ML18016A583
| ML18016A583 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 09/11/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18016A582 | List: |
| References | |
| NUDOCS 9809170063 | |
| Download: ML18016A583 (6) | |
Text
gP,S Af00
~o'p I
0O I
C Y/
l7 gO
++*++
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 205554001 N BY HE OFF CE OF EA E
T E
EA IS U LEAR DO E
1.0 IHTTI By letter dated March 12, 1998, as supplemented by letter dated August 14, 1998, Carolina Power 8 Light Company (licensee) requested changes to a portion of the Technical Specifications (TS), in accordance with 10 CFR 50.90, for the Harris Nuclear Plant (HNP).
Specifically, the request proposed to delete TS surveillance requirement (SR) 4.9.12.d.4, which requires verification at least once every 18 months that the filter cooling bypass valve of the fuel handling building emergency exhaust system (FHBEES) is locked in the balanced position. The August 14, 1998, supplemental letter provided clarifying information only, and did not change the initial no significant hazards consideration determination.
HNP's FHBEES is designed to (1) mitigate the consequences of a fuel handling accident by removing the airborne radioactivity from the fuel handling building exhaust air prior to releasing to the atmosphere, and (2) maintain the site boundary dose within the guideline of 10 CFR 100 following a fuel handling accident.
The system consists of two 100-percent capacity redundant air cleaning units.
Each unit includes an exhaust fan, charcoal adsorber beds and HEPA filters.
To prevent potential auto-ignition of the charcoal in the idle unit due to heat generated from the decay of the radionuclides captured by the charcoal, an interconnecting duct between the two air cleaning units was designed to allow the on-line unit to draw a small amount of bleed flow (approximately 5 percent of total flow) through the idle unit for decay heat cooling. This bleed duct that connects the two units has a filtercooling bypass butterfly valve which is manually locked in the throttled position for this purpose.
Currently, TS SR 4.9.12.d.4 requires that the filtercooling'bypass valve be locked in the balanced position such that bleed flow can pass through the discharge of the idle unit to the suction of the on-line unit. This design is intended to ensure that any releases would be filtered through a charcoal filterwith the appropriate design efficiency prior to release.
On September 22, 1997, the licensee identified a design deficiency in the FHBEES and submitted a Licensee Event Report (LER) 97-021-01.
The LER indicated that, contrary to the intended design, bleed flow from the discharge of the idle unit passes to the discharge of the on-line unit.
In order to prevent degradation of the charcoal bed airborne removal efficiency, the units contain heaters to control humidity of the air passing through the charcoal.
However, these heaters do not run when the idle unit is not in service; consequently, the humidity in that unit will not be controlled. Without controlling the humidty in the idle unit, the efficiency of the charcoal filter in that unit could be degraded and air flowing through the unit could be filtered at an efficiency lower than the 95% value assumed in the fuel handling accident analysis of the HNP 9809i700b3 9809if PDR ADQCK 05000400 P
,I F
Final Safety Analysis Report (FSAR), Chapter 15. This incident could have resulted in higher calculated off-site doses for a fuel handling accident than that assumed in the FSAR analysis.
Upon discovery of the FHBEES design deficiency, the licensee performed an engineering calculation in October 1997 to estimate the temperature increase in the charcoal beds of the FHBEES due to iodine decay and oxidation following a design-basis fuel element drop accident in the fuel handling building.
The licensee also developed a modification to "permanently isolate the filtercooling flowpath." In July 1998, the licensee updated their calculations.
The following evaluation addresses the licensee's supporting engineering calculation.
3.0
~ALUATt The licensee performed a calculation to demonstrate that the charcoal in the FHBEES will not exceed either the iodine liberation (desorption) temperature or the ignition temperature when the interconnecting duct is isolated.
This calculation assumes that both units of the FHBEES are in service following a design-basis fuel handling accident.
The 300 cfm bleed duct that connects the two units with a bypass valve is closed.
For the worst case, one of the FHBEES trains is then assumed to shut down, causing the failed filter unit to become isolated with the heating element off. With no cooling flow, the charcoal begins to heat up due to decay of the iodine isotopes which have been adsorbed by the charcoal while the unit was in service.
The following assumptions were made in its calculation:
The initial charcoal temperature is assumed to be 150'F.(while the heater exit temperature under design conditions was calculated to be 138'F).
The limiting iodine liberation (desorption) temperature for charcoal is 300'F based on ANSI/ASME N-509-1980.
The minimum ignition temperature for TEDA-impregnated charcoal is 356'F based on the ERDA Handbook.
The initial heat generation rate due to'iodine decay was calculated to be 16 Btu/hr (assume all the iodine and energy from disintegration are deposited in the FHBEES charcoal adsorbers).
No credit is given for heat loss from the charcoal.
The specific heat of charcoal is 0.25 Btu/Ib/'F.
The mass of the charcoal in the filter unit is 910 Ibs based on HNP Technical Specification.
The result of the calculation shows that the total temperature increase of the charcoal is 27'F (based on 56 days decay of the radionuclides in the charcoal).
Given a starting temperature of 150'F, the maximum charcoal temperature resulting from Iodine decay heat will be 177'F. The licensee stated that this temperature is well below the limiting iodine desorption temperature of 300'F and the minimum ignition temperature of 356'F, which is the limiting temperature for the fuel drop accident scenario.
~
q
~ I The staff has reviewed the information provided by the licensee for the TS change and the supporting engineering calculation. The staff finds that the calculated temperatures in the
.charcoal beds without bleed floware still within the safe limits defined by industry standards.
As a result of the above evaluation, the staff concludes that the temperature increase in the charcoal filterdue to heat generated from the decay of radionuclides has no potential for iodine desorption or auto-ignition of the charcoal. A low-flowair bleed system for the purposes of ensuring flowthrough the idle unit to prevent iodine liberation or charcoal ignition is not required for the FHBEES. Therefore, TS SR 4.9.12.d.4 should be deleted, and the modification to permanently isolate the two air cleaning units should be implemented.
4.0 0
DE In accordance with the Commission's regulations, the State of North Carolina officialwas notified of the proposed issuance of the amendment.
The State official had no comments.
P 50 VIR N
N N
The amendment changes a surveillance requirement.
The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (63 FR 17222). Accordingly, the amendment meets the eligibilitycriteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
DHCulLWI Based on the above evaluation, the staff concludes that the bleed flow is not required for the FHBEES. The staff also concludes that the licensee's analysis is conservative and remains within the guidance of Regulatory Guide 1.52, Revision 2. Therefore, based on the licensee's calculation, the proposed TS change is acceptable.
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public willnot be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments willnot be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: J. Guo Date:
September 11, 1998
~
~
~
4 t