptions outlin~d earlier.
Current NRC criteria are satisfied as indicated in the table below.
Thyroid Doses <rem)
Staff estimate with 20 f'Ci/ml I-131 EAB 80 GE STS equilibrium limit C0.2 pCi/gm DEI-131) 0.8 GE STS spike limit (4.0 pCi/gm DEI-131) 16*
VI.
CONCLUSION The staff's highly conservative analyses show that the LPZ 8
0.08 1.54 exposure guidelines of 10 CFR Part 100 are met assuming the coolant concentation is at the shutdown limit and is entirely I-131.
However, the analyses also show that the D-2 shutdown limit does not assure the small fraction criterion is met.
On the basis of the steam line break accident analyses, the staff concludes that the D-2 TS is inadequate wiih respect ~o sampling frequency to assure that spikes are
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detected and monitored and that uncontrolled iodine spikes above the shutdown limit are prevented.
The staff concludes th~t one acceptable approach would be the adoption of the STS for primary coolant activity.
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