ML20207C548
| ML20207C548 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 12/29/1986 |
| From: | Kowalski S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Butler W Office of Nuclear Reactor Regulation |
| References | |
| CON-#187-2117 OL, NUDOCS 8612300171 | |
| Download: ML20207C548 (5) | |
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PHILADELPHIA ELECTRIC COMPANY 23O1 MARKET STREET P.O. BOX 8699 PHILADELPHIA, PA.19101 (2151 841 4oo0 ENGINEERING AND RESEARCN DEPARTMENT Mr. Walter R. Butler, Director BWR Project Directorate n DEC 291986 Division of Licensing U.S. Nuclear Regulatory Conmission Washington, DC 20555 Docket No.:
50-353
Subject:
Limerick Generating Station, Unit 2 Charcoal Filter Cooldown Mode for Reactor Enclosure Recirculation System File:
GOVT 1-1 (NRC)
Dear Mr. Butler:
Philadelphia Electric Company proposes to make changes to the design and operation of the Reactor Enclosure Recirculation System (RERS) for Limerick Generating Station Unit #2. The RERS is a safety-related air recirculation and flitration system consisting of two 100 percent capacity filter train / fan assemblier. The function of the RERS is to provide for the recirculation (mixing) and flitration (Pre-HEPA-Charcoal-HEPA) of the Reactor Enclosure Secondary Containment post accident air voltme to reduce the concentration of radioactive lodides and particulates. Additional flitration (HEPA-Charcoal-HEPA) is provided by the safety-related Standby Gas Treatment System (SGTS),
which is downstream of RERS, for effluent discharged to the environment.
The RERS does not run during normal plant operation.
The design of the RERS has provisions to provide a cooldown flow path to a charcoal adsorber that is not in operation and is experiencing excessive temperature increases due to radioactive decay heat.
To accomplish this, cooldown air inlet ductwork is provided upstream of each charcoal adsorber and a ductwork inter-tle is provided downstream of each charcoal adsorber prior to the fans. Safety-related electro-hydraulically actuated isolation valves are provided in the ductwork to establish the required flow paths (See attached sketch).
Control logic is provided to place a non-operating charcoal adsorber in the appropriate cooldoval configuration when the associated RERS handswitch is placed in the "COOLDOWN" position. Different flow paths are estab11shed depending on whether the redundant RERS filter train is operating or neither RERS filter train is in operation.
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The charcoal adsorber cooldown mode was originally provided in the design to limit potential radioactive decay heat build-up to assure that the charcoal temperature is kept below the point where significant desorption (3000F) or auto-Ignition (626 F) could occur.
At the time, the radioactive decay heat built-up in the charcoal adsorbers was not quantified and cooldown modes were conservatively provided.
Since the original design, calculations have been perfonned to quantify the potential radioactive decay heat buildup in the RERS charcoal adsorbers. The calculations have used a source tenn consistent with the SER Supplement #3 LOCA analysis and have conservatively assuned that one of the RERS filter trains operates post LOCA and provides for a 100% removal efficiency for radioactive lodides postulated to be filtered by the charcoal adsorber. At the point of maxinun loading, it is assuned that the charcoal adsorber is isolated (no air flow) and the resultant charcoal bed temperature rise due to decay heat was calculated. The resultant maximun temperature rise in the adsorber was calculated to be 3.2 F.
Using the conservative assunption that the Reactor Enclosure Secondary Containment post LOCA atmosphere is 150 F, this results in a cunulative charcoal bed termerature of 153.2 F.
This is well below the temperature where significant lodine desorption could occur (300 F) and the minimun charcoal auto-Ignition temperature (626 F).
Based on the foregoing, we propose to eliminate the charcoal adsorber cooldown mode from RERS for Limerick Unit 2.
The approach to provide a charcoal adsorber cooldown mode only if a potential need exists is consistent with existing regulatory guidelines and Industry standards. The appilcable guidance on charcoal adsorber cooldown modes is as follows:
1.
NRC Regulatory Guide 1.52, Rev. 2, Position C.3.K.
"The design of the adsorber section should consider possible iodine desorption and adsorbent auto-Ignition that may result from radioactivity-induced heat in the adsorbent and concomitant temperature rise. Acceptable designs include a low-flow air bleed system, cooling coils, water sprays for the adsorber section, or other cooling mechanisms."
2.
Nuclear Power Plant Air Cleaning Units and Components, ANSI N509-1980, Paragraph 4.9 "Where heat of radioactive decay or heat of oxidation or both may be significant, means shall be provided to remove this heat from the adsorbent beds to limit temperatures to values below 300oF to prevent significant iodine desorption."
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3.
Nuclear Air Cleanino Handbook, ERDA 76-21, Section 2.2.4 (1969)
"The 11miting temperature of adsorbents for capturing radioactive lodine and lodine compounds is related to the desorption temperature of the adsorbed compound and of the Impregrants with which the material has been treated to enhance its adsorption of organic radiolodides. For triethylenedlamine (TEDA) Impregnated activated carbon, this temperature may be as low as 300 to 3500F.
When temperatures higher than the operating limits of air cleaning system cmponents must be acconmodated, heat sinks, dilution with cooler air, or some other means of cooling must be provided to reduce temperatures to levels that those components can tolerate."
Based on the above guidance, it is concluded that a charcoal adsorber cooling mechanism need only be provided when the potential for significant radioactive decay heat buildup exists. Since it has been determined that there is no potential for significant RERS charcoal adsorbent radioactive decay heat build-up the elimination of the cooldown mode would comply with both regulatory and industry guidance.
The elimination of the RERS charcoal adsorbent cooldown mode does not reduce the margin of safety for Limerick Generating Station - Unit 2.
There will be no increase in offsite doses reported in the FSAR since the worst case charcoal adsorber temperature is well below the desorption tenperature.
In addition, the RERS charcoal adsorbers will be monitored with temperature sensors that provide temperature Indication and alarm annunciation on three distinct levels of off-design temperature conditions (200oF, 250 F, 550 F).
In the unilkely event of a charcoal adsorber fire the operators would have sufficient infonnation to be aware of off-design temperatures.
It should be noted that no external source for initiating a charcoal adsorber fire has been identified. Mitigating actions of isolating the charcoal adsorber and actuating the manual charcoal adsorber water spray fire protection system could be taken.
The elimination of the RERS cooldown mode will result in simplification and increased reliability for this safety-related system.
It will also result in significant first cost savings, as well as annual savings by not having to perform the monthly, yearly and five-yearly inspection and maintenance activities on the system cmponents as reconmended by the vendor.
Philadelphia Electric Company is therefore requesting NRC review and approval for the deletion of the RERS cooldown mode for Limerick Unit 2.
The installation of the cooldown mode equipment has been placed on-hold, with Installation activities planned to ccnmence in June 1987 to support system completion.
In order to realize the maximtm advantage
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fran the deletion of the cooldown mode, we request your decision on this proposal by April, 1987. We will proceed with the appropriate FSAR changes upon approval of this request.
If we can be of further assistance in this matter, please contact us.
Sincerely,
}n y
S. J. Kowalski Vice President Engineering and Research RBA/pms/11248603 Enclosure cc: Troy B. Conner, dr. Esq.
(w/ enclosure)
Benjamin H. Vogler, Esq.
(w/ enclosure)
Mr. Frank R. Romano (w/ enclosure)
Mr. Robert L. Anthony (w/ enclosure)
Ms. Maureen Mulligan (w/ enc 1csure)
Charles W. Elliot, Esq.
(w/ enclosure)
Barry M. Hartman, Esq.
(w/ enclosure)
Mr. Thomas Gerusky (w/ enclosure)
Director, Penna Emergency (w/ enclosure)
Management Agency Angus R. Love, Esq.
(w/ enclosure)
David Wersan, Esq.
(w/ enclosure)
Robert d. Sugarman, Esq.
(w/ enclosure)
Kathryn S. Lewis, Esq.
(w/enclosuro)
Spence W. Perry, Esq.
(w/ enclosure) day M. Gutierrez, Esq.
(w/ enclosure)
Atomic Safety & Licensing (w/ enclosure)
Appeal Board Atomic Safety & Licensing (w/ enclosure)
Board Panel Docket & Service Section (w/ enclosure)
Mr. E. M. Kelly (w/erclosure)
Mr. Timothy R. S. Champbell (w/ enclosure)
I
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