ML19319D831
| ML19319D831 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 10/16/1974 |
| From: | Spencer G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Thornburg H US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML19319D832 | List: |
| References | |
| NUDOCS 8003250821 | |
| Download: ML19319D831 (2) | |
See also: IR 05000312/1974008
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UMTED STATES
ATOMIC ENERGY COMMISSION
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oiREcroRArc OF REGgATORY CPERATIONS
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H. D. Thornburg, Chief, Field Support and Enforcement Branch
Directorate of Regulatory Operations, Headquarters
SACRAMENTO MUNICIPAL UTILITY DISTRICT
RANCHO SECO
DOCKET N0. 50-312
The attached report by our field inspector of an inspection at the
subject facility on September 15,16, 24 and 25,1974 is forwarded
for action.
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The discrepancy between the predicted and measured worth of a control
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rod raises some questions concerning the validity of certain assumptions
used in the analysis of the hypothetical rod ejection accident in the
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FSAR (Section 14.2.2.4); the adequacy of the Technical Specifications
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relative to control rod grouping and operation; and possible generic
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implications concerning these matters as they relate to other 88W
plants. We feel that the hypothetical control rod ejection accident
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should be reviewed by the Directorate of Licensing in light of the
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greater than predicted worth of the Rancho Seco control rods and that
Licensing should also consider the possible need for an additional
Technical Specification to prohibit critical operation of the reactor
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with rod group 5 less than 50% withdrawn from the core. Some reasons
for our concern are the following.
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The FSAR assumes that the severity of a rod ejection accident is
inherently limited because the amount of reactivity available in the form
of control rod worth is relatively small. A detailed analysis was per-
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formed at rated power and zero power for rod worths from 0.2 to 0.7%
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delta K/K. A maximum rod worth of 0.65% delta K/K at rated power has
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been considered as a limiting value to demonstrate the inherent ability
of the system to safely _ terminate the postulated transient. Furthermore,
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it was concluded that an ejected rod worth greater than 1.52% delta K/K
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would be required to cause rupture of the pressure vessel, whereas the
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maximum rod worths used in the analysis were about a factor of two less
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than 1.52% (Table 14.2-8).
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H. D. Thornburg
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Results of the measurements during the pseudo rod ejection test show
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that the worth of a single control rod with specified boration and rod
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pattern conditions was considerably greater than had been predicted.
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In our opinion, this considerably increases the importance of reliance
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on administrative controls for rod withdrawal operations to avoid
Although the Technical
potentially unsafe operating conditions.
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Specifications (3.5.2.3) do provide that "the worth of a single inserted
control rod shall not exceed 0.65% delta K/K at rated power or 1.0%
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delta K/K at hot zero power," we do feel that~an additional Technical
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Specification requirement is needed to specifica1.ly prohibit critical
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We feel that such a
operation with rod group 5 less than 50% withdrawn.
specification is necessary to reinforce existing administrative controls
which implement the Technical Specifications requirement not to exceed
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the 0.65% limit for an inserted control rod. This is particularly so
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since some of the information available to the operator in the current
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Technical Specifications could be misleading to the operator in that
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Figuie 3.5.2-1 could be construed to allow operation of the reactor
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with rod group 5 fully inserted.
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G. S. Spencer, Chief
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Reactor Construction and
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Operations Branch
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Enclosure:
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R0 Inspection Report
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No. 50-312/74-08 (21)
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cc w/ enc 1.
R0:HQ (5)
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