ML20037D337
| ML20037D337 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 06/30/1981 |
| From: | Counsil W CONNECTICUT YANKEE ATOMIC POWER CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-04-02, TASK-4-2, TASK-RR A01452, A1452, NUDOCS 8107100042 | |
| Download: ML20037D337 (5) | |
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CONNECTICUT YANKEE AT G MIC POWER COMPANY E3 E R L 1 N. CONNECT l CUT P O BOR 270 HARTFORD CONN ECTICUT 06101
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June 30, 1981
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' I Director of Nuclear Reactor Regulation n %a si i
Attn:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch #5
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Nuclear Regulatory Commission 4
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20555 W
References:
(1)
D. G. Eisenhut letter to SEP Plant Licensees, dated January 14, 1981.
(2)
W.
G.
Counsil letter to D. G. Eisenhut, dated February 27, 1981.
Gentlemen:
Haddam Neck Plant SEP Topic IV-2, Reactivity Control Systems Including Functional Design and Prctection Against Single Failures As part of the redirection of the Systematic Evaluation Program, Reference (1), Connecticut Yankee Atomic Power Company (CYAPCO) committed to develop Safety Assessment Reports (SAR's) for certain SEP topics which would be submitted for Staff review.
CYAPCO detailed this commitment and provided a schedule for submittal of SAR's in Reference (2).
In accordance with this commitment, CYAPCO hereby provides the Safety Assessment Report for SEP Topic IV-2, Reactivity Control Systems In-cluding Functional Design and Protection Against Single Failures, which is included as Attachment 1.
We trust the Staff will appropriately use this information to develop a Safety Evaluation Report for this SEP topic.
Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY
/
[M G.'
W.~ G.
Counsil Senior Vice President
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8107100042 810630 PDR ADOCK 05000213 P
Docket No. 50-213 i
P Attar-hment 1 n
S..fety Assessment Report i
SEP Topic IV-2, Reactivity Control Systems Including Functional Design and Protection Against Single Failures i.
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June, 1981
Haddam Neck Plant SEP Safety Assessment Report Topic IV-2, Reactivity Control Systems, Including Functional Design and Protection Against Single Failures
1.0 INTRODUCTION
The purpose of this assessment is to ensure that the design basis for the Haddam Neck Plant reactivity control systems is consistent with analyses performed to verify that the protection system meets General Design Criterion 25.
This assessment is limited to the identification and evaluation of inadvertent control rod withdrawls and malpositioning of control rods which may occur as a result of single Failures in the electrical circuits of the reactivity control systems.
In References (1) and (2), CYAPCO evaluated possible boron dilution events at the Haddam Neck Plant. CYAPCO has concluded that References (1) and (2) adequately address the consequences of single failures in the Chemical and Volume Control System (CVCS). Additionally, boron dilution events will be evalua'?d as part of SEP Topic XV-lO.
2.0 CRITERIA General Design Criterion 25 requires that the Reactor Protection System be designed to assure that specified acceptable fuel design limits are not exceeded for any single malfunction of the reactivity control systems, such as accidental withdrawal of control rods but not including a control rod ejection incident. Reactivity control systems need not be single failure proof; however, the protection system must be capable of assuring that the specified acceptable fuel design limits are not exceeded in the event of a single failure in the reactivity control systems.
Standard Review Plan, Section 7.7 states:
The control systems not required for safety are acceptable if failures of control system components or total systems would not significantly affect the ability of plant safety systems to function as required, or cause plant conditions more severe than those for which the plant safety systems are designed.
3.0 DISCUSSION In Reference (3). CYAPCO described control rod withdrawals and malpositioning of control rods which could be caused by cingle failures within the Rod Control System (RCS) at the Haddam Neck Plant.
l The RCS controls the movement of 45 control rods (assemblies) composed of control banks "A" (17 rods) and "B" (8 rods), and shutdown banks "C"
l (8 rode) and "D" (12 rods).
Rod movement is directed by either an RCS developed signal, in " AUTO" control, or by manual operation through use of a " Group / Mode" switch, a rod speed selector switch, and a rod direction switch.
Each mode of operation has been evaluated for single failures leading to inadvertent rod withdrawal or rod malposition.
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, Non-faulted operation with the RCS in " AUTO" will move only bank A or B,
or, in a preselected range, move A and B simultaneously on receipt of a motion signal from the RCS logic. CYAPCO has determined that the following events may occur as a result of a single failure in the RCS while the RCS is in the " AUTO" mode, 1.
Inadvertent out-motion of A, B, or A and B in the preselected range.
2.
Simultaneous motion of A and B outside the preselected range on receipt of a valid out-motion signal.
3.
Individual rods may fail to move with the associated bank.
4.
Bank subgroups of 2, 4, or 5 symmetrically placed rods may fail to move with their associated banks.
5.
One or more syrmetrically placed dropped rods.
In the " AUTO" mode, no single failure can cause inadvertent withdrawal of either shutdown bank C or D.
No single failure can lead to AUTO rod withdrawal below 15% reactor power.
CYAPCO has also determined that the following events may occur as a result of a single failure in the RCS while in the manual operation mode.
1.
Inadvertent out-motion of A, B, A and B, C, or D.
2.
Individual rods may fail to move with the associated bank.
3.
Bank subgroups of 2, 4, or 5 symmetrically placed rods may fail to move with their associated banks.
4.
One or more symmetrically placed dropped rods.
In manual operation, no single failure can lead to simultaneous withdrawal of both shutdown banks, C and D, or simultaneous withdrawal of either shutdown bank and either or both control banks.
The availability of alarms and interlocks associated with the Rod Control Systen ensures that single failures in the RCS will not cause rod motions other than those described above.
These alarms and interlocks were thoroughly discussed in Reference (3).
The effects of single failures occurring after an undetacted failure has occurred in the alarm and inter-lock system is beyond the scope of current licensing criteria and, as such, will not be included in this assessment, j
Control rod withdrawal incidents are addressed in Section 10.2 of the l
Haddam Neck FDSA.
Control rod worths and reactivity evaluations have l
been provided in reload submittals.
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. The FDSA analyses have demonstrated that reactivity insertion events at power are more severe for a relatively low reactivity addition rate.
Thus, single failure considerations as discussed above will not lead to a more severe event.
Also, rod malpositions below the power ratJe are not significant.
Therefore, only single failures leading to reactivity insertion events below the power range and rod malpositions in tbs power range need be considered.
In either the AUTO or manual mode with the reactor at high power and all the rods located at the top of the core, the failure of a single rod or several symmetrically placed rods to move with the associated banks will produce radial and axial flux maldistributions. The in-dividual rod positions are monitored by a system separate from the rod group / bank position indication circuit. During reactor operation and especially during power level changes, all individual rods are chec) *d by both the plant computer and reactor operator for rods out of alignment with their respective rod banks. Analyses have shown that single rod out-of-bank misalignments of up to + 40 steps at various power levels will not result in local power peaks in excess of the limiting value ststed in the Technical Specifications.
The worth of any ecd in the current Haddam Neck Plant fuel design is less than that as;vn.ad in the dropped rod analyses docketed in Reference (6).
Therefore, thc Peference (6) analyses are limiting and are accep-table. Should a single failure cause more than one rod to drop, the operator is required to immediately trip the reactor.
As stated earlier, a single failure can cause inadvertent withdrawal of bank A, B, A and B, C, or D.
For the current Haddam Neck Plant fuel design, the incremental worth of each of these banks, as well as the worth of banks A and B together, is less than the 9x10-4 Ak/k/ inch assumed in the FDSA analyses. Other parameters such as fuel and moderator temperature feedback coefficients are also bounded by the FDSA analyses. Therefore, the FDSA analyses are limiting.
4.0 CONCLUSION
S l
CYAPCO has determined that single failures in the Rod Control System will not lead to reactivity insertions more severe than those pre-viously analyzed, and thus the requirements of General Design Criteria 25 are met.
Control rod misoperation will also be addressed as part of SEP Tcpic XV-8 to verify that specified acceptable fuel damaJe limits are not exceeded.
5.0 REFERENCES
1 1.
D. C. Switzer letter to A. Schwencer, dated January 13, 1978.
2.
W. G. Counsil letter to D. M. Crutchfield, dated June 4, 1980.
3.
W. G. Counsil letter to D. M. Crutchfield, dated May 18, 1981.
4.
10CFR50 Appendix A, General Design Criterion 25.
5.
Standard Review Plan Section 7.7, 1975.
l 6.
D. C. Switzer letter to K. R. Goller, dated Scptember 19, 1974.
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