ML19283B815
| ML19283B815 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/01/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19283B813 | List: |
| References | |
| NUDOCS 7903260396 | |
| Download: ML19283B815 (6) | |
Text
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UNITED STATES y*
?g NUCLEAR REGULATORY COMMISSION j
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 49 TO FACILITY OPERATING LICENSE NO. DPR-65 NORTHEAST NUCLEAR ENERGY COMPANY, ET AL MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 DOCKET NO. 50-336 Introduction By letter dated August 15, 1978, Northeast Nuclear Energy Company (NNECO or the licensee) requested an amendment to Facility Operating License No. DPR-65 for the Millstone Nuclear Power Station, Unit No. 2.
The proposed amendment would change the Technical Specifications for engineered safety feature actuation system and radiation monitoring instrumentation (Sections 3.3.2.1 and 3.3.3.1) concerning the alarm / trip setpoints, the minimum channels operable and the action statements _for the following instruments:
. containment airborne radioactivity monitor
. spent fuel storage area monitors
. spent fuel storage airborne radioactivity monitor We have modified the proposed changes somewhat and the licensee has agreed with these modifications.
Discussion The licensee proposed increasing the allowable value of the trip setpoint on the containment airborne radioactivity monitor in specification 3.3.2.1 to permit containment purging when the levels of airborne radioactivity inside containment are above the current containment purge valve isolation setpoint.
He has experienced difficulty with the current setpoint when the airborne radioactivity levels are high because the purge valves will not stay open.
The valves and the monitor were designed to close the purge valves to prevent the release of excessive radioactivity from the containment in the event of an accicent. However, in the case of Millstone 2, setpoints specified are presently lower than necessary to perform that function. The present allowable setpoint values are less than or equal to 9100 counts per minute for gaseous activity and 1.0 x 10D counts per minute per hour for particulate activi ty. A major purpose of purging at Millstone 2 is to recuce the levels of airborne radioactivity inside the containment. during normal operation.
The licensee has found that the levels of airborne radioactivity inside con-tainment have been higner than the monitor setpoints at the tire of the attempted purges. Therefore, with the current setpoints, the valves would close, and the licensee could not purge.
790326DE46
. The licensee proposed increasing the allowable value of alam/ trip setpoint of the spent fuel storage area monitors in specification 3.3.3.1 to help The value prevent spurious alarms and auxiliary exhaust system starts.
of the setpoint is presently specified to be less tnan or equal to two These monitors are designed 1) to provide an alam if times ba:kground.
a criticality occurs in the new fuel storage area and 2) to switch the ventilation exnaust from the spent fuel pool area to an auxiliary exhaust system if an accident causes radioactivity to be released f rom the stored However, for low background levels of radiation, less than spent fuel.
five mR/nr, a setpoint of two times background can cause inadvertent alams and trips from handling small radiation sources in the area and it is impractical to constantly change the setpoint as the radiation background Also, for simplicity and to be consistent with in the area changes.
ANSI N16.2-1969, the licensee proposed to consolidate the specifications for the two monitor functions:
- 1) criticality alam and 2) auxiliary exhaust system actuation.
The licensee proposed to change specification 3.3.3.1 such that the spent fuel storage airborne radioactivity monitor alam setpoint would have units consistent with the other proposed change for the containment airborne radioactivity monitor.
Evaluation The containment airborne radioactivity monitors (gaseous and particulate) are provided to initiate closure of the containment purge valves upon de-4 Closure of these tection of high radioactivity levels in the containment.
valves prevents excessive amounts of radioactivity from being released to the environs in the event of an accident inside containment.
The maximum allowable trip value for these monitors will correspond to the calculated concentrations of airborne radioactivity at the site boundary j
which would not exceed the concentrations listed in 10 CFR Part 20, Appen-I dix B, TaDle II. Exposure for a year to the concentrations in 10 CFR Part i
20, Appendix B, Table 11 corresponds to a thyroid dose to an individual of 1.5 rem or a total body dose of 0.5 rem; these doses are a small f raction of the guidelines of 10 CFR Part 100 for an individual at any point on the exclusion area boundary for two hours, i.e., 300 rem thyroid and 25 This analysis bounds the dose consequences of a situation rem total body.
i in which air containing a level of radioactivity just below the trip setpoint would be purged for a long period of time. Reali s tically,
plant operators, based on indications from the effluent monitors, would terminate the release long before such doses could be approached.
Realistically, other signals such as the safety injection signal would be more likely to occur before the high radiation signal in the event of a Loss-of-Coolant-Accident (LOCA).
However, high radiation is one of the signals which would isolate the containment including closing the purge valves.
If a LOCA or any other accident occurs, the in-crease in the level of airborne radicactivity inside containment would be rapid.
The rate of increase in radioactivity would be sufficiently rapid that the proposed setpoint would essentially be reached as quickly as the present setpoint.
Therefore, the isolation signal and the closure of the purge valves would not be delayed nor wou.d the amount of radioactivity released before purge valve closure increase sianificantly.
For the purposes of calculating the trip value setpoint, the licensee will be required to assume (1) the highest offsite annual average atmospheric dispersion factor of 5.8 X 10-6 seconds per cubic meter (site boundary, 0.48 miles in the NE sector) for purge releases through the building vent and (2) the hiahest offsite annual average atmospheric dispersion factor of 7.5 X 10-8 seconds per cubic meter (3 miles in the NNE sector) for purge releases through the Millstone Unit No.1 stack.
The licensee will also be required to assume that the gaseous and particulate radioactivity is xenon-133 and cesium-137, respectively.
The spent fuel storage area monitor serves two functions. First, the monitor detects any increase in radiation levels which may be caused by an accidental criticality in the new fuel storage area and provides an alann to warn personnel of the criticality. The setpoint of 100 milli-rads / hour meets the sensitivity requirements of 10 CFR Part 70.24(a)(1).
A radiation field of the magnitude specified in 10 CFR Part 70.24 (a)(1) caused by a criticality in the new fuel storage area would cause a radia-tion field of at least 100 millirads/ hour at the spent fuel storage area monitors.
Second, the spent fuel storage area monitor provides a signal to airect the ventilation exhaust from the spent fuel storage area through an auxili-ary exhaust system with HEPA and charcoal filters when the dose rate exceeds the monitor setpoint. The HEPA and charcoal filters reduce the particulate and iocine radioactivity released to the atmosphere. Specifi-cation 3.9.14 requires the use of the auxiliary exhaust system to exnaust
. the ventilation air from the pool area when fuel is being handled in the pool or loads are handled ov'er the spent fuel pool. Specification 3.9.14 applies when spent fuel which has decayed less than 60 days is stored in the pool. We have performed an analysis of the potential ton-sequences of a fuel handling accident in the spent fuel pool when speci-fication 3.9.14 is not applicable. Our calculation assumes that the entire release occurs before the auxiliary system is fully actuated; therefore, no credit was taken for charcoal filtration or elevated re-lease. Our other assumptions and the resulting calculated potential
- onsequences of such an accident are given in Table 1.
The calculated dose consequences are less than one percent of the guidelines of 10 CFR Part 100.11. Therefore, the dose consequences of the accident, with the monitor switching the exhaust to the auxiliary system at a setpoint of 100 mrad / hour, are also less than one percent of the guidelines of 10 CFR Part 100.11.
We have consolidated the two functions of the spent fuel storage area moni-tor in Specification 3.3.3.1 and established requirements which are more stringent than before with regard to the minimum number of operable chan-nels. The requirement for the minimum number of operable channels has been increased from one to two for che criticality monitor function and the applicable mode requirement for the ventilation system isolation func-tion has been changed from when irradiated fuel is being stored to when any fuel is in the storage building.
The spent fuel storage airborne activity monitor has no automatic safety feature actuation function. The monitor does provide an alarm, but that alarm is not required by regulation (as is the spent fuel storage area moni-tor). Therefore, specifications regarding the monitor are no longer neces-sary and have been deleted.
Based on our evaluation discussed above, we find the proposed changes to the Technical Specifications, as modified to meet our requirements, meet all regulatory requirements and are, therefore, acceptable.
e
. TABLE 1 ASSUMPTIONS FOR AND POTENTIAL CONSEQUENCES AT THE EXCLUSION AREA BOUNDARY OF THE POSTULATED FUEL HANDLING ACCIDENT IN SPENT FUEL POOL FOR MILLSTONE UNIT 2 Assumptions.
Guidance in Regulator-Guide 1.25 Power Level 2700 Mat Fuel Exposure Time 3 years Peaking Factor 1.8 Equivalent Number of Assemblies Damaged 1
Number of Assemblies in Core 217 Charcoal Filters Available None Decay Time Before Moving Fuel 60 days 0 - 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> y/Q Value, Exclusion Area Boundary (Ground Level Release) 6.6 x 10-4 sec/9 3
Doses, Rem Thyroid Whole Body Exclusion Area Boundary (EAB)
Consequences from Accidents Inside Containment 1.1
<0.1 Environmental Considerations We have determined that the amendment does not authorize a change in effluent types or an increase in total amounts of effluents nor an in-crease in power level and will not result in any significant environ-Havir.g made this determination, we have further concluded mental impact.
that the amendment involves an action which is insignificant from the standpoint of environmental impact and purscant to 10 CFR 51.5(d)(4),
that an environmental impact statement or negative declaration and en-vironmental appraisal no =d not be prepared in connection with the issuance of this amendment.
Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and saf ety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common dc#ense and security or to the health and safety of the public.
Dated: March 1, 1979 O