Bulletin 94-01: Potential Fuel Pool Draindown Caused by Inadequate Maintenance Practices at Dresden
OMB No.: 3150-0011
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION AND
OFFICE OF NUCLEAR MATERIALS SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
April 14, 1994
NRC BULLETIN 94-01: POTENTIAL FUEL POOL DRAINDOWN CAUSED BY INADEQUATE
MAINTENANCE PRACTICES AT DRESDEN UNIT 1
All holders of licenses for nuclear power reactors that are permanently shut
down with spent fuel in the spent fuel pool (except Shoreham). [Humboldt Bay,
Indian Point 1, La Crosse, Rancho Seco, San Onofre 1, Trojan, Yankee Rowe, and
All holders of operating licenses or construction permits for nuclear power
reactors and all fuel cycle and materials licensees authorized to possess
The U.S. Nuclear Regulatory Commission (NRC) is issuing this bulletin: (1) to
inform addressees of the results of a special NRC inspection at Dresden
Nuclear Power Station Unit 1 (Dresden 1), (2) to request that all action
addressees implement the actions described herein, and (3) to require that all
action addressees provide to NRC written responses to this bulletin relating
to implementation of the requested actions.
Description of Circumstances
Dresden 1, one of three boiling water reactors at the Dresden site near
Morris, Illinois, was licensed for operation on September 28, 1959, and was
permanently shut down on October 31, 1978. On January 25, 1994, the licensee
for Dresden 1 discovered approximately 200 m [55,000 gallons] of water in the
basement of the unheated Unit 1 containment. The water originated from a
rupture of the service water system piping inside the containment that had
been caused by freeze damage to the system. The licensee investigated further
and found that, although the fuel transfer system was not damaged, there was a
potential for a portion of the system inside the containment to fail and
result in a partial draindown of the spent fuel pool (SFP) that contained
94-01 April 14,
1994 Page 2 of 6
660 spent fuel assemblies. The licensee implemented several specific actions
to guard against further damage from freezing and appointed a team to
investigate the status of Dresden 1.
The NRC dispatched a team of inspectors from the Offices of Nuclear Reactor
Regulation (NRR), Nuclear Material Safety and Safeguards, and Region III to
conduct a special inspection of the circumstances surrounding the event. The
details of that inspection will be in an NRC inspection report to be issued
shortly. Based on these reviews the following conditions existed:
Heating had not been provided to the Dresden 1 containment for the
1989/1990 and subsequent heating seasons. The lack of heating inside
the containment under more severe weather conditions could potentially
have resulted in the freezing and rupture of the fuel transfer tube.
Failure of the fuel transfer tube could have drained the SFP to several
feet below the top of the stored fuel assemblies. The loss of water
shielding would have created onsite personnel hazards from the high
The water quality in the SFP was poor. The original cleanup and cooling
system was shut down in 1983; by 1987 the water quality had degraded to
the point that an influx of microorganisms had developed. Concerned
that the microorganisms might cause microbiologically induced corrosion,
the licensee installed a temporary system to clean up the pool. The
temporary system proved to be incapable of restoring the water quality
to an acceptable level. Licensee records show that the conductivity in
the pool exceeded the technical specification limit of 10 mho per
centimeter by about a factor of two. Also, the licensee estimated that
approximately 90 stored fuel bundles had leaking fuel pins resulting in
elevated concentrations of cesium-137 of about 370 Becquerels/ml [1 x
A number of obsolete piping lines from the original pool cleanup and
cooling system remained in the SFP and were potential siphon paths that
could reduce the pool level.
Because the SFP gate was not installed it could not have prevented a
draindown of the pool if the fuel transfer pool or tunnel had emptied.
The NRC inspectors noted that the gaskets and steel mating surfaces for
the spent fuel gate had been exposed to adverse biological, chemical,
and radiological conditions that may have affected their ability to seal
had the gate been installed.
The licensee had no SFP leak detection or water inventory program. The
observed cracks in the unlined concrete pool indicated a potential for
Site personnel had for some time focused their attention on the operating
units and assumed that no significant problems would occur at Dresden 1. .
April 14, 1994
Page 3 of 6
Interviews with personnel at the Dresden site (which includes two operating
units in addition to Dresden 1) showed that, in part, the weaknesses
identified above were based on an incorrect belief that Dresden 1 could not
cause a serious safety problem because it was permanently shut down. This
belief resulted in audits and safety evaluations that were not rigorously
implemented or that did not include the Dresden 1 systems and programs.
However, as noted above, significant safety considerations did exist.
It is necessary to maintain an adequate inventory of water in the spent fuel
pool to safely store spent fuel. A proper depth of SFP water provides
protection for plant personnel from excessive exposure to radiation from spent
fuel and other materials stored in the spent fuel pool. Control of the
exposure of plant personnel is required by Part 20 of Title 10 of the Code of
Federal Regulations (10 CFR Part 20). Rapid loss of SFP water inventory may
result from a failure of piping connected to the SFP or from a siphoning
action of piping as a result of an improper valve alignment. A loss of SFP
water inventory may also result from a failure of seals or gaskets used as
part of the SFP boundary. If seals and gaskets are allowed to become
degraded, a leak may increase rapidly once it initiates. Failure to have a
leak detection system or a water inventory program may allow leakage of SFP
water to go undetected.
Proper maintenance and operation of SFP systems is necessary to maintain water
quality and radionuclides at acceptable levels. Maintenance of water quality
is necessary to prevent degradation of the spent fuel and other stored
materials stored in the SFP (i.e., control rod blades or incore instrument
strings). Proper SFP water treatment programs prevent the buildup of
excessive concentrations of radionuclides. Proper maintenance of the SFP and
the support systems would also mitigate the consequences of any potential
release from the SFP.
Immediately upon receipt of this bulletin, all action addressees are requested
to take the following actions to ensure that the quality of the SFP coolant,
and the cooling and shielding for fuel or equipment stored in the SFP is not
compromised and that all necessary structures and support systems are
maintained and are not degraded.
1.Verify that the structures and systems required for containing, cooling,
cleaning, level monitoring and makeup of water in the SFP are operable
and adequate, consistent with the licensing basis, to preclude high
levels of radionuclides in the pool water and adverse effects on stored
fuel, the SFP, fuel transfer components, and related equipment.
2.Ensure that systems for essential area heating and ventilation are
adequate and appropriately maintained so that potential freezing
failures that could cause loss of SFP water inventory are precluded.
. NRCB 94-01
April 14, 1994
Page 4 of 6
3.Ensure that piping or hoses in or attached to the SFP cannot serve as
siphon or drainage paths in the event of piping or hose degradation or
failure or the mispositioning of system valves.
4.Ensure that operating procedures address conditions and observations
that could indicate changes in SFP level and address appropriate
maintenance, calibration and surveillance of available monitoring
equipment. This should include any leak detection systems.
All action addressees are required to submit the following written response to
1.Within 30 days of the date of this bulletin, a written response
indicating whether or not the addressee will implement the actions
requested above. If the addressee intends to implement the requested
actions, provide a schedule for completing implementation. If an
addressee chooses not to take the requested actions, provide a
description of any proposed alternative course of action, the schedule
for completing the alternative course of action (if applicable), and the
safety basis for determining the acceptability of the planned
alternative course of action.
2.Within 30 days of completion of the requested actions, a report
Address the required written reports to the U.S. Nuclear Regulatory
Commission, ATTN: Document Control Desk, Washington, D.C. 20555, under oath
or affirmation under the provisions of Section 182a, Atomic Energy Act of
1954, as amended, and 10 CFR 50.54(f). In addition, submit a copy to the
appropriate regional administrator.
Actions 2, 3 and 4 requested in this bulletin may represent new staff
positions and these requests are considered backfits in accordance with NRC
procedures. Because established regulatory requirements exist but were not
satisfied, these backfits are to bring facilities into compliance with
existing requirements. Therefore, a full backfit analysis was not performed.
A documented evaluation was performed in accordance with NRC procedures
including a statement of the objectives of and reasons for the modifications
and the basis for invoking the compliance exception. It will be made
available in the Public Document Room with the minutes of the 256th meeting of
the Committee to Review Generic Requirements.
A notice of opportunity for public comment was not published in the
Federal Register because of the urgent nature of the actions requested by the
. NRCB 94-01
April 14, 1994
Page 5 of 6
Paperwork Reduction Act Statement
The information collections contained in this request are covered by the
Office of Management and Budget clearance number 3150-0011, which expires
June 30, 1994. The public reporting burden for this collection of information
is estimated to average 300 hours per response, including the time for
reviewing instructions, searching existing data sources, gathering and
maintaining the data needed, and completing and reviewing the collection of
information. Send comments regarding this burden estimate or any other aspect
of this collection of information, including suggestions for reducing this
burden, to the Information and Records Management Branch (MNBB-7714),
U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, and to the Desk
Officer, Office of Information and Regulatory Affairs, NEOB-3019, (3150-0011),
Office of Management and Budget, Washington, D.C. 20503.
Compliance with the following request for information is purely voluntary.
The information would assist NRC in evaluating the cost of complying with this
(1)the licensee staff time and costs to perform requested inspections,
corrective actions, and associated testing;
(2)the licensee staff time and costs to prepare the requested reports and
(3)the additional short-term costs incurred as a result of the inspection
findings such as the costs of the corrective actions or the costs of
(4)an estimate of the additional long-term costs which will be incurred in
the future as a result of implementing commitments such as the estimated
costs of conducting future inspections or increased maintenance.
NRC is issuing this bulletin to the information addressees to alert them to
the potential for spent fuel pool draindown under the described conditions.
It is expected that recipients will review the information for applicability
to their facilities and consider actions, as appropriate, to avoid similar
problems. However, the requested actions and required responses applicable to
the action addressees are not applicable to the information addressees;
therefore, no specific action or written response is required from them. The
NRC staff is reviewing the need to request actions related to siphon or
drainage paths at older operating power plants and certain fuel cycle
. NRCB 94-01
April 14, 1994
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If you have any questions about this matter, please contact one of the persons
listed below or the appropriate NRC project manager.
/s/'d by JTGreeves/for /s/'d by LAReyes
Malcolm R. Knapp, Director Luis A. Reyes
Division of Waste Management Acting Associate Director for Projects
Office of Nuclear Material Safety Office of Nuclear Reactor Regulation
Technical contacts: Steve Jones, NRR
Lee Thonus, NRR
Larry Bell, NMSS
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