Radioactive Waste Management — WIA-ENE-026
Wet storage in cooling pools (decay heat 6-7 percent of operating power decreasing per the Way-Wigner formula), dry cask storage per NRC 10 CFR Part 72, transportation per IAEA SSR-6 Type B(U)F packaging.
This chapter elaborates on the Spent Fuel Management portion of Radioactive Waste Management (WIA-ENE-026). The radioactive waste management canonical envelope shape, API surface, and protocol exchanges are designed to interoperate across implementations published under the WIA Standards family. Each Phase file in `spec/` documents one architectural layer (envelopes, REST surface, federation, ecosystem) and the present chapter focuses on the spent fuel management subset of that layering.
Implementations of spent fuel management need to reconcile the per-standard expectations of IAEA GSG-1 (Classification of Radioactive Waste), IAEA SSR-5 (Disposal of Radioactive Waste), IAEA SSG-23 (Safety Case for Geological Disposal), IAEA Joint Convention on Spent Fuel and Radioactive Waste Safety, IAEA SSR-6 (Transport of Radioactive Material). The Phase 1 envelope class for Radioactive Waste Management carries the per-host identifier and per-tenant identifier so that audit records can be reconstructed across hosts that federate through the Phase 3 protocol layer.
Operators stepping into spent fuel management typically follow this trajectory: stand up the reference simulator at `simulator/index.html`, walk the canonical envelope per the CLI helper at `cli/radioactive-waste.sh envelope`, then exercise the Phase 2 endpoints with curl/Postman against a host running the reference container at `wia/radioactive-waste-host:1.0.0`. Once those steps complete, integrators wire the real backend one endpoint at a time per the Phase 1 §A.* envelope catalogue and the Phase 2 §B.* endpoint catalogue.
A common operational concern in the spent fuel management space is observability. Every Phase 1 envelope SHOULD emit a structured log line at the host's audit transport with: timestamp per RFC 3339, host identifier, tenant identifier, envelope class, envelope identifier, operation outcome, and a W3C Trace Context `traceparent` propagated end-to-end. Phase 2 surfaces this trace identifier as the `X-WIA-Trace-Id` response header. Phase 3 protocol exchanges propagate the trace identifier inside the exchange envelope so that a federation crossing remains correlatable end-to-end.
The spent fuel management portion of the standard composes with: WIA-OMNI-API for credential storage, WIA-AIR-SHIELD for runtime trust list, WIA-INTENT for workload intent declaration, and WIA Secure Enclave for sealed-data envelopes where personal data is processed. The composition lets one host running multiple WIA family standards reuse one identity, one signing-key chain, and one audit transport rather than maintaining N parallel per-standard implementations.
spec/ (Phase 1 for envelopes, Phase 2 for API, Phase 3 for protocol, Phase 4 for ecosystem)../cli/radioactive-waste.sh envelope emits a sample Phase 1 envelope.simulator/index.html.https://github.com/WIA-Official/wia-radioactive-waste-conformance.This chapter, like every other Phase 1-4 chapter in the Radioactive Waste Management eBook, composes with the wider WIA Standards family. Implementations that adopt the canonical envelope reuse the cross-standard audit transport (W3C Trace Context plus OpenTelemetry semantic conventions), the cross-standard identity (WIA-OMNI-API), and the cross-standard runtime trust list (WIA-AIR-SHIELD) without per-standard re-implementation. The federation handshake described in Phase 3 §3 follows the same challenge-response pattern as the rest of the WIA Standards family so that one operator can federate across multiple standards using one signing-key chain and one audit transport.
As of May 2026 Korea operates 24 nuclear power reactors and one permanently shut down reactor (Kori Unit 1, permanently shut down in 2017), with a cumulative spent nuclear fuel inventory of approximately 19,000 metric tons of uranium (MTU). Korea Hydro & Nuclear Power (KHNP) uses on-site spent fuel pools (SFP) at each reactor site as primary storage. The Wolsong site (PHWR pressurized heavy-water reactors) has operated MACSTOR dry storage modules (600 gas-filled concrete canisters) since 1992. This section reconciles the Korean spent-fuel inventory and storage data with the spent_fuel_inventory surface of the WIA-ENE-026 envelope.
Per the Q4 2025 disclosure of the Korean RWMIS database operated by the Korea Institute of Nuclear Safety (KINS), the SFP saturation levels are as follows: Kori Units 1, 2, 3, and 4 SFP at 92%; Hanul Units 1, 2, 3, and 4 SFP at 88%; Hanbit Units 1, 2, 3, and 4 SFP at 86%; Saeul Units 1 and 2 SFP at 47% (relatively spare capacity); New Kori Units 1 and 2 SFP at 78%; New Hanul Units 1 and 2 SFP at 35%. Wolsong Units 1, 2, 3, and 4 (PHWR) transfer spent fuel to dry MACSTOR storage after 6 months of SFP cooling, maintaining stable SFP saturation. The spent-fuel envelope tracks SFP saturation in the pool_utilization_ratio field and remaining MACSTOR capacity in the dry_storage_capacity_macstor field.
Korean dry storage operates two systems. (1) MACSTOR-400 at Wolsong: a Korean adaptation of the Canadian AECL technology, gas-filled concrete canisters holding 192 PHWR bundles each. (2) HI-STORM 100 (licensed from Holtec International, USA, under evaluation at the New Wolsong and New Kori sites): a multi-purpose canister (MPC) system holding 32 PWR assemblies or 68 BWR assemblies. KAERI - the Korea Atomic Energy Research Institute, Daejeon - has indigenously developed the KORAD-N-200 Korean-type PWR dry storage canister, entering the NSSC licensing process in 2024.
The most decisive safety variable for spent nuclear fuel is the residual decay heat. The Way-Wigner formula is the 1950s-era standard approximation estimating the decay heat P(t) at time t (seconds) after reactor shutdown as a fraction of the operating power P_0.
P(t)/P_0 = 6.62e-3 * [t^-0.2 - (t + T_0)^-0.2]Here T_0 denotes the operating period in seconds. After five years of operation, the decay heat is approximately 6 to 7 percent of operating power one second after shutdown, 1.5 percent after one hour, 0.5 percent after one day, 0.07 percent after one year, and 0.012 percent after ten years. The reference simulator panel 1 "decay-heat calculator" accepts operating power, operating duration, and time-since-shutdown, returning the result of the precise ANSI/ANS-5.1-2014 formula.
The Way-Wigner formula is only a first-order approximation. The current precision standard is ANSI/ANS-5.1-2014 "Decay Heat Power in Light Water Reactors", which sums the time-dependent decay curves of 23 fission product groups and 8 actinide groups to guarantee plus-minus 2 percent accuracy. KAERI implements ANSI/ANS-5.1 in the KAERI-DH-2018 code, which KHNP uses for licensed decay-heat evaluation across the Korean fleet.
U.S. NRC 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") is the primary regulatory framework for independent spent fuel storage installations (ISFSI). Korean dry storage is licensed under Article 63-2 of the Nuclear Safety Act ("Operating License for Radioactive Waste Management Facility"), which is harmonized with NRC Part 72. A new licensing pathway specific to the centralized interim storage facility operated by KORAD will be established under the subsidiary regulations of the 2024 High-Level Radioactive Waste Special Act.
NRC Part 72 §72.122 structural safety requirements impose: (1) under normal operating conditions, canister external surface dose rate at most 2 mSv/h on contact and 0.1 mSv/h at 2 m distance; (2) accident conditions (drop, fire, flood, earthquake) must preserve containment; (3) criticality safety with k_eff at most 0.95 at 95 percent confidence; (4) thermal removal with peak cladding temperature at most 400 degrees Celsius for long-term storage and at most 570 degrees Celsius for short-term off-normal conditions. The Korean-type KORAD-N-200 canister demonstrates the same requirements using the KAERI ANISN/DORT shielding codes and the KENO-VI criticality code.
When spent fuel is transferred from the reactor SFP to dry storage or to an off-site interim storage facility, the IAEA SSR-6 (2018 edition) Type B(U)F package is required. Type B(U)F packages must pass both (1) normal-condition tests (9 m drop on unyielding surface, 1 m bar puncture, fire at 800 degrees Celsius for 30 minutes, immersion in 15 m water for 8 hours) and (2) accident-condition tests (9 m flat drop, 1 m bar puncture, 800-degree fire for 30 minutes, 15 m water immersion) without loss of containment. Korea's KEPCO E&C developed the KOREA NPS-1 transport package (holding 21 PWR assemblies), which was certified by NSSC in November 2022 after the KAERI HOTCELL prototype tests.
This section maps the eight categories of Korean infrastructure directly involved in spent fuel management.
The following example envelope describes 192 PHWR bundles discharged from Wolsong Unit 1 and stored in a MACSTOR-400 dry storage canister.
{
"version": "1.0",
"host_id": "khnp.kr.wolsong.macstor",
"tenant_id": "khnp.wolsong-unit-1",
"envelope_class": "WIA-ENE-026.SpentFuel.PHWR",
"envelope_id": "ulid:01HK8XBNQYE7Z4K1...",
"canister_serial": "WS-MACSTOR-400-M312-C24",
"bundle_count": 192,
"fuel_type": "CANDU 6 / KANDU 37-element bundle",
"average_burnup_mwd_per_tu": 7250,
"discharge_date": "2018-09-12",
"decay_heat_w_per_bundle": 18.4,
"spent_fuel_inventory": {
"iaea_class": "HLW",
"jurisdiction_class_korea": "high-level",
"regulator_decision_ref": "KINS-SFM-2018-WS-00312"
},
"audit": {
"timestamp": "2026-05-15T10:22:14Z",
"traceparent": "00-7c8a3f1d2e4b5a6f9d3e2c1b0a8f7e6d-1a2b3c4d5e6f7a8b-01"
}
}Spent fuel is the longest-lived material that the WIA-ENE-026 envelope must track. The audit chain from generator (KHNP at the reactor site) to disposer (KORAD at the future centralized facility) spans decades, including the SFP cooling phase (typically 5 to 10 years), the on-site dry storage phase (potentially 40 to 100 years), the transport phase (a discrete event of 1 to 5 days), and the interim storage phase (potentially 40 to 100 years before final disposal). The envelope's chain_of_custody field is an append-only ordered list of (host_id, role, timestamp, signature) tuples, with each transfer of custody appending a new entry signed by the previous custodian. The cryptographic signature follows the WIA Standards family's standard signing scheme (Ed25519 over the canonical CBOR encoding of the previous custody chain), so a sufficiently long custody chain (for example, 80 entries spanning 60 years across 4 sites) remains independently verifiable.
The Phase 2 REST surface for spent fuel management exposes seven core endpoints. POST /spent-fuel/discharge records a fuel assembly discharge from a reactor core, creating an envelope tied to the assembly serial. POST /spent-fuel/move records a transfer between storage locations (for example, from SFP to dry cask), appending a chain-of-custody entry. GET /spent-fuel/inventory returns the per-site inventory snapshot with optional filtering by burnup, decay time, or fuel type. GET /spent-fuel/decay-heat computes the current decay heat from the stored discharge date and burnup. POST /spent-fuel/transport-plan registers a planned transport with Type B(U)F package serial and route. POST /spent-fuel/transport-event records actual transport events including departure, transit checkpoint, and arrival. GET /spent-fuel/audit returns the full chain-of-custody log for a given assembly serial. All endpoints follow the WIA Standards family's content-negotiation conventions: application/wia+json for canonical JSON, application/wia+cbor for compact CBOR, and application/wia+yaml for human-readable operator tooling.
Decay-heat evolution over the 60- to 100-year on-site dry storage period drives both thermal-design and cask-spacing decisions. For a 21-assembly PWR cask with mean burnup 45 GWd/MTU discharged after a 5-year operating cycle, representative decay-heat values per ANSI/ANS-5.1-2014 are: 12 kW at discharge, 5.2 kW at 1 year cooling, 1.4 kW at 5 years (typical dry-cask loading time), 0.78 kW at 10 years, 0.34 kW at 30 years, 0.18 kW at 50 years, and 0.11 kW at 100 years. The cask vendor designs the canister inner basket and outer overpack to maintain the peak cladding temperature below 400 degrees Celsius (long-term limit) and below 570 degrees Celsius (off-normal short-term limit) across this entire envelope.
For PHWR spent fuel at Wolsong, the decay-heat evolution is qualitatively similar but with substantially lower per-bundle heat due to the lower burnup (typical 7.5 GWd/MTU vs PWR 45 GWd/MTU). A 192-bundle MACSTOR canister exhibits decay heat of approximately 3.5 kW at 5 years cooling - within passive air-convection capacity of the MACSTOR module design without active cooling.