ML19260B198
| ML19260B198 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 11/16/1979 |
| From: | JERSEY CENTRAL POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML19210C977 | List: |
| References | |
| TASK-04-02, TASK-06-07.C2, TASK-16, TASK-4-2, TASK-6-7.C2, TASK-RR NUDOCS 7912070404 | |
| Download: ML19260B198 (5) | |
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SAFETY EVALUATION TECHNICAL SPECIFICATION CHANGE REQUEST NO. 78 1.
Introduction This safety evaluation pertains to Technical Specification Change Request No. 78 which is proposed to,aodify Sections 3 9 and 4.9 of the Oyster Creek Technical Specification' to provide for single and multiple control rod removals. These specifications would be applicable when performing various core alterations, r aintenance, surveill'ance, or other activities which require control rod removal.
2.
Scope The evaluation will serve to identify those areas of possible r;Taty concern which might arise during the performance of activities related to the proposed specification. These include both situations which might occur through obeyance of Technical Specification requirements or as a result of accident conditions postulated to occur from failure to obey these requirements.
Through resolution of each of these concerns, it will be denonstrated that there are no unreviewed safety questions associated with the proposed Technical Specification. These safety concerns are identified as follows:
a)
Criticality considerations during single and multiple control rod removals, b)
Effect of bypassing refueling interlocks, and c) A review of the refueling accident.
These are reviewed separately in the following sections.
3 Safety Evaluation 3.1 Criticality Consioc-ations Specification 3.9.E provides for removal of. single control rod or rod drive mechanism.
The core reactivity is within Specification 3 2.A prior to the removal of the control rod ensuring that adequate margin to criticality is maintained in the core with any operable control rod withdrawn and all other operable control rods inserted.
Removal of more than one control rod is prevented by the refueling interlocks which allow only one control rod to be withdrawn when the reactor mode switch is in the REFUEL position.
Consequently, there is sufficient assurance that no inadvertent criticality can 1512 032 f'
~ arise. The requirement that at least two (2) source range monitors (~SRM) shall be operable (Specification 3 9.E.2.), one in the core quadrant location of the control rod being removed and the other in an adjacent quadrant,,:rovides assurance that adequate continual surveillance of the neutron flux level is maintained.
The requirement in Specification 3 9.F.1. that the refueling interlocks associated with the rod being withdrawn be bypassed only after the fuel assemblies in the cell have been removed, presents the possibility of a criticality which might arise from the withdrawal of adjacent control rods in cells containing fuel.
For example, if a rod interlock is bypassed prior to fuel assembly removal in a given control cr'.1, then it would be possible to withdraw both the rod in the cell and an adjacent rod before any fuel is removed.
Further, the rtquirement in Specification 3 9.F.4.to remove fuel prior to rod emoval also precludes this.
Specification 3.9.F.5. provides assurance that adequate shutdown margin is maintained throughout the sequence of control cell defuelings and antic pated control rod removals.
Consequently, i
the single operator error or withdrawing a control rod in a single fueled cell during multiple rod removal operations does not have criticality implications. Thus, prevention of multiple control rod withdrawals in adjacent fueled cells, as stated above, precludes an occurrence of an inadvertent criticality.
Other single errors nave been considered as well and are discussed in Section 3 2.
3.2 Effect of Bypassing Refueling Interlocks Refueling interlocks are provided as a procedural backup to prevent the addition of large amounts of reactivity to the core.
The interlocks are associated with control rod withdrawal, movement of the refueling platform, and movement of the refueling hoists when the mode switch is in the REFUEL position.
Rod withdrawal is prevented whenever the refueling platform is over the core and the refuell y hoist is either loaded or not in the full up position.
Additionally, if any rod is withdrawn and the platform is positioned over the core, hoist movcment is blocked and platform movement is limited to travel only in the direction of the frel pool. The interlock system also prevents the withdrawal of more than one contrcl rod.
The proposed Technical Specifications do not provide for bypassing the refueling interlocks except on those control cells which have been previously defueled. Consequently, the function cf the i512 083
' interlock system during fuel and control rod removal has not been impaired since the interlocks on all other fueled cells in the core are still functional. Thus, one need consider only those errors which result from violation of the specifi-cation requirements.
If the fuel in a cell is removed prior to interlock bypassing, the interlock functicn is not degraded.
Safety concerns with regard to bypassing refueling interlocks involve the possible human errors which might occur in bypassing the interlock for the wrong rod and the worst case effects that such errors might cause.
Consider, for example, the single error where the interlock is bypassed for the wrong rod and subsequently the correct rod is withdrawn.
Note that the interlock on the withdrawn rod is functional in this case. This type of error should be immediately detected since it will prove impossible to either discharge addi-tional fuel assemblies from the core or withdraw additional rods due to the response of blocks of the interlock system on (a) the refueling platform a;id hoist, and (b) the control rod drives caused by the detection of the unbypassed withdrawn control. rod.
Likewise, the single error where the interlock for the correct rod is bypassed,but the wrong control rod is withdrawn, should also be similarly detected.
In order to arrive at the worst case situaticm during fuel and control rod removal, which is the occurrence of two or more adjacent control rods withdrawn in adjacent fueled cells, it is nc> ussary to make multiple errors in violation of the speci-fications.
For example, if a cell is defueled but the adjacent rod is withdrawn and bypassed (2 errors), and the next adjacent rod is withdrawn (1 error), the result would be the worst case mentioned above. This required three errors.
Other scenarios have been considered, and in all cases it was determined that they would require at least three or more errors to arrive at the worst case condition.
in addition, the proposed Technical Specifications provide that prior to the reloading of fuel into a core cell, the refueling interlocks associated with the control rod in that cell are unbypassed (i.e., reactivated) and verification of full blade insertion is made.
It is noted that prior to refueling, the one rod out refueling interlocks on the control rods in the defueled cells are bypassed with the associated control rods withdrawn.
Consequently, a core cell could be fueled without interlock intervention and in this sense the refueling interlock system has been degraded. The Technical Specification require-ments mentioned above and administrative procedures prevent the occurrence of this situation.
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Consideration has also been made to errors during refueling which might result in the occurrence of adjacent uncontrolled fueled cells.
In all postuated scenarios, it was determined that at least three errors would be required to arrive at this worst case condition.
33 Refueling Accident The refueling accident is described in Section 13 2 of the oyster Creek FDSAR. The accident involves the scenas'o whereby during handling or movement of a fuel assembly, the fuel grapple or grapple cable breaks and allows the fuel assembly to fall at a sufficient velocity to result in fuel damage and subsequent radiation release into secondary containment.
The FDSAR indicates that the rod withdrawal interlock system assures that no nuclear excursion can take place from this accident, even in the event the dropped fuel assembly falls into a vacant fuel location in the core. This is justified since at least two control rods adjacent to the empty fuel location must be withdrawn and the emaining fuel locations in those cells fully loaded for a nuclear excursion criticality to occur.
The rod withdrawal interlock system, of course, prevents such a condition from occurring during fuel handling maneuvers.
et has already been denonstrated in Section 3.2 that the proposed bypass of the rod withdrawal interlocks on fuel cells, which have been previously defueled, in no way detracts from the capability of the resuling interlock system to prevent large amounts of re.ctivity from being inserted into the core during fuel and control rod removal.
During subsequent reloading operations, procedural controls prevent the reconstitution of two adjacent uncontrolled cells.
Further-mo re, it was shown that in order to arrive at a situation in which the control rods were withdrawn from fully loaded fuel cells, at least three separate violations of the procedures.
as set fcrth in this proposed Technical Specification would be required.
The probability of this occurring is extremely small.
Therefore, if the rod withdrawal interlocks are bypassed and procedures in this proposed Technical Specification are followed, the statement that no nuclear excursion may take place in the refueling accident is still justified.
The consequences of the refueling accident which result from the analysis in the Oyster Creek FDSAR are, therefore, still valid and are in no way altered by the systematic bypassing of interlocks in the manner proposed in the Technical Specifi-cations.
F }{} 4. Conclusions The proposed Technical Specification change does not increase the probability of occurrence or the consequences of an accident previously evaluated in the FDSAR. It does not introduce the
. possibility for an accident or malftaction of a type not previously considered in the FDSAR, nor does it. educe the margin of safety in the basis for the Technical Specifications. It is not cycle dependent. 1512 036}}