Information Notice 2011-10, Thermal Issues Identified During Loading of Spent Fuel Storage Casks
| ML111090200 | |
| Person / Time | |
|---|---|
| Issue date: | 05/02/2011 |
| From: | Vonna Ordaz NRC/NMSS/SFST |
| To: | |
| Gee F, NMSS/SFST 492-3329 | |
| References | |
| IN-11-010 | |
| Download: ML111090200 (4) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, DC 20555-0001 May 2, 2011 NRC INFORMATION NOTICE 2011-10: THERMAL ISSUES IDENTIFIED DURING
LOADING OF SPENT FUEL STORAGE CASKS
ADDRESSEES
All holders of and applicants for an independent spent fuel storage installation license under
Title 10 of the Code of Federal Regulations (10 CFR) Part 72, Licensing Requirements for the
Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, and Reactor- Related Greater than Class C Waste and Part 72 Certificate of Compliance holders.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of an incident that occurred during the loading of spent fuel storage canisters at the
Byron Generating Station. The NRC expects that recipients will review the information for
applicability to their facilities and take actions, as appropriate, to avoid similar problems.
Suggestions contained in this IN are not NRC requirements; therefore, no specific action or
written response is required.
DESCRIPTION OF CIRCUMSTANCES
On August 28-29, 2010, a Holtec HI-STORM 100 spent fuel storage system multipurpose
canister (MPC) containing fuel assemblies and located within a transfer cask was left
unattended for the evening. A cooling system, which circulated water in the annulus between
the canister and transfer cask to keep cladding temperatures below allowable limits, was found
to be inoperable the next morning. The NRC conducted a reactive team inspection at the Byron
Generating Station in September 2010 and issued Inspection Report Nos. 05000454/2010007,
05000455/2010007, and 07200068/2010002 (Agencywide Documents Access and
Management System (ADAMS) Accession No. ML103140226). Issues that arose as a result of
the reactive team inspection were also addressed during a scheduled design and quality
assurance inspection at Holtec, International, who holds the HI-STORM 100 Certificate of
Compliance (CoC), from October 25 to 29, 2010 (Inspection Report No. 72-1014/10-201, ADAMS Accession No. ML110450157).
DISCUSSION
The inspection reports referenced above provide detailed summaries of the incident as well as
findings and observations, underlying implications, and other information. As a result of the
inspections and subsequent reviews and technical analyses, the NRC identified several
potential issues related to the incident:
(1) There were no means to prevent or mitigate air ingress into the canister containing fuel
assemblies, which could cause fuel oxidation, if certain failures of the vacuum drying
system occurred, such as a hose rupture between the vacuum pump and canister or
valve failure. Drying systems typically are classified as not important to safety when
there is appropriate operator attendance to address system failures because operator
actions, such as backfilling the canister with helium or returning the fuel assemblies to
the spent fuel pool, can mitigate the event.
(2) Cladding temperatures could exceed CoC technical specification limits if the annulus
cooling system is inoperable for an extended period of time. As stated above, vacuum
drying equipment, including the annulus cooling system often used to cool the canister
during vacuum drying, typically has been classified as not important to safety when there
is appropriate operator attendance to address system failures. With operators in
attendance, failure of the cooling system to provide proper cooling can be mitigated by
operator action so as to prevent cladding temperatures from reaching the allowable
limits.
(3) The CoC technical specifications for vacuum drying were non-conservative for the
particular heat load of spent fuel being loaded.
(4) CoC technical specifications typically mandate that helium backfilling should occur if a
vacuum drying time limit has been reached, in order to prevent fuel cladding from
reaching temperature limits. Thermal analyses determine the permissible vacuum
drying time period based on a canister decay heat load and a known, initial temperature
of the fuel assemblies. However, in the event that backfilling of helium is required
because the vacuum drying time limit is reached, the CoC Final Safety Analysis Report
(FSAR) and technical specifications did not address the need for a new vacuum drying
time limit for the subsequent vacuum drying attempt.
(5) The CoC FSAR and technical specifications specified the total canister fuel assembly
decay heat above which annulus cooling would be required during the vacuum drying
process in order to keep cladding temperatures below allowable limits, but did not
address necessary requirements for annulus cooling when the decay heat of an
individual fuel assembly reached a limiting condition for operation (LCO).
(6) While the operating procedures section of the CoC FSAR allowed the use of either
helium or nitrogen during the canister blowdown operation, no evaluation was performed
by the licensee to justify the use of nitrogen.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to one of the technical contacts listed below.
/RA/
Vonna L. Ordaz, Director
Division of Spent Fuel Storage
and Transportation
Office of Nuclear Material Safety
and Safeguards
Technical Contacts: Joseph Borowsky, SFST
301-492-3563 E-mail: Joseph.Borowsky@nrc.gov
John Goshen, SFST
301-492-3325 Email: John.Goshen@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ML111090200 TAC MXXXXX
OFFICE NMSS/DSFST Tech Editor BC: D: D:
NAME FGee JDougherty EBenner DWeaver VOrdaz
DATE 03/30/11 04/5/11 e-mail 04/18/11 e-mail 04/20/11 05/02/11 OFFICE NMSS/DSFST NMSS/DSFST NMSS/DSFST BC: BC, Region III
NAME JBorowsky JGoshen JSolis NGarcia-Santos CLipa
DATE 04/7/11 04/7/11 04/12/11 04/12/11 04/12/11